document_title: Pennsylvania Railroad

question_text: when did the prr first begin its passenger service between pittsburgh and philadelphia

question_tokens: when did the prr first begin its passenger service between pittsburgh and philadelphia

text: Pennsylvania Railroad

text: History[edit]

text: Main Line[edit]

text: Background[edit]

text: With the opening of the Erie Canal (1825) and the beginnings of the Chesapeake and Ohio Canal (1828), Philadelphia business interests became concerned that the port of Philadelphia would lose traffic. The state legislature was pressed to build a canal across Pennsylvania and thus the Main Line of Public Works was commissioned in 1826.[6] It soon became evident that a single canal would not be practical and a series of railroads, inclined planes, and canals was proposed.[7] The route consisting of the Philadelphia and Columbia Railroad, canals up the Susquehanna and Juniata rivers, an inclined plane railroad and tunnel across the Allegheny Mountains, and canals down the Conemaugh and Allegheny rivers to Pittsburgh on the Ohio River was completed in 1834. Because freight and passengers had to change cars several times along the route and canals froze in winter, it soon became apparent that the system was cumbersome and a better way was needed.[7][8]

text: Early history[edit]

text: The Commonwealth of Pennsylvania granted a charter to the Pennsylvania Railroad in 1846 to build a private rail line that would connect Harrisburg to Pittsburgh.[9] The Directors chose John Edgar Thomson, an engineer from the Georgia Railroad, to survey and construct the line. He chose a route that followed the west bank of the Susquehanna River northward to the confluence with the Juniata River, following its banks until the foothills of the Allegheny Mountains were reached at a point that would become Altoona, Pennsylvania.[7] In order to traverse the mountains, the line climbed a moderate grade for 10 miles until it reached a split of two mountain ravines which were cleverly crossed by building a fill and having the tracks ascend a 220-degree curve known as Horseshoe Curve that limited the grade to less than 2 percent. The crest of the mountain was penetrated by the 3,612-foot Gallitzin Tunnels and then descended by a more moderate grade to Johnstown.

text: The western end of the line was simultaneously built from Pittsburgh east along the banks of the Allegheny and Conemaugh rivers to Johnstown. PRR was granted trackage rights over the Philadelphia and Columbia and gained control of the three short lines connecting Lancaster and Harrisburg, instituting an all-rail link between Philadelphia and Pittsburgh by 1854. In 1857, the PRR purchased the Main Line of Public Works from the state of Pennsylvania, and abandoned most of its canals and inclined planes. The line was double track from its inception, and by the end of the century a third and fourth track were added. Over the next 50 years, PRR expanded by gaining control of other railroads by stock purchases and 999-year leases.[8]

text: Thomson (1808–1874) was the entrepreneur who led the PRR from 1852 until his death in 1874, making it the largest business enterprise in the world and a world-class model for technological and managerial innovation. He served as PRR's first Chief Engineer and third President.[10] Thomson's sober, technical, methodical, and non-ideological personality had an important influence on the Pennsylvania Railroad, which in the mid-19th century was on the technical cutting edge of rail development, while nonetheless reflecting Thomson's personality in its conservatism and its steady growth while avoiding financial risks. His Pennsylvania Railroad was in his day the largest railroad in the world, with 6,000 miles of track, and was famous for steady financial dividends, high quality construction, constantly improving equipment, technological advances (such as replacing wood fuel with coal), and innovation in management techniques for a large complex organization.[11]

text: New York, Philadelphia, Baltimore, and Washington lines[edit]

text: In 1861 the PRR gained control of the Northern Central Railway, giving it access to Baltimore, Maryland, as well as points along the Susquehanna River via connections at Columbia, Pennsylvania or Harrisburg.[12]

text: On December 1, 1871, the PRR leased the United New Jersey Railroad and Canal Company, which included the original Camden and Amboy Railroad from Camden, New Jersey (across the Delaware River from Philadelphia) to South Amboy, New Jersey (across Raritan Bay from New York City), as well as a newer line from Philadelphia to Jersey City, New Jersey, much closer to New York, via Trenton, New Jersey. Track connection in Philadelphia was made via the PRR's Connecting Railway and the jointly owned Junction Railroad (Philadelphia).[13]

text: The PRR's Baltimore and Potomac Rail Road opened on July 2, 1872, between Baltimore and Washington, D.C. This route required transfer via horse car in Baltimore to the other lines heading north from the city. On June 29, 1873, the Baltimore and Potomac Tunnel through Baltimore was completed. The PRR started the misleadingly named Pennsylvania Air Line service via the Northern Central Railway and Columbia, Pennsylvania. This service was 54.5 miles (87.5 km) longer than the old route but avoided the transfer in Baltimore. The Union Railroad line opened on July 24, 1873. This route eliminated the transfer in Baltimore. PRR officials contracted with both the Union Railroad and the Philadelphia, Wilmington and Baltimore Railroad (PW&B) Railroad for access to this line. The PRR's New York–Washington trains began using the route the next day, ending Pennsylvania Air Line service. In the early 1880s, the PRR acquired a majority of PW&B Railroad's stock. This action forced the Baltimore and Ohio Railroad (B&O) to build the Baltimore and Philadelphia Railroad to keep its Philadelphia access, where it connected with the Reading Railroad for its competing Royal Blue Line passenger trains to reach New York.

text: In 1885, the PRR began passenger train service from New York City via Philadelphia to Washington with limited stops along the route. This service became known as the "Congressional Limited Express."[14] The service expanded, and by the 1920s, the PRR was operating hourly passenger train service between New York, Philadelphia and Washington. In 1952, 18-car stainless steel streamliners were introduced on the Morning Congressional and Afternoon Congressional between New York and Washington, as well as the Senator from Boston to Washington.[15]

text: New York-Chicago[edit]

text: On July 1, 1869, the Pennsylvania Railroad leased the Pittsburgh, Fort Wayne and Chicago Railway in which it had previously been an investor. The lease gave the PRR complete control of that line's direct route through northern Ohio and Indiana as well as entry into the emerging rail hub city of Chicago, Illinois. Acquisitions along the Pittsburgh, Fort Wayne and Chicago Railway: Erie and Pittsburgh Railroad, Cleveland and Pittsburgh Railroad, Toledo, Columbus and Ohio River Railroad, and Pittsburgh, Youngstown and Ashtabula Railway gave the PRR access to the iron ore traffic on Lake Erie.[8]

text: On June 15, 1887, the Pennsylvania Limited began running between New York and Chicago. This was also the introduction of the vestibule, an enclosed platform at the end of each passenger car, allowing protected access to the entire train. In 1902 the Pennsylvania Limited was replaced by the Pennsylvania Special which in turn was replaced in 1912 by the Broadway Limited which became the most famous train operated by the Pennsylvania Railroad.[16][17] This train ran from New York City to Chicago, via Philadelphia, with an additional section between Harrisburg and Washington (later operated as a separate Washington–Chicago train, the Liberty Limited).

text: New York-St. Louis[edit]

text: In 1890, the PRR gained control of the Pittsburgh, Cincinnati, Chicago and St. Louis Railroad, itself the merged product of numerous smaller lines in Ohio, Indiana, and Illinois. Commonly called the Panhandle Route, this line ran west from Pittsburgh to Bradford, Ohio, where it split, with one line to Chicago and the other to East St. Louis, Illinois, via Indianapolis, Indiana. In 1905, the acquisition of the Vandalia Railroad gave the PRR access across the Mississippi River to St. Louis, Missouri.[8]

text: Double-tracked for much of its length, the line served the coal region of southern Illinois and as a passenger route for the Pennsylvania Railroad's Blue Ribbon named trains The St. Louisan, the Jeffersonian, and the Spirit of St. Louis.[18]

text: "Low-grade" lines[edit]

text: Around 1900, the PRR built several low-grade lines for freight to bypass areas of steep grade (slope). These included:

text:
1892: Trenton Branch (PRR) and Trenton Cut-Off Railroad from Glen Loch, Pennsylvania east to Morrisville, Pennsylvania (not only a low-grade line but a long-distance bypass of Philadelphia and shortcut)
1892: Waverly and Passaic Railroad (finished by the New York Bay Railroad) from Waverly, New Jersey to Kearny, New Jersey
1904: Reopening of the New Portage Railroad from the Gallitzin Tunnels east to New Portage Junction (abandoned), then continuing north over the Hollidaysburg Branch to Altoona
1906: Philadelphia and Thorndale Branch from Thorndale, Pennsylvania east to Glen Loch (abandoned by Conrail in 1989)
1906: Atglen and Susquehanna Branch from Harrisburg via the Northern Central Railway south to Wago Junction, then east to Parkesburg (the latter abandoned by Conrail in 1990)

text: The Pennsylvania and Newark Railroad was incorporated in 1905 to build a low-grade line from Morrisville, Pennsylvania to Colonia, New Jersey. It was never completed, but some work was done in the Trenton area, including bridge piers in the Delaware River. North of Colonia, the alignment was going to be separate, but instead two extra tracks were added to the existing line. Work was suspended in 1916. Another low-grade line across the mountains of Pennsylvania, to avoid the congestion of Pittsburgh, was contemplated but never built.

text: Pennsylvania Railroad electrification[edit]

text: Early in the 20th century the PRR tried electric power for its trains. First was the New York terminal area, where tunnels and a city law restricting the burning of coal precluded steam locomotives. There a direct current (DC) 650-volt third rail powered PRR locomotives (and LIRR passenger cars). The system was put into service in 1910.[19]

text: The next area to be electrified was the Philadelphia terminal area, where PRR officials decided to use overhead lines to supply power to the suburban trains running out of Broad Street Station. Unlike the New York terminal system, overhead wires would carry 11,000-volt 25-Hertz alternating current (AC) power: the system used for all future installations. In 1915, electrification of the line from Philadelphia to Paoli, Pennsylvania was completed.[20] Other Philadelphia lines electrified were the Chestnut Hill Branch (1918), White Marsh (1924), West Chester (1928), the main line to Wilmington, Delaware, and in 1930 the Schuylkill Branch to Norristown, along with the rest of the main line to Trenton.[citation needed]

text: PRR's president William Wallace Atterbury announced in 1928 plans to electrify the lines between New York, Philadelphia, Washington and Harrisburg. In January 1933, through main-line service between New York and Philadelphia/Wilmington/Paoli was placed in operation. The first test run of an electric train between Philadelphia and Washington occurred on January 28, 1935. On February 1 the Congressional Limiteds in both directions were the first trains in regular electric operation between New York and Washington, drawn by the first of the GG1-type locomotives. All regular passenger trains between these cities were electrified by March 15.[citation needed]

text: In 1934 the PRR received a $77 million loan from the New Deal's Public Works Administration[21] To complete the electrification project initiated in 1928, work was started January 27, 1937, on the main line from Paoli to Harrisburg; the low-grade freight line from Morrisville through Columbia to Enola Yard in Pennsylvania; the Port Road Branch from Perryville, Maryland to Columbia; the Jamesburg Branch and Amboy Secondary freight line from Monmouth Junction to South Amboy; and the Landover-South End freight line from Landover, Maryland through Washington to Potomac Yard in Alexandria, Virginia (now called the Landover Subdivision and RF&P Subdivision of CSX). In less than a year, on the following January 15, the first passenger train, the Metropolitan, went into operation over the newly electrified line from Philadelphia to Harrisburg. On April 15, the electrified freight service from Harrisburg and Enola Yard east was inaugurated, thus completing the Pennsy's eastern seaboard electrification program. The railroad had electrified 2,677 miles (4,308 km) of its track, representing 41% of the country's electrically operated standard railroad trackage. Portions of the electrified trackage are still in use, owned and operated by Amtrak as the Northeast Corridor and Keystone Corridor high-speed rail routes,[22] by SEPTA, and by NJTransit]].[citation needed]

text: Penn Central merger and Conrail[edit]

text:
Year
Traffic

1925
48,890

1933
26,818

1944
71,249

1960
42,775

1967
50,730

tag: table

text:
Year
Traffic

1925
4,518

1933
2,017

1944
13,047

1960
2,463

1967
1,757

text: On February 1, 1968, the PRR merged with its arch-rival, the New York Central railroad, to form the Penn Central. The Interstate Commerce Commission (ICC) required that the ailing New York, New Haven & Hartford Railroad be added in 1969. A series of events including inflation, poor management, abnormally harsh weather conditions and the withdrawal of a government-guaranteed $200 million operating loan forced the Penn Central to file for bankruptcy protection on June 21, 1970.[5] The Penn Central rail lines were split between Amtrak (Northeast Corridor and Keystone Corridor) and Conrail in the 1970s.

text: After the breakup of Conrail in 1999, the portion which had been PRR territory largely became part of the Norfolk Southern Railway. The few parts of the PRR that went to CSX after the Conrail split are (1) the western end of the Fort Wayne Line across western Ohio and northern Indiana, (2) the Pope's Creek Secondary in Maryland, just to the east of Washington, (3) the Landover Subdivision, a former Pennsy freight line in DC which connects to Amtrak's ex-Pennsy Northeast Corridor and CSX's ex-B&O Alexandria Extension on the north end and CSX's RF&P Subdivision on the south end via the ex-Pennsy "Long Bridge" across the Potomac River, and (4) the Terre Haute, Ind.-to-East St. Louis, Ill. segment of the St. Louis main line (the segment east of Terre Haute is former-New York Central).

text: Timeline[edit]

text:
1846: PRR is chartered to construct a rail line from Harrisburg to Pittsburgh, Pennsylvania.
1850: Construction begins on Altoona Works repair shop at Altoona, Pennsylvania.
1860–1890: PRR expands throughout the eastern U.S.

1869: PRR leases the Pittsburgh, Ft. Wayne & Chicago, formally giving it control of a direct route into the heart of the Midwest.

1885: The Congressional Limited Express from New York City-Washington, D.C. is introduced.
1887: Pennsylvania Limited service begins between New York-Chicago; first vestibuled train.[25]
1894: The Pennsylvania Pacific Corporation is formed by the PRR.
1902: Pennsylvania Special service begins between New York and Chicago replacing the Pennsylvania Limited.[26]
1906: An accident in Atlantic City kills 53 people
1910: Completion of the North River Tunnels under the Hudson River, providing direct service from New Jersey to Manhattan on electrified lines, terminating at the massive new Penn Station
1912: The Second Vice-President of the PRR, John Borland Thayer, is lost in the sinking of RMS Titanic at age of 49.[27]
1912: Broadway Limited was inaugurated, replacing the Pennsylvania Special.
1915: PRR electrifies its suburban Philadelphia lines to Paoli, Pennsylvania.[28][29]
1916: PRR adopts new motto, Standard Railroad of the World. The first I1s Decapod locomotive is completed, and switching locomotives of the A5s and B6sb class are introduced.
1917: Completion of the New York Connecting Railroad and the Hell Gate Bridge
1918: PRR stock bottoms at $40¼ (equal to $654.86 today), the lowest since 1877, due largely to Federal railroad control. Emergency freight is routed through New York Penn Station and the Hudson River tunnels by the USRA to relieve congestion. Locomotive class N1s is introduced for PRR's western lines; PRR electrifies suburban commuter line to Chestnut Hill.
1928–1938: PRR electrifies its New York–Washington, D.C. and Chicago–Philadelphia line between Harrisburg and Paoli, several Philadelphia and New York area commuter lines, and major through freight lines.
1943: An accident at Frankford Junction, Pennsylvania kills 79.
1946: PRR reported a net loss for the first time in its history.[30]
1951: An accident in Woodbridge, New Jersey kills 85 people.
1957: Steam locomotives are removed from active service in the PRR fleet.
1968: PRR merges with NYC to form the Penn Central Transportation Company (PC).

text: Equipment[edit]

text: The PRR's corporate symbol was the keystone, the commonwealth of Pennsylvania's state symbol, with the letters "PRR" intertwined inside. When colored, it was bright red with a silver-grey inline and lettering.

text: Paint schemes[edit]

text: As noted, PRR colors and paint schemes were standardized. Locomotives were painted in a shade of green so dark it seemed almost black. The official name for this color was DGLE (Dark Green Locomotive Enamel), though often referred to as "Brunswick Green." The undercarriage of the locomotives were painted in black, referred to as "True Black." The passenger cars of the PRR were painted Tuscan Red, a brick-colored shade of red. Some electric locomotives and most passenger-hauling diesel locomotives were also painted in Tuscan Red. Freight cars of the PRR had their own color, known as "Freight Car Color," an iron-oxide shade of red. On passenger locomotives and cars the lettering and outlining was originally done in real gold leaf. After World War II the lettering was done in a light shade of yellow called Buff Yellow.[31]

text: Signaling[edit]

text: PRR was one of the first railroads to replace semaphore signals with position-light signals.[32] Such signals, which featured a large round target with up to eight amber-colored lights in a circle and one in the center, could be lit in various patterns to convey different meanings, were more visible in fog, and remained effective even when one light in a row was inoperative.[33]

text: Signal aspects, or meanings, were displayed as rows of three lit lights. The aspects corresponded with upper-quadrant semaphore signal positions: vertical for "proceed", a 45° angle rising to the right for "approach", horizontal for "stop", a 45° angle rising to the left for "restriction", a "X" shape for "take siding", and a full circle (used in electrified territory) for "lower pantograph". Additional aspects were conveyed with a second target head below the first, either a single light, a partial target, or a full target. Separate Manual Block signal aspects existed as well.[33]

text: In later years, interlocking home signals north and west of Rockville (near Harrisburg) were modified so that the two outside lights in the horizontal "stop" row had red lenses; the center lamp would be extinguished when the signal displayed "stop".[33] Such "red-eye" lenses were also temporarily installed at Overbrook Interlocking near Philadelphia.[33]

text: Starting in the late 1920s, the PRR installed Pulse code cab signaling along certain tracks used by high-speed passenger trains. Information traveled through the rails using track circuits, was picked up by a sensor on the locomotive, and displayed in the engineer's cab. PRR ultimately installed cab signals on its New York-Washington, Philadelphia-Pittsburgh, and Pittsburgh-Indianapolis lines (the latter which was later downgraded by PC and ultimately abandoned by Conrail). PRR also experimented with cab signals without wayside signals, an approach later expanded by Conrail (Conemaugh line) and Norfolk Southern Railway (Cleveland line). Cab signals were subsequently adopted by several other U.S. railroads, especially on passenger lines. This technology, advanced for its time, is still used by Amtrak.[33]

text: Steam locomotives[edit]

text: For most of its existence, PRR was conservative in its locomotive choices and pursued standardization, both in locomotive types and their component parts.[34] Almost alone among U.S. railroads, the PRR designed most of its steam locomotive classes itself. It built most of them in Altoona, outsourcing only when PRR facilities could not keep up with the railroad's needs. In such cases, subcontractors were hired to build to PRR designs,[35] unlike most railroads that ordered to broad specifications and left most design choices to the builder.[34]

text: The PRR's favorite outsourcer was Baldwin Locomotive Works, which received its raw materials and shipped out its finished products on PRR lines. The two companies were headquartered in the same city; PRR and Baldwin management and engineers knew each other well. When the PRR and Baldwin shops were at capacity, orders went to the Lima Locomotive Works in Lima, Ohio.[35] Only as a last resort would the PRR use the American Locomotive Company (Alco), based in Schenectady, New York, which also built for PRR's rival, NYC.

text: The PRR had a design style that it favored in its locomotives. One example was the square-shouldered Belpaire firebox. This British-style firebox was a PRR trademark that was rarely used by other locomotive builders in the U. S. PRR also used track pans extensively to retrieve water for the locomotive while in motion. Using this system meant that the tenders of their locomotives had a comparatively large proportion of coal (which could not be taken on board while running) compared to water capacity. Locomotives of the PRR had a clean look to them. Only necessary devices were used and they were mounted neatly on the locomotive.[34] Smoke box fronts bore a round locomotive number board denoting a freight locomotive or a keystone number board denoting a passenger locomotive. Otherwise the smoke box was uncluttered except for a headlamp at the top and a steam-driven turbo-generator behind it. In later years the positions of the two were reversed, since the generator needs more maintenance than the lamp.[34]

text: Each class of steam locomotive was assigned a class designation.[32] Early on this was simply a letter, but when these ran short the scheme was changed so that each wheel arrangement had its own letter, and different types in the same arrangement had different numbers added to the letter. Subtypes were indicated by a lower-case letter; superheating was designated by an "s" until the mid-1920s, by which time all new locomotives were superheated. A K4sa class was a 4-6-2 "Pacific" type (K) of the fourth class of Pacifics designed by PRR. It was superheated (s) and was of the first variant type (a) after the original (unlettered). Steam locomotives remained part of the PRR fleet until 1957.

text: PRR's reliance on steam locomotives in the mid-20th century contributed to its decline. Steam locomotives require more maintenance than diesel locomotives, are less cost efficient, and require more personnel to operate. PRR was unable to update its roster during the World War II years; by the end of the war their roster was in rough shape. In addition, PRR was saddled with unsuccessful experimental steam locomotives such as the Q1, S1, and T1 "Duplex Drive" locomotives, and the S2 turbine locomotive. Unlike most of their competition, PRR did not acquire any 4-8-4 locomotives.

text: PRR's competitors managed this period better with their diesel locomotive rosters.[3] PRR voluntarily preserved a roundhouse full of representative steam locomotives at Northumberland, Pennsylvania in 1957 and kept them there for several decades. These locomotives, with the exception of I1sa #4483 which is on display at Hamburg, New York, are now at the Railroad Museum of Pennsylvania in Strasburg, Pennsylvania. In sharp contrast, NYC's Alfred E. Perlman deliberately scrapped all but two large steam locomotives, and these survived only by accident.

text: On December 18, 1987, the Commonwealth of Pennsylvania designated PRR's K4s as the official State Steam Locomotive. The two surviving locomotives are housed at Strasburg and Altoona.[36]

text: As of 2016[update] the only operable PRR Steam Locomotive is class B4a engine # 643, built in July 1901 in Altoona. Engine 643 is maintained by volunteers of the Williams Grove Historical Steam Engine Association outside of Harrisburg, and is operated several weekends each summer.[37] As of 2017[update] however, a major construction project has been underway since 2014, building a new operational example of a class T1 engine numbered 5550, as all original class T1 locomotives have been scrapped. The project is being undertaken by the Pennsylvania Railroad T1 Steam Locomotive Trust and is projected to be finished by 2030.[38]

text: Electric locomotives[edit]

text: When work on the Hudson River tunnels and New York's Penn Station was in progress, the type of electric locomotives to be used was an important consideration. At that time only a few electric locomotives existed. Several experimental locomotives were designed by railroad and Westinghouse engineers and tried on the West Jersey & Seashore Railroad track. From these tests the DD1 class was developed.[19] The DD1s were used in pairs (back to back). Thirty-three of these engines having Westinghouse equipment were built at Altoona. They were capable of speeds up to 85 miles per hour (137 km/h). Placed in service in 1910, they proved to be quite efficient.[citation needed]

text: Steel suburban passenger cars capable of being electrified for MU operation were designed due to the need for such cars in service to Penn Station through its associated tunnels and were designated MP54.[39] Designs for corresponding cars accommodating baggage and mail were produced also. Eight of these cars were electrified with DC equipment to provide shuttle service from Penn Station to Manhattan Transfer between 1910 and 1922. More extensive electrification plans required AC electrification, starting with 93 cars for the Paoli Line in 1915. With the expansion of the AC electrification, additional MP54 cars were electrified or purchased new until a total of 481 cars was reached in 1951. Replacement with newer types of cars began in 1958 and the last MP54 cars were retired in 1980.[citation needed]

text: The single FF1 appeared in 1917 and ran experimentally for a number of years in preparation for electrification over the Allegheny Mountains that never came to fruition. Its AC induction motors and side-rod drive powered six axles.[19] It developed a starting tractive force of 140,000 pounds, which was capable of ripping couplers out of the fragile wooden freight cars in use at the time.[40]:123

text: In 1924 another side-rod locomotive was designed: (the L5 class).[19] Two DC locomotives were built for the New York electrified zone and a third, road number 3930, was AC-equipped and put in service at Philadelphia. Later 21 more L-5 locomotives were built for the New York service. A six-wheeled switching engine was the next electric motive power designed, being classified as B1.[19] Of the first 16 AC engines, two were used at Philadelphia and 14 on the Bay Ridge line, while 12 DC-equipped engines were assigned to Sunnyside Yard in Queens, New York.

text: The O1 class was a light passenger type.[19] Eight of these engines were built from June 1930 to December 1931. The P5 class was also introduced, with two of this class being placed in service during July and August 1931.[41] Following these came the P5A, a slightly heavier design capable of traveling 80 miles per hour (130 km/h) and with a tractive force of 56,250 pounds. In all, 89 of these locomotives were built. The first had a box cab design and were placed in service in 1932. The following year, the last 28 under construction were redesigned to have a streamlined type of cab. Some engines underwent regearing for freight service.[citation needed]

text: In 1933 two entirely new locomotives were being planned: the R1 and the GG1 class. The R-1 had a rigid frame for its four driving axles, while the GG-1 had two frames which were articulated. Both of these prototypes, along with an O-1, a P5A and a K4s steam locomotive underwent exhaustive testing. Testing was conducted over a special section of test track near Claymont, Delaware and lasted for nearly two years.[41] As a result of these experiments, the GG1 type was chosen and the construction of 57 locomotives was authorized. The first GG1 was finished in April and by August 1935 all 57 were completed. These first GG1 engines were designated for passenger service, while most of the P5A type were made available for freight service. Some of the later-built GG1s were assigned to freight service as well. The total number of GG1s built was 139. They are rated at 4,620 horsepower (3,450 kW) at speeds of 100 mph (160 km/h).[citation needed]

text: On August 26, 1999, the U.S. Postal Service issued commemorative 33-cent All Aboard! 20th Century American Trains stamps. These commemorative stamps featured five celebrated American passenger trains from the 1930s and 1940s. One of the five stamps features an image of a GG-1 locomotive pulling the "Congressional Limited Express." The official Pennsylvania State Electric Locomotive is the GG-1 #4859. It received this designation on December 18, 1987, and is currently on display in Harrisburg, Pennsylvania.[36]

text: Diesel locomotives[edit]

text: In the mid-1940s, the PRR began to add diesel locomotives to their fleet. From 1945 through 1949 it purchased 60 E7 class locomotives from General Motors EMD (Electro-Motive Diesel). These units were given the classification EP20 by the PRR. Sixty of this number were designated "A" units, meaning that they had a cab for the train crew. The remaining 14 were designated "B" units; these were cabless booster units that were controlled by an "A" unit.[citation needed]

text: Another addition to the PRR diesel locomotive fleet was the Baldwin DR-12-8-1500/2, referred to as the "Centipede." Twenty-four of these units were purchased, and PRR classified them as BP60. These units had reliability problems and were soon obsolete. They were relegated to helper service.[citation needed]

text: In 1948 the PRR purchased twenty-seven DR-6 locomotives from Baldwin Locomotive Works. These units were given the PRR classification BP20. Originally for the passenger service fleet, these locomotive proved troublesome, and some were reclassified as BF16z freight locomotives.[citation needed]

text: From 1950–1952, the PRR purchased another group of 74 locomotives from EMD. These were EMD's E8 locomotives (successor to the E7). All of this group were "A" units. The PRR gave these units the classification EP22s. In 1956, the Pennsy opened bidding for a large order of diesel replacement locomotives. GM/EMD gave the PRR an exceptional deal on new, reliable GP9s, so the entire bid went to EMD. When this large diesel order arrived, the PRR was able to retire its entire remaining steam fleet, in 1957. Baldwin Locomotive Works (BLW) was counting on PRR (BLW's lifelong loyal customer) to keep the struggling company in business by purchasing at least some Baldwin diesels. When that did not happen, the 126-year-old company went bankrupt.[42]

text: From 1964-1965, they purchased 31 Alco C425's, numbered 2416-2446.[43][44]

text: Facilities[edit]

text: Altoona Works[edit]

text: In 1849, PRR officials developed plans to construct a repair facility at Altoona. Construction was started in 1850, and soon a long building was completed that housed a machine shop, woodworking shop, blacksmith shop, locomotive repair shop and foundry. This facility was later demolished to make room for continuing expansion. Additional PRR repair facilities were located in Harrisburg, Pittsburgh and Mifflin, and the Altoona Works expanded in adjacent Juniata, Pennsylvania. Inventor Alexander Graham Bell sent two assistants to the Altoona shops in 1875 to study the feasibility of installing telephone lines. In May 1877, telephone lines were installed for various departments to communicate with one another. Fort Wayne, Indiana, also held a key position for the railroad. By the turn of the 20th century, its repair shops and locomotive manufacturing facilities became known as the "Altoona of the West."[45]

text: By 1945 the Altoona Works had become one of the largest repair and construction facilities for locomotives and cars in the world.[46] During World War II, PRR facilities (including the Altoona Shops) were on target lists of German saboteurs. They were caught before they could complete their missions.[3]

text: In 1875, the Altoona Works started a testing department for PRR equipment. In following years, the Pennsylvania Railroad led the nation in the development of research and testing procedures of practical value for the railroad industry.[47] Use of the testing facilities was discontinued in 1968 and many of the structures were demolished.

text: Major passenger stations[edit]

text: The PRR built several grand passenger stations, alone or with other railroads. These architectural marvels, whose city name was usually preceded by "Penn Station", were the hubs for the PRR's passenger service. Many are still in use today, served by Amtrak and regional passenger carriers.

text: Broad Street Station – Philadelphia, Pennsylvania[edit]

text: Broad Street Station was the first of the great passenger stations built by the PRR. Opened in 1881, the station was expanded in the early 1890s by famed Philadelphia architect Frank Furness. For most of its existence it was with City Hall one of the crown jewels of Philadelphia's architecture, and until a 1923 fire had the largest train shed in the world (a 91 m span). It was the terminal for the PRR in Philadelphia, bringing trains into the center of the city. It was demolished in 1953 after the PRR moved to 30th Street Station.

text: 30th Street Station – Philadelphia, Pennsylvania[edit]

text: 30th Street Station displays its majestic—and traditional—architectural style with its enormous waiting room and its vestibules. The station, in spite of its architectural classicism, opened in 1933, when modern and Art Deco styles were more popular. Its construction was needed to accommodate increased intercity and suburban traffic. It replaced the 32nd Street Station (West Philadelphia). It is now the primary rail station in Philadelphia, serving long-distance and commuter trains.

text: Penn Station – Pittsburgh, Pennsylvania[edit]

text: Built 1898-1903, renovated in 1954 and partially repurposed in 1988, it was originally called "Union Station" as the terminal for some Pennsylvania Railroad subsidiaries.

text: Penn Station – Baltimore, Maryland[edit]

text: The main station of Baltimore, this Beaux-Arts building was built in 1911 from a design by architect Kenneth MacKenzie Murchison. It is currently served by Amtrak and MARC commuter service. Both approaches to the station are via tunnels, the B&P Tunnel to the south and the Union Tunnel to the north.

text: Union Station – Chicago, Illinois[edit]

text: The PRR, along with the Milwaukee Road and the Burlington Route, built Chicago's Union Station, the only one of Chicago's old stations still used as an intercity train station. It was designed by Graham, Anderson, Probst & White in the Beaux-Arts style.

text: Penn Station – Newark, New Jersey[edit]

text: Newark's Pennsylvania Station was designed by McKim, Mead and White. It opened in 1935, was completed in 1937 and was refurbished in 2007.[48] Its style is a mixture of Art Deco and Neo-Classical. All Amtrak trains stop here, and the station serves three commuter lines, PATH rapid transit to Jersey City and Manhattan, and the Newark Light Rail.

text: Penn Station – New York City, New York[edit]

text: The original Pennsylvania Station was designed by the noted architectural firm of McKim, Mead and White and was modeled on the Roman Baths of Caracalla; it was notable for its high vaulted ceilings. The station opened in 1910 to provide access to Manhattan from New Jersey without having to use a ferry, and was served by PRR's own trains as well as those of its subsidiary, the Long Island Rail Road. Infamously, the station was demolished for redevelopment in 1963. The only pieces to survive the demolition were the platforms, the tracks, and even some of the staircases. The station continues as an underground operation (serving Amtrak, New Jersey Transit and the LIRR) and is the busiest intercity railroad station in the United States.[49]

text: Union Station – Washington, D.C.[edit]

text: Union Station, built jointly with the B&O, served as a hub for PRR passenger services in the nation's capital, with connections to the B&O, and Southern Railway. The station was designed by architect Daniel Burnham and opened in 1908. The Richmond, Fredericksburg & Potomac Railroad provided a link to Richmond, Virginia, about 100 miles (160 km) to the south, where major north–south lines of the Atlantic Coast Line and Seaboard Air Line railroads provided service to the Carolinas, Georgia and Florida. Today Union Station is the location of Amtrak headquarters and serves Amtrak and regional commuter railroads (MARC and VRE).

text: Presidents[edit]

text:
Samuel V. Merrick (1847–1849)
William C. Patterson (1849–1852)
J. Edgar Thomson (1852–1874)
Thomas A. Scott (1874–1880)
George Brooke Roberts (1880–1896)
Frank Thomson (1897–1899)
Alexander J. Cassatt (1899–1906)
James McCrea (1907–1912)
Samuel Rea (1913–1925)
William W. Atterbury (1925–1935)
Martin W. Clement (1935–1948)
Walter S. Franklin (1948–1954)
James M. Symes (1954–1959)
Allen J. Greenough (1959–1968)
Stuart T. Saunders (1968–1970) Penn Central, CEO

text: The controlling non-institutional shareholders of PRR were, during the early 1960s, Henry Stryker Taylor, who was a part of the Jacob Bunn business dynasty of Illinois, and Howard Butcher III, a principal in the Philadelphia brokerage house of Butcher & Sherrerd (later Butcher & Singer).

text: Gallery[edit]

text:
PRR system map, November 1857

PRR system map, 1893

PRR eastern system map, 1899

Share of the Pennsylvania Railroad Company, issued 29. February 1912

PRR M1a at 1939 New York World's Fair

PRR S1 at 1939 New York World's Fair

PRR herald, Newark Penn Station

PRR Exchange Place Station, Jersey City, 1893

Penn Station New York, 1911

A DD1 electric locomotive approaching New York Penn Station, 1910

Amtrak and SEPTA commuter trains on electrified Main Line, Rosemont, Pennsylvania

Amtrak's Pennsylvanian on the electrified Main Line, Bryn Mawr, Pennsylvania.

text: Heritage Unit[edit]

text: As a part of Norfolk Southern's 30th anniversary, they painted 20 new locomotives into predecessor schemes. NS #8102, a GE ES44AC, was painted into the Pennsylvania RR scheme.


document_title: Canadian Open (badminton)

question_text: who has won the canada open women's doubles

question_tokens: who has won the canada open women 's doubles

root

text: Canadian Open (badminton)

text: Previous winners[edit]

text: Canadian National Championships and Canadian Open together[edit]

text:
Year
Men's singles
Women's singles
Men's doubles
Women's doubles
Mixed doubles

1957
 Dave F. McTaggart
 Judy Devlin
 Don K. Smythe
 H. "Budd" Porter
 Sue Devlin
 Judy Devlin
 Bobby Williams
 Ethel Marshall

1958
 Dave F. McTaggart
 Jean Miller
 Don K. Smythe
 H. "Budd" Porter
 Marjorie Shedd
 Joan Hennessy
 William Purcell
 Marjorie Shedd

1959
 Tan Joe Hok
 Judy Devlin
 Lim Say Hup
 Teh Kew San
 Sue Devlin
 Judy Devlin
 Don P. Davis
 Judy Devlin

1960
 Tan Joe Hok
 Marjorie Shedd
 Lim Say Hup
 Teh Kew San
 Lois Alston
 Beulah Armendariz
 Finn Kobberø
 Jean Miller

1961
 Erland Kops
 Marjorie Shedd
 Finn Kobberø
 Jörgen Hammergaard Hansen
 Marjorie Shedd
 Dorothy Tinline
 Finn Kobberø
 Jean Miller

text: Canadian Open[edit]

text:
Year
Men's singles
Women's singles
Men's doubles
Women's doubles
Mixed doubles

1962
 Ferry Sonneville
 Marjorie Shedd
 Jim Poole
 Bobby Williams
 Marjorie Shedd
 Dorothy Tinline
 Berndt Dahlberg
 Dorothy Tinline

1963
 Erland Kops
 Marjorie Shedd
 Erland Kops
 B. McGoig
 Marjorie Shedd
 Dorothy Tinline
 Erland Kops
 Claire Lovett

1964
 C. Ratanaseangsuang
 Jean Miller
 Eiichi Nagai
 Eiichi Sakai
 Marjorie Shedd
 Dorothy Tinline
 James Carnwath
 Marjorie Shedd

1965
 C. Ratanaseangsuang
 Jean Miller
 Jim Poole
 C. Ratanaseangsuang
 Tyna Barinaga
 Caroline Jensen
 B. McCoig
 Margaret Barand

1966
 Tan Aik Huang
 Judy Hashman
 Ng Boon Bee
 Tan Yee Khan
 Judy Hashman
 Susan Peard
 Ng Boon Bee
 Ulla Strand

1967
 Erland Kops
 Alison Daysmith
 Roger Mills
 Colin Beacom
 Patricia Moody
 Jean Miller
 Roger Mills
 Sharon Whittaker

1968
 Bruce Rollick
 Sharon Whittaker
 Sangob Rattanusorn
 Chavalert Chumkum
 Sharon Whittaker
 Mimi Nilsson
 Sangob Rattanusorn
 Lois Alston

1969
 Rudy Hartono
 Eva Twedberg
 Tony Jordan
 B. McGoig
 Retno Kustijah
 Minarni
 Darmadi
 Minarni

1970
 Ippei Kojima
 Tyna Barinaga
 Raphi Kanchanaraphi
 C. Ratanaseangsuang
 Susan Whetnall
 Margaret Boxall
 Ippei Kojima
 Susan Whetnall

1971
 Rudy Hartono
 Hiroe Yuki
 Ng Boon Bee
 Punch Gunalan
 Noriko Takagi
 Hiroe Yuki
 Ng Boon Bee
 Sylvia Ng

1972
 Derek Talbot
 Eva Twedberg
 Mike Tredgett
 Ray Stevens
 Anne Berglund
 Pernille Kaagard
 Flemming Delfs
 Pernille Kaagard

1973
 Jamie Paulson
 Nancy McKinley
 Jamie Paulson
 Yves Pare
 Margaret Beck
 Joke van Beusekom
No competition

1974
 Jamie Paulson
 Jane Youngberg
 Shoichi Toganoo
 Nobutaka Ikeda
 Jane Youngberg
 Barbara Welch
 Raphi Kanchanaraphi
 Barbara Welch

1975
 Ray Stevens
 Margaret Beck
 Mike Tredgett
 Ray Stevens
 Margaret Beck
 Joke van Beusekom
No competition

1976
 Bandid Jaiyen
 Wendy Clarkson
 Mike Tredgett
 Ray Stevens
 Margaret Lockwood
 Nora Gardner

1977
 Flemming Delfs
 Wendy Clarkson
 Thomas Kihlström
 Bengt Fröman
 Nora Perry
 Karen Puttick
 David Eddy
 Nora Perry

1978
 Flemming Delfs
 Wendy Clarkson
 Thomas Kihlström
 Bengt Fröman
 Sonoe Ohtsuka
 Kazuk Sekine
 Steen Skovgaard
 Wendy Clarkson

1979
 Morten Frost
 Fumiko Tookairin
 Christian Hadinata
 Ade Chandra
 Imelda Wiguno
 Verawaty Wiharjo
 Christian Hadinata
 Imelda Wiguno

1980
 Morten Frost
 Gillian Gilks
 Mike Tredgett
 Ray Stevens
 Nora Perry
 Jane Webster
 Mike Tredgett
 Nora Perry

1981
 Nick Yates
 Sam Yanquin
 Thomas Kihlström
 Ray Stevens
 Nora Perry
 Jane Webster
 Thomas Kihlström
 Gillian Gilks

1982
 Torbjörn Peterson
 Sally Podger
 Torbjörn Peterson
 Lars Wengberg
 Gillian Gilks
 Gillian Clark
 Billy Gilliland
 Karen Chapman

1983
 Misbun Sidek
 Kenneth Larsen
 Rashid Sidek
 Misbun Sidek
 Sally Podger
 Karen Beckman
 Mike Butler
 Claire Backhouse

1984
 Michael Kjeldsen
 Hong Chen
 Razif Sidek
 Misbun Sidek
 Gillian Gowers
 Karen Chapman
 Nigel Tier
 Gillian Gowers

1985
 Jens Peter Nierhoff
 Claire Backhouse-Sharpe
 Jens Peter Nierhoff
 Henrik Svarrer
 Johanne Falardeau
 Denyse Julien
 Billy Gilliland
 Nora Perry

1986
No competition

1987[1]
 Park Sung-bae
 Chun Sung-Suk
 Lee Deuk-choon
 Lee Sang-bok
 Kim Jung-Ja
 Cho Young-Suk
 Andy Goode
 Gillian Gowers

1988
 Steve Butler
 Zheng Baojun
 Jens Peter Nierhoff
 Henrik Svarrer
 Erica van Dijck
 Eline Coene
 Henrik Svarrer
 Erica van Dijck

1989
 Anders Neilson
 Denyse Julien
 Bryan Blanshard
 Mike Bitten
 Hwa Jung-Eun
 Joo Shon-hye
 Mike Bitten
 Doris Piché

1990
 Fung Permadi
 Vlada Chernyavskaya
 Ong Ewe Chye
 Rahman Sidek
 Denyse Julien
 Doris Piché
 Bryan Blanshard
 Denyse Julien

1991
 Steve Butler
 Elena Rybkina
 Jalani Sidek
 Razif Sidek
 Gillian Gowers
 Sara Sankey
 Nick Ponting
 Gillian Gowers

1992
 Ahn Jae-chang
 Hisako Mizui
 Cheah Soon Kit
 Soo Beng Kiang
 Pernille Dupont
 Lotte Olsen
 Thomas Lund
 Pernille Dupont

1993
 Thomas Stuer-Lauridsen
 Camilla Martin
 Thomas Lund
 Jon Holst-Christensen
 Pernille Dupont
 Lotte Olsen
 Thomas Lund
 Pernille Dupont

1994
 Lioe Tiong Ping
 Pernille Nedergaard
 Ade Sutrisna
 Candra Wijaya
 Rikke Olsen
 Helene Kirkegaard
 Jürgen Koch
 Irina Servova

1995
 Lee Kwang-jin
 Bang Soo-hyun
 Ha Tae-kwon
 Kang Kyung-jin
 Gil Young-ah
 Jang Hye-ock[2]
 Kim Dong-moon
 Gil Young-ah

1996
1998
No competition

1999
 Brian Abra
 Charmaine Reid
 Wang Wen
 Darryl Yung
 Robbyn Hermitage
 Milaine Cloutier
 Iain Sydie
 Denyse Julien

2000
 Jyri Aalto
 Takako Ida
 Ma Che Kong
 Yau Tsz Yuk
 Joanne Davies
 Sara Hardaker
 Peter Blackburn
 Rhonda Cator

2001
No competition

2002
 Colin Haughton
 Petra Overzier
 Brian Prevoe
 Philippe Bourett
 Lisa Parker
 Suzanne Rayappan
 Kristian Roebuck
 Natalie Munt

2003
 Hong Seung-ki
 Lee Eun-woo
 Hwang Ji-man
 Jung Hoong-min
 Lee Eun-woo
 Ha Jung-eun
 Hwang Ji-man
 Lee Eun-woo

2004
 Aamir Ghaffar
 Julia Mann
 Paul Trueman
 Ian Palethorpe
 Lisa Parker
 Suzanne Rayappan
 Kristian Roebuck
 Lisa Parker

2005
 Hariawan
 Lee Yun-hwa
 Han Sung-wook
 Kang Kyung-jin
 Jun Woul-sik
 Ra Kyung-min
 Han Sung-wook
 Joo Hyun-hee

2006
 Toby Honey
 Eva Lee
 William Milroy
 Mike Beres
 Mesinee Mangkalakiri
 Eva Lee
 Howard Bach
 Eva Lee

2007
 Lee Tsuen Seng
 Lee Yun-hwa
 William Milroy
 Mike Beres
 Hwang Yu-mi
 Ha Jung-eun
 William Milroy
 Tammy Sun

2008
2009
No competition

2010
 Taufik Hidayat
 Zhu Lin
 Fang Chieh-Min
 Lee Sheng-Mu
 Chien Yu-Chin
 Cheng Wen-Hsing
 Lee Sheng-Mu
 Cheng Wen-Hsing

2011
 Marc Zwiebler
 Cheng Shao-chieh
 Ko Sung-hyun
 Lee Yong-dae
 Cheng Shu
 Bao Yixin
 Michael Fuchs
 Birgit Michels

2012
 Chou Tien-chen
 Nozomi Okuhara
 Takeshi Kamura
 Keigo Sonoda
 Misaki Matsutomo
 Ayaka Takahashi
 Ryota Taohata
 Ayaka Takahashi

2013
 Tan Chun Seang
 Nichaon Jindapon
 Maneepong Jongjit
 Nipitphon Puangpuapech
 Huang Yaqiong
 Yu Xiaohan
 Lee Chun Hei
 Chau Hoi Wah

2014
 Lee Hyun-il
 Michelle Li
 Liang Jui-wei
 Lu Chia-bin
 Choi Hye-in
 Lee So-hee
 Max Schwenger
 Carla Nelte

2015
 Lee Chong Wei
 Michelle Li
 Li Junhui
 Liu Yuchen
 Jwala Gutta
 Ashwini Ponnappa
 Lee Chun Hei
 Chau Hoi Wah

2016
 B. Sai Praneeth
 Michelle Li
 Manu Attri
 B. Sumeeth Reddy
 Setyana Mapasa
 Gronya Somerville
 Do Tuan Duc
 Pham Nhu Thao

2017
 Kanta Tsuneyama
 Saena Kawakami
 Peter Briggs
 Tom Wolfenden
 Mayu Matsumoto
 Wakana Nagahara
 Kim Won-ho
 Shin Seung-chan

text: Performances by nation[edit]

text:
Pos
Nation
MS
WS
MD
WD
XD
Total

1
 Canada
7
20
8
9.5
14.5
59

2
 England
5
2
7.5
13.5
12.5
40.5

3
 Denmark
10
3
5.5
4
10.5
33

4
 South Korea
5
5
5
6
4
25

5
 Japan
2
4
3
5
2.5
16.5

6
 Malaysia
4
0
9
0
2.5
15.5

7
 Indonesia
7
1
2
1
1
12

8
 Thailand
3
1
3.5
0
1.5
9

9
 Sweden
1
2
3
0
2.5
8.5

10
 Germany
1
1
0
0
2
4

11
 India
1
0
1
1
0
3

12
 Scotland
0
0
0
0
1
1


document_title: Sohrai

question_text: jharkhand which festival is associated with cattle worship

text: Sohrai

text: This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2017) (Learn how and when to remove this template message)

text: Sohrai is a festival of Santal and oraon people of the Indian states of Jharkhand , Bihar ,Orisa, Chattisgarh and West Bengal. It is a cattle worship festival and is celebrated during October -November (in Ranchi), December–January (in Dumka)

tag: p

text: In Hazaribagh district of Jharkhand an indigenous art form is practised by the women. Ritualistic art is done on mud walls to welcome the harvest and to celebrate the cattle.

text: Legend[edit]

text: Marang Buru (God of mountain), Jaher Ayo (Goddess of forest) and the elder sister of the Santhals would descend on earth from heaven to visit their brothers.

text: Arts[edit]

text: The women clean their houses and decorate their walls with murals of Sohrai arts. This art form has continued since 10,000-4,000 BC. It was prevalent mostly in caves, but shifted to houses with mud walls[1].

text: This Sohrai art form is usually either monochromatic or colorful. The people coat the wall with a layer of white mud, and while the layer is still wet, they draw with their fingertips on it. Their designs range from flowers and fruits to various other nature-inspired designs. The cow dung that was earlier used to cake the walls of the house is used to add colour. The dark outline is visible due to the previously applied contrasting white mud coat. Sohrai artists are spontaneous in their drawing. Little pre-planning is evident. The canvases range up to 12 x 18 feet..The designs are usually drawn from the artist's memory. The personal experience of the artist, and their interaction with nature are the biggest influence.

text: Girls are little educated or uneducated. This form of art is derived from the study of nature

text: The harvest festival is the time of the year when they exhibit their artistic skills and expressions. Every year, after the festival is over, the drawings and patterns created during this time are erased. This festival usually takes place in the month October or November for three days.


document_title: Cell nucleus

question_text: what is the center of heredity in a cell

text: Cell nucleus

text: History

text: The nucleus was the first organelle to be discovered. What is most likely the oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek (1632–1723). He observed a "lumen", the nucleus, in the red blood cells of salmon.[1] Unlike mammalian red blood cells, those of other vertebrates still contain nuclei.

text: The nucleus was also described by Franz Bauer in 1804[2] and in more detail in 1831 by Scottish botanist Robert Brown in a talk at the Linnean Society of London. Brown was studying orchids under microscope when he observed an opaque area, which he called the "areola" or "nucleus", in the cells of the flower's outer layer.[3]

text: He did not suggest a potential function. In 1838, Matthias Schleiden proposed that the nucleus plays a role in generating cells, thus he introduced the name "cytoblast" (cell builder). He believed that he had observed new cells assembling around "cytoblasts". Franz Meyen was a strong opponent of this view, having already described cells multiplying by division and believing that many cells would have no nuclei. The idea that cells can be generated de novo, by the "cytoblast" or otherwise, contradicted work by Robert Remak (1852) and Rudolf Virchow (1855) who decisively propagated the new paradigm that cells are generated solely by cells ("Omnis cellula e cellula"). The function of the nucleus remained unclear.[4]

text: Between 1877 and 1878, Oscar Hertwig published several studies on the fertilization of sea urchin eggs, showing that the nucleus of the sperm enters the oocyte and fuses with its nucleus. This was the first time it was suggested that an individual develops from a (single) nucleated cell. This was in contradiction to Ernst Haeckel's theory that the complete phylogeny of a species would be repeated during embryonic development, including generation of the first nucleated cell from a "monerula", a structureless mass of primordial mucus ("Urschleim"). Therefore, the necessity of the sperm nucleus for fertilization was discussed for quite some time. However, Hertwig confirmed his observation in other animal groups, including amphibians and molluscs. Eduard Strasburger produced the same results for plants in 1884. This paved the way to assign the nucleus an important role in heredity. In 1873, August Weismann postulated the equivalence of the maternal and paternal germ cells for heredity. The function of the nucleus as carrier of genetic information became clear only later, after mitosis was discovered and the Mendelian rules were rediscovered at the beginning of the 20th century; the chromosome theory of heredity was therefore developed.[4]

text: Structures

text:
The nucleus is the largest cellular organelle in animal cells.[5]
In mammalian cells, the average diameter of the nucleus is approximately 6 micrometres (µm), which occupies about 10% of the total cell volume.[6] The viscous liquid within it is called nucleoplasm (or karyolymph), and is similar in composition to the cytosol found outside the nucleus.[7] It appears as a dense, roughly spherical or irregular organelle. The composition by dry weight of the nucleus is approximately: DNA 9%, RNA 1%, Histone Protein 11%, Residual Protein 14%, Acidic Proteins 65%.

text: Nuclear envelope and pores

text:
The eukaryotic cell nucleus. Visible in this diagram are the ribosome-studded double membranes of the nuclear envelope, the DNA (complexed as chromatin), and the nucleolus. Within the cell nucleus is a viscous liquid called nucleoplasm, similar to the cytoplasm found outside the nucleus.

 A cross section of a nuclear pore on the surface of the nuclear envelope (1). Other diagram labels show (2) the outer ring, (3) spokes, (4) basket, and (5) filaments.

text: The nuclear envelope, otherwise known as nuclear membrane, consists of two cellular membranes, an inner and an outer membrane, arranged parallel to one another and separated by 10 to 50 nanometres (nm). The nuclear envelope completely encloses the nucleus and separates the cell's genetic material from the surrounding cytoplasm, serving as a barrier to prevent macromolecules from diffusing freely between the nucleoplasm and the cytoplasm.[8] The outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum (RER), and is similarly studded with ribosomes.[8] The space between the membranes is called the perinuclear space and is continuous with the RER lumen.

text: Nuclear pores, which provide aqueous channels through the envelope, are composed of multiple proteins, collectively referred to as nucleoporins. The pores are about 125 million daltons in molecular weight and consist of around 50 (in yeast) to several hundred proteins (in vertebrates).[5] The pores are 100 nm in total diameter; however, the gap through which molecules freely diffuse is only about 9 nm wide, due to the presence of regulatory systems within the center of the pore. This size selectively allows the passage of small water-soluble molecules while preventing larger molecules, such as nucleic acids and larger proteins, from inappropriately entering or exiting the nucleus. These large molecules must be actively transported into the nucleus instead. The nucleus of a typical mammalian cell will have about 3000 to 4000 pores throughout its envelope,[9] each of which contains an eightfold-symmetric ring-shaped structure at a position where the inner and outer membranes fuse.[10] Attached to the ring is a structure called the nuclear basket that extends into the nucleoplasm, and a series of filamentous extensions that reach into the cytoplasm. Both structures serve to mediate binding to nuclear transport proteins.[5]

text: Most proteins, ribosomal subunits, and some DNAs are transported through the pore complexes in a process mediated by a family of transport factors known as karyopherins. Those karyopherins that mediate movement into the nucleus are also called importins, whereas those that mediate movement out of the nucleus are called exportins. Most karyopherins interact directly with their cargo, although some use adaptor proteins.[11] Steroid hormones such as cortisol and aldosterone, as well as other small lipid-soluble molecules involved in intercellular signaling, can diffuse through the cell membrane and into the cytoplasm, where they bind nuclear receptor proteins that are trafficked into the nucleus. There they serve as transcription factors when bound to their ligand; in the absence of a ligand, many such receptors function as histone deacetylases that repress gene expression.[5]

text: Nuclear lamina

text: In animal cells, two networks of intermediate filaments provide the nucleus with mechanical support: The nuclear lamina forms an organized meshwork on the internal face of the envelope, while less organized support is provided on the cytosolic face of the envelope. Both systems provide structural support for the nuclear envelope and anchoring sites for chromosomes and nuclear pores.[6]

text: The nuclear lamina is composed mostly of lamin proteins. Like all proteins, lamins are synthesized in the cytoplasm and later transported to the nucleus interior, where they are assembled before being incorporated into the existing network of nuclear lamina.[12][13] Lamins found on the cytosolic face of the membrane, such as emerin and nesprin, bind to the cytoskeleton to provide structural support. Lamins are also found inside the nucleoplasm where they form another regular structure, known as the nucleoplasmic veil,[14] that is visible using fluorescence microscopy. The actual function of the veil is not clear, although it is excluded from the nucleolus and is present during interphase.[15] Lamin structures that make up the veil, such as LEM3, bind chromatin and disrupting their structure inhibits transcription of protein-coding genes.[16]

text: Like the components of other intermediate filaments, the lamin monomer contains an alpha-helical domain used by two monomers to coil around each other, forming a dimer structure called a coiled coil. Two of these dimer structures then join side by side, in an antiparallel arrangement, to form a tetramer called a protofilament. Eight of these protofilaments form a lateral arrangement that is twisted to form a ropelike filament. These filaments can be assembled or disassembled in a dynamic manner, meaning that changes in the length of the filament depend on the competing rates of filament addition and removal.[6]

text: Mutations in lamin genes leading to defects in filament assembly cause a group of rare genetic disorders known as laminopathies. The most notable laminopathy is the family of diseases known as progeria, which causes the appearance of premature aging in its sufferers. The exact mechanism by which the associated biochemical changes give rise to the aged phenotype is not well understood.[17]

text: Chromosomes

text: The cell nucleus contains the majority of the cell's genetic material in the form of multiple linear DNA molecules organized into structures called chromosomes. Each human cell contains roughly two meters of DNA. During most of the cell cycle these are organized in a DNA-protein complex known as chromatin, and during cell division the chromatin can be seen to form the well-defined chromosomes familiar from a karyotype. A small fraction of the cell's genes are located instead in the mitochondria.

text: There are two types of chromatin. Euchromatin is the less compact DNA form, and contains genes that are frequently expressed by the cell.[18] The other type, heterochromatin, is the more compact form, and contains DNA that is infrequently transcribed. This structure is further categorized into facultative heterochromatin, consisting of genes that are organized as heterochromatin only in certain cell types or at certain stages of development, and constitutive heterochromatin that consists of chromosome structural components such as telomeres and centromeres.[19] During interphase the chromatin organizes itself into discrete individual patches,[20] called chromosome territories.[21] Active genes, which are generally found in the euchromatic region of the chromosome, tend to be located towards the chromosome's territory boundary.[22]

text: Antibodies to certain types of chromatin organization, in particular, nucleosomes, have been associated with a number of autoimmune diseases, such as systemic lupus erythematosus.[23] These are known as anti-nuclear antibodies (ANA) and have also been observed in concert with multiple sclerosis as part of general immune system dysfunction.[24] As in the case of progeria, the role played by the antibodies in inducing the symptoms of autoimmune diseases is not obvious.

text: Nucleolus

text: The nucleolus is a discrete densely stained structure found in the nucleus. It is not surrounded by a membrane, and is sometimes called a suborganelle. It forms around tandem repeats of rDNA, DNA coding for ribosomal RNA (rRNA). These regions are called nucleolar organizer regions (NOR). The main roles of the nucleolus are to synthesize rRNA and assemble ribosomes. The structural cohesion of the nucleolus depends on its activity, as ribosomal assembly in the nucleolus results in the transient association of nucleolar components, facilitating further ribosomal assembly, and hence further association. This model is supported by observations that inactivation of rDNA results in intermingling of nucleolar structures.[25]

text: In the first step of ribosome assembly,  a protein called RNA polymerase I transcribes rDNA, which forms a large pre-rRNA precursor. This is cleaved into the subunits 5.8S, 18S, and 28S rRNA.[26] The transcription, post-transcriptional processing, and assembly of rRNA occurs in the nucleolus, aided by small nucleolar RNA (snoRNA) molecules, some of which are derived from spliced introns from messenger RNAs encoding genes related to ribosomal function. The assembled ribosomal subunits are the largest structures passed through the nuclear pores.[5]

text: When observed under the electron microscope, the nucleolus can be seen to consist of three distinguishable regions: the innermost fibrillar centers (FCs), surrounded by the dense fibrillar component (DFC), which in turn is bordered by the granular component (GC). Transcription of the rDNA occurs either in the FC or at the FC-DFC boundary, and, therefore, when rDNA transcription in the cell is increased, more FCs are detected. Most of the cleavage and modification of rRNAs occurs in the DFC, while the latter steps involving protein assembly onto the ribosomal subunits occur in the GC.[26]

text: Other subnuclear bodies

text:
Subnuclear structure sizes

Structure name

Structure diameter

Cajal bodies
0.2–2.0 µm
[27]

Clastosomes

0.2-0.5 µm

[28]

PIKA
5 µm
[29]

PML bodies
0.2–1.0 µm
[30]

Paraspeckles
0.2–1.0 µm
[31]

Speckles
20–25 nm
[29]

text: Besides the nucleolus, the nucleus contains a number of other non-membrane-delineated bodies. These include Cajal bodies, Gemini of coiled bodies, polymorphic interphase karyosomal association (PIKA), promyelocytic leukaemia (PML) bodies, paraspeckles, and splicing speckles. Although little is known about a number of these domains, they are significant in that they show that the nucleoplasm is not a uniform mixture, but rather contains organized functional subdomains.[30]

text: Other subnuclear structures appear as part of abnormal disease processes. For example, the presence of small intranuclear rods has been reported in some cases of nemaline myopathy. This condition typically results from mutations in actin, and the rods themselves consist of mutant actin as well as other cytoskeletal proteins.[32]

text: Cajal bodies and gems

text: A nucleus typically contains between 1 and 10 compact structures called Cajal bodies or coiled bodies (CB), whose diameter measures between 0.2 µm and 2.0 µm depending on the cell type and species.[27] When seen under an electron microscope, they resemble balls of tangled thread[29] and are dense foci of distribution for the protein coilin.[33] CBs are involved in a number of different roles relating to RNA processing, specifically small nucleolar RNA (snoRNA) and small nuclear RNA (snRNA) maturation, and histone mRNA modification.[27]

text: Similar to Cajal bodies are Gemini of Cajal bodies, or gems, whose name is derived from the Gemini constellation in reference to their close "twin" relationship with CBs. Gems are similar in size and shape to CBs, and in fact are virtually indistinguishable under the microscope.[33] Unlike CBs, gems do not contain small nuclear ribonucleoproteins (snRNPs), but do contain a protein called survival of motor neuron (SMN) whose function relates to snRNP biogenesis. Gems are believed to assist CBs in snRNP biogenesis,[34] though it has also been suggested from microscopy evidence that CBs and gems are different manifestations of the same structure.[33] Later ultrastructural studies have shown gems to be twins of Cajal bodies with the difference being in the coilin component; Cajal bodies are SMN positive and coilin positive, and gems are SMN positive and coilin negative.[35]

text: RAFA and PTF domains

text: RAFA domains, or polymorphic interphase karyosomal associations, were first described in microscopy studies in 1991. Their function remains unclear, though they were not thought to be associated with active DNA replication, transcription, or RNA processing.[36] They have been found to often associate with discrete domains defined by dense localization of the transcription factor PTF, which promotes transcription of small nuclear RNA (snRNA).[37]

text: PML bodies

text: Promyelocytic leukaemia bodies (PML bodies) are spherical bodies found scattered throughout the nucleoplasm, measuring around 0.1–1.0 µm. They are known by a number of other names, including nuclear domain 10 (ND10), Kremer bodies, and PML oncogenic domains. PML bodies are named after one of their major components, the promyelocytic leukemia protein (PML). They are often seen in the nucleus in association with Cajal bodies and cleavage bodies.[30] PML bodies belong to the nuclear matrix, an ill-defined super-structure of the nucleus proposed to anchor and regulate many nuclear functions, including DNA replication, transcription, or epigenetic silencing.[38] The PML protein is the key organizer of these domains that recruits an ever-growing number of proteins, whose only common known feature to date is their ability to be SUMOylated. Yet, pml-/- mice (which have their PML gene deleted) cannot assemble nuclear bodies, develop normally and live well, demonstrating that PML bodies are dispensable for most basic biological functions.[38]

text: Splicing speckles

text:
Speckles are subnuclear structures that are enriched in pre-messenger RNA splicing factors and are located in the interchromatin regions of the nucleoplasm of mammalian cells. At the fluorescence-microscope level they appear as irregular, punctate structures, which vary in size and shape, and when examined by electron microscopy they are seen as clusters of interchromatin granules. Speckles are dynamic structures, and both their protein and RNA-protein components can cycle continuously between speckles and other nuclear locations, including active transcription sites. Studies on the composition, structure and behaviour of speckles have provided a model for understanding the functional compartmentalization of the nucleus and the organization of the gene-expression machinery[39]
splicing snRNPs[40][41] and other splicing proteins necessary for pre-mRNA processing.[42] Because of a cell's changing requirements, the composition and location of these bodies changes according to mRNA transcription and regulation via phosphorylation of specific proteins.[43]
The splicing speckles are also known as nuclear speckles (nuclear specks), splicing factor compartments (SF compartments), interchromatin granule clusters (IGCs), B snurposomes.[44]
B snurposomes are found in the amphibian oocyte nuclei and in Drosophila melanogaster embryos. B snurposomes appear alone or attached to the Cajal bodies in the electron micrographs of the amphibian nuclei.[45]
IGCs function as storage sites for the splicing factors.[46]

text: Paraspeckles

text: Discovered by Fox et al. in 2002, paraspeckles are irregularly shaped compartments in the nucleus' interchromatin space.[47]  First documented in HeLa cells, where there are generally 10–30 per nucleus,[48] paraspeckles are now known to also exist in all human primary cells, transformed cell lines, and tissue sections.[49] Their name is derived from their distribution in the nucleus; the "para" is short for parallel and the "speckles" refers to the splicing speckles to which they are always in close proximity.[48]

text: Paraspeckles are dynamic structures that are altered in response to changes in cellular metabolic activity. They are transcription dependent[47] and in the absence of RNA Pol II transcription, the paraspeckle disappears and all of its associated protein components  (PSP1, p54nrb, PSP2, CFI(m)68, and PSF) form a crescent shaped perinucleolar cap in the nucleolus. This phenomenon is demonstrated during the cell cycle. In the cell cycle, paraspeckles are present during interphase and during all of mitosis except for telophase. During telophase, when the two daughter nuclei are formed, there is no RNA Pol II transcription so the protein components instead form a perinucleolar cap.[49]

text: Perichromatin fibrils

text: Perichromatin fibrils are visible only under electron microscope. They are located next to the transcriptionally active chromatin and are hypothesized to be the sites of active pre-mRNA processing.[46]

text: Clastosome

text: Clastosomes are small nuclear bodies (0.2-0.5 µm) described as donut-shaped due to the peripheral capsule around these bodies.[28] This name is derived from the Greek klastos, broken and soma, body.[28] Clastosomes are not typically present in normal cells, making them hard to detect. They form under high proteolysis conditions within the nucleus and degrade once there is a decrease in activity or if cells are treated with proteasome inhibitors.[28][50] The scarcity of clastosomes in cells indicates that they are not required for proteasome function.[51] Osmotic stress has also been shown to cause the formation of clastosomes.[52] These nuclear bodies contain catalytic and regulatory sub-units of the proteasome and its substrates, indicating that clastosomes are sites for degrading proteins.[51]

text: The Clastosome would be an important addition to the ‘Cell Nucleus’ Wiki page because it plays a role in cell function. With further research, we may discover that this nuclear body has a more influential job in cell function than what is already known.[28]

text: Function

text: The nucleus provides a site for genetic transcription that is segregated from the location of translation in the cytoplasm, allowing levels of gene regulation that are not available to prokaryotes. The main function of the cell nucleus is to control gene expression and mediate the replication of DNA during the cell cycle.

text: The nucleus is an organelle found in eukaryotic cells. Inside its fully enclosed nuclear membrane, it contains the majority of the cell's genetic material. This material is organized as DNA molecules, along with a variety of proteins, to form chromosomes.

text: Cell compartmentalization

text: The nuclear envelope allows the nucleus to control its contents, and separate them from the rest of the cytoplasm where necessary. This is important for controlling processes on either side of the nuclear membrane. In most cases where a cytoplasmic process needs to be restricted, a key participant is removed to the nucleus, where it interacts with transcription factors to downregulate the production of certain enzymes in the pathway. This regulatory mechanism occurs in the case of glycolysis, a cellular pathway for breaking down glucose to produce energy. Hexokinase is an enzyme responsible for the first the step of glycolysis, forming glucose-6-phosphate from glucose. At high concentrations of fructose-6-phosphate, a molecule made later from glucose-6-phosphate, a regulator protein removes hexokinase to the nucleus,[53] where it forms a transcriptional repressor complex with nuclear proteins to reduce the expression of genes involved in glycolysis.[54]

text: In order to control which genes are being transcribed, the cell separates some transcription factor proteins responsible for regulating gene expression from physical access to the DNA until they are activated by other signaling pathways. This prevents even low levels of inappropriate gene expression. For example, in the case of NF-κB-controlled genes, which are involved in most inflammatory responses, transcription is induced in response to a signal pathway such as that initiated by the signaling molecule TNF-α, binds to a cell membrane receptor, resulting in the recruitment of signalling proteins, and eventually activating the transcription factor NF-κB. A nuclear localisation signal on the NF-κB protein allows it to be transported through the nuclear pore and into the nucleus, where it stimulates the transcription of the target genes.[6]

text: The compartmentalization allows the cell to prevent translation of unspliced mRNA.[55] Eukaryotic mRNA contains introns that must be removed before being translated to produce functional proteins. The splicing is done inside the nucleus before the mRNA can be accessed by ribosomes for translation. Without the nucleus, ribosomes would translate newly transcribed (unprocessed) mRNA, resulting in malformed and nonfunctional proteins.

text: Gene expression

text: Gene expression first involves transcription, in which DNA is used as a template to produce RNA. In the case of genes encoding proteins, that RNA produced from this process is messenger RNA (mRNA), which then needs to be translated by ribosomes to form a protein. As ribosomes are located outside the nucleus, mRNA produced needs to be exported.[56]

text: Since the nucleus is the site of transcription, it also contains a variety of proteins that either directly mediate transcription or are involved in regulating the process. These proteins include helicases, which unwind the double-stranded DNA molecule to facilitate access to it, RNA polymerases, which bind to the DNA promoter to synthesize the growing RNA molecule, topoisomerases, which change the amount of supercoiling in DNA, helping it wind and unwind, as well as a large variety of transcription factors that regulate expression.[57]

text: Processing of pre-mRNA

text: Newly synthesized mRNA molecules are known as primary transcripts or pre-mRNA. They must undergo post-transcriptional modification in the nucleus before being exported to the cytoplasm; mRNA that appears in the cytoplasm without these modifications is degraded rather than used for protein translation. The three main modifications are 5' capping, 3' polyadenylation, and RNA splicing. While in the nucleus, pre-mRNA is associated with a variety of proteins in complexes known as heterogeneous ribonucleoprotein particles (hnRNPs). Addition of the 5' cap occurs co-transcriptionally and is the first step in post-transcriptional modification. The 3' poly-adenine tail is only added after transcription is complete.

text: RNA splicing, carried out by a complex called the spliceosome, is the process by which introns, or regions of DNA that do not code for protein, are removed from the pre-mRNA and the remaining exons connected to re-form a single continuous molecule. This process normally occurs after 5' capping and 3' polyadenylation but can begin before synthesis is complete in transcripts with many exons.[5] Many pre-mRNAs, including those encoding antibodies, can be spliced in multiple ways to produce different mature mRNAs that encode different protein sequences. This process is known as alternative splicing, and allows production of a large variety of proteins from a limited amount of DNA.

text: Dynamics and regulation

text: Nuclear transport

text: The entry and exit of large molecules from the nucleus is tightly controlled by the nuclear pore complexes. Although small molecules can enter the nucleus without regulation,[58] macromolecules such as RNA and proteins require association karyopherins called importins to enter the nucleus and exportins to exit. "Cargo" proteins that must be translocated from the cytoplasm to the nucleus contain short amino acid sequences known as nuclear localization signals, which are bound by importins, while those transported from the nucleus to the cytoplasm carry nuclear export signals bound by exportins. The ability of importins and exportins to transport their cargo is regulated by GTPases, enzymes that hydrolyze the molecule guanosine triphosphate to release energy. The key GTPase in nuclear transport is Ran, which can bind either GTP or GDP (guanosine diphosphate), depending on whether it is located in the nucleus or the cytoplasm. Whereas importins depend on RanGTP to dissociate from their cargo, exportins require RanGTP in order to bind to their cargo.[11]

text: Nuclear import depends on the importin binding its cargo in the cytoplasm and carrying it through the nuclear pore into the nucleus. Inside the nucleus, RanGTP acts to separate the cargo from the importin, allowing the importin to exit the nucleus and be reused. Nuclear export is similar, as the exportin binds the cargo inside the nucleus in a process facilitated by RanGTP, exits through the nuclear pore, and separates from its cargo in the cytoplasm.

text: Specialized export proteins exist for translocation of mature mRNA and tRNA to the cytoplasm after post-transcriptional modification is complete. This quality-control mechanism is important due to these molecules' central role in protein translation. Mis-expression of a protein due to incomplete excision of exons or mis-incorporation of amino acids could have negative consequences for the cell; thus, incompletely modified RNA that reaches the cytoplasm is degraded rather than used in translation.[5]

text: Assembly and disassembly

text:
During its lifetime, a nucleus may be broken down or destroyed, either in the process of cell division or as a consequence of apoptosis (the process of programmed cell death). During these events, the structural components of the nucleus — the envelope and lamina — can be systematically degraded.
In most cells, the disassembly of the nuclear envelope marks the end of the prophase of mitosis. However, this disassembly of the nucleus is not a universal feature of mitosis and does not occur in all cells. Some unicellular eukaryotes (e.g., yeasts) undergo so-called closed mitosis, in which the nuclear envelope remains intact. In closed mitosis, the daughter chromosomes migrate to opposite poles of the nucleus, which then divides in two. The cells of higher eukaryotes, however, usually undergo open mitosis, which is characterized by breakdown of the nuclear envelope. The daughter chromosomes then migrate to opposite poles of the mitotic spindle, and new nuclei reassemble around them.

text: At a certain point during the cell cycle in open mitosis, the cell divides to form two cells. In order for this process to be possible, each of the new daughter cells must have a full set of genes, a process requiring replication of the chromosomes as well as segregation of the separate sets. This occurs by the replicated chromosomes, the sister chromatids, attaching to microtubules, which in turn are attached to different centrosomes. The sister chromatids can then be pulled to separate locations in the cell. In many cells, the centrosome is located in the cytoplasm, outside the nucleus; the microtubules would be unable to attach to the chromatids in the presence of the nuclear envelope.[59] Therefore, the early stages in the cell cycle, beginning in prophase and until around prometaphase, the nuclear membrane is dismantled.[14] Likewise, during the same period, the nuclear lamina is also disassembled, a process regulated by phosphorylation of the lamins by protein kinases such as the CDC2 protein kinase.[60] Towards the end of the cell cycle, the nuclear membrane is reformed, and around the same time, the nuclear lamina are reassembled by dephosphorylating the lamins.[60]

text: However, in dinoflagellates, the nuclear envelope remains intact, the centrosomes are located in the cytoplasm, and the microtubules come in contact with chromosomes, whose centromeric regions are incorporated into the nuclear envelope (the so-called closed mitosis with extranuclear spindle). In many other protists (e.g., ciliates, sporozoans) and fungi, the centrosomes are intranuclear, and their nuclear envelope also does not disassemble during cell division.

text: Apoptosis is a controlled process in which the cell's structural components are destroyed, resulting in death of the cell. Changes associated with apoptosis directly affect the nucleus and its contents, for example, in the condensation of chromatin and the disintegration of the nuclear envelope and lamina. The destruction of the lamin networks is controlled by specialized apoptotic proteases called caspases, which cleave the lamin proteins and, thus, degrade the nucleus' structural integrity. Lamin cleavage is sometimes used as a laboratory indicator of caspase activity in assays for early apoptotic activity.[14] Cells that express mutant caspase-resistant lamins are deficient in nuclear changes related to apoptosis, suggesting that lamins play a role in initiating the events that lead to apoptotic degradation of the nucleus.[14] Inhibition of lamin assembly itself is an inducer of apoptosis.[61]

text: The nuclear envelope acts as a barrier that prevents both DNA and RNA viruses from entering the nucleus. Some viruses require access to proteins inside the nucleus in order to replicate and/or assemble. DNA viruses, such as herpesvirus replicate and assemble in the cell nucleus, and exit by budding through the inner nuclear membrane. This process is accompanied by disassembly of the lamina on the nuclear face of the inner membrane.[14]

text: Disease-related dynamics

text: Initially, it has been suspected that immunoglobulins in general and autoantibodies in particular do not enter the nucleus. Now there is a body of evidence that under pathological conditions (e.g. lupus erythematosus) IgG can enter the nucleus.[62]

text: Nuclei per cell

text: Most eukaryotic cell types usually have a single nucleus, but some have no nuclei, while others have several. This can result from normal development, as in the maturation of mammalian red blood cells, or from faulty cell division.

text: Anucleated cells

text: An anucleated cell contains no nucleus and is, therefore, incapable of dividing to produce daughter cells. The best-known anucleated cell is the mammalian red blood cell, or erythrocyte, which also lacks other organelles such as mitochondria, and serves primarily as a transport vessel to ferry oxygen from the lungs to the body's tissues. Erythrocytes mature through erythropoiesis in the bone marrow, where they lose their nuclei, organelles, and ribosomes. The nucleus is expelled during the process of differentiation from an erythroblast to a reticulocyte, which is the immediate precursor of the mature erythrocyte.[63] The presence of mutagens may induce the release of some immature "micronucleated" erythrocytes into the bloodstream.[64][65] Anucleated cells can also arise from flawed cell division in which one daughter lacks a nucleus and the other has two nuclei.

text: In flowering plants, this condition occurs in sieve tube elements.

text: Multinucleated cells

text: Multinucleated cells contain multiple nuclei. Most acantharean species of protozoa[66] and some fungi in mycorrhizae[67] have naturally multinucleated cells. Other examples include the intestinal parasites in the genus Giardia, which have two nuclei per cell.[68] In humans, skeletal muscle cells, called myocytes and syncytium, become multinucleated during development; the resulting arrangement of nuclei near the periphery of the cells allows maximal intracellular space for myofibrils.[5] Multinucleated and binucleated cells can also be abnormal in humans; for example, cells arising from the fusion of monocytes and macrophages, known as giant multinucleated cells, sometimes accompany inflammation[69] and are also implicated in tumor formation.[70]

text: A number of dinoflagellates are known to have two nuclei.[71] Unlike other multinucleated cells these nuclei contain two distinct lineages of DNA: one from the dinoflagellate and the other from a symbiotic diatom. The mitochondria and the plastids of the diatom somehow remain functional.

text: Evolution

text: As the major defining characteristic of the eukaryotic cell, the nucleus' evolutionary origin has been the subject of much speculation. Four major hypotheses have been proposed to explain the existence of the nucleus, although none have yet earned widespread support.[72]

text: The first model known as the "syntrophic model" proposes that a symbiotic relationship between the archaea and bacteria created the nucleus-containing eukaryotic cell. (Organisms of the Archaea and Bacteria domain have no cell nucleus.[73]) It is hypothesized that the symbiosis originated when ancient archaea, similar to modern methanogenic archaea, invaded and lived within bacteria similar to modern myxobacteria, eventually forming the early nucleus. This theory is analogous to the accepted theory for the origin of eukaryotic mitochondria and chloroplasts, which are thought to have developed from a similar endosymbiotic relationship between proto-eukaryotes and aerobic bacteria.[74] The archaeal origin of the nucleus is supported by observations that archaea and eukarya have similar genes for certain proteins, including histones. Observations that myxobacteria are motile, can form multicellular complexes, and possess kinases and G proteins similar to eukarya, support a bacterial origin for the eukaryotic cell.[75]

text: A second model proposes that proto-eukaryotic cells evolved from bacteria without an endosymbiotic stage. This model is based on the existence of modern planctomycetes bacteria that possess a nuclear structure with primitive pores and other compartmentalized membrane structures.[76]  A similar proposal states that a eukaryote-like cell, the chronocyte, evolved first and phagocytosed archaea and bacteria to generate the nucleus and the eukaryotic cell.[77]

text: The most controversial model, known as viral eukaryogenesis, posits that the membrane-bound nucleus, along with other eukaryotic features, originated from the infection of a prokaryote by a virus. The suggestion is based on similarities between eukaryotes and viruses such as linear DNA strands, mRNA capping, and tight binding to proteins (analogizing histones to viral envelopes). One version of the proposal suggests that the nucleus evolved in concert with phagocytosis to form an early cellular "predator".[78] Another variant proposes that eukaryotes originated from early archaea infected by poxviruses, on the basis of observed similarity between the DNA polymerases in modern poxviruses and eukaryotes.[79][80] It has been suggested that the unresolved question of the evolution of sex could be related to the viral eukaryogenesis hypothesis.[81]

text: A more recent proposal, the exomembrane hypothesis, suggests that the nucleus instead originated from a single ancestral cell that evolved a second exterior cell membrane; the interior membrane enclosing the original cell then became the nuclear membrane and evolved increasingly elaborate pore structures for passage of internally synthesized cellular components such as ribosomal subunits.[82]