Hypophosphorylated SR splicing factors transiently localize around active nucleolar organizing regions in telophase daughter nuclei.
Upon completion of mitosis, daughter nuclei assemble all of the organelles necessary for the implementation of nuclear functions. We found that upon entry into daughter nuclei, snRNPs and SR proteins do not immediately colocalize in nuclear speckles. SR proteins accumulated in patches around active nucleolar organizing regions (NORs) that we refer to as NOR-associated patches (NAPs), whereas snRNPs were enriched at other nuclear regions. NAPs formed transiently, persisting for 15-20 min before dissipating as nuclear speckles began to form in G1. In the absence of RNA polymerase II transcription, NAPs increased in size and persisted for at least 2 h, with delayed localization of SR proteins to nuclear speckles. In addition, SR proteins in NAPs are hypophosphorylated, and the SR protein kinase Clk/STY colocalizes with SR proteins in NAPs, suggesting that phosphorylation releases SR proteins from NAPs and their initial target is transcription sites. This work demonstrates a previously unrecognized role of NAPs in splicing factor trafficking and nuclear speckle biogenesis.
Bubulya
Paula A
PA
Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
Prasanth
Kannanganattu V
KV
Deerinck
Thomas J
TJ
Gerlich
Daniel
D
Beaudouin
Joel
J
Ellisman
Mark H
MH
Ellenberg
Jan
J
Spector
David L
DL
D002466:Cell Nucleolus / Q000648:ultrastructure*; D002467:Cell Nucleus / Q000201:enzymology / Q000378:metabolism / Q000648:ultrastructure; D018076:DNA, Complementary / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D009687:Nuclear Proteins / Q000378:metabolism; D009697:Nucleolus Organizer Region; D010766:Phosphorylation; D012319:RNA Polymerase II / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013692:Telophase; D013997:Time Factors; D014158:Transcription, Genetic; D014162:Transfection
D018076:DNA, Complementary; D009687:Nuclear Proteins; D012333:RNA, Messenger; D017411:Ribonucleoproteins, Small Nuclear; C068921:p80-coilin; D012319:RNA Polymerase II