title: Spliceosomal small nuclear ribonucleoprotein particles repeatedly cycle through Cajal bodies.
abstract: The Cajal body (CB) is a nuclear structure closely associated with import and biogenesis of small nuclear ribonucleoprotein particles (snRNPs). Here, we tested whether CBs also contain mature snRNPs and whether CB integrity depends on the ongoing snRNP splicing cycle. Sm proteins tagged with photoactivatable and color-maturing variants of fluorescent proteins were used to monitor snRNP behavior in living cells over time; mature snRNPs accumulated in CBs, traveled from one CB to another, and they were not preferentially replaced by newly imported snRNPs. To test whether CB integrity depends on the snRNP splicing cycle, two human orthologues of yeast proteins involved in distinct steps in spliceosome disassembly after splicing, hPrp22 and hNtr1, were depleted by small interfering RNA treatment. Surprisingly, depletion of either protein led to the accumulation of U4/U6 snRNPs in CBs, suggesting that reassembly of the U4/U6.U5 tri-snRNP was delayed. Accordingly, a relative decrease in U5 snRNPs compared with U4/U6 snRNPs was observed in CBs, as well as in nuclear extracts of treated cells. Together, the data show that particular phases of the spliceosome cycle are compartmentalized in living cells, with reassembly of the tri-snRNP occurring in CBs.
authors: Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, 142 20 Prague 4, Czech Republic. stanek@img.cas.cz
authors: David
authors: D
authors: Stanek
authors: Jarmila
authors: J
authors: Pridalová-Hnilicová
authors: Ivan
authors: I
authors: Novotný
authors: Martina
authors: M
authors: Huranová
authors: Michaela
authors: M
authors: Blazíková
authors: Xin
authors: X
authors: Wen
authors: Aparna K
authors: AK
authors: Sapra
authors: Karla M
authors: KM
authors: Neugebauer
mesh_terms: D015415:Biomarkers / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D020541:Coiled Bodies / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D034741:RNA, Small Interfering / Q000378:metabolism; D016601:RNA-Binding Proteins; D017414:Ribonucleoprotein, U4-U6 Small Nuclear / Q000378:metabolism; D017415:Ribonucleoprotein, U5 Small Nuclear / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear / Q000378:metabolism*; D017381:Spliceosomes / Q000378:metabolism*; D055533:Survival of Motor Neuron 1 Protein / Q000378:metabolism
chemical_list: D015415:Biomarkers; D002352:Carrier Proteins; C115374:PRPF8 protein, human; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D017414:Ribonucleoprotein, U4-U6 Small Nuclear; D017415:Ribonucleoprotein, U5 Small Nuclear; D017411:Ribonucleoproteins, Small Nuclear; D055533:Survival of Motor Neuron 1 Protein