Control of Cajal body number is mediated by the coilin C-terminus.
Cajal bodies (CBs) are nuclear suborganelles implicated in the post-transcriptional maturation of small nuclear and small nucleolar RNAs. The number of CBs displayed by various cell lines and tissues varies, and factors that control CB numbers within a given cell have yet to be described. In this report, we show that specific regions within the C-terminus of coilin, the CB marker protein, are responsible for regulating the number of nuclear foci. Despite the fact that the coilin N-terminal domain is responsible for its self-oligomerization activity, truncation or mutation of predicted sites of phosphorylation in the conserved C-terminal region leads to a striking alteration in the number of nuclear bodies. Similarly, coilin constructs from various species display differential propensities to form nuclear foci when expressed in heterologous backgrounds. We mapped the domain responsible for this variability to the coilin C-terminus utilizing chimeric proteins. Furthermore, the activities responsible for regulating coilin self-association must reside in the nucleus, as constructs lacking critical nuclear localization sequences fail to form foci in the cytoplasm. Factors controlling the putative signal transduction cascade that phosphorylates coilin are also discussed. The results point to a model whereby phosphorylation of the coilin C-terminus regulates the availability of the N-terminal self-interaction domain.
Shpargel
Karl B
KB
Department of Genetics, Center for Human Genetics and Program in Cell Biology, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, OH 44106-4955, USA.
Ospina
Jason K
JK
Tucker
Karen E
KE
Matera
A Gregory
AG
Hebert
Michael D
MD
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism* / Q000648:ultrastructure; D020541:Coiled Bodies / Q000378:metabolism* / Q000648:ultrastructure; D003593:Cytoplasm / Q000235:genetics; D005057:Eukaryotic Cells / Q000378:metabolism* / Q000648:ultrastructure; D005809:Genes, Regulator / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D017434:Protein Structure, Tertiary / Q000502:physiology; D012342:RNA, Small Nuclear / Q000235:genetics / Q000378:metabolism; D020537:RNA, Small Nucleolar / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics
D009687:Nuclear Proteins; D012342:RNA, Small Nuclear; D020537:RNA, Small Nucleolar; D011993:Recombinant Fusion Proteins; C068921:p80-coilin; D012694:Serine