title: snRNP protein expression enhances the formation of Cajal bodies containing p80-coilin and SMN.
abstract: Splicing snRNPs (small nuclear ribonucleoproteins) are essential sub-units of the spliceosome. Here we report the establishment of stable cell lines expressing fluorescently tagged SmB, a core snRNP protein. Analysis of these stable cell lines has allowed us to characterize the nuclear pathway that leads to snRNP accumulation in nuclear speckles and has identified a limiting nucleolar step in the pathway that can be saturated by overexpression of Sm proteins. After nuclear import, newly assembled snRNPs accumulate first in a subset of Cajal bodies that contain both p80-coilin and the survival of motor neurons protein (SMN) and not in bodies that contain p80-coilin but lack SMN. Treatment of cells with leptomycin B (LMB) inhibits both the accumulation of snRNPs in nuclear bodies and their subsequent accumulation in speckles. The formation of Cajal bodies is enhanced by Sm protein expression and the assembly of new snRNPs. Formation of heterokaryons between HeLa cell lines expressing Sm proteins and primary cells that usually lack Cajal bodies results in the detection of Cajal bodies in primary cell nuclei. Transient over-expression of exogenous SmB alone is sufficient to induce correspondingly transient Cajal body formation in primary cells. These data indicate that the level of snRNP protein expression and snRNP assembly, rather than the expression levels of p80-coilin or SMN, may be a key trigger for Cajal body formation.
authors.affiliation: School of Life Sciences, University of Dundee, MSI/WTB Complex, Dow Street, Dundee, DD1 5EH, UK.
authors.forename: J E
authors.initials: JE
authors.lastname: Sleeman
authors.forename: P
authors.initials: P
authors.lastname: Ajuh
authors.forename: A I
authors.initials: AI
authors.lastname: Lamond
mesh_terms: D001324:Autoantigens / Q000096:biosynthesis / Q000235:genetics; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D002459:Cell Fusion; D002467:Cell Nucleus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D020541:Coiled Bodies / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D017362:Cyclic AMP Response Element-Binding Protein; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D008164:Luminescent Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D009134:Muscular Atrophy, Spinal / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D017411:Ribonucleoproteins, Small Nuclear / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D055532:SMN Complex Proteins; D014162:Transfection; D055517:snRNP Core Proteins
chemical_list: D001324:Autoantigens; D001426:Bacterial Proteins; D017362:Cyclic AMP Response Element-Binding Protein; D005231:Fatty Acids, Unsaturated; D008164:Luminescent Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D017411:Ribonucleoproteins, Small Nuclear; D055532:SMN Complex Proteins; C526407:SNRPB protein, human; C526417:SNRPN protein, human; C409504:blue fluorescent protein, Aequorea victoria; D055517:snRNP Core Proteins; C054562:yellow fluorescent protein, Bacteria; C068921:p80-coilin; C038753:leptomycin B