title: U bodies are cytoplasmic structures that contain uridine-rich small nuclear ribonucleoproteins and associate with P bodies.
abstract: Uridine-rich small nuclear ribonucleoproteins (U snRNPs) are involved in key steps of pre-mRNA processing in the nucleus of eukaryotic cells. U snRNPs are enriched in the nucleus in discrete organelles that include speckles, Cajal bodies, and histone locus bodies. However, most U snRNPs are assembled in the cytoplasm, not in the nucleus. Despite extensive biochemical information, little is known about the spatial organization of U snRNPs in the cytoplasm. Here we show that U snRNPs in Drosophila are concentrated in discrete cytoplasmic structures, which we call U bodies, because they contain the major U snRNPs. In addition to snRNPs, U bodies contain essential snRNP assembly factors, suggesting that U bodies are sites for assembly or storage of snRNPs before their import into the nucleus. U bodies invariably associate with P bodies, which are involved in RNA surveillance and decay. Genetic disruption of P body components affects the organization of U bodies, suggesting that the two cytoplasmic bodies may cooperate in regulating aspects of snRNP metabolism. The identification of U bodies provides an opportunity to correlate specific biochemical steps of snRNP biogenesis with structural features of the cytoplasm.
authors.affiliation: Department of Embryology, Carnegie Institution of Washington, 3520 San Martin Drive, Baltimore, MD 21218, USA.
authors.forename: Ji-Long
authors.initials: JL
authors.lastname: Liu
authors.forename: Joseph G
authors.initials: JG
authors.lastname: Gall
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D004331:Drosophila melanogaster / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D005260:Female; D006367:HeLa Cells; D006801:Humans; D008830:Microbodies / Q000737:chemistry* / Q000378:metabolism*; D010053:Ovary / Q000166:cytology; D020885:Ribonucleoprotein, U7 Small Nuclear / Q000737:chemistry / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear / Q000737:chemistry / Q000378:metabolism*; D014529:Uridine / Q000737:chemistry / Q000378:metabolism*; D014981:Xenopus
chemical_list: D020885:Ribonucleoprotein, U7 Small Nuclear; D017411:Ribonucleoproteins, Small Nuclear; D014529:Uridine