Sm proteins, the constituents of the spliceosome, are components of nuage and mitochondrial cement in Xenopus oocytes.
A conserved feature of germ cells in many animal species is the presence of perinuclear electron-dense material called the "nuage" that is believed to be a precursor of germinal (or polar or P) granules. In Xenopus oogenesis the nuage is first observed near the nuclear envelope and subsequently in close contact with mitochondria, at which stage it is called the mitochondrial cement. In this study, we found that, in Xenopus pre-stage I and stage I oocytes, nuage and mitochondrial cement contain the spliceosomal Sm proteins, Xcat2 mRNA, and DEAD-box RNA helicase XVLG1. Other components of Cajal bodies or splicing machinery such as coilin, SMN protein, and snRNAs are absent from the nuage and mitochondrial cement. We suggest that Xenopus Sm proteins have adapted to a role independent of pre-mRNA splicing and that instead of binding to their traditional spliceosomal partner such as snRNA, they bind mRNAs that are the components of germinal granules (i.e., Xcat2 mRNA) and facilitate the transport of these mRNAs from the nucleus to the nuage that is a precursor of germinal granules. In addition, the presence of Vasa-like DEAD-box helicase in Xenopus nuage suggests involvement of nuage in the microRNA and/or RNAi pathway, similar to the role of nuage in Drosophila.
Institute of Zoology, Jagiellonian University, Cracow, Poland.
Szczepan M
SM
Bilinski
Mariusz K
MK
Jaglarz
Beata
B
Szymanska
Laurence D
LD
Etkin
Malgorzata
M
Kloc
D021581:Active Transport, Cell Nucleus / Q000235:genetics; D000818:Animals; D001324:Autoantigens; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism; D005260:Female; D035683:MicroRNAs / Q000235:genetics; D008854:Microscopy, Electron; D008928:Mitochondria / Q000378:metabolism* / Q000648:ultrastructure; D009865:Oocytes / Q000378:metabolism* / Q000648:ultrastructure; D011485:Protein Binding / Q000235:genetics; D012326:RNA Splicing / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D012342:RNA, Small Nuclear / Q000235:genetics; D016601:RNA-Binding Proteins / Q000235:genetics*; D012097:Repressor Proteins; D017411:Ribonucleoproteins, Small Nuclear / Q000235:genetics / Q000378:metabolism*; D017381:Spliceosomes / Q000378:metabolism* / Q000648:ultrastructure; D029867:Xenopus Proteins / Q000235:genetics*; D014982:Xenopus laevis / Q000033:anatomy & histology / Q000378:metabolism*; D055517:snRNP Core Proteins
D001324:Autoantigens; C086637:DDX4 protein, Xenopus; D035683:MicroRNAs; D012333:RNA, Messenger; D012342:RNA, Small Nuclear; D016601:RNA-Binding Proteins; D012097:Repressor Proteins; D017411:Ribonucleoproteins, Small Nuclear; D029867:Xenopus Proteins; C558784:nanos1 protein, Xenopus; D055517:snRNP Core Proteins