[Interchromatin granule clusters of mouse preovulatory oocytes, organization, molecular composition and possible...

At the diplotene stage of meiotic prophase, the nucleus of mouse preovulatory oocytes contains multiple interchromatin granule clusters (IGC). These nuclear compartments are universal and evolutionary conserved and enriched in pre-mRNA splicing factors. Nowadays, IGCs are believed to play an important role in gene expression events and contain different molecular components that allow coupling of many processes from transcription to mRNA export. We obtained the data on the distributions of poly(A)+RNA, hnRNPS A/B, and NXF1/TAP factor of mRNA export. These factors were found to associate with IGCs of mouse preovulatory oocytes. In the present study, we have demonstrated for the first time the dynamics of large IGCs after specific phosphorilation of SR-proteins with okadaic acid, an inhibitor of protein phosphatases. Using electron microscopy, conventional fluorescent and confocal microscopies, as well as microinjections of olygonucleotide probes in mouse oocytes, some features of structural organization and molecular compositions of IGCs in the nuclei of mouse oocyte from antral follicles were established. Possible roles of IGCs in pre-mRNA metabolism and the participation of these structures in mRNA export are discussed.