Functional and molecular reorganization of the nucleolar apparatus in maturing mouse oocytes.
In mammalian preovulatory oocytes, rRNA synthesis is down-regulated until egg fertilization and zygotic genome reactivation, but the underlying regulatory mechanisms of this phenomenon are poorly characterized. We examined the molecular organization of the rRNA synthesis and processing machineries in fully grown mouse oocytes in relation to ongoing rDNA transcription and oocyte progression throughout meiosis. We show that, at the germinal vesicle stage, the two RNA polymerase I (RNA pol I) subunits, RPA116 and PAF53/RPA53, and the nucleolar upstream binding factor (UBF) remain present irrespective of ongoing rDNA transcription and colocalize in stoichiometric amounts within discrete foci at the periphery of the nucleolus-like bodies. These foci are spatially associated with the early pre-rRNA processing protein fibrillarin and in part with the pre-ribosome assembly factor B23/nucleophosmin. After germinal vesicle breakdown, the RNA pol I complex disassembles in a step-wise manner from chromosomes, while UBF remains associated with chromosomes until late prometaphase I. Dislodging of UBF, but not of RNA pol I, is impaired by the phosphatase inhibitor okadaic acid, thus strengthening the idea of a relationship between UBF dynamics and protein phosphorylation. Since neither RNA pol I, UBF, fibrillarin, nor B23 is detected at metaphase II, i.e., the normal stage of fertilization, we conclude that these nucleolar proteins are not transported to fertilized eggs by maternal chromosomes. Together, these data demonstrate an essential difference in the dynamics of the major nucleolar proteins during mitosis and meiosis.
Zatsepina
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A. N. Belozersky Institute of Physical and Chemical Biology, Moscow University, Moscow, 119899, Russia.
Bouniol-Baly
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Amirand
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Debey
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D000818:Animals; D002466:Cell Nucleolus / Q000502:physiology* / Q000648:ultrastructure; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D002875:Chromosomes / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D005260:Female; D005455:Fluorescent Antibody Technique; D007091:Image Processing, Computer-Assisted; D008540:Meiosis; D051379:Mice; D008856:Microscopy, Fluorescence; D008957:Models, Genetic; D009687:Nuclear Proteins / Q000378:metabolism; D000090243:Nucleophosmin; D019319:Okadaic Acid / Q000494:pharmacology; D009865:Oocytes / Q000502:physiology* / Q000648:ultrastructure; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D035463:Pol1 Transcription Initiation Complex Proteins; D012318:RNA Polymerase I / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012335:RNA, Ribosomal / Q000096:biosynthesis; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic
D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; C000715570:Npm1 protein, mouse; D009687:Nuclear Proteins; D035463:Pol1 Transcription Initiation Complex Proteins; D012335:RNA, Ribosomal; D014157:Transcription Factors; C047458:fibrillarin; C063844:transcription factor UBF; D000090243:Nucleophosmin; D019319:Okadaic Acid; D012318:RNA Polymerase I; D010749:Phosphoprotein Phosphatases