title: Cdc6 synthesis regulates replication competence in Xenopus oocytes.
abstract: The early division cycles of an embryo rely on the oocyte's ability to replicate DNA. During meiosis, oocytes temporarily lose this ability. After a single round of pre-meiotic S-phase, oocytes enter meiosis and rapidly arrest at prophase of meiosis I (G2). Upon hormonal stimulation, arrested oocytes resume meiosis, re-establish DNA replication competence in meiosis I shortly after germinal vesicle breakdown (GVBD), but repress replication until fertilization. How oocytes lose and regain replication competence during meiosis are important questions underlying the production of functional gametes. Here we show that the inability of immature Xenopus oocytes to replicate is linked to the absence of the Cdc6 protein and the cytoplasmic localization of other initiation proteins. Injection of Cdc6 protein into immature oocytes does not induce DNA replication. However, injection of Cdc6 into oocytes undergoing GVBD is sufficient to induce DNA replication in the absence of protein synthesis. Our results show that GVBD and Cdc6 synthesis are the only events that limit the establishment of the oocyte's replication competence during meiosis.
authors.affiliation: Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, 3601 4th Street, Lubbock, Texas 79430, USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Whitmire
authors.forename: Bettina
authors.initials: B
authors.lastname: Khan
authors.forename: Martine
authors.initials: M
authors.lastname: Coué
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002455:Cell Division; D002457:Cell Extracts; D002868:Chromosomal Proteins, Non-Histone / Q000096:biosynthesis* / Q000378:metabolism*; D004261:DNA Replication; D004268:DNA-Binding Proteins; D005260:Female; D005306:Fertilization; D008540:Meiosis; D009687:Nuclear Proteins / Q000378:metabolism; D009865:Oocytes / Q000166:cytology* / Q000378:metabolism*; D010063:Ovum / Q000166:cytology / Q000378:metabolism; D010766:Phosphorylation; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D029867:Xenopus Proteins; D014982:Xenopus laevis
chemical_list: C102209:CDC45 protein, S cerevisiae; D002352:Carrier Proteins; C118388:Cdc6 protein, Xenopus; D002457:Cell Extracts; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D029867:Xenopus Proteins