Activation of the anaphase-promoting complex and degradation of cyclin B is not required for progression from Meiosis I to II in Xenopus oocytes.
Sister chromatid separation and cyclin degradation in mitosis depend on the association of the anaphase-promoting complex (APC) with the Fizzy protein (Cdc20), leading to the metaphase/anaphase transition and exit from mitosis [1--3]. In Xenopus, after metaphase of the first meiotic division, only partial cyclin degradation occurs, and chromosome segregation during anaphase I proceeds without sister chromatid separation [4--7]. We investigated the role of xFizzy during meiosis using an antisense depletion approach. xFizzy accumulates to high levels in Meiosis I, and injection of antisense oligonucleotides to xFizzy blocks nearly all APC-mediated cyclin B degradation and Cdc2/cyclin B (MPF) inactivation between Meiosis I and II. However, even without APC activation, xFizzy-ablated oocytes progress to Meiosis II as shown by cyclin E synthesis, further accumulation of cyclin B, and evolution of the metaphase I spindle to a metaphase II spindle via a disc-shaped aggregate of microtubules known to follow anaphase I [8]. Inhibition of the MAPK pathway by U0126 in antisense-injected oocytes prevents cyclin B accumulation beyond the level that is present at metaphase I. Full synthesis and accumulation can be restored in the presence of U0126 by the expression of a constitutively active form of the MAPK target, p90(Rsk). Thus, p90(Rsk) is sufficient not only to partially inhibit APC activity [7], but also to stimulate cyclin B synthesis in Meiosis II.
Taieb
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Howard Hughes Medical Institute and Department of Pharmacology, University of Colorado School of Medicine, 4200 East Ninth Avenue, Denver, CO 82062, USA.
Gross
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Lewellyn
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Maller
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JL
D000705:Anaphase; D000818:Animals; D016375:Antisense Elements (Genetics); D064199:Cdc20 Proteins; D064200:Cdh1 Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism / Q000502:physiology; D019926:Cyclin B / Q000378:metabolism*; D008540:Meiosis / Q000502:physiology*; D008677:Metaphase; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009865:Oocytes / Q000737:chemistry / Q000166:cytology* / Q000502:physiology; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D014981:Xenopus; D029867:Xenopus Proteins
D016375:Antisense Elements (Genetics); C577495:CDC20 protein, S cerevisiae; D064199:Cdc20 Proteins; D064200:Cdh1 Proteins; D018797:Cell Cycle Proteins; D019926:Cyclin B; D029701:Saccharomyces cerevisiae Proteins; D029867:Xenopus Proteins; C577588:fzr1 protein, Xenopus; D019893:Ribosomal Protein S6 Kinases; D020928:Mitogen-Activated Protein Kinases