Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 102, Issue 12, Pages 4318-4323Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0501108102
Keywords
cyclin B; meiosis; maturation-promoting factor; oocyte maturation
Categories
Funding
- NCI NIH HHS [T32 CA009151, 5T32 CA09302-27, T32 CA009302] Funding Source: Medline
- NIGMS NIH HHS [R01 GM60439, R01 GM054811, GM54811, R01 GM060439] Funding Source: Medline
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Unfertilized vertebrate eggs are arrested in metaphase of meiosis II with high cyclin B/Cdc2 activity to prevent parthenogenesis. Until fertilization, exit from metaphase is blocked by an activity called cytostatic factor (CSF), which stabilizes cyclin B by inhibiting the anaphase-promoting complex (APC) ubiquitin ligase. The APC inhibitor early mitotic inhibitor 1 (Emi1) was recently found to be required for maintenance of CSF arrest. We show here that exogenous Emi1 is unstable in CSF-arrested Xenopus eggs and is destroyed by the SCF beta TrCP ubiquitin ligase, suggesting that endogenous Emi1, an apparent 441-kDa protein, requires a stabilizing factor. However, anti-Emi1 antibodies crossreact with native Emi2/ Erp1/FBXO43, a homolog of Emi1 and conserved APC inhibitor. Emi2 is stable in CSF-arrested eggs, is sufficient to prevent CSF release, and is rapidly degraded in a Polo-like kinase 1-dependent manner in response to calcium-mediated egg activation. These results identify Emi2 as a candidate CSF maintenance protein.
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