Submitted April 2, 2008
Returned for revision May 5, 2008
Accepted June 13, 2008
Gamete Biology
BRCA1 Is Required for Meiotic Spindle Assembly and Spindle Assembly Checkpoint Activation in Mouse Oocytes
Bo Xiong ,
Sen Li ,
Jun-Shu Ai ,
Shen Yin ,
Ying-Chun OuYang ,
Shao-Chen Sun ,
Da-Yuan Chen ,
and
Qing-Yuan Sun *
* To whom correspondence should be addressed. E-mail: sunqy{at}ioz.ac.cn.
Abstract
BRCA1, as a tumor suppressor, has been widely investigated in mitosis, but its functions in meiosis are unclear. In the present study, we examined the expression, localization and function of BRCA1 during mouse oocyte meiotic maturation. We found that expression level of BRCA1 was increased progressively from GV to MI stage, and then remained stable till MII stage. Immunofluorescent analysis showed that BRCA1 was localized to the spindle poles at metaphase I and metaphase II stages, colocolizing with centrosomal protein gamma-tubulin. Taxol treatment resulted in the presence of BRCA1 onto the spindle microtubule fibers, while nocodazole treatment induced the localization of BRCA1 onto the chromosomes. Depletion of BRCA1 by both antibody injection and siRNA injection caused severely impaired spindles as well as misaligned chromosomes. Furthermore, BRCA1-depleted oocytes could not arrest at the metaphase I in the presence of low-dose nocodazole, suggesting that the spindle checkpoint is defective. Also, in BRCA1-depleted oocytes, gamma-tubulin dissociated from spindle poles and MAD2L1 failed to rebind to the kinetochores when exposed to nocodazole at metaphase I stage. Collectively, these data indicate that BRCA1 regulates not only meiotic spindle assembly, but also spindle assembly checkpoint, implying a link between BRCA1 deficiency and aneuploid embryos.
Key words:
Gamete Biology •
Meiosis •
Oocyte development •
spindle assembly •
spindle assembly checkpoint
