XCdh1 is involved in progesterone-induced oocyte maturation

The molecular events triggered during progesterone-induced oocyte maturation in Xenopus are not well understood. One of the first events is the activation of the MAPK cascade and the maturation-promoting factor (MPF). The latter triggers meiosis I resumption and meiosis II progression until the metaphase II arrest. The release of the metaphase II is mediated by the anaphase-promoting complex (APC)-dependent degradation of cyclin B. This degradation activity requires the APC activator Cdc20 that activates ubiquitination reactions by recruiting substrates to the APC. However, recent reports in different organisms involve other APC regulators during different phases of the meiotic cycle. Therefore, we investigated the role of another APC regulator, XCdh1 during the G2/M transition in meiosis I in the Xenopus oocyte. Here, we report that XCdh1 protein is expressed in oocytes. Besides, injection of specific XCdh1 antisense inhibits progesterone-induced G2/M transition that can be rescued by adding back the purified human Cdh1 protein. On the other hand, ectopic expression of low levels of XCdh1 protein has a positive effect on the G2/M transition by facilitating this process. Moreover, the sole injection of XCdh1 mRNA triggers Mos protein synthesis and biphosphorylation of MAPK in absence of progesterone. Altogether, these data show that XCdh1 has a positive role during the G2/M transition in the oocyte. According to our results, its role could be independent of the APC.