Pharmacological manipulation of meiotic maturation in vitro: a comparative study between the amphibian-(Xenopus) and the mammalian (mouse)-oocyte.

The pharmacological manipulation of oocyte maturation in vitro offers an interesting tool for the study of the cell division cycle. The molecular mechanisms which are involved in this process are initiated at the oocyte plasma membrane and lead to a cascade of events, such as breakdown of the nuclear membrane (GVBD), chromosome condensation and cell division. Our pharmacological results point to an essential role for membrane in the communication between external information and intracellular signals mediating the physiological process. In Xenopus as well as in mouse oocytes, protein phosphorylation processes appear to be involved, either through the activation/inhibition of protein C kinase (calcium activated and phospholipid-dependent) and/or protein-A-kinase (cAMP dependent). Indeed in both systems, forskolin inhibits the first step of the process (GBVD) assessing the existence of an oocyte adenylate cyclase. Moreover, inhibitors of protein kinase C induce maturation in Xenopus oocyte whereas activators of this kinase prevent the process in denuded mouse oocytes. Interestingly, inhibitors of transmethylation reactions maintain the prophase block in both systems suggesting a role for membrane fluidity (phospholipid methylation) in the regulation of oocyte maturation.