Pharmacological regulation in vitro of meiotic resumption in oocytes of Xenopus laevis.

The pharmacological control in vitro of meiotic resumption in Xenopus laevis oocytes was undertaken with a variety of drugs or agents which either mimic a steroidal hormone, progesterone, the physiological inducer of meiosis in vivo and in vitro, potentiate progesterone-induced meiosis (e.g. insulin) or inhibit the action of steroidal and non-steroidal inducers. Most steroidal and non-steroidal inducers trigger a cascade of cellular events which seem to be initiated at the oocyte membrane. One membrane target seems to be the enzyme adenylate cyclase which is inhibited (with concomitant dephosphorylation of yet unknown cellular substrates) by progesterone as well by several other inducers, or activated by inhibitors of meiosis such as cholera toxin or forskolin. However, additional, complementary or subsequent interaction(s) of inducers with other membrane and/or cellular constituents, such as calcium, phospholipids and protein kinase C have been also suggested by experiments with cycloheximide (a protein synthesis inhibitor) or with a serine protease inhibitor, which both inhibit progesterone-induced meiosis. Furthermore, dideoxyadenosine was shown to decrease particulate adenylate cyclase, although it did not induce meiosis in vitro. It is hoped that the great variety of pharmacological agents which can be used at the present time to study in vitro the meiotic resumption of Xenopus laevis oocytes may help to clarify the complex sequence of meiotic events which start at the cell membrane level and progress to the second meiotic metaphase.