Xenopus oocyte prophase I meiotic arrest is released independently from a decrease in cAMP levels or PKA activity

Abstract

Vertebrate oocytes arrest at prophase of meiosis I due to high levels of cAMP and PKA activity. In Xenopus progesterone is believed to release meiotic arrest by inhibiting adenylate cyclase, lowering cAMP levels, and repressing protein kinase A (PKA). However the exact timing and extent of cAMP decrease is unclear with conflicting reports in the literature. Using various in vivo reporters for cAMP and PKA at the single cell level in real time, we fail to detect any significant changes in cAMP or PKA in response to progesterone. More interestingly, there was no correlation between the levels of PKA inhibition and the release of meiotic arrest. Furthermore, we devised condition where meiotic arrest could be released in the presence of sustained high levels of cAMP. Consistently, lowering endogenous cAMP levels by over 65% for prolonged time periods failed to induce spontaneous maturation. These results argue that the release of oocyte meiotic arrest in Xenopus occurs independently from lowering either cAMP levels or PKA activity, but rather through a parallel cAMP-PKA-independent pathway.