Spontaneous Exit from Diplotene Arrest in Mammalian Oocytes in vitro: Is It ROS-Mediated?

The diplotene arrest is maintained for a long period within the follicular microenvironment of mammalian ovary. Normally, resumption from diplotene arrest occurs in response to pituitary gonadotrophin surge at puberty. However, gonadotrophin-independent meiotic exit from diplotene arrest was reported in rabbit oocytes cultured in vitro and thereafter in several mammalian species. Since no obvious stimulus is required, scientists consider it as spontaneous exit from diplotene arrest that initiates oocyte maturation in vitro. Emerging evidence suggests that in vitro culture conditions do not meet to the follicular microenvironment and result in generation of reactive oxygen species (ROS) in oocytes. A moderate increase of ROS modulates 3′,5′-cyclic adenosine monophosphate (cAMP) as well as Ca2+ levels and initiates downstream pathways to destabilize maturation promoting factor (MPF). MPF destabilization results in meiotic exit from diplotene arrest under in vitro culture conditions. Thus, spontaneous exit from diplotene arrest under in vitro culture conditions in mammalian oocyte is ROS-mediated.