Characterization of membrane progestin receptor α (mPRα) of the medaka and role in the induction of oocyte maturation.

Oocyte maturation in medaka is induced by the maturation-inducing hormone (MIH) via its membrane receptor. The most likely candidates for the membrane receptor are membrane progestin receptors (mPRs). In order to characterize the mPRα subtype of medaka, a human cell line expressing the mPRα gene of medaka was established and its steroid binding property was assessed. The α subtype exhibited high binding affinity for 17,20β-DHP, the MIH in medaka. Treatment with a morpholino antisense oligonucleotide to mPRα blocked oocyte maturation in vivo. These results suggest that the medaka mPRα protein acts as an intermediary during MIH-induced oocyte maturation in medaka in a manner similar to that described previously for fish species.