Localization of progesterone binding sites on the plasma membrane of oocyte in amphibians, Rana dybowskii

Progesterone receptor in amphibian oocyte surface was visualized by laser scanning confocal microscopy using fluorescein labeled progesterone 3-O - carboxymethyloxime-BSA (P-BSA-FITC). When denuded oocytes were cultured with P-BSA-FITC, fluorescence appeared on the oocyte surface. Binding of P-BSA-FITC to the oocyte was saturable and specific for progesterone. P-BSA caused germinal vesicle breakdown (GVBD) of denuded oocytes in a dose dependent manner. Treatment of denuded oocytes with P-BSA resulted increase in protein kinase C (PKC) activity by 30 min. This study demonstrates the presence of progesterone binding sites on amphibian oocyte surface and its involvement in the activation of PKC pathway during oocyte maturation in amphibians.