MOUSE OOCYTES PENETRATED BY SPERM AT GV OR GVBD STAGE LOSE THE ABILITY TO FUSE WITH ADDITIONAL SPERMATOZOA

Mouse oocytes penetrated by spermatozoa during germinal vesicle (GV) b reakdown undergo maturation and are arrested at metaphase of the secon d meiotic division despite the presence of sperm nuclei within the oop lasm. When these oocytes were re-inseminated, none was penetrated by n ewly added spermatozoa. When GV oocytes were inseminated and cultured in the presence of dibutyryl cAMP, the oocytes remained at GV stage, y et they did not permit entry of additional spermatozoa. These observat ions suggest that the plasma membrane of maturing oocytes is modified by precociously penetrating spermatozoa independently from cortical gr anule exocytosis. Sperm components incorporated into the oocytes seem to be responsible for the modification of the oocyte's plasma membrane .