THE RESPONSE OF MOUSE OOCYTES INJECTED WITH SEA-URCHIN SPERMATOZOA

Sea urchin spermatozoa were injected into mature mouse oocytes to dete rmine whether they can activate mouse oocytes and, if so, how they beh ave within the oocyte cytoplasm of such a distant species. While injec tion of a single spermatozoon into each oocyte did not activate any of the oocytes, injection of 10 spermatozoa activated about 20%. Within the cytoplasm of unactivated oocytes, sperm heads commonly transformed into chromosome-like structures. When a single spermatozoon was injec ted, and oocytes were then activated by Sr2+, about 30% of the activat ed oocytes had both female (mouse) and male (sea urchin) pronuclei whe n examined 8 h after sperm injection. These results indicated that spe rm-borne oocyte activating factor(s) and the cytoplasmic factors contr olling the development of the sperm pronucleus are not strictly specie s-specific.