IN-VITRO FERTILIZATION OF CHINESE-HAMSTER OOCYTES BY SPERMATOZOA THATHAVE UNDERGONE IONOPHORE A23187-INDUCED ACROSOME REACTION, AND THEIR SUBSEQUENT DEVELOPMENT INTO BLASTOCYSTS

To enhance potential use of the Chinese hamster, Cricetulus griseus, i n developmental and cytogenetic studies of mammalian gametes and embry os, techniques for in vitro fertilisation and embryo culture were deve loped in the species. Spermatozoa were recovered from the vasa deferen tia of mature males, and incubated in modified TYH medium for 1 h at 3 7 degrees C under 5% CO2 in air. They were then treated with ionophore A23187 (20 mu M) for 10 min to induce the acrosome reaction. Followin g ionophore treatment, superovulated oocytes were collected from hormo nally stimulated females and incubated with the acrosome-reacted sperm atozoa for 2 h at 37 degrees C under 5% CO2 in air. In this study, 245 oocytes were used for insemination, and 198 (80.8%) were found to be penetrated by sperm; among them, 194 ova (98.0%) were determined to be monospermic. The monospermic ova were then cultured in TYH supplement ed with 1 mM hypotaurine under the same gas phase. Within 30 h of fert ilisation, 182 ova (93.8%) cleaved to the 2-cell stage, and subsequent ly 163 ova (84.0%) developed beyond the 2-cell stage. Thus, obstinate developmental arrest at the 2-cell stage ('2-cell block') was not obse rved in this species. Ultimately, 65.5% of monospermic ova reached mor ula to blastocyst stages.