Following fertilisation, the sperm triggers a series of intracellular changes which initiate oocyte activation and pronuclear formation. Oocyte activation can also be induced artificially by several chemicals, such as the calcium ionophore A23187. The sperm nucleus is transformed into the male pronucleus through the interaction of oocyte cytoplasmic factors. The profile of protein synthesis is different in bovine oocytes following fertilisation and parthenogenetic activation. The formation of male and female pronuclei was not blocked by the presence of the protein synthesis inhibitor cycloheximide. These results suggest that bovine oocyte activation by sperm and parthenogenetic activation induce different cytoplasmic responses for protein synthesis and that new protein synthesis is not required for male pronuclear formation in bovine zygotes.

To enhance potential use of the Chinese hamster, Cricetulus griseus, in developmental and cytogenetic studies of mammalian gametes and embryos, techniques for in vitro fertilisation and embryo culture were developed in the species. Spermatozoa were recovered from the vasa deferentia of mature males, and incubated in modified TYH medium for 1 h at 37°C under 5% CO2 in air. They were then treated with ionophore A23187 (20¼M) for 10min to induce the acrosome reaction. Following ionophore treatment, superovulated oocytes were collected from hormonally stimulated females and incubated with the acrosome-reacted spermatozoa for 2 h at 37°C under 5% CO2 in air. In this study, 245 oocytes ova (98.0%) were determined to be monospermic. The monospermic ova were then cultured in TYH supplemented with 1mM hypotaurine under the same gas phase. Within 30h of fertilisation, 182 ova (93.8%) cleaved to the 2-cell stage, and subsequently 163 ova (84.0%) developed beyond the 2-cell stage. Thus, obstinate developmental arrest at the 2-cell stage(‘2-cell block’) was not observed in this species. Ultimately, 65.5% of monospermic ova reached morula to blastocyst stages.