Transfer of embryonic nuclei to fertilised mouse eggs and development of tetraploid blastocysts

Abstract

THE transfer of nuclei from embryonic or differentiated cells into eggs is the most sensitive method of testing whether those nuclei change irreversibly during development. However, among the metazoa its use has been restricted to amphibians and insects^1,2 because of problems associated with the microsurgery of the very small and delicate mammalian egg. A few attempts have been made to introduce somatic nuclei into unfertilised mouse oocytes or blastomeres with the help of virus-mediated cell fusion^3–7, but the fate of the transplanted nucleus has not been followed beyond the cleavage following the operation. The transfer of nuclei from morula cells both by virus-mediated fusion and by microsurgery has been reported in the rabbit⁸, the evidence suggesting that such eggs can very occasionally develop to the morula stage. I describe here experiments involving a technique developed independently for use with mouse eggs. After transfer of nuclei from morula cells to fertilised one-cell eggs, more than 25% of the surviving eggs incorporated the donor genome and developed as tetraploids to the morula or blastocyst stage.