Nuclear transplantation in the rabbit egg

Abstract

SINCE the experiments of Briggs and King¹, in which nuclei from blastula cells were transplanted by microinjection into enucleated frogs' eggs, the technique of nuclear transplantation has been used extensively to study interactions between nucleus and cytoplasm during differentiation in amphibians^2–5. But severe difficulties are encountered in attempts to apply this technique to the mammalian egg. The rabbit egg, with a diameter of 100 µm, is 1,000 times smaller in volume than a frog's egg, and the mouse egg has a volume one-third that of a rabbit's egg. An alternative, and technically easier method of transplanting a nucleus is by inducing fusion of an egg and a cell with Sendai virus. The technique of virus-induced fusion, originally developed for hybridising somatic cells^6–7, has been adapted to fuse somatic cells with unfertilised or fertilised mouse eggs^8–13. Although Sendai virus was shown not to harm mouse embryos in these experiments, and cells were successfully fused, the transplanted nuclei did not survive. Unfertilised mouse eggs which were fused with cells from embryos at the 2–8-cell stage failed to cleave⁸.