Abstract
Previous work has shown that nuclei of young embryos (to gastrula stage) promote normal development when transplanted into enucleated eggs. As development proceeds to later stages, the nuclei become increasingly restricted in their capacity to promote normal cleavage and development, and the majority of the embryos that do develop possess abnormal chromosome complements (see references 1 through 4). Experiments reported in this paper show that a reduction in the temperature at which the transplantation operation is performed (from 20-11 degrees C) improves the capacity of the nuclei to promote cleavage of recipient eggs, but appears not to improve later development. The capacity to promote postgastrula development is significantly improved when the donor cells are exposed to the polyamine, spermine, prior to and during nuclear transfer. This improvement is correlated with a reduction in the incidence of chromosomal abnormalities. The mechanism of this effect of spermine, and its relationship to the nuclear differentiation problem, is considered.