Factors responsible for the abnormal development of embryos obtained by nuclear transplantation in Xenopus laevis.

IN Xenopus the embryos derived from nuclear transplantation often develop abnormally. These abnormalities must be due to the limited potentiality for development of either the donor nucleus or the egg cytoplasm; this limited potentiality will in turn be due to technical damage during transplantation or to the innate condition of the nucleus or cytoplasm before the experiment. The extent to which these technical and innate factors are responsible for abnormalities of transplant-embryo development has been analysed by considering the effect of each factor in turn. Nuclei from early donor stages have been used, since these nuclei are believed to be undifferentiated (see p. 338) and therefore to have the innate capacity for entirely normal development. The effects of other factors have been investigated by experiments in which each factor is varied in different ways. Any correlation between variations in one factor and the resulting proportion of abnormal transplant-embryos is then recorded. In this way the effect of each factor on the development of transplant-embryos can be analysed. These experiments show how nuclei can be transplanted with least damage, and whether small inconsistencies in carrying out the technique can bring about abnormalities of development. It is thus made clear to what extent abnormal transplant-embryos may be considered to represent innate qualities of donor nuclei.