Abstract

ABSTRACT Nuclei from differentiated intestinal epithelium cells of feeding tadpoles and from control blastulae of Xenopus have been transplanted into enucleated recipient eggs. The differentiated state of the intestinal epithelium cells was shown by their possession of a striated border. The cleavage and embryonic development resulting from the intestinal epithelium cell nuclei was much more abnormal than that resulting from control blastula transfers. per cent. (10 out of 726) of the first transfers of intestine nuclei resulted in normal feeding tadpoles. The serial transplantation of nuclei and of their mitotic products showed that some of the intestine nuclei which promoted abnormal development after first transfer could nevertheless promote the formation of normal feeding tad-poles after serial transfer. The combined results of first transfers and of serial transfers demonstrated that at least 7 per cent, of the intestine nuclei possessed the genetic information required for the formation of normal feeding tadpoles. The cytological examination of eggs fixed soon after receiving transplanted nuclei indicated that the lack of cleavage and abortive cleavage following trans-plantation result from nuclei which were not effectively exposed to the recipient egg cytoplasm or which were transplanted at an unsuitable stage in their mitotic cycle. If these cases are excluded from the results, the intestine nuclei capable of promoting the formation of feeding tadpoles then constitute 24 per cent, of the remaining successful transfers. A similar interpretation of the experimental results shows that 70 per cent, of the successfully transplanted intestine nuclei have the genetic information required to form muscular response stage tadpoles with functional muscle- and nerve-cells. These results show that a nucleus can promote the formation of a differentiated intestine cell and at the same time contain the genetic information necessary for the formation of all other types of differentiated somatic cell in a normal feeding tadpole. It is concluded that the differentiation of a cell cannot be dependent upon the incapacity of its nucleus to give rise to other types of differentiated cell.