ABSTRACT
Nuclei from a monolayer of cultured epithelial cells have been transplanted singly to enucleated unfertilized eggs of Xenopus laevis.
About three-quarters of the injected eggs failed to cleave or cleaved abortively. Most of the remainder formed partial blastulae. Less than 1 % reached postneurula stages of development.
Nuclei from first-transfer blastulae were used for serial transplantation. The nuclei of partial blastulae promoted normal or nearly normal development more often than those of complete blastulae. Several clones were obtained which included nearly normal tadpoles with apparently normal muscle, nerve, blood, and other specialized cell types. Three tadpoles commenced feeding and have completed metamorphosis into young frogs.
To prove that the donor- and not egg-nucleus participated in the formation of nuclear-transplant tadpoles, genetically marked 2-nu and l-nu diploid nuclei were transplanted to 2-nu eggs; the resulting tadpoles had the nucleolar number characteristic of donor, not egg, nuclei. Chromosome counts and nuclear diameter measurements on the epidermal cells of these tadpoles revealed the presence of diploid mitoses and the absence of haploid nuclei.
The behaviour of egg and donor nuclei immediately after nuclear transfer was determined by tracing the early cleavage pattern of individual eggs and by following, autoradiographically, the fate of donor nuclei whose DNA had been previously labelled with 3H-thymidine.
These experiments show that the serial transplantation of nuclei from monolayer cell cultures can lead to sufficiently normal nuclear-transplant embryo development to provide a useful test of the genetic properties of the donor cell line.
