Adult frogs derived from the nuclei of single somatic cells.

The technique of nuclear transplantation has been used to investigate the question whether somatic cell nuclei undergo changes in the course of embryonic differentiation (King and Briggs, 1955; Briggs and King, 1960; Fischberg et al., 1958; Gurdon, 196Oc). Such changes may affect those constituents of a nucleus which are required for embryonic development, and changes of this kind can be discovered by observing the development of nuclear transplant embryos. It is possible that other changes take place in those parts of a nucleus which concern adult characters and reproduction, and it is to expose these (if they exist) that the following survey of adult frogs is presented, each frog having been derived from the development of a single somatic nucIeus and enucleated egg. A description has already been published (Gurdon, 196Oc) of the changes in developmental capacity undergone by nuclei of endoderm cells in the frog Xenopus Zaevis, using donors ranging from blastulae to swimming tadpoles. The frogs described below have been derived from a similar range of donor embryos, and therefore provide complementary results to the former, making a more complete survey of nuclear changes in differentiating cells. Particular interest attaches to the reproductive capacity of nuclear transplant frogs, since this provides the most critical test of whether the nuclei from which they are derived are equivalent to germ-cell nuclei in the range of differentiation that they can promote. In Xenopus, and probably in other animals, a special germinal cytoplasm