Cell differentiation in ascidian studied by nuclear transplantation.

The egg of the ascidian Ciona Intestinalis was divided 20 min after fertilization into two fragments, one nucleated and the other non-nucleated. Nucleus of ectodermal, mesodermal, or endodermal cell, taken from gastrula or tail-bud embryo was transplanted into the non-nucleated fragment. The fragment developed into abnormal or partial embryo, of which the cells or tissues were differentiated mainly according to the regional distribution of presumptive organ-forming substances of the egg cytoplasm that the fragment contained. The result indicated that differentiation of cells in ascidians was principally determined by the components of the mature egg cytoplasm, not by the transplanted nucleus, and the activity of the nucleus was, to some degree, controlled by the surrounding cytoplasm.