CHANGES IN THE NUCLEI OF DIFFERENTIATING GASTRULA CELLS, AS DEMONSTRATED BY NUCLEAR TRANSPLANTATION

Abstract

An improved nuclear transplantation technique was developed in which the embryo was placed in 0.5% commercial trypsin made up in a Niu-Twitty solution lacking Ca++and Mg++ and buffered at pH 7.1 with phosphate. The trypsin cemented together the embryonic layers so that they could be separated, and part of the desired layer was placed in 5x 10-4 [image] versene in the modified Niu-Twitty solution. After action of the versene on the intercellular material, individual cells could be picked up singly in a transfer pipette and nuclei transplanted. With this method the proportion of transfer of nuclei of undifferentiated early gastrula cells resulting in normal cleavage of the recipient eggs was increased from 21 to 41%. With late gastrula chorda-mesoderm nuclei, successful cleavage and blastula formation in the recipient eggs was increased from 8 to 22%, but most of the blastulae were arrested in blastula, gastrula or abnormal post-neurula stages. In the latter embryos the inductor system was differentiated, but the central nervous system was deficient or absent. Transplantations of nuclei from the endoderm of late gastrulae resulted in normal cleavage and blastula formation in 40% of the test eggs. but whereas most of the control blastulae (from undifferentiated early gastrula cells) developed into larvae, the endoderm blastulae were usually arrested in blastula, gastrula or abnormal embryonic stages. The abnormal embryos displayed a combination of deficiencies involving the ectodermal derivatives. These studies indicate that there is a progressive specialization of nuclear function during cell differentiation, and that endoderm nuclei of late gastrulae are restricted in their differentiating potential.