Cytoplasmic alteration of an established pattern of Rana pipiens chromosomal DNA replication

Abstract

Cells from Rana pipiens embryos were incubated in 3H-thymidine for the duration of the last quarter of the S period plus the G 2 period of the cell cycle. Chromosomes of animal hemisphere cells of stage 9 embryos showed uniform labeling, whereas chromosomes of endodermal cells of stage 17 embryos showed terminal labeling. We tested whether egg cytoplasm would alter an established temporal pattern of chromosomal DNA replication. Nuclei from disaggregated endodermal cells of stage 17 embryos were transplanted into activated and enucleated eggs. The eggs were then allowed to develop to the blastula stage. Animal hemisphere explants of these blastulae were incubated in 3H-thymidine. Radioautographic localization of silver halide grains demonstrated a chromosomal DNA replication pattern that was uniform over the the metaphase chromosomes. The egg cytoplasm had evidently altered an established temporal pattern of chromosomal DNA replication.