REUTILIZATION OF MATERNAL NUCLEAR MATERIAL BY EMBRYONIC AND TROPHOBLASTIC CELLS IN THE RAT FOR THE SYNTHESIS OF DEOXYRIBONUCLEIC ACID

Normal blastocysts were transferred to the uteri of rats previously injected systemically with thymidine- 3 H. Autoradiography of the 9th day implantation sites showed that the embryo, the yolk sac and the ectoplacental cone were lightly labeled because of reutilization of thymidine- 3 H from the maternal circulation. The giant trophoblastic cells were as heavily labeled as the uterine cells. After transplantation of normal blastocysts to uteri previously injected locally with thymidine- 3 H, a number of giant trophoblastic cells were found labeled. No radioactivity was present on other embryonic structures. The conclusion was reached that the embryo does not utilize for its deoxyribonucleic acid synthesis nucleosides or nucleotides from the uterine "histotroph." The giant cells, instead, appear to incorporate a substantial amount of label in the form of macromolecular deoxyribonucleic acid.