HYPOXANTHINE PHOSPHORIBOSYLTRANSFERASE ACTIVITY IN BOVINE EMBRYOS DURING THE EARLY EMBRYONIC-DEVELOPMENT

The activity of hypoxanthine phosphoribosyltransferase (HPRT) was dete rmined in the bovine embryo during early embryonic development. Microa ssay, using H-3!hypoxanthine, was improved to measure enzyme activity in the embryonic extract. This activity depended on the reaction time and the concentration of phosphorybosyl pyrophosphate (PRPP) in a rea ction mixture. Maximum activity was obtained at 4 hours of reaction ti me and at a concentration of 1 mM PRPP, but was much lower than the ac tivity recorded in the mouse embryo. During early embryonic developmen t, HPRT activity rapidly increased beyond the 8-cell stage. When distr ibutions and activities of HPRT, adenine phosphorybosyltransferase (AP RT), and the ratio of HPRT:APRT were examined in individual blastocyst s, HPRT activity was broadly distributed, but it did not clearly show the bimodal distribution expected. Six of demi-embryos with high or lo w HPRT:APRT ratios were transferred to recipient cows from which 2 cal ves were obtained. Both offspring were of the sex predicted by the HPR T:APRT ratio. These results indicate that HPRT activity of bovine prei mplantation embryos can be microassayed using radiolabeled hypoxanthin e, and this assay could provide an alternative method for embryo sexin g.