MEASUREMENT OF UPTAKE AND INCORPORATION OF NUCLEIC-ACID PRECURSORS BY PREIMPLANTATION MOUSE EMBRYOS AFTER DEVELOPMENT INVIVO AND INVITRO

Purpose: To assay DNA and RNA synthesis by developing mouse embryos in vitro and in vivo, we measured the uptake and incorporation of H-3-thymidine and H-3-uridine by morulae and blastocysts. We also evaluated the effect of adding EDTA to the culture medium on the uptake and incorporation of nucleic acid precursors by blastocysts. Results: Thymidine and uridine incorporation increased after morulae developed into early blastocysts both in vitro and in vivo. However, the rates of uptake and incorporation were significantly lower by embryos grown in vitro than by those grown in vivo. The ratios of incorporation to total uptake were similar in embryos grown in vitro and in vivo. EDTA (100 muM) added to the culture medium significantly increased the incorporation of uridine into RNA by blastocysts grown in vitro (P < 0.01) but did not increase the total uptake of uridine. Conclusion: These observations showed that both DNA and RNA synthesis increased during the early development of preimplantation embryos and that those activities were reduced in embryos undergoing development in vitro. The results also suggested that through the mechanism of EDTA effect in embryo culture remains unknown, it appeared to reduce the retardation of RNA synthesis by embryos cultured in vitro through a selective stimulation of uridine incorporation.