Effects of ultrasound on DNA and RNA synthesis in preimplantation mouse embryos

Compaction in preimplantation mouse embryos is regulated by a cytoplasmic regulatory factor that alters between 1- and 2-cell stages in a concentration-dependent manner

Present studies were performed to investigate what factors affect the morphogenesis of preimplantation mouse embryos, and to find the action mechanism of that factor by using cytoplasm removal and its reconstitution from a different developmental stage embryo. Half (HP group) or one-third of cytoplasm (TP group) was removed from 1-cell mouse embryos by micromanipulation, and their morphogenesis and genome expression were compared with sham-operated embryos (SP group). The compaction and blastocoel formation of embryos in both the HP and TP groups were accelerated in time and cell stage when compared with those of the SP group. However, the total activity and time of RNA synthesis, and gene expression of ZO-1alpha+ isoform were not different. To change the cytoplasm composition without altering the nucleus/cytoplasmic ratio, half a 1-cell embryo with both pronuclei was reconstituted with the half enucleated cytoplasm of 1-cell embryo (P + P group), 2-cell (P + 2 group) or 4-cell (P + 4 group) by electrofusion. Embryonic compaction, timing of RNA synthesis, and stage-specific gene expression of the ZO-1alpha(+) isoform in the P + 2 and P + 4 groups were accelerated in time and cell stage than that in the P + P group, but not different between the P + 2 and P + 4 groups. In addition, a blastomere of 2-cell embryo was reconstituted with the enucleated cytoplasm of 1-cell embryo (2 + P group) or 2-cell (2 + 2 group) in equal volume by electrofusion. Also, the karyoplast of 2-cell was fused with the enucleated 1-cell embryo (2 + PP group). Embryonic development, total activity of RNA synthesis, and gene expression of the ZO-1alpha(+) isoform of embryos in the 2 + P and 2 + PP groups were delayed when compared with those of the 2 + 2 group. Also, the phenomena of compaction and blastocoel formation were delayed in the development time and cell stage. From these results, the nucleus/cytoplasm ratio was found to have no direct effect on the regulation of embryonic morphogenesis, although it accelerated compaction and blastocoel formation. However, cytoplasmic factors that altered between 1- and 2-cell stages regulate embryonic morphogenesis, especially compaction, of preimplantation mouse embryos in concentration-dependent manner.

Measurement of uptake and incorporation of nucleic acid precursors by preimplantation mouse embryos after development in vivo and in vitro

PURPOSE

To assay DNA and RNA synthesis by developing mouse embryos in vitro and in vivo, we measured the uptake and incorporation of 3H-thymidine and 3H-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 microM) 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.