[Embryonic development of 2 strains of mice in the early cleavage period]

RNA metabolism at 1-, 2- and 8-celled stages was studied in C3H and C57Bl mice by means of detection of RNA content in individual embryos and microcolumnal chromatography of lysate of the embryos labelled with 3H-uridine. The increase of RNA content in the 8-celled embryos of the both strains is due to active synthesis of high and low molecular weight RNAs during this period. A comparison of 3H-uridine incorporation in RNA, and nucleotide fractions of 2-celled embryos has shown that the embryonic genome per se is activated earlier in C3H mice. The embryonic development and RNA changes in them are similar in the pure bred and hybrid embryos with common mothers. This serves as an additional evidence of the leading role of maternal factors in embryonic development during the first cleavage divisions.