Transcriptional activity of blastomeres in mouse embryos during delayed implantation and after oestradiol benzoate-induced resumption of development.

The relative activities of endogenous DNA-bound RNA polymerases have been quantified in individual blastocysts of ovariectomized mice during delayed implantation and following oestradiol-induced resumption of development. Incorporation of [3H]UMP into an acid insoluble product was detected in the cell nuclei by autoradiography. Nucleolar polymerase I and the nucleoplasmic polymerase II were present in delayed blastocysts harvested from progesterone- or oil-treated ovariectomized females. However, the activities of these enzymes were considerably reduced in comparison with those of blastocysts of intact mice. A stimulation of transcription appeared to occur 18 h after oestradiol benzoate injection of progesterone-treated females but more rapidly in blastocysts from oil-treated females. The data indicate that progesterone may retard the rate of oestradiol-induced reactivation in delayed blastocysts.