Relative changes in the RNA contents of oocytes and preimplantation embryos of the mouse

Changes in Azur B basophilia of isolated oocytes and preimplantation embryos of the mouse have been quantitated cytophotometrically. Components of the nuclei and cytoplasm bound Azur B but most of the dye-binding capacity was lost after RNase treatment indicating that RNA was the main basophilic constituent. The amount of dye bound by oocytes of the resting pool was relatively low but increased during growth reaching a peak in oocytes of about 100 microns in diameter. Thereafter, there was a significant decline during progression through to ovulation. No change in dye-binding was observed between ovulation and the 1 cell embryo stage. However, there were significant declines between the 1 and 2 cell stages and between the 2 and 4 cell stages. Azur B basophilia increased again in the 8 cell embryo and was very high in the blastocyst 5 days after ovulation. These data are discussed in relation to the storage of developmental information in the oocyte and its utilization during early embryonic development.