Sperm-induced cell cycle activities in blastomeres arrested by the cytostatic factor of unfertilized eggs in Rana pipiens.

Suspensions of lysolecithin-treated sperm were injected into blastomeres of two-cell embryos which had been arrested with the extract of unfertilized eggs containing cytostatic factor (CSF). Whereas the CSF-arrested blastomeres remained unchanged if no sperm were injected, those injected with sperm formed abortive cleavage furrows. The injected sperm exhibited characteristics similar to those associated with sperm injected into activated eggs. These were nuclear decondensation to the pronucleus, DNA synthesis, and late chromosome condensation to the metaphase stage. The activity of CSF-arrested blastomere cytoplasm to promote meiotic maturation when injected into ovarian oocytes rapidly decreased following sperm injection, but later fluctuated at low levels. It was suggested that the CSF-arrested blastomeres retained the potential to reinitiate cell cycle activities which could be evoked by sperm injection.