Behavior of sperm nuclei injected into intact ripening and ripe toad oocytes and into oocytes ripening after removal of the germinal vesicle.

The behavior of frog sperm nuclei (obtained by treating a sperm suspension with pronase) in the cytoplasm of intact ripening and ripe toad oocytes and in the cytoplasm of oocytes ripening after removal of the germinal vesicle was studied. Sperm nuclei treated with pronase in the cytoplasm of intact ripe oocytes behave like the nuclei of sperm cells penetrating during normal fertilization: they increase in volume, synthesize DNA, and start to divide. They undergo no changes in the cytoplasm of oocytes ripening in the absence of karyoplasm. Transformations of sperm nuclei into pronuclei and DNA synthesis in them are found initially at the metaphase stage of the second maturation division.