Microsurgical injection of spermatozoa into hamster eggs with subsequent transformation of sperm nuclei into male pronuclei

Abstract

At the time of normal fertilization in mammals, the sperm plasma membrane fuses with the egg plasma membrane and the structural elements of the spermatozoon (e.g., nucleus and axial elements of sperm tail) are incorporated into the egg cytoplasm. This membrane fusion apparently activates the egg cytoplasm and the sperm and egg nuclei in the activated egg cytoplasm gradually transform into male and female pronuclei. Isolated nuclei of hamster spermatozoa develop into male pronuclei when injected into hamster eggs. The nuclei of fresh, frozen thawed and freeze dried human spermatozoa are equally capable of developing into male pronuclei when injected into hamster eggs. These results indicate that sperm nuclei are stable organelles and the egg cytoplasmic factors controlling the transformation of sperm nuclei into male pronuclei are not strictly species specific.