Ultrastructural observations of the incorporation of guinea-pig spermatozoa into zona-free hamster oocytes

Abstract

Zona-free hamster oocytes inseminated in vitro with acrosome-reacted guinea-pig spermatozoa were examined with the EM. Guinea-pig spermatozoa, in the vicinity of the oocytes, consistently lacked the whole acrosome including the equatorial segment region. In cross fertilization, sperm-egg membrane fusion does not differ significantly from that of normal fertilization. It was sometimes possible to observe protrusions of oocyte cytoplasm containing sperm chromatin in the process of dispersion.