Role of the Rodent Acrosome and Perforatorium in Fertilization

A study has been made of the morphology of spermatozoa recovered from the female genital tract shortly after coitus, including spermatozoa entering and within eggs, in five rodent species. Elevation and loss of the acrosome was observed to occur in actively motile golden-hamster spermatozoa found in the cumulus oophorus and tubal fluid. Motile spermatozoa lacking the acrosome were also seen in the tubal fluid in guinea-pigs, in the cumulus oophorus in the guinea-pig and Libyan jird, and in the zona pellucida or perivitelline space of guinea-pig, golden-hamster, Chinese-hamster and jird eggs. It is concluded that the acrosome becomes modified in spermatozoa passing through the female genital tract and is detached before the spermatozoon penetrates the zona pellucida. These changes in the acrosome are considered to constitute ‘capacitation’. Removal of the acrosome exposes the perforatorium, which may carry a lysin capable of altering the zona substance in such a way as to permit the spermatozoon to pass through into the perivitelline space. The function of the acrosome is thought most likely to be the carriage of hyaluronidase, which probably enables the spermatozoon to pass through the cumulus oophorus. The separation of the nucleus from the perforatorium was observed in the vitellus of rat and golden-hamster eggs.