Penetration of zona free mouse ova

Abstract

Zona free mouse ova were prepared by exposure of hyaluronidase treated tubal oocytes to chymotrypsin or pronase. Alternatively, a mechanical method was developed for zonae removal involving aspiration of oocytes in and out of small bore micropipettes. Oocytes exposed to proteolytic enzymes displayed reduced penetrability relative to zona intact or mechanically denuded controls. In contrast, mechanically denuded ova showed very high levels of penetration and polyspermy. Morphologically, unfertilized mechanically denuded ova were indistinguishable from tubal oocytes. Cortical granules, present in unfertilized ova, disappeared following 1 h exposure to sperm, and formation of multiple pronuclei was observed 4 h post insemination in naked polyspermic zygotes. Observations on the kinetics of ovum penetration by fresh and capacitated sperm supported the contention that capacitation and the occurrence of an acrosome reaction were prerequisites to both zona penetration and to sperm egg fusion.