Fertilization of pronase-treated mouse ova in vitro

In order to obtain consistently a large number of zona-free mouse ova for studies of sperm-egg interactions, a study was made of the relative effectiveness of removing the zona pellucida from ova by mechanical or enzymatic treatments. Ova exposed to pronase before mechanical removal of the zona pellucida in medium devoid of pronase had similar fertilization rates in vitro compared with ova mechanically denuded in the absence of pronase. Ova with pronase-weakened zonae were easier to denude and survived the mechanical manipulations better than the ova denuded by vigorous aspiration in narrow-bore pipettes. However, exposure to pronase did significantly lower the incidence of polyspermy in the naked ova, indicating that some of the enzyme may have diffused across the perivitelline space and damaged sperm-binding sites on the vitelline plasma membrane. The enzyme treatment also reduced the fertilization rate of zona-intact ova.