Mouse eggs were fertilized in vitro, in the presence and absence of cumulus cells and the zona pellucida, confirming that cumulus cells are not necessary for the fertilization of mouse eggs with capacitated spermatozoa. The findings suggest that cumulus cells produce a substance capable of inducing capacitation.
After lysis of the zona pellucida, the fertilization rate with capacitated (uterine) spermatozoa was higher than, and with non-capacitated (epididymal) spermatozoa was at least as high as, the fertilization rate of control eggs with an intact zona. Washing and resuspension in a chemically defined medium almost entirely prevented fertilization with epididymal spermatozoa when the zona was present, but had no effect after its removal. Capacitation of mouse spermatozoa appears to be required for the penetration of the zona pellucida only, not for entry into the vitellus.
When the eggs and spermatozoa were incubated in the same chymotrypsin solution which had induced lysis of the zona, the percentage of eggs penetrated by more than one spermatozoon was increased.
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