Effect of removal of the zona pellucida on subsequent development of mouse blastocysts in vitro.

Removal of the zona pellucida allowed mouse blastocysts incapable of hatching in vitro to develop in culture. Blastocysts denuded by pronase always developed further than those of identical age that had hatched spontaneously. More blastocysts mechanically denuded and treated with pronase developed egg cylinder-like structures than did blastocysts mechanically denuded and not treated with pronase. Plastic support gave better development of blastocysts than did glass.