Experimental Study of the Developing Mammalian Egg: Removal of the Zona Pellucida.

The zona pellucida may be removed from all stages of the mouse egg by digestion with pronase. Cumulus and corona cells are also dispersed by the enzyme. No change in membrane disgestibility occurs at fertilization. In tests thus far of two-cell eggs and later stages, development continues. Blastocysts exhibit "hatching" behavior despite absence of the zona. Functions of the zona include maintenance of the normal cleavage pattern and prevention of egg fusion.