Cinemicrographic observations on the trophoblast and zona pellucida of the mouse blastocyst

Abstract

The mammalian ovum is surrounded by a secondary membrane, the zona pellucida, which is produced by the follicle cells round the ovarian oocyte. The major constituents of this membrane are neutral or weakly acidic mucoproteins, and it is sensitive to dissolution by a variety of proteases, depending on species (Gwatkin, 1964), especially the bacterial protease “Pronase” (Mintz, 1962). In the rabbit and rat the zona is impermeable to compounds with a molecular weight above 1200 (Austin & Lovelock, 1958). Since in all mammals, an intact zona surrounds the cleavage stages and early blastocyst, this membrane must be removed, or penetrated by the trophoblast cells before implantation can take place. This could result from the interaction of chemical or mechanical factors produced either by the conceptus or by the uterus, or from a combination of some or all of these.