The mouse zona pellucida: folliculogenesis, fertility and pre-implantationdevelopment

Perinatally, oocytes within the mouse ovary become surrounded by a layer of flattened granulosa cells and form primordial follicles. The subsequent ac cretion of the zona pellucida between the oocytes and granulosa cells provi des a biochemical marker of folliculogenesis. In mice, the zona matrix is c omposed of three proteins (ZP1: ZP2, ZP3). Mouse lines lacking either ZP1 o r ZP3 have been established and have abnormal folliculogenesis. Without ZP1 , structurally defective zonae are formed resulting in decreased fecundity due to early embryonic loss. More strikingly, without ZP3, the zona matrix is absent, no 2-cell embryos are formed and females are infertile. The stru ctural integrity of the zona matrix can be restored by substituting human h omologues for the missing mouse protein and these 'humanized' zona matrices should prove useful in investigating the molecular basis of fertilization. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.