Targeted disruption of the mZP3 gene results in production of eggs lacking a zona pellucida and infertility in female mice

Mammalian eggs are surrounded by a thick extracellular coat, the zona pellucida, that plays important roles during early development. The mouse egg zona pellucida is constructed of three glycoproteins, called mZP1, mZP2, and mZP3. The gene encoding mZP3 is expressed only by growing oocytes during a 2- to 3-week period of oogenesis. Here, the mZP3 gene was disrupted by targeted mutagenesis using homologous recombination in mouse embryonic stem cells. Viable female mice homozygous for the mutated mZP3 allele (mZP3(-/-)) were obtained. These mice are indistinguishable in appearance from wild-type (mZP3(+/+)) and heterozygous (mZP3(+/-)) littermates. However, although ovaries of juvenile and adult mZP3(-/-) females possess growing and fully grown oocytes, the oocytes completely lack a zona pellucida. Consistent with this observation, eggs recovered from oviducts of superovulated, adult mZP3(-/-) females also lack a zona pellucida. Thus far, mZP3(-/-) females mated with wild-type males have failed to become pregnant.