ZP4 confers structural properties to the zona pellucida essential for embryo development

Zona pellucida (ZP), the extracellular matrix sheltering mammalian oocytes and embryos, is composed by 3 to 4 proteins. The roles of the three proteins present in mice have been elucidated by KO models, but the function of the fourth component (ZP4), present in all other eutherian mammals studied so far, has remained elusive. Herein, we report that ZP4 ablation impairs fertility in female rabbits. Ovulation, fertilization and in vitro development to blastocyst were not affected by ZP4 ablation. However, in vivo development is severely impaired in embryos covered by a ZP4-devoided zona, suggesting a defective ZP protective capacity in the absence of ZP4. ZP4-null ZP was significantly thinner, more permeable, and exhibited a more disorganized and fenestrated structure. The evolutionary conservation of ZP4 in other mammals, including humans, suggests that the structural properties conferred by this protein are required to ensure proper embryo sheltering during in vivo preimplantation development.