Mutant Zp1 results in Zona Pellucida Lacking and Female Infertility in Rats and Humans

Zona pellucida (ZP) plays a vital role in reproductive processes including oogenesis, fertilization and preimplantation development of embryo. The ZP of humans is composed of four glycoproteins (ZP1-ZP4), same as rats ZP. Our previous research reported a first case of human infertility due to ZP1 mutation, but the mechanism was unclear. Here we developed a genome editing in vivo rat model and a co-transfected in vitro cell model to investigate the pathogenic effect. In rat homozygous for the homologous mutation, ZP were absent in all of collected eggs. Further the growing and fully grown oocytes in the mutant ovaries completely lack a ZP but with detectable intracellular ZP1 protein. After mating with male rats, none of the mutant female rats got pregnant. Moreover, the co-transfected cell experiments and the ovarian experiments showed that the truncated ZP1 sequestered intracellularly ZP3 and ZP4 to impede their release outside, resulting in an intracellular accumulation of ZP1, ZP3 and ZP4, leading to absence of ZP in mutant oocytes. Our results clearly establish the causal role of ZP1 mutation on ZP defects and female infertility.\n\nSummary statementRat model mirrored completely the phenotypes observed in humans, infertility and abnormal eggs that lack a zona pellucida, through the negative effects of ZP1 mutation.