Transglutaminase 2 reduces the polyspermy of porcine oocytes by promoting the hardening of zona pellucida.

Polyspermy is a type of abnormal fertilization that would increase the risk of embryonic death and hence reduced female fecundity. To avoid this occurrence, mammalian oocytes develop the complicated mechanisms of blocks to polyspermy. Our previous study discovered that transglutaminase 2 (Tgm2) is a newly identified molecule responsible for the post-fertilization block to sperm penetration through zona pellucida (ZP) and polyspermy in mice. However, whether this function of Tgm2 is conserved across species has not been clarified. This study applied the porcine oocytes as a model to address this question. It was observed that inhibition of TGM2 activity by using its specific inhibitor LDN-27219 exhibited a substantially increased rate of polyploid zygotes after in vitro fertilization. In addition, our study validated that recombinant TGM2 protein interacted with zona pellucida glycoprotein 3 (ZP3) and crosslinked it to promote the ZP hardening. Further, incubation of porcine oocytes with recombinant TGM2 protein effectively reduced the occurrence of polyploid zygotes. Collectively, our data reveal that TGM2 performs a conserved function in porcine oocytes for zona block and polyspermy prevention.