Effects of Vitrification on Mouse ZP Ultrastructural Changes and in vitro Fertilization

The aim of our study is to investgate the effect of freezing on the ultrastructural changes of zona pellucida(ZP) surface,embryo subsequential development in vitro fertilization and the capacity of sperm penetrating ZP.The results showed that,compared with the other two groups,the ZP surface network structure of frozen group fades or disappears,with the occurrence of surface melting-like and smaller-pore-like changes.The proportion of A-type ZP in Frozen-group(57.14%) is significantly lower than the toxicity of the experimental group(79.32%)and control-group(81.25%)(P0.05),while the proportion of melt-like changes(C-type) is significantly higher than the other two groups(P0.05).The cleavage and blastocyst rates of frozen-group are significantly lower(P0.05) than these of the toxicitygroup and control-group(60.90%,81.74%,87.47%;39.51%,55.72%,61.63%).After in vitro fertilization,there shows no significant difference(P0.05) among the 3 groups in the the number of sperm binding to ZP(10.56,10.26,10.21),but digestion treatment after IVF,the number of sperm binding to oocytes tightly of frozen-group(3.28) is significant lower(P0.05)than that of the other 2 groups(5.11,5.21).Thus,freezing does lead changes in the ultrastructure of ZP,and decrease the fertilization rate in vitro.