Antigen changes of monoclonal antibody MSH27 in process of post-testicularmaturation (in mice)

An anti-mouse spermatozoon monoclonal antibody, MSH27, as well as its purif ied antigen, can block sperm-egg membrane fusion. As a candidate protein fo r sperm-egg membrane fusion, the sperm antigen was investigated in the proc ess of post-testicular maturation (PTM). The molecule was produced in teste s and located on the plasma membrane of the postacrosomal area of the sperm atozoon. However, the epitope recognized by the MSH27 (MSH27Ep) was not exp osed until the occurrence of the acrosome reaction. In the process of ferti lization, spermatozoa must complete the acrosome reaction before penetratin g across the zona pellucidas (ZPs) to approach the plasma membrane of eggs. The effects of the acrosome reaction and penetration of the ZP on the expo sure of the MSH27Ep were also studied. It was shown that the percentage of the spermatozoa with the MSH27Ep exposed increased followed with their matu re status in PTM. In fact, it had a linear correlativity with the rate of t he acrosome reaction. After spermatozoa had passed ZPs, almost all of them became the MSH27-positive in immuno-staining compared with only a part of t he spermatozoa after the acrosome reaction. In a word, the exposure of MSH2 7Ep was coincident with attaining the ability to penetrate the plasma membr ane of eggs.