Presence, processing, and localization of mouse ADAM15 during sperm maturation and the role of its disintegrin domain during sperm egg binding

Abstract

Successful fertilization requires gametes to complete several stages, beginning with maturation and transport along the male and femalereproductive tracts and ending with the interaction between the sperm and the egg. This last step involves spermegg adhesion andmembrane fusion. ADAMs (disintegrin and metalloprotease domain proteins) are a family of membrane-anchored glycoproteins that arethought to play diverse roles in cellcell adhesion through their interaction with integrins. This study analyzes the presence, location,processing, and possible role of ADAM15 in mouse sperm. The presence of ADAM15 in mouse spermatozoa was detected by Westernblotting, which revealed that ADAM15 is post-translationally processed, during epididymal sperm maturation and the acrosome reaction.The 35 kDa antigen present in the acrosome-reacted sperm is the last proteolytic product of the 110/75 kDa ADAM15 found in noncapacitatedsperm. This 35 kDa protein contains the disintegrin domain. By indirect immunofluorescence, ADAM15 was identified in theacrosomal region and along the flagellum of mouse spermatozoa. In acrosome-reacted sperm, ADAM15 was lost from the acrosomalregion, but remained diffusely distributed throughout the head and flagellum. Furthermore, the ADAM15 disintegrin domain(RPPTDDCDLPEF) partially inhibited fusion and almost completely inhibited spermoolemma adhesion. In conclusion, our data indicatethat ADAM15 is present in the testis and in spermatozoa from the caput, corpus, and cauda epididymis, as well as in non-capacitated andacrosome-reacted gametes. Results also indicate that ADAM15 is processed during epididymal maturation and acrosome reaction andthat it may play a role during spermegg binding.