Delayed translation and posttranslational processing of cyritestin, an integral transmembrane protein of the mouse acrosome.

This paper presents data on the cellular localization of the testis-expressed mouse Cyrn gene product, cyritestin. This cysteine-rich protein is a member of a family including various rodent and primate proteins and snake venom proteins of the metalloproteinase and disintegrin types. By using antibodies raised against recombinant proteins generated in bacteria and against synthetic peptides we show that (i) Cyrn mRNA is present in germ cells 4 days prior to translation; (ii) cyritestin protein is localized in the acrosomal region of spermatids and spermatozoa; and (iii) cyritestin has an apparent molecular weight of 110,000 Daltons, but is subject to processing during epididymal sperm transport, resulting in a shorter molecule lacking approximately 55 kDa from the N-terminal half. We conclude that cyritestin becomes exposed on the sperm surface after successful acrosome reaction and thus may play a role in sperm function rather than in testicular germ cell maturation.