A novel testis-specific metallothionein-like protein, tesmin, is an early marker of male germ cell differentiation.

We have cloned a novel cDNA encoding testis-specific metallothionein-like protein, tesmin, by randomized RT-PCR on RNA from mouse tissues. Two tesmin-related transcripts (2.2 and 1.8 kb) in mouse and one (2.1 kb) in human were detected and cloned. These encode a cysteine-rich 32-kDa protein that contained a metallothionein-like motif. In situ hybridization analysis in adult mouse testis showed that tesmin is specifically expressed in spermatocytes. Quantitative RT-PCR at different stages of mouse postnatal development (days 4, 8, 12, 18, and 42) revealed that tesmin is expressed as early as day 8 and coincides with the entry of germ cells into meiosis. Furthermore, adult W/Wv sterile mice that harbor the c-kit mutation lacked tesmin expression. The gene is assigned to mouse chromosome 19B, which has been reported to translocate (11;19) in male sterile mice.