Expression of the leptin receptor during germ cell development in the mouse testis

Leptin, a recently identified hormonal product of the ob gene, is known to regulate appetite, body metabolism, and reproductive functions. We investigated the expression of the leptin receptor (Ob-R) in testes from different age groups. The messenger RNA for Ob-R was found in testes from all age groups using RT-PCR. Using immunohistochemistry, we observed age- and stage-dependent distribution of the Ob-R in mouse testis. In testis of 5-day-old mice, its expression was mainly in type A spermatogonia. In the 20- and 30-day-old testis, Ob-R expression was in the spermatocytes; in the adult testis, it was specific to spermatocytes in stages XI and X of the cycle of the seminiferous epithelium. Five main immunoreactive proteins were detected using Western blot (220, 120, 90, 66, and 46 kDa). The 120-kDa protein was evident only in 20-day-old and older testes, whereas the 90-kDa band was present only in the 5- and 10-day-old testis. Leptin treatment induced phosphorylation of signal transducer and activator of transcription-3 in cultured seminiferous tubules from adult and 5-day-old testes. Our results show for the first time age- and stages-specific localization of a functional Ob-R in testicular germ cells. We hypothesize a direct role for leptin, through phosphorylation of signal transducer and activator of transcription-3, in proliferation and differentiation of germ cells, which may partially explain the infertility observed in leptin-deficient mice.