Postnatal changes in the expression of p60c‐Src in mouse testes

Src family non‐receptor tyrosine kinases are involved in signaling pathways which mediate cell growth, differentiation, transformation and tissue remodeling in various organs. In an effort to elucidate functional involvement of p60c‐Src (c‐Src) in spermatogenesis, the postnatal changes in c‐src mRNA and c‐Src protein together with kinase activity and subcellular localization were examined in mouse testes. c‐src mRNA levels in testes increased during the first 2 weeks of postnatal development (PND). Following a decrease at puberty (PND 28), the c‐src mRNA levels re‐increased at adulthood (PND 50). Src kinase activity of testes was low at PND 7 but sharply increased prepubertally (PND 15) and highest at adulthood. Upon Western blotting, the level of c‐Src protein was the highest in prepubertal testes but rather decreased in adult testes at PND 50. In adult testes, ubiquitination of c‐Src proteins was apparent compared with immature one at PND 7, suggesting active turnover of c‐Src by ubiquitination. In immature testes, c‐Src immunoreactivity was largely found in the cytoplasm of the Sertoli cells. By contrast, in pubertal and adult testes intense immunoreactivity was localized at the adluminal and basal cytoplasm of Sertoli cells bearing elongated spermatids and early germ cells, respectively. The immunoreactivity of c‐Src in the Leydig cells was increased during pubertal development, suggesting the functional involvement of c‐Src in differentiated adult Leydig cells. Throughout postnatal development, some spermatogonia and spermatocytes showed intensive c‐Src immunoreactivity compared with other germ cells, suggesting a possible role of c‐Src in germ cell death. Taken together, it is suggested that c‐Src may participate in the remodeling of the seminiferous epithelia and functional differentiation of Leydig cells during the postnatal development of mouse testes.