Role of transforming growth factor-alpha and the epidermal growth factor receptor in embryonic rat testis development

Embryonic testis development requires the morphogenesis of cords and growth of all cell populations to allow organ formation, It is anticipated that c oordination of the growth and differentiation of various cell types involve s locally produced growth factors. The current study was an investigation o f the hypothesis that transforming growth factor-alpha (TGF-alpha) is invol ved in regulating embryonic testis growth. TGF-alpha has previously been sh own to function in the postnatal testis. TGF-alpha and other members of the epidermal growth factor (EGF) family act through the epidermal growth fact or receptor (EGFR) to stimulate cell proliferation and tissue morphogenesis . To understand the potential actions of TGF-alpha in the embryonic testis, general cell proliferation was investigated. Characterization of cell prol iferation in the rat testis throughout embryonic and postnatal development indicated that each cell type has a distinct pattern of proliferation. Germ cell; growth was transiently suppressed around birth. Interstitial cell gr owth was high embryonically and decreased to low levels around birth. A low level of Sertoli cell proliferation was observed at the onset of testis co rd formation. Sertoli cell proliferation in early embryonic development was low; the levels were high later in embryonic development and remained high until the onset of puberty. Both TGF-alpha and the ECFR were shown to be e xpressed in the embryonic and postnatal rat and mouse testis. Perturbation of TGF-alpha function using neutralizing antibodies to TGF-alpha on testis organ cultures dramatically inhibited the growth of both embryonic and neon atal testis, TGF-alpha antibodies had no effect on cord formation. The TGF- alpha antibody was found to be specific for TGF-alpha in Western blots when compared to EGF and heregulin. Testis growth was also inhibited by perturb ation of EGFR signaling using an ECFR kinase inhibitor. Therefore, TGF-alph a appears-to influence embryonic testis growth but not morphogenesis (i.e., cord formation). Treatment of embryonic testis organ cultures with exogeno us TGF-alpha also perturbed development, leading to an increased proliferat ion of unorganized cells. Testis from EGFR and TGF-alpha knockout mice were analyzed for testis morphology. TGF-alpha knockout mice had no alterations in testis phenotype, while ECFR knockout mice hall a transient decrease in the relative amount of interstitial cells before birth. Observations sugge st that there may be alternate or compensatory factors that allow testis gr owth to occur in the apparent absence of TGF-alpha actions in the mutant mi ce. In summary, the results obtained suggest that TGF-alpha is an important factor in the regulation of embryonic testis growth, but other factors wil l also be involved in the process.