Immunolocalization of Hepatocyte Growth Factor System Proteins During Embryonic and Postnatal Development in the Testis.

Abstract

Within the testis, hepatocyte growth factor (HGF) has been shown to regulate seminiferous cord formation and development, Leydig cell (LC) steroidogenesis and survival, Sertoli cell (SC) proliferation and terminal differentiation, and germ cell function and/or survival. Prior reports using rodents have debated the compartment-specific changes in the expression of testicular HGF and its receptor, c-met. However, the presence of another important component of the HGF system, HGF activator protein (HGFA) has not been previously reported within the testis. In this study, embryonic day [(E) 11.5, 12.5, 13.5, 15.5, 16.5, and 18.5)] and postnatal day [(P) 7, 14, 25, 35, and 56)] testes were harvested from CD-1 mice and immunohistochemistry was performed to establish the ontogeny and cellular localization of HGF, c-met and HGFA proteins. Although neither HGF, c-met, nor HGFA were detected at E11.5, low but distinct expression of c-met protein was detected inside the cord at E12.5. At E13.5, germ cells and SC had a weak HGF signal; by comparison, more robust levels of c-met and HGFA were detected in both cell types. At E15.5-16.5 c-met protein continued to be localized in germ cells as well as SC. The SC-specific expression was restricted to the cells towards the center of the cord, but not in the SC closer to the basement membrane. A modicum of HGF was observed in the cytoplasm of germ cells; a weak HGFA signal was present within the SC cell membranes, but was relatively stronger in germ cells. At E18.5, HGF, c-met, and HGFA were localized in the germ cells. In addition, HGFA was localized in some SC. Following birth, the pattern of expression of HGF, c-met, and HGFA shifted whereby HGF was specific to LC (P7-56), except at P14 when it was found in both LC and late stage spermatocytes. c-met was detected in peritubular myoid cells (PTMC) early on (P7), appeared within both PTMC and LC on P14-56, and then in round spermatids on P56. A faint HGFA signal was present in select germ cells and possibly LC on P7. Definitive expression of HGFA was present within LC on P14-56, and was concomitantly expressed within spermatids (P25) and then elongating spermatids (P35-56). Changes in the cellular distribution of HGF, c-met, and HGFA during fetal and postnatal testicular development suggest that HGF regulates important aspects of testicular cell morphogenesis and differentiation which enable male sexual viability. Further experiments are required to fully appreciate the importance of the HGF system during embryonic development as well as in the establishment of adult testicular function. (poster)