Postnatal Cell-Type-Specific Localization of EGFR and Its Ligands (EGF, TGF-α and AREG) in the Rat Testis

The epidermal growth factor receptor (EGFR) signalling network and its ligands, including epidermal growth factor (EGF), transforming growth factor-α (TGF-α) and amphiregulin (AREG), are involved in the regulation of testicular development and function. However, their postnatal cell-type-specific localization patterns in the testis remain incompletely understood. This study investigated the postnatal cell-type-specific localization patterns of EGFR, EGF, TGF-α and AREG in the rat testis using histological and immunohistochemical approaches at four developmental stages. EGFR immunoreactivity was predominantly localized in Sertoli cells, peritubular myoid cells and vascular smooth muscle cells, whereas Leydig cells exhibited weaker immunoreactivity and germ cells lacked staining. In contrast, EGF and AREG exhibited strong and persistent expression in Leydig cells throughout postnatal development. TGF-α demonstrated stage-dependent immunoreactivity in Leydig cells and spermatids. Although semiquantitative scores did not reveal significant stage-dependent differences, distinct cell-type-specific localization patterns were observed throughout postnatal development. These findings indicate that EGF family signalling in the postnatal rat testis is primarily mediated through somatic cell populations and support the presence of a paracrine regulatory network involved in the organization of the testicular microenvironment and the regulation of spermatogenesis.