Cellular distribution of EGF, TGF alpha and their receptor during postnatal development and spermatogenesis of the boar testis

The epidermal growth factor (EGF), the transforming growth factor alpha (TGF alpha) and the epidermal growth factor receptor (EGFr) have been immunolocalized, (i) during the testicular postnatal development (i.e. at the perinatal, prepubertal and adult periods), and (ii) during the seminiferous epithelium cycle in the different germ cell types. While TGF alpha was essentially observed in somatic cells, specifically in perinatal Leydig cells and in mature Sertoli cells, EGF was localized both in germ cells and in somatic cells with a preferential tubular expression. Furthermore, identification of EGFr in different testicular cell types indicates that during postnatal development and spermatogenesis, testicular cells are potentially responsive to EGF in that they express EGFr. Indeed, in the course of the gonadal development, the EGFr distribution was evidenced both in somatic and germ cells with a specific germ cell pattern depending upon the seminiferous epithelium cycle. A predominant EGFr staining was evidenced during the meiotic process and the spermiogenesis. Together, the present data are in favor of the involvement of the TGF alpha/EGF system in the local control of testicular cells during development and particularly of its potential direct implication in crucial steps of spermatogenesis such as meiosis and spermiogenesis.