Cellular distribution of transforming growth factor betas 1, 2, and 3 and their types I and II receptors during postnatal development and spermatogenesis in the boar testis.

Transforming growth factor betas (TGF betas) 1, 2, and 3 and their types I and II receptors (TGF betas RI and RII) were immunolocalized 1) during testicular development from the perinatal to the adult period and 2) in maturing germ cell populations at successive seminiferous epithelium stages. In the perinatal testis, TGF beta isoforms and receptors were both preponderant in Leydig cells and in spermatogonia. At prepuberty, their expression appeared in Sertoli cells, while germ cells showed specific TGF beta1 and TGF betaRI staining in the spermatocytes. In the adult testis, TGF beta ligands exhibited a preferential tubular distribution. TGF beta1 was mainly detected in young spermatocytes, TGF beta2 in Sertoli cells, and TGF beta3 in Sertoli and premeiotic germ cells. Although the two receptors were systematically observed together in various cells, our data indicate a predominance of one in comparison with the other depending on the cell type. TGF betaRI was predominant in meiotic and differentiated germ cells and TGF betaRII in somatic cells. Finally, in the adult testis, TGF betas 1, 3, and RI showed a germ-cell pattern that depended upon the stage of the seminiferous epithelium cycle. Specifically, staining for the ligands was predominant before meiosis, and TGF betaRI was present particularly during meiosis and spermiogenesis. Together, the temporal and spatial distribution of the TGF beta system components suggests that these signaling molecules may play a crucial role during specific steps of testicular development and during different waves of seminiferous epithelium maturation leading to spermatogenesis.