Paracrine interaction in testicular somatic cells

Initiation of spermatogenesis is regulated by signals derived from intratub ular Sertoli cells as well as extratubular Leydig cells, both being systemi c targets of hypophyseal gonadotropins. In addition to Leydig and Sertoli c ells, a number of other cell types are present in the testis viz, peritubul ar cells, macrophages and vascular components. The specific paracrine funct ions of these cells are only partially understood. The peritubular and Sert oli cells form the structural scaffold of the germinal epithelium and are r esponsible for intratubular pressure, release and transport of spermatozoa and the formation of the blood-testis barrier. We have performed ex vivo an d in vitro studies on the ultrastructure of peritubular and Sertoli cells a nd the distribution of steroid hormone receptors, cytoskeletal and extracel lular matrix proteins using rat testes from different stages of postnatal d evelopment. Morphological observations were related to in vitro findings of gene expression on the respective hormones and structural proteins. In the developing rat testis, the peritubular cells showed a strong and consisten t expression of fibronectin, entactin, laminin as well as the glucocorticoi d, androgen, estrogen and partially also the progesterone receptor, while t he Sertoli cells were devoid of glucocorticoid receptor and entactin. The g lucocorticoid receptor was present in around 20% of the intratubular germ c ells (in the 2(nd) postnatal week) and in 50% of the peritubular cells. In Leydig cells also, the expression reached its climax in the 3(rd) weak and declined thereafter. This is perhaps pointing to a differentiation-inhibiti ng role of glucocorticoids in gonocyte differentiation. In the 3(rd) develo pmental week, the androgen receptor was present in about 15% of all gonocyt es and later in 50% of peritubular cells and about 40% of interstitial cell s. The estrogen receptor was absent in peritubular cells of the adult testi s. The progesterone receptor was present in about 30% of the peritubular an d 25% of the Leydig cells. Taking into account the significant increase in seminiferous tubules following postnatal developmental day 18, the peritubu lar cells seem to exert an androgen dependent growth stimulus to the semini ferous cords perhaps via the Sertoli cells. In vitro studies of peritubular and Sertoli cells cultured either alone or in co-culture showed by RT-PCR the expression of the androgen and the glucocorticoid receptors in both cel l types, as well as fibronectin. Secretion of fibronectin occurred in a cle ar-cut time-dependent increase in monocultures of peritubular cells (on day 3 of culture). In co-cultures of Sertoli and peritubular cells, fibronecti n biosynthesis was down-regulated. The paracrine interplay between extracel lular matrix and hormonal signals joining peritubular and Sertoli cells is essential in the differentiation of the seminiferous tubules.