Developmental and hormonal regulation of the expression of oligodendrocyte-specific protein/claudin 11 in mouse testis.

The proliferation and differentiation of testicular progenitor stem cells into highly specialized germ cells (spermatozoa) are largely controlled by the hormonally (FSH and testosterone) regulated adjacent supporting Sertoli cells. However, the factors involved in this control remain largely unknown. In the present study, the technique of differential display PCR was used to identify target transcripts to FSH action in cultured murine Sertoli cells. Among these target transcripts, we identified the oligodendrocyte-specific protein (OSP), also known as claudin 11, which had recently been shown to play a key role in the formation of the hematotesticular barrier. Our data show that the testicular expression of OSP is dependent upon male gonad development and systemic and local signaling molecules. Indeed, OSP is expressed early in fetal development in Sertoli cells, immediately after the peak of SRY (sex-determining region, Y gene) expression, but just before that of the anti-Mullerian hormone. Postnatally, OSP expression starts to increase from day 3 to reach a plateau between days 6 and 16 postnatally. In the prepubertal and adult testes, an apparent decline in OSP messenger RNA (mRNA) levels was found, probably because of the increasing number of germ cells (which do not express OSP). Among the signaling molecules that control testicular OSP expression, we have identified FSH and tumor necrosis factor-alpha (TNFalpha). Indeed, using a model of purified cultured mouse Sertoli cells, we demonstrate that FSH inhibits, in a dose (ED50 = 4 ng/ml)- and time (maximal effect after 24 h)-dependent manner, the levels of OSP mRNA. Such an inhibitory effect was mimicked by 8-bromo-cAMP, suggesting that FSH may use the cAMP/protein kinase A pathway to inhibit OSP mRNA levels. TNFalpha was also shown to inhibit OSP expression in cultured Sertoli cells. The maximal effect was observed after 48 h of TNFalpha treatment with an ED50 of 4.5 ng/ml. Together, our results indicate that OSP expression 1) starts during fetal life at a critical period, probably under SRY control and during testicular formation; and 2) is regulated by hormones (FSH) and cytokines (TNFalpha) in the adult testis, suggesting a critical role for these molecules in the (re)modeling process of the hematotesticular barrier during spermatogenesis.