LOCALIZATION OF FOLLISTATIN IN THE RAT TESTIS

The cellular localization of the activin-binding protein, follistatin, in the rat testis has been a matter of some controversy with differen t investigators claiming that Sertoli cells, Leydig cells or germ cell s are the primary cell types containing this protein. The localization of mRNA encoding follistatin was re-examined using reverse transcript ion-polymerase chain reaction (RT-PCR) and in situ hybridization as we ll as the distribution of follistatin by immunohistochemistry. The res ults demonstrate that mRNA encoding follistatin is located in many ger m cells including type B spermatogonia, primary spermatocytes with the exception of the late leptotene and early zygotene stages, and sperma tids at steps 1 to 11. It is also found in Sertoli cells and endotheli al cells but not in Leydig cells. Immunohistochemistry, using two diff erent antisera to follistatin, showed that this protein was localized to spermatogonia, primary spermatocytes at all stages except the zygot ene stage, spermatids at all stages and to endothelial cells and Leydi g cells in the intratubular regions. The failure to detect mRNA for fo llistatin in Leydig cells using RT-PCR and in situ hybridization sugge sts that the immunohistochemical localization in these cells reflects binding of follistatin produced elsewhere. The widespread localization of follistatin, taken together with its capacity to neutralize the ac tions of activin, may indicate that follistatin modulates a range of t esticular actions of activin, many of which remain unknown.