Ultrastructure of steroidogenic cells and immunolocalization of 17-beta-hydroxysteroid dehydrogenase type 3 (17β-HSD3) in mature testes of Potamotrygon wallacei (Chondrichthyes: Potamotrygoninae)

Spermatogenesis is regulated by sex steroids secreted by Sertoli and Leydig cells present in the testis. However, in South American freshwater stingrays, knowledge regarding the contribution of testicular cells in this process is still limited. This study aimed to describe the ultrastructure of the steroidogenic cells in mature testes of cururu stingray, Potamotrygon wallacei and examine the localization of 17-beta-hydroxysteroid dehydrogenase type 3 (17 beta-HSD3) as a marker of the site of testosterone (T) production. Using Transmission Electron Microscopy and polyclonal antibodies, we examined the steroidogenic cells of P. wallacei testes in three different reproductive stages. The ultrastructural study showed the presence of Sertoli cells and Leydig cells, which feature organelles engaged in steroid hormone production, such as the smooth endoplasmic reticulum (SER) and mitochondria. The Sertoli cells change their morphology according to the spermatogenic stage, thus increasing the organelles needed for steroid production from mitotic to spermiogenic zones. Sertoli cells show immunoreactivity to 17 beta-HSD3 and seem to have the ability to produce T in the spermatogonia, spermatids, and spermatozoa zones. In the spermatogonia cyst of all the analyzed males, the reactivity of 17 beta-HSD3 was observed, which suggests that spermatogonia, in association with Sertoli cells, can produce T in males with the absence of spermiogenic zones, as seen in regressing males. The Leydig cells showed reactivity to 17 beta-HSD3 in all the analyzed males. These findings demonstrated that Leydig, Sertoli, and spermatogonia cells could actively participate in T production in P. wallacei testes.