Endocrine Abstracts

In vertebrates, ARs have been detected in spermatogonia and also fetal gonocytes, confirming the importance of testosterone for the initial process of spermatogenesis. During seasonal spermatogenesis of adult bullfrogs (Lithobates catesbeianus), primordial germ (PG) cells show testosterone immunoexpression in winter; however, a weak or none testosterone immunoexpression was detected in summer. With the aim to confirm the role of testosterone in these cells, the immunogold localization of testosterone and the immunohistochemical (IHC) detection of AR and SHBG in PG cells were performed. Regarding the important role of estrogen for spermatogenesis, the immunoexpression of aromatase (CYP1A1), ERβ and PCNA was also evaluated in PG cells according to seasonality. The bullfrog testes were collected in winter and summer and were embedded in glycol methacrylate, for PG cells quantitative analysis; or in paraffin, for detection of stem cell markers (alkaline phosphatase activity and GFRα1), AR, SHBG, CYP1A1, ERβ and PCNA. The mitotic index of PG cells and the semiquantitative score (HSCORE) of ERβ-immunolabeled PG cells were obtained. Some fragments were processed for transmission electron microscopy for testosterone immunocytochemistry. PG cells were positive to stem cell markers. Immunogold-labeling of testosterone was usually observed in the cytoplasmic regions next to mitochondria. Moreover, cytoplasm immunoexpression of ARs and SHBG was also detected in the winter PG cells, confirming the participation of testosterone in these cells. In summer, the cytoplasm immunoexpression of CYP1A1 and the high ERβ HSCORE in PG cells confirm that testosterone is converted into estrogen. At winter, the number of PG cells was significantly higher (P≤0.05) than summer; however, a high number of PCNA-positive PG cells was coincident to the high ERβ HSCORE at summer. Therefore, the results indicate that testosterone and estrogen seems to play a role in the control of the seasonal mitotic activity of PG cells during spermatogenesis of bullfrogs.

FAPESP (2009/17895–5).

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details unavailable.