Gone with the Wnt: the canonical Wnt signaling axis is present and androgen dependent in the rodent gubernaculum

Abstract

Background/aims: How androgens control inguinoscrotal descent remains controversial but may include canonical Wnt signaling via the transcriptional co-activator β-catenin. The canonical Wnt pathway transcribes genes regulating mesenchymal cell migration, fate, extracellular matrix remodeling, and in addition Axin2, a feedback product that reliably identifies Wnt activation. The relationship between β-catenin and androgen receptor warranted investigation into the involvement of the canonical Wnt pathway in testicular descent.

Methods: Gubernacula from male Sprague-Dawley control (n = 22) and flutamide-treated (n = 18) rats at E17, E19, and D0 time-points were processed for immunohistochemistry. Sagittal sections stained for presence of androgen receptor, Axin2, and β-catenin were analyzed by fluorescent confocal microscopy.

Results: At E19, β-catenin was strongly expressed in the membrane of developing cremaster muscle cells and the cytoplasm of gubernacular core cells. Axin2 expression was ubiquitous in nuclei of gubernacular mesenchymal cells, representing canonical Wnt signaling. After androgen blockade, Axin2 was conspicuously absent in the fibroblasts of the gubernacular core while remaining unaffected elsewhere. Reduced staining of Axin2 in E17 and D0 gubernacula suggests that Wnt signaling coincides with androgen programming.

Conclusion: Axin2 expression in the E19 gubernaculum confirms canonical Wnt pathway activation. Its absence in the core of flutamide-treated gubernacula indicates Wnt down-regulation. As androgen is required for inguinoscrotal descent, downstream Wnt signaling may control initial gubernacular remodeling. Defects in this complex molecular process may play a role in cryptorchidism.