Wnt9b enables androgen action to maintain Wolffian ducts in mice

The Wolffian duct (WD) is the embryonic primordium that gives rise to the epididymis, vas deferens, and seminal vesicle. The androgen action in the mesenchyme is the predominant driver for fetal WD maintenance, which is essential for male fertility. However, the androgen's capability of promoting WD maintenance was completely lost in the absence of Wnt9b in mice. In this study, we followed up with this interesting phenomenon and revealed cellular and molecular mechanisms whereby Wnt9b facilitates WD maintenance in male embryos. Wnt9b belongs to the WNT family of secreted proteins and is expressed in the WD epithelium. We found that WD degeneration in Wnt9b-/- male embryos was accompanied by decreased cell proliferation in the epithelium but not in the mesenchyme during sexual differentiation. Wnt9b deletion did not impair testicular androgen synthesis but altered androgen receptor (AR) expression pattern. The percentage of AR-positive cells in the mesenchyme was significantly reduced, which can be the cause of decreased epithelial proliferation. Wnt9b actions can be transduced by both β-catenin-dependent and β-catenin-independent pathways in the context of target cells. Transcriptomic analysis of embryonic day (E) 12.5 Wnt9b+/+ and Wnt9b-/- mesonephroi revealed that expression of multiple WNT/β-catenin-target genes was reduced in the absence of Wnt9b. Deletion of mesenchymal β-catenin led to caudal WD degeneration and cystic formation in the cranial region. Taken together, our study uncovers the important WNT9B-AR signaling axis that mediates the epithelial-mesenchymal interaction in WD development.