# Visualizing androgen signaling and assessing its interaction with canonical Wnt signaling pathways in prostate development, morphogenesis, and regeneration

## TL;DR

This study introduces a new mouse model to track androgen receptor-expressing cells during prostate development and regeneration, revealing their role in glandular cell polarity and death signaling.

## Contribution

A novel genetically engineered mouse model enables spatiotemporal labeling of AR-expressing cells to study their role in prostate development and signaling pathways.

## Key findings

- AR-expressing cells labeled with mGFP were detected in urogenital mesenchyme and epithelium during prostate development.
- Deleting β-catenin in AR-expressing cells disrupts prostate development and activates Fas death signaling.
- The new model allows tracing AR-expressing cells through multiple stages of prostate growth and regeneration.

## Abstract

The androgen receptor (AR) is a nuclear hormone receptor, and its activation through binding to androgens is essential for prostate development, morphogenesis, growth, and tumorigenesis. Although significant efforts have been devoted to understanding the critical role of AR, the cellular properties and functions of the AR-expressing cells acting as prostatic progenitors in controlling prostatic cell differentiation and growth still remain elusive. Additionally, dynamic paracrine interactions between urogenital mesenchyme and epithelia initiated by the AR activation through prostate development are also largely unknown. Recently, we modified the mouse Ar gene locus, which enables us to genetically label AR-expressing cells spatiotemporally and trace them through prostate development, morphogenesis, and growth in combination with a double-fluorescent reporter mouse model. The membrane-bound green fluorescent protein (mGFP)-expressing cells were revealed in both urogenital sinus mesenchyme (UGM) and epithelium (UGE) at embryonic day E18.5 when Tamoxifen was administrated at E13.5 to activate CreER recombinase directed by the endogenous Ar promoter. The AR-expressing cells and their descendants were further detected at postnatal days 10, 35, and 56, and through three cycles of prostatic regeneration by repeated androgen deprivation and replacement. Deletion of β-catenin through the AR-driven CreER in embryonic AR-expressing cells impairs prostate development and morphogenesis. Specifically, altered β-catenin expression results in loss of prostatic glandular cell polarity and activation of Fas death signaling pathways. These lines of experimental evidence demonstrate the biological relevance and significance of this new genetic tool to assess and visualize AR-mediated signaling pathways through prostatic development, growth, and tumorigenesis.

Prostate formation, growth, regeneration, and tumorigenesis depend on androgens and androgen receptor (AR)-mediated signaling pathways. Early tissue recombination assays demonstrated a decisive role for stromal androgen signaling in prostatic epithelium development. However, the identity of the mesenchymal cells in the urogenital sinus mesenchyme that convey androgen signaling and control prostate epithelium development, morphogenesis, and regeneration remains elusive. Additionally, how epithelial AR responds to stromal signaling to regulate differentiation, morphogenesis, and growth during embryonic development and prepubescence is unclear. Moreover, the molecular mechanisms underlying androgen signaling that initiate the paracrine regulation between prostatic mesenchymal and epithelial cells are largely unknown. One of the key bottlenecks in addressing these critical questions has been the lack of relevant Genetically Engineered Mouse Models (GEMMs) to evaluate androgen and AR action during these biological events.

To directly address this challenge, we developed a new GEMM, the Ar
IRES-CreER/Y model. The fundamental difference between this model and previous ones is that AR-expressing cells can be labeled in a temporal and spatial manner. In this study, we tested AR-driven CreER activity using both a double reporter mouse strain and floxed β-catenin alleles. Deletion of β-catenin in embryonic AR-expressing cells impairs prostate development and morphogenesis. Specifically, altered β-catenin expression results in the loss of prostatic glandular cell polarity and activation of Fas death signaling pathways. These lines of experimental evidence demonstrate the relevance and significance of this new genetic tool, which will enable us to design and perform a series of experiments to fully evaluate the role and regulatory mechanisms of AR activation in prostate development, morphogenesis, growth, and tumorigenesis.