Testosterone acts through membrane protein GPRC6A to cause cardiac edema in zebrafish embryos

Androgens are classically thought to act through intracellular androgen receptors (AR/NR3C4), but they can also trigger non-genomic effects via membrane proteins. Although several membrane androgen receptors have been characterized in vitro, their functions in vivo remain unclear. Using a chemical-genetic screen in zebrafish, we found that GPRC6A, a G-protein coupled receptor, mediates non-genomic androgen actions during embryonic development. Exposure to androgens (androstanedione, DHT, and testosterone) caused cardiac edema or tail curvature in wild-type embryos, as well as in ar mutants, suggesting AR-independent pathways. We then mutated putative membrane androgen receptors (gprc6a, hcar1-4, and zip9) and found that only gprc6a mutants exhibited a significant reduction in cardiac edema following testosterone exposure. Additionally, co-treatment of wild-type embryos with testosterone and GPRC6A antagonists significantly suppressed the cardiac edema phenotype. Using RNA-seq and RNA rescue approaches, we found that testosterone-GPRC6A causes cardiac phenotypes by reducing Pak1 signaling. Our results indicate that testosterone induces cardiac edema in zebrafish embryos through GPRC6A, independent of nuclear androgen receptors, highlighting a novel non-genomic androgen signaling pathway in embryonic development.