Endocrine Abstracts

Sexually dimorphic organogenesis of the prostate is a key function of androgens during mammalian development. Mesenchymal AR signalling is essential for prostate development, while epithelial AR is not required. Within the mesenchyme there are distinct mesenchymal subsets that show differential effects of androgens; androgens regulate the thickness of the urethral smooth muscle layer, while in the inductive mesenchymal pad, androgens stimulate branching and growth of prostate epithelia. However, there is little knowledge of AR target genes in mesenchyme or mesenchymal subsets. We used ChIPseq to define AR binding sites (ARBs) in microdissected mesenchymal subsets during prostate development. Our focus was upon urethral smooth muscle (SM, female), inductive pad mesenchyme (MP, female), ventral prostate (VP, male) and dorsolateral prostate (DDLP, male). Tissues were microdissected from day of birth rats where AR expression is largely restricted to mesenchymal cells. Western blotting for AR showed higher levels in males (VP and DDLP) than females (SM and MP). ChIPseq was performed on pooled tissue, and ARBs co-identified with both MACS2.0 and HOMER. We validated promoter ARBs using RNAseq transcript profiling of the same tissues used for ChIPseq, to restrict our focus to tissue expressed genes and to define a mesenchymal AR cistrome. 80% of promoter specific ARBs were validated by transcript expression. Mesenchymal pad and smooth muscle cistromes showed a 70% and 68% overlap respectively with developing human fetal prostate transcripts suggesting that a high proportion of our defined mesenchymal ARBs may play a functional role in vivo during human prostate organogenesis.

Funding: Canadian Cancer Research Society.

Presenting Author: Axel Thomson, Department for Surgery, Division of Urology, MUHC Research Institute, 1001 Decarie Blvd Montreal, Quebec H4A 3J1 1 514 934 1934 ext 76307, Canada. Email: [email protected]