An extended regulatory landscape drives Tbx18 activity in a variety of prostate-associated cell lineages

The evolutionarily conserved transcription factor, Tbx18, is expressed in a dynamic pattern throughout embryonic and early postnatal life and plays crucial roles in the development of multiple organ systems. Previous studies have indicated that this dynamic function is controlled by an expansive regulatory structure, extending far upstream and downstream of the gene. With the goal of identifying elements that interact with the Tbx18 promoter in developing prostate, we coupled chromatin conformation capture (4C) and ATAC-seq from embryonic day 18.5 (E18.5) mouse urogenital sinus (UGS), where Tbx18 is highly expressed. The data revealed dozens of active chromatin elements distributed throughout a 1.5 million base pair topologically associating domain (TAD). To identify cell types contributing to this chromatin signal, we used lineage tracing methods with a Tbx18 Cre "knock-in" allele; these data show clearly that Tbx18-expressing precursors differentiate into wide array of cell types in multiple tissue compartments, most of which have not been previously reported. We also used a 209 kb Cre-expressing Tbx18 transgene, to partition enhancers for specific precursor types into two rough spatial domains. Within this central 209 kb compartment, we identified ECR1, previously described to regulate Tbx18 expression in ureter, as an active regulator of UGS expression. Together these data define the diverse fates of Tbx18+ precursors in prostate-associated tissues for the first time, and identify a highly active TAD controlling the gene's essential function in this tissue.