BMP4 signaling regulates the expression of signals and transcription factors for coordinated cytodifferentiation in the murine ureter

Mutations in BMP4 have been associated with malformations of the urinary tract in human patients. Genetic studies in mice have shown that these defects are linked to the expression of Bmp4 in the mesenchymal primordium of the ureter, where it acts as a critical signal for coordinated cytodifferentiation of the mesenchymal and epithelial tissues. Here, we used unbiased transcriptional profiling of ureters with genetic depletion of Bmp4 and pharmacological inhibition of BMP4 signaling to decipher the gene regulatory network controlled by BMP4 in the early ureter, focusing on transcription factors as possible drivers of cytodifferentiation. We show that in Bmp4-deficient ureters, expression of Grhl3, Msx2, Pparg, Trp63 and Foxa1 in the epithelial compartment, and of Gata6, Hopx, Id2, Id4, Myocd, Snai1 and Tbx18 in the mesenchymal primordium is reduced. Expression of Msx2, Pparg, Gata6, Id genes, Tbx18 and Snai1 requires direct BMP4 signaling input, whereas reduced expression of the other genes is likely due to secondary changes, including increased retinoic acid signaling. Conditional gene targeting of Smad4 revealed that BMP4-dependent activation of transcription factor genes is mediated in part by SMAD effectors in both ureteral tissues. Thus, our work links BMP4 (signaling) to known transcriptional regulators of ureteral cytodifferentiation and uncovers additional factors that may be relevant to this program.