Molecular control of early and late urothelial differentiation in the murine ureter

• Applicant: Professor Dr. Andreas Kispert
• Subject Area: Developmental Biology
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 417240095

The urothelium, the inner epithelial lining of the mature urinary drainage system, serves as a physical barrier towards the urine. In both the ureter and bladder, the mature tissue consists of three major cell types that are organized in radial layers. Bordering the lumen are large binucleated tightly-sealing superficial (S-)cells. Underneath are much smaller intermediate (I-)cells. Finally, a layer of small but highly abundant cuboidal basal (B-)cells tethers the epithelium to the basal lamina. B-, I- and S-cells arise from epithelial progenitors through poorly understood molecular and cellular programs. Work in the first funding period has shown that a FGFR2-SHH-FOXF1-BMP4 signaling module is required for proliferation, stratification and differentiation of the epithelial compartment in the fetal mouse ureter. This is achieved in part by direct activation of pro-differentiation genes and in part by suppression of RA signaling that represses such genes. We showed that the transcription factor DNP63 is required for epithelial stratification, whereas PPARG activates expression of a large set of S-cell specific genes. Our further preliminary work has shown that not only DNP63 and PPARG but also the transcription factors MSX2, GRHL3 and FOXA1 require BMP4 signaling for expression in the ureteric epithelium. In the second funding period, we want to characterize the individual function of MSX2, GRHL3 and FOXA1 in the differentiation of B-, I- and S-cells in the fetal ureter. For this, we will analyze the cellular and molecular changes resulting from conditional genetic loss of these factors in the ureteric epithelium, and identify targets of their transcriptional activity. We will determine the relative contribution of these transcription factors to the transcriptional profile of B-, I- and S-cells and investigate their ability to activate individually or combinatorially the urothelial cytodifferentiation programs. To characterize the cellular processes during early postnatal ureter development, we aim to analyze ureters of a staggered series of stages ranging from P0 to P250 for changes in the number, size, contact, proliferation and apoptosis of B-, I- and S-cells. We aim to monitor global transcriptional changes in isolated B-, I- and S-cells between P0 and P14, to uncover molecular changes underlying the differentiation programs. We aim to explore the input of external signals on postnatal urothelial development and characterize the role of canonical RBPJ-dependent Notch signaling therein. We expect from these experiments decisive insights in the molecular control mechanism of urothelial differentiation in the ureter which may serve as a paradigm for other components of the urinary tract. From a clinical point of view, it may shed light on the etiology and possible molecular causes of congenital and acquired anomalies of the urothelial lining of the urinary tract.

• DFG Programme: Research Grants