HNF1B controls epithelial organization and cell polarity during ureteric bud branching and collecting duct morphogenesis

Kidney development depends critically on proper ureteric bud branching giving rise to the entire collecting duct system. The transcription factor HNF1B is required for the early steps of ureteric bud branching. Yet, the molecular and cellular events regulated by HNF1B are poorly understood. We report that specific removal of Hnf1b from the ureteric bud leads to defective cell-cell contacts and apico-basal polarity during the early branching events. High resolution ex vivo imaging combined with a membranous fluorescent reporter strategy show decreased mutant cell-rearrangements during mitosis-associated cell dispersal and severe epithelial disorganisation. Molecular analysis reveals downregulation of Gdnf-Ret pathway components and suggests that HNF1B acts both upstream and downstream of Ret-signaling by directly regulating Gfrα1 and Etv5. Subsequently, Hnf1b-deletion leads to massively mispatterned ureteric tree network, defective collecting duct differentiation and disrupted tissue architecture leading to cystogenesis. Consistently, mRNA-seq analysis shows that the most impacted genes encode intrinsic cell-membrane components with transporter activity. Our study uncovers a fundamental and recurrring role of HNF1B in epithelial organization during early ureteric bud branching and further patterning and differentiation of the collecting duct system.