Luminal mitosis drives epithelial cell dispersal within the branching ureteric bud.

The ureteric bud is an epithelial tube that undergoes branching morphogenesis to form the renal collecting system. Although development of a normal kidney depends on proper ureteric bud morphogenesis, the cellular events underlying this process remain obscure. Here, we used time-lapse microscopy together with several genetic labeling methods to observe ureteric bud cell behaviors in developing mouse kidneys. We observed an unexpected cell behavior in the branching tips of the ureteric bud, which we term "mitosis-associated cell dispersal." Premitotic ureteric tip cells delaminate from the epithelium and divide within the lumen; although one daughter cell retains a basal process, allowing it to reinsert into the epithelium at the site of origin, the other daughter cell reinserts at a position one to three cell diameters away. Given the high rate of cell division in ureteric tips, this cellular behavior causes extensive epithelial cell rearrangements that may contribute to renal branching morphogenesis.