The developing kidney actively negotiates geometric packing conflicts to avoid defects

The physiological functions of several organs rely on branched tubular networks, but little is known about conflicts in development between building enough tubules for adequate function and geometric constraints imposed by organ size. We show that the mouse embryonic kidney epithelium negotiates a physical packing conflict between tubule tip duplication and limited area at the organ surface. Imaging, computational, and soft material modeling of tubule ‘families’ identifies six geometric packing phases, including two defective ones. Experiments in kidney explants show that a retrograde tension on tubule families is necessary and sufficient for them to avoid defects by switching to a vertical orientation that increases packing density. These results reveal developmental contingencies in response to physical limitations, and create a framework for classifying kidney defects. One-Sentence Summary Epithelial branching in the kidney causes a geometric packing conflict that is resolved through internally generated tensions