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Abstract: SA-PO320

The Developing Kidney Actively Negotiates Geometric Packing Conflicts to Avoid Defects

Session Information

Category: Development, Stem Cells, and Regenerative Medicine

  • 600 Development, Stem Cells, and Regenerative Medicine

Authors

  • Prahl, Louis Skjei, University of Pennsylvania, Philadelphia, Pennsylvania, United States
  • Hughes, Alex, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Background

Ureteric bud (UB) tubules branch at the kidney’s surface, where their tips specify sites of nephron induction through interactions with the surrounding cap mesenchyme. The extent of UB branching determines nephron endowment at birth (up to ~1 million in humans) and low nephron count poses a risk of hypertension and adult disease. Here, we examine physical and geometric factors involved in UB tip packing into a limited organ surface area and how UB morphology changes across developmental stages to accommodate branching.

Methods

We use confocal immunofluorescence of embryonic day (E)14-18 mouse kidneys and tissues to investigate the organization of UB and cap mesenchyme. Live kidney explants were treated with dispase to disrupt adhesion between the UB and mesenchyme and tubule retraction was measured by confocal microscopy. We used a computational model to predict branching tubule structures and defects that occur as a function of packing density, repulsion between tips, and node depth. Models were compared to our acquired data and previously published imaging studies of genetic mouse models.

Results

Surface packing density of UB tips increases between E14-18, accompanied by morphological changes in the size and shape of cap mesenchyme clusters and intervening stromal tissue boundaries. Branching tip morphologies change across this interval as well, with branch points progressively moving into deeper tissue layers. Physics-based computational modeling predicts these anatomical changes using geometric parameters. Consistent with model predictions, experimental measurements of tubule retraction following dispase treatment show that actomyosin-based forces are necessary for progressive restructuring of tubules. Our model also predicts conditions where ‘packing defects’ form, including colliding, or overlapping tubules (‘short circuits’) or tips being forced into deeper tissue layers (‘buried tips’). We successfully reproduce the buried tips defect in microdissected kidney tissues and investigate published literature examples of mouse mutations that exhibit packing defects.

Conclusion

Our work indicates that the UB must actively restructure during development to avoid organizational defects. We suggest new classification criteria for branching morphogenesis-related congenital defects.

Funding

  • NIDDK Support