BDM is pervasive in development but difficult to understand due to the necessity of incorporating multiple tissue deformations in their global context. We absorb these into simple and measurable parameters and provide both a model and model system to understand boundary-driven morphogenesis. (8/8)

Finally, we follow up the model's predictions by comparing phenotypes in genetic mutants lacking active behaviors by some of the neighboring tissues. We find that without a decrease in enclosed area or movement of the ring off of the posterior pole, it fails to break symmetry. (7/8)

We found that the hindgut deforms in two stages. The first involves uniform dilation and contraction of the rings. The second involves a rapid change in the shape (described by the rapid change in roundness, a shape metric) we explain in the model above. (6/8)

We then acquired a light sheet dataset and tracked each nucleus within the hindgut (~40,000 annotations for one embryo!) as it deformed. We constructed closed space curves, or "contours," that follow the movements of nuclei and mirror the minimal model's representation of the tissue. (5/8)

Using a minimal model, we found that neighbors moving the hindgut onto one side of the embryo and decreasing enclosed apical area is sufficient to drive the break in shape symmetry. The anisotropic curvature of the underlying surface results in the ring-to-keyhole transition. (4/8)

The hindgut itself deforms no less dramatically, quickly breaking shape symmetry and transforming from a circular ring to a triangular keyhole. Does the hindgut deform merely as a result of its neighbors? (3/8)

At the onset of gastrulation, the hindgut primordium is a ring of ~400 cells bordered by canonical examples of actively-deforming tissues such as the germ band (GB), ventral furrow, and posterior midgut (PMG). These neighbors deform either in-plane or out-of-plane. (2/8)

A ring of cells deforms into a triangular keyhole in just 15 minutes. Meet the hindgut, a model for boundary-driven morphogenesis!

Out now in @pnas.org at doi.org/10.1073/pnas... with @zhaoshh.bsky.social, Alex Jacinto, Eric Wieschaus, Stas Shvartsman, @lepuslapis.bsky.social (1/8)