From genes to geometry: how a visceral organ takes form*

During morphogenesis, tissues fold into complex shapes to form visceral organs. Genetic signals are known to govern form, but the mechanical processes by which interacting tissue layers generate vital organ shapes remain elusive. Here, we trace an organ's in toto dynamics and uncover the mechanical interactions across tissue layers, from sub-cellular to organ scale. Using deep tissue light-sheet microscopy for whole-organ live imaging, we find a mechanical program folding the embryonic midgut of Drosophila: hox genes control the emergence of high-frequency calcium pulses, which trigger muscle contractions. These contractions, in turn, induce cell shape change in the adjacent tissue layer, collectively driving a pattern of convergent extension. Analysis of the kinematics shows that patterned convergent extension (ie, in-plane shear) is linked to out-of-plane organ folding. These findings offer a mechanical route for gene expression to induce organ shape change: genetic patterning in one layer triggers a physical process in the adjacent layer to drive organ shape change.