Decoding the Mechanical Interactions between Tissue Layers Sculping Organ Shape

Project Summary [The project summary remains as described in the original application.] Organ shape is vital for proper function. Malformations in the looping and folding of the heart, for instance, represent the leading cause of birth defect mortality in humans. Visceral organs rely on the coordinated activity of multiple laminar tissue layers to fold and coil into targeted shapes. While the community has learned much about the genetic signals governing cell fates during development, less is understood about the mechanical stresses and tissue dynamics that translate gene expression into the shapes of organs. This proposal aims to understand the connection between Hox patterning and mechanical stresses driving organ folding and rotational torques driving organ looping using the D. melanogaster midgut as a model system. The midgut begins as a tube of two concentric tissue layers that undergoes a sequence of constrictions to fold into chambers. Advances in light-sheet microscopy now enable live visualization of the whole organ at cellular resolution during development. During the K99 period, we integrated these imaging methods with physics approaches to follow cell dynamics across tissue layers across the whole organ throughout morphogenesis (see K99 phase publications). This technology enables us to quantitatively relate genetic patterning in the tissue to the tissue mechanics and dynamic cellular behaviors driving 3D shape change. During the R00 phase, I am leveraging the tools developed during the K99 phase for three aims. First, we will decode the relationship between Hox gene patterning and the downstream pattern of calcium pulses in the midgut using quantitative measurements in WT and mutant embryos. The second aim, which builds on these results, will address the role of the endoderm in driving tissue folding, with particular attention to the role of the Hox gene labial. The final aim, performed in parallel with the others, addresses how the midgut coils into a chiral tube at later stages of development. Recent discoveries have shown that ‘cell intrinsic’ chirality, in which cytoskeletal machinery breaks left-right symmetry, plays a key role in determining organ-scale chirality. The mechanical process by which cell chirality translates into 3D organ-scale shape change, however, remains largely unknown. By combining the in toto imaging toolkit, molecular tools learned during the K99 phase, and my expertise in chiral mechanics from my PhD, this aim will link cellular chirality to the dynamics of organ-scale coiling.