Mechanical feedback in Drosophila embryonic development

Morphogenesis, the forming organism shape, raises deep questions in biology and physics. Two principles coordinate morphogenetic force-generation: genetic programs and dynamic response to mechanical stimuli. Any understanding requires disentangling them, which is challenging. We address this in the D. melanogaster embryo, combining in-toto imaging, (opto-)genetic perturbations, and quantitative modeling. During convergent extension (CE), a fundamental developmental motive, non-muscle myosin II is recruited to cell-cell junctions to generate forces. Myosin gradients drive tissue flow. Previous work linked myosin to the pattern of the so-called pair-rule genes. We show that at the onset of CE, myosin is recruited by mechano-sensation in proportion to the strain rate, a long-range effect establishing the initial myosin gradient. The effect’s strength is spatially graded, possibly via genetics. Next, as tissue flows, gene patterns deform yet myosin anisotropy remains aligned to a static source, potentially tension. Factoring in the time myosin is bound to junctions, we can describe the dynamics of the anisotropy orientation. Our results indicate mechanical feedback regulates embryo-scale cytoskeletal organization and tissue flow, casting CE as an autonomous, self-organized process.