Abstract: Understanding how complex organ shape emerges during development remains a major challenge. Here, we use high spatio-temporal live imaging with biophysical modelling to explore at cellular and tissue scales the underlying biophysical processes driving morphogenesis of zebrafish skeletal muscle.

The skeletal muscle of swimming vertebrates forms a distinctive chevron morphology, which is believed to aid swimming. This shape can be altered by perturbing muscle cell differentiation or the interaction between muscle segments (myotomes) and surrounding tissues. We find that, soon after segmentation from the presomitic mesoderm, the future myotome spreads across the underlying tissues. The mechanical coupling between the future myotome and the surrounding tissues appears to spatially vary, effectively resulting in spatially heterogeneous friction. Using a vertex model combined with experimental validation, we show that the interplay of tissue spreading and friction is sufficient to drive the initial phase of chevron shape formation. However, local anisotropic stresses, generated during muscle cell differentiation, combined with tissue plasticity, are necessary to reach the acute angle of the wild-type chevron. This work reveals how a sequence of local cellular events can have a nonlocal and irreversible mechanical impact at the tissue scale. I will also discuss our work revealing how multiple morphogens work synergistically to ensure precise timing of cell fate specification within the myotome.