A mechanical wave travels along a genetic guide to drive the formation of an epithelial furrow

Epithelial furrowing is a morphogenetic process that is pivotal during embryo gastrulation, neurulation and the shaping of the animal body. A furrow often results from a fold that propagates along a line. How fold formation and propagation are initiated, driven and controlled is still poorly understood. To shed new light on this fundamental morphogenetic process, we study the formation of the cephalic furrow: a fold that runs along the dorsal-ventral axis of the embryo during early Drosophila gastrulation and the developmental role of which is still unknown. Here, we provide evidence of its function and show that the cephalic furrow is initiated by two groups of cells located on the left and right lateral sides of the embryo. These cellular clusters work as a pacemaker triggering a bi-directional morphogenetic wave powered by actomyosin contractions and sustained by de novo medial apex-to-apex cell adhesion. The Cartesian position of the pacemakers is under the cross-control of the embryo anterior-posterior and dorsal-ventral gene patterning systems. Thus, furrow initiation and propagation are driven by a mechanical trigger wave that travels under the control of a multidimensional genetic guide.