Multiple contact sites between cells and the vitelline envelope coordinate tissue flows in Drosophila gastrulation

Abstract

Gastrulation is thought to be driven primarily by forces generated within individual cells. These cell-intrinsic forces collectively induce tissue-scale flows and transform the monolayered embryo into a multilayered structure. However, as the embryo constitutes a mechanically closed system, these flows must be balanced by regions of resistance or anchoring to enable asymmetric morphogenesis. In the Drosophila embryo, integrin-mediated attachment of the blastoderm to the vitelline envelope has been shown to stabilize germ band extension at the organismal scale. Disrupting such an attachment leads to a characteristic twisting phenotype. Yet, how this attachment shapes concurrent global morphogenetic events remains unclear. We discovered that the integrin -subunit scab, which mediates the attachment, is expressed in three different regions of the cellular blastoderm near prominent invagination events. Through a combination of light-sheet imaging, genetic and mechanical perturbations, we demonstrate that integrin-enhanced friction is essential for unidirectional tissue flows in those regions, with effects including cephalic furrow positioning and epithelial stability. Guided by a minimal physical model, we further show that multiple attachment sites enhance the robustness and reproducibility of global tissue movements. Together, our results indicate that Drosophila gastrulation emerges from a balance between cell-intrinsic force generation and spatially distributed adhesion to the surrounding envelope, which together shape tissue flows at the embryo scale.