What basal membranes can tell us about viscous forces in Drosophila ventral furrow formation

Ventral furrow (VF) formation in Drosophila melanogaster is an important model of epithelial folding. Past studies of VF formation focus on apical forces in driving folding, while other forces are largely unexplored. When basal membrane formation is genetically blocked using anillin knockdown ( scra RNAi), the VF can still fold. To interpret our observations, we developed a computational model of VF formation that explicitly simulates the flows of viscous cytoplasm. The viscosity included in our model is required for tissue invagination in the absence of basal membranes. This strongly suggests that epithelial folding requires the presence of viscous shear forces from cytoplasm. Our model characterizes folding during VF formation as a “swimming phenomenon”, where tissue deforms by pushing against the ambient viscous surroundings. Since VF formation is successful in scra RNAi embryos, we propose that models of gastrulation should be able to replicate this folding in the absence of basal membranes. ### Competing Interest Statement The authors have declared no competing interest.