ABSTRACT
Ventral furrow (VF) formation in Drosophila melanogaster is an important model of epithelial folding. Past studies of VF formation focus on the role of apical constriction in driving folding. However, the relative contributions of other forces are largely unexplored. When basal membrane formation is genetically blocked using RNAi-mediated anillin knockdown (scra RNAi), the VF is still capable of folding. scra RNAi and control embryos display quantifiable cell length differences throughout gastrulation, as well as qualitative differences in membrane integrity. To interpret our observations, we developed a computational model of VF formation that explicitly simulates the flows of the viscous cytoplasm. The viscosity included in our model is required for tissue invagination in the complete absence of basal membranes and explains the observed differences in membrane lengths across conditions. In the absence of basal membranes, 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 also be tested for their ability to replicate folding in the absence of basal membranes.
Competing Interest Statement
The authors have declared no competing interest.