PI 4-kinases promote cell surface expansion and facilitate tissue morphogenesis during Drosophila cellularization and gastrulation

During epithelial morphogenesis, dynamic cell shape change driven by intrinsic or extrinsic forces requires prompt regulation of cell surface area. Using Drosophila ventral furrow formation as a model, we identified the PI 4-kinase Fwd as an important regulator for apical constriction-mediated cell shape changes. These morphological changes involve prompt lateral surface expansion in the constricting cells and apical surface expansion in the non-constricting cells adjacent to the constriction domain, both of which are impeded upon depletion of Fwd. Computer modeling demonstrates that restricting apical and lateral cell surface expansion will result in specific tissue-level morphological abnormalities during furrow formation, which well predicts the phenotypes observed in the fwd deficient embryos. Fwd also promotes cell surface expansion during cellularization, but this function is largely redundant with another PI 4-kinase, PI4KII. Together, our findings uncover an important role of Fwd in facilitating cell surface expansion in support of dynamic epithelial remodeling.