Heterotrimeric G protein signaling governs the cortical stability during apical constriction in Drosophila gastrulation

During gastrulation in Drosophila melanogaster, coordinated apical constriction of the cellular surface drives invagination of the mesoderm anlage. Forces generated by the cortical cytoskeletal network have a pivotal role in this cellular shape change. Here, we show that the organisation of cortical actin is essential for stabilisation of the cellular surface against contraction. We found that mutation of genes related to heterotrimeric G protein (HGP) signaling, such as Gβ13F, Gγ1, and ric-8, results in formation of blebs on the ventral cellular surface. The formation of blebs is caused by perturbation of cortical actin and induced by local surface contraction. HGP signaling mediated by two Gα subunits, Concertina and G-iα65A, constitutively regulates actin organisation. We propose that the organisation of cortical actin by HGP is required to reinforce the cortex so that the cells can endure hydrostatic stress during tissue folding.