The GEF/GAP ratio is a developmentally controlled mechanism to modulate cell shape. A low RhoGEF2/C-GAP ratio, such as twist RNAi or C-GAP OE, results in fewer medioapical myosin fibers, less persistent myosin (orange arrows), and more unratcheted pulses. A high RhoGEF2/C-GAP ratio, as in C-GAP shRNA, results in “constitutive” ratcheting and less pulsing. In WT embryos, the ratio transitions, gradually increasing persistent myosin and ratchet-like contractions over time.