 (A) Schematic representation of the RhoGEF2-CRY2/CIBN optogenetic system employed to control myosin-II activity during early Drosophila embryogenesis. The photosensitive domain of CRY2 is fused to the catalytic domain of the GTP Exchange factor RhoGEF2, while CIBN is anchored at the plasma membrane. In the dark RhoGEF2-CRY2 is present in the cytoplasm (left). Blue light illumination triggers the CRY2/CIBN interaction and causes the translocation of RhoGEF2-CRY2 to the plasma membrane, where it activates endogenous Rho1 signaling (right), and myosin-II 