View Program - 63rd Annual Drosophila Research Conference

Epithelial morphogenesis is fundamental to animal development and the understanding of congenital disorders. In the fly retina, the repeated assembly and disassembly of contractile actomyosin and branched F-actin networks drive epithelial morphogenesis. However, the roles and the mechanisms that control the pulsatile dynamics of each network are poorly understood. The Rho1 RhoGTPase regulates the assembly of the contractile actomyosin network by activating both the formin Diaphanous (Dia) to promote the assembly of linear actin filaments and non-muscle Myosin II (MyoII) to bind and contract these filaments. We hypothesized that actomyosin turnover is essential for rebalancing forces in the epithelium for proper remodeling and for preventing tissue damage. To test this idea, we overexpressed a constitutively active myosin light chain kinase (MLCK.ct) and separately a constitutively active Dia (Dia.ca) to respectively activate either MyoII or the assembly of linear F-actin. Both manipulations led to defects in epithelial remodeling. MLCK.ct inhibited pulsatile actomyosin assembly and induced ruptures in the epithelium. Likewise, Dia.ca disrupted epithelial remodeling. To determine the mechanisms that regulate actomyosin turnover, we searched for RhoGEFs and GAPs affecting epithelial remodeling. We identified RhoGEF2 and RhoGAP71E as regulators of actomyosin turnover in this process. RhoGEF2 localized medioapically, while RhoGAP71E localized both medioapically and at the cell surface. Genetic analysis combined with live imaging revealed that RhoGAP71E inhibits pulsatile actomyosin dynamics and decreases MyoII levels, while RhoGEF2 has opposite effects. Our data suggest that RhoGEF2 and RhoGAP71E activate and inhibit Rho1, respectively, to sustain actomyosin turnover, promote proper remodeling and rebalance forces in the tissue to inhibit tissue rupture.

Regulated actomyosin turnover is essential for eye epithelial morphogenesis