Tammy Qiu, Columbia University

Using optogenetics to disentangle how mechanical cues coordinate cell behaviors and maintain bilateral symmetry during tissue elongation

During Drosophila axis elongation, both global embryo-scale forces and local cell-scale forces contribute to the elongation of the germband epithelium along the anterior-posterior axis of the embryo. Divided by the invaginated mesoderm, the left and right sides of the germband extend to the same length and display a remarkable degree of symmetry at the cellular scale in terms of rearrangement rates. The co-elongation of neighboring tissues, which is a conserved symmetry-breaking mechanism in many embryos, is an understudied but interesting phenomenon that requires coordination of cell behaviors across embryonic length scales. With optogenetics, we can disentangle these relationships by inducing spatiotemporally defined biomechanical perturbations in vivo in a way that is not feasible via pharmacological or genetic interventions. Using previously described optogenetic tools that target the Rho/Rho-kinase signaling pathway and actomyosin force generation, we demonstrate a protocol for corralling optogenetic perturbation to either the left or right side of the germband epithelium while simultaneously monitoring the effects on actomyosin and cell behaviors on both sides of the embryo. Notably, we find that local optogenetic perturbation leads to disruption of myosin recruitment and planar polarity within the activated side of the embryo as well as unexpected effects in distant, unactivated regions of the embryo, such as prominent dorsal folds, which suggests coupling that contributes to overall axis elongation. These studies provide a foundation for unraveling how mechanical interaction and feedback help coordinate cell behaviors, even over long distances, to ensure robust morphogenesis and development.