Optogenetic perturbations reveal temporal integration of Wnt signaling during pattern formation
The Wnt signaling pathway is a conserved regulator of tissue patterning and regeneration, yet how cells interpret dynamic Wnt inputs to generate robust developmental outcomes remains poorly understood. Here, we establish the first optogenetically activatable Hydra line, enabling precise temporal control of canonical Wnt signaling in vivo. Optogenetic stimulation induced dose-dependent patterning phenotypes whose rate of progression scaled with stimulation intensity. Transcriptomic analysis revealed that distinct combinations of signal intensity and duration converged onto shared transcriptional trajectories and could be described by an effective exposure metric that represents the cumulative signaling input. Functionally, Wnt activation rescued head regeneration under conditions that normally prevent organizer formation, and equivalent regenerative outcomes could be achieved through either strong, short-lived stimulation or weaker, prolonged activation. Together, our results indicate that Hydra tissues decode Wnt signaling through temporal integration of cumulative pathway activity, progressively accumulating transcriptional responses until patterning thresholds are reached. These findings establish a quantitative framework for understanding how dynamic morphogen signaling is translated into stable developmental decisions during regeneration.