| Abstract: | Hydra is a classic model for studying animal morphogenesis due to its simple body plan and exceptional regeneration capabilities. Excised Hydra tissue fragments fold into hollow spheroids that contain an inherited array of parallel actin fibers and a disordered region around the closure site. During regeneration, nematic topological defects emerge with an aster-shaped +1 defect forming at the future head site, and a pair of +1/2 defects appearing at the future foot. The head organizer, which plays a central role in axial patterning in Hydra, coincides with the +1 defect site and has been linked to the Wnt signaling pathway. However, the mechanisms coupling signaling and cytoskeletal organization remain poorly understood. To explore this interplay, we applied targeted perturbations. Elevated medium osmolarity (+70 mM sucrose) reduces osmotic tissue inflations and has been shown to suppress Wnt expression and prevent regeneration. We find that elevated osmolarity favors an unusual defect configuration with four +1/2 defects. Upon returning to normal medium, regeneration resumes and a stable +1 defect appears, consistent with the original tissue polarity. Direct perturbation of Wnt signaling further revealed that inhibiting β-catenin/TCF interaction (iCRT14) disrupts fiber organization and defect formation, while stabilizing β-catenin (Alsterpaullone) induces highly deformed animals with excess defects. These findings demonstrate the coupling between Wnt signaling and actin fiber organization, advancing our understanding of the mechanochemical feedbacks underlying Hydra regeneration. |