Wnt signaling modulates tissue mechanics, actin order, and regeneration in Hydra vulgaris

Hydra vulgaris is a powerful model organism in the study of axial patterning and regeneration. While recent models emphasize the importance of mechanical cues in establishing body axis symmetry in Hydra tissue spheres, the precise role of the Wnt pathway, known to be central to axial patterning, in regulating tissue mechanics and cytoskeletal organization remains unclear. In this paper, we pharmacologically modulated the canonical Wnt pathway using Alsterpaullone and iCRT14 and assessed their effects on regeneration, tissue rheology, and actin organization in Hydra tissue spheres. We found that Wnt activation prevents full regeneration, softens the constitutive tissues, disrupts osmotic oscillations, leads to an accumulation of dense actin filaments but impairs their orientational order. Conversely, we found that Wnt inhibition partially impairs regeneration and reduces actin filament presence while preserving alignment. Using micro-aspiration and time-lapse imaging, we characterized the changes in the nonlinear elasticity and osmotic oscillations under both conditions. These results support and unify two existing mechano-chemical models of Hydra patterning, suggesting that Wnt-driven feedbacks on both tissue stiffness and actin order contribute to the robust emergence of body axes. Our findings highlight the possibility of redundant mechanisms in the Hydra patterning system, potentially explaining its robustness.