How randomly injured animals can appropriately re-establish positional information and control the deployment of repair programs are key questions of regenerative biology. The hydrozoan jellyfish Clytia hemisphaerica has recently emerged as an original model organism for probing repair phenomena, thanks to its remarkable regenerative abilities. Coping with frequent injuries in the planktonic environment, Clytia efficiently restores its circular morphology within 12 hours and regenerates missing structures, such as the mouth, in 4 days. Our investigations uncovered a complex interplay of mechanical forces, cellular migration, and proliferation, underlying this rapid recovery process. During umbrella reshaping, the distinct configurations of the rearranging radial muscle fibres – which can be likened to topological defects - correlate with differential patterns of Wnt signalling activation; they function as positional cues, regulating the fate of the wound and the initiation of organ regenerative programs. Regenerative morphogenesis involves a combination of localized cell proliferation and long-range cell recruitment. Leveraging the unique regenerative process of Clytia, and the recent technological developments of the model, we have started unravelling the mechanical and transcriptional interplay in repairing tissues - combining omics, live imaging, modelling and functional approaches. Our findings not only offer insights into the universal principles governing patterning formation and morphogenesis in physiologically complex adult organisms, but also shed light on the evolutionary trajectories of regenerative capacities and stem cells within metazoans.

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