Agam, O.; Braun, E.

The formation of a body-axis is central to animal development and involves both polarity and morphology. While polarity is traditionally associated with biochemical patterning, the morphological aspect of axis formation remains elusive. In regenerating Hydra tissues, we find that morphological evolution in all tissue samples depends on inherited positional information from the donor axis, and a foot precursor emerges early in the process. The Ca excitations that drive actomyosin forces for tissue reshaping follow a polarity-aligned gradient from the onset of regeneration. We conclude that polarity and morphological axis progression occur concurrently through interlinked processes, and that the foot plays a dominant role in this process, a role usually attributed to the head organizer. These insights from Hydra likely extend to broader developmental systems.