Generic injuries are sufficient to induce ectopic Wnt organizers in Hydra

During whole-body regeneration, a bisection injury can trigger two
different types of regeneration. To understand the transcriptional
regulation underlying this adaptive response we characterized transcript
abundance and chromatin accessibility during oral and aboral regeneration
in the cnidarian Hydra vulgaris. We found that the initial response to
amputation at both wound sites is identical and includes widespread
apoptosis and the activation of the oral-specifying Wnt signaling pathway.
By 8 hours post-amputation, Wnt signaling became restricted to oral
regeneration. Wnt pathway genes were also upregulated in puncture wounds
and these wounds induced the formation of ectopic oral structures if
pre-existing organizers were simultaneously amputated. Our work suggests
that oral patterning is activated as part of a generic injury response in
Hydra, and that alternative injury outcomes are dependent on signals from
the surrounding tissue. Furthermore, Wnt signaling is likely part of a
conserved wound response predating the split of cnidarians and
bilaterians.