Progressive cell fate specification in morphallactic regeneration

Through regeneration various species replace lost parts of their body. This is achieved either by growth of new structures at the amputation side (epimorphosis), as is the case of axolotl limb regeneration, or through remodeling of the remaining tissue (morphallaxis), as happens in Hydra. Whereas work on epimorphic regeneration support a gradual proximal to distal establishment of cell identities, morphallactic regeneration is believed to rely on initial establishment of boundary conditions that organize the re-adjustment of the pattern. Performing single cell RNA sequencing during regeneration in Hydra, we revealed the sequence of cells transdifferentiation into the missing identities. We provide evidence that morphallaxis proceeds with progressive specification of cell fates, unifying its mechanism with the one found for epimorphosis.