Several fundamentally different pathways may exist to restore a lost structure in closely related species or within the same species of multicellular animals; this phenomenon is described using the example of the echinoderm digestive system. We propose to call this phenomenon "variability of regeneration mechanisms." In echinoderms, it is manifested as differences in the spatial organization of the regeneration process and in the cell sources that are involved. The variability of regeneration mechanisms in the phylum Echinodermata can probably be explained by the availability of several regeneration pathways in the ancestral forms of deuterostomes, which differ in the involvement of various cell types, the depth of reprogramming of their genome (dedifferentiation or transdifferentiation), and the role of epithelial-mesenchymal transition.
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