Loss of organ regeneration for scarring is an evolutionary adaptation to the terrestrial environment in invertebrates and vertebrates

Abstract

The present paper summarizes previous theoretical studies that have suggested why broad regeneration in present only in some animals. It is speculated that the evolution of regenerative versus non-regenerative species is linked to specific environments where genes involved in regeneration can or cannot be expressed. While the marine conditions allow regeneration since PreCambrian and Paleozoic, the conquest of the mainland from invertebrates and vertebrates met conditions un-compatible with broad organ regeneration, such as drying, higher oxygen, nitrogen and UV radiation. It is speculated that adaptation to the life on land changed numerous anatomical and physiological characteristics of marine animals, also increasing the immune competence, which often negatively affected the process of organ regeneration. The loss of regenerative abilities was an unavoidable consequence, as extensively discussed in previous studies. The ability to regenerate organs is linked to developmental gene pathways, only partially known, that evolved in harmony with the remaining anatomical-physiological characteristics of these species. These genes or gene-modules cannot be simply transferred into non-regenerative species, with the likely effect to disrupt their genomes and transcriptomes with lethal or teratogenic consequences. Animals are not jigsaw puzzles where a genetic engineer can shift a gene module of a puzzle (from a regenerative-competent animal) into another puzzle (non-regenerating animal). Present knowledge indicates that, while minor injuries could be improved using genetic technologies by transferring genetically engineered cells into damaged organs, the replacement and not a real organ regeneration will be feasible by the combination of future biotechnological and bioengineering interventions.