Epimorphosis

Epimorphosis is a mode of regeneration in which new tissue is formed primarily through cell proliferation and the development of a blastema at the injury or amputation site, followed by differentiation to reconstitute missing structures. It is one of the classic categories used to describe regenerative growth, and it is typically contrasted with morphallaxis, a process in which existing tissues are reorganized and reshaped with little or no cell proliferation.

In epimorphic regeneration, an initial wound healing phase is followed by the rapid formation of a blastema, a mass of undifferentiated or lineage-restricted cells that contains progenitors for the missing tissues. These cells may arise by dedifferentiation of mature cells or by recruitment and proliferation of resident stem or progenitor cells. The blastema then undergoes patterning and differentiation to restore anatomy and function, often along proximodistal or other axes. Signaling pathways and interactions among growing tissues coordinate growth, tissue specification, and reinnervation and revascularization.

Epimorphosis has been studied in diverse taxa. Classic examples include limb and tail regeneration in salamanders, zebrafish fin regeneration, and certain invertebrate regenerative events. Although the underlying cellular sources and molecular controls can vary among species, blastema formation and proliferative growth are common hallmarks of epimorphic regeneration.

Etymology-wise, epimorphosis derives from Greek elements meaning “upon form” or “upon growth.” The term helps distinguish regeneration that builds new tissue through active growth from processes that primarily reorganize existing tissues.

See also: morphallaxis, blastema, regeneration.