epimorphic

Epimorphic is an adjective used in developmental and regenerative biology to describe a mode of tissue regeneration characterized by the rapid proliferation of cells and the formation of a blastema after injury. In epimorphic regeneration, the wound environment induces dedifferentiation and/or expansion of progenitor cells to generate a mass of relatively undifferentiated cells (the blastema), which then grows and undergoes orderly differentiation to restore the original structure.

This process contrasts with morphallaxis, where largely intact tissues reorganize to replace lost parts with minimal cell proliferation. Epimorphic regeneration relies on signaling networks that regulate cell proliferation, patterning, and morphogenesis, including pathways such as FGF, Wnt/β-catenin, BMP, Notch, and sometimes hedgehog, though the exact roles vary by organism and tissue.

Organisms with well-documented epimorphic regeneration include urodele amphibians (newts, salamanders and axolotls), which can regenerate limbs, tails, and lenses; zebrafish, which regenerate fins and heart tissue via blastema formation; and in humans, limited epimorphic-like regeneration is observed in distal digit tip regeneration in some adults. In mammals, epimorphic regeneration is generally restricted and not capable of full limb replacement, though research aims to induce blastema-like growth for regenerative medicine.

Etymology: from Greek epi- "upon" and morphe "form". See also blastema, morphallaxis, regeneration.