Rapid Regeneration

Lore & Background

Regeneration as a fundamental biological process mediated by molecular gene regulation and cellular processes including cell proliferation, morphogenesis, and cell differentiation. It occurs in two multi-step phases: the preparation phase and the redevelopment phase. After an amputation, migrating epidermal cells form a wound epithelium that thickens into a cap. Underneath, cells rapidly divide to form a blastema — a cone-shaped end containing skin, muscle, and cartilage cells that de-differentiate into stem-like cells. These cells then divide until enough are available, then re-differentiate to their original tissue types. The second phase involves gene signaling that directs cells to differentiate and develop the various parts of the lost structure, resulting in a limb that looks and operates identically to the original. Hydra and planarian flatworms serve as model organisms for their highly adaptive regenerative capabilities, and that Caudata (salamanders and newts) are possibly the most adept vertebrate group at regeneration, capable of regenerating limbs, tails, jaws, eyes, and internal structures.

Reader's Guide

The source distinguishes between two types of regeneration: physiological (homeostatic cell renewal during normal aging) and reparative (restoring function after injury or loss). Mammals are usually adept at the former but have limited capability for the latter. Among reparative regeneration, several types exist in animals. Epimorphosis involves proliferation before new tissue development, and can be further divided into epimorphic or compensatory regeneration (largely independent of stem cells, relying on proliferation of differentiated cells, as in liver regeneration) and blastema-mediated epimorphic regeneration (where extreme injury recruits lineage-restricted progenitor cells into a blastema that matures and reshapes to replace the missing structure, as seen in salamander limb regrowth and human fingertip regeneration). Morphallaxis involves re-patterning existing tissue with little new growth, common in invertebrates. Regeneration strategies include rearrangement of pre-existing tissue, use of adult somatic stem cells, and dedifferentiation or transdifferentiation of cells. Dedifferentiation means cells lose their tissue-specific characteristics during remodeling, while transdifferentiation involves losing those characteristics and then re-differentiating into a different cell type.

Did You Know?

• Hydra perform regeneration but reproduce by budding — regeneration is different from reproduction.
• Some animals, like planarians, can reproduce asexually by splitting in half, with each half regenerating a complete new individual.