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 Article Draft for Epimorphosis 

= Epimorphosis =

Epimorphosis is defined as the regeneration of a specific part of an organism in a way that involves extensive cell proliferation, as well as blastema formation. Epimorphosis can be considered a simple model for development, though it only occurs in tissues surrounding the site of injury rather than occurring system-wide.

History of Epimorphosis
Thomas Hunt Morgan, an evolutionary biologist who also worked with embryology, argued that limb and tissue reformation bore many similarities to embryonic development. Building off of the work of German embryologist Wilhelm Roux, who suggested regeneration was two cooperative but distinct pathways instead of one, Morgan named the two parts of the regenerative process epimorphosis and morphallaxis. Specifically, Morgan wanted epimorphosis to specify the process of entirely new tissues being regrown from an amputation or similar injury, with morphallaxis being coined to describe regeneration that did not use cell proliferation, such as in hydra.

Epimorphosis in vertebrates
In vertebrates, epimorphosis relies on blastema formation to proliferate cells into the new tissue. Through studies involving zebrafish fins, the toetips of mice, and limb regeneration in axolotls, researchers at the Polish Academy of Sciences found evidence for epimorphosis occurring in a variety of vertebrates, including instances of mammal epimorphosis.

Salamanders
Immediately after the limb is amputated, a plasma clot forms over the wound. Epidermal cells at the wound margins migrate to cover the wound and will become the wound epidermis. No scar tissue forms, as it would in mammals.

An apical ectodermal cap (AEC) forms on the tip of the stump. This is similar to the embryonic apical ectodermal ridge, which forms during normal limb development. The AEC causes the progress zone to re-establish; this means the cells under the AEC dedifferentiate and become mesenchymal. The AEC releases factors that drive the development of the new limb, essentially resetting the limb back to its embryonic development stage.

But even though some of the limb cells are able to dedifferentiate, they are not able to fully dedifferentiate to the level of multipotent progenitor cells. During regeneration, only cartilage cells can form new cartilage tissue, only muscle cells can form new muscle tissue, and so on. The dedifferentiated cells still retain their original specification. . ]]

Periplaneta americana
The American cockroach is capable of regenerating limbs that have been damaged or destroyed, such as legs and antennae, as well parts of its compound eye. It does this with a lectin--a protein made for binding proteins--named regenectin, which shares a family with other lipopolysaccharide (LPS) binding proteins. Regenectin carries both a regenerative function and a system defense function, and it is produced by the cockroach's paracrine system to work with muscle reformation.

Capitella teleta
C. teleta is a segmented worm found in North America that is capable of regenerating posterior segments after amputation. This regeneration uses the interaction of several sets of Hox genes, as well as blastema formation. All of the Hox genes concerned in epimorphosis are present in the abdominal area of the worm, but not in the anterior portion. However, the genes do not, themselves, direct the anterior-posterior patterning of the worm's thorax.