Objective
Studies have demonstrated the mechanism of the actin cable, which performed purse-string contractility and accomplished scarless skin wound healing, in embryos of several species including mammals. However, there is no evidence of actin cable formation in adult animals. Adult newts have been reported to possess amazing regenerative abilities, which can be a model for postnatal humans. Therefore, we used the Japanese fire-bellied newt, Cynops pyrrhogaster, to survey the actin fiber formation and alignment during re-epithelialization.

Material and Methods
We used the surgical blade under the dissecting microscope to complete full-thickness skin excision over the forelimb of the adult newt. Tissue samples were collected at a desired time and underwent Phalloidin dye for actin fiber. Electron microscopy was also performed to observe detailed structure.

Results
Instead of actin cable, a mesh-like structure of actin, actin mesh, was found. The actin mesh developed accompanying wound epidermis extension and still existed after complete re-epithelialization. Inhibition of actin formation also showed the delay of re-epithelialization. Under electron microscopy, fiber-rich expression in cytoplasm and cell-cell adhesion via E-cadherin was found.

Conclusions
A mesh structure distinct from actin cables was identified in wound epidermis during skin regeneration in adult newts. Early re-epithelialization is important for reducing inflammation and preventing infection, and the unique re-epidermalization of adult newts may provide a new research model for intractable ulcers such as severe burns, diabetic ulcers.

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