In transected nerves, distal repair Schwann cells are required at the injury site to direct and accelerate axonal regrowth.

In vertebrate peripheral nerves, damaged axons can regrow after injury, but the outcomes of regeneration are variable and often incomplete. Schwann cells in injured nerves are important for repair, but their actions at different positions and stages of nerve repair are not well understood. We have investigated the roles of Schwann cells in a larval zebrafish nerve injury model, in which nerves are visible in living animals during development, the initial injury response, and regrowth of the transected axons. After mechanical injury, distal Schwann cells adopt a repair phenotype characterized by changes in marker expression, elongation, and ability to guide axons across the injury site. In contrast, proximal Schwann cells are not sufficient to guide axons across the injury site, and they associate with axons that regrow along aberrant paths. In Main Points: After nerve transection in larval zebrafish, proximal and distal Schwann cells have distinct functions at injury siteA single distal repair Schwann cell is sufficient for axonal regrowthAxonal regrowth is normal in mutants without macrophages.