A small molecule screen identifies in vivo modulators of peripheral nerve regeneration in zebrafish.

Adult vertebrates have retained the ability to regenerate peripheral nerves after injury, although regeneration is frequently incomplete, often leading to functional impairments. Small molecule screens using whole organisms have high potential to identify biologically relevant targets, yet currently available assays for in vivo peripheral nerve regeneration are either very laborious and/or require complex technology. Here we take advantage of the optical transparency of larval zebrafish to develop a simple and fast pectoral fin removal assay that measures peripheral nerve regeneration in vivo. Twenty-four hours after fin amputation we observe robust and stereotyped nerve regrowth at the fin base. Similar to laser mediated nerve transection, nerve regrowth after fin amputation requires Schwann cells and FGF signaling, confirming that the fin amputation assay identifies pathways relevant for peripheral nerve regeneration. From a library of small molecules with known targets, we identified 21 compounds that impair peripheral nerve regeneration. Several of these compounds target known regulators of nerve regeneration, further validating the fin removal assay. Twelve of the identified compounds affect targets not previously known to control peripheral nerve regeneration. Using a laser-mediated nerve transection assay we tested ten of those compounds and confirmed six of these compounds to impair peripheral nerve regeneration: an EGFR inhibitor, a glucocorticoid, prostaglandin D2, a retinoic acid agonist, an inhibitor of calcium channels and a topoisomerase I inhibitor. Thus, we established a technically simple assay to rapidly identify valuable entry points into pathways critical for vertebrate peripheral nerve regeneration.