Appendage-resident epithelial cells expedite wound healing response in adult zebrafish

Adult zebrafish are able to heal large-sized cutaneous wounds in hours with little to no scarring. This rapid re-epithelialization is crucial for preventing infection and jumpstarting the subsequent regeneration of damaged tissues. Despite significant progress in understanding this process, it remains unclear how vast numbers of epithelial cells are orchestrated on an organismic scale to ensure the timely closure of millimeter-sized wounds. Here, we report an unexpected role of adult zebrafish appendages (fins) in accelerating the re-epithelialization process. Through whole-body monitoring of single-cell dynamics in live animals, we found that fin-resident epithelial cells (FECs) are highly mobile and migrate to cover wounds in nearby body regions. Upon injury, FECs readily undergo organ-level mobilization, allowing for coverage of body surfaces of up to 4.78 mm² in less than 8 h. Intriguingly, long-term fate-tracking experiments revealed that the migratory FECs are not short-lived at the wound site; instead, the cells can persist on the body surface for more than a year. Our experiments on "fin-less" and "fin-gaining" individuals demonstrated that the fin structures are not only capable of promoting rapid re-epithelialization but are also necessary for the process. We further found that fin-enriched extracellular matrix laminins promote the active migration of FECs by facilitating lamellipodia formation. These findings lead us to conclude that appendage structures in regenerative vertebrates, such as fins, may possess a previously unrecognized function beyond serving as locomotor organs. The appendages may also act as a massive reservoir of healing cells, which speed up wound closure and tissue repair.