Neuromast hair cells retain the capacity of regeneration during heavymetal exposure

The neuromast is the morphological unit of the lateral line of fishes and is composed of a cluster of centralsensory cells (hair cells) surrounded by support and mantle cells. Heavy metals exposure leads to disrup-tion of hair cells within the neuromast. It is well known that the zebrafish has the ability to regeneratethe hair cells after damage caused by toxicants. The process of regeneration depends on proliferation,differentiation and cellular migration of sensory and non-sensory progenitor cells. Therefore, our studywas made in order to identify which cellular types are involved in the complex process of regenerationduring heavy metals exposure. For this purpose, adult zebrafish were exposed to various heavy metals(Arsenic, cadmium and zinc) for 72 h. After acute (24 h) exposure, immunohistochemical localization ofS100 (a specific marker for hair cells) in the neuromasts highlighted the hair cells loss. The immunoreac-tion for Sox2 (a specific marker for stem cells), at the same time, was observed in the support and mantlecells, after exposure to arsenic and cadmium, while only in the support cells after exposure to zinc. Afterchronic (72 h) exposure the hair cells were regenerated, showing an immunoreaction for S100 protein.At the same exposure time to the three metals, a Sox2 immunoreaction was expressed in support andmantle cells. Our results showed for the first time the regenerative capacity of hair cells, not only after,but also during exposure to heavy metals, demonstrated by the presence of different stem cells that candiversify in hair cells.