The Effect of Environmental Contaminants on Hair Cell Regeneration in Larval Zebrafish
Many contaminants, such as industrial pollutants, can be found in aquatic environments and may affect fish and other aquatic life. Some of these contaminants can also be found in trace amounts in water sources that are used for human consumption. Three of these contaminants are PCB-95, BPA, and fluoride. In this study we investigated the effect each of these contaminants has on hair cell regeneration in the larval zebrafish. Hair cells are the mechanosensory receptors that allow sound perception by transducing sound waves and vibrations into electrical impulses that are transmitted to the brain via stimulation of the auditory nerve. Unlike mammals, birds, fish, and amphibians have the ability to regenerate hair cells following a toxic insult. This study looks specifically at hair cells of the lateral line. The lateral line is a system of hair cells along the exterior of the fish that are homologous to the hair cells located in the mammalian inner ear. To test if a contaminant is having an effect on hair cell regeneration, we exposed fish to the hair cell toxin neomycin, and then let the fish recover for 24 or 48 hours in variable contaminant concentration. We saw no significant effect of PCB-95 and fluoride on hair cell regeneration, but observed that exposure to higher concentrations of BPA resulted in reduced hair cell regeneration. We then asked if hair cell regeneration occurs after recovery from BPA exposure, as BPA itself can kill hair cells. We observed reduced hair cell numbers 48 hrs post-BPA treatment, which suggests BPA continues to kill hair cells post-exposure, similar to treatment with the ototoxic antibiotic gentamicin. These findings add to the growing list of harmful effects of BPA for both humans and aquatic life. Future experiments will distinguish if BPA continues to kill hair cells while they are trying to regenerate, or if BPA disrupts the proliferative regeneration process.