Regeneration of the gill filaments and replacement of serotonergic neuroepithelial cells in adult zebrafish (Danio rerio).
Respiratory epithelia and chemoreceptors of the gills and mammalian lung derive from the same embryonic structures. While the lung is limited to facultative regeneration, the regenerative capacity of the gill has not been adequately explored. We report regeneration of gill filaments and respiratory lamellae in adult zebrafish (Danio rerio). Gill filaments retained a constitutive population of mitotic cells identified by the proliferating cell nuclear antigen (PCNA). Within 24 h of resection, a new mass of PCNA-positive cells appeared at the filament tip. At 40 days post-resection, approximately half of resected tissue was replaced; and at 160 days post-resection, regeneration was nearly complete. Chemoreceptive neuroepithelial cells, identified by serotonin immunohistochemistry, were present in regenerates and established innervation by nerve fibres. Use of the transgenic zebrafish line Tg(fli1a:EGFP), in which the gill vasculature was labelled with enhanced green fluorescent protein, indicated that angiogenesis occurred during the regenerative process. Thus, the zebrafish is capable of substantive gill regeneration and replacement of respiratory chemoreceptors.