Identification of signalling pathways involved in gill regeneration in zebrafish

ABSTRACT The occurrence of regeneration of the organs involved in respiratory gas exchange amongst vertebrates is heterogeneous. In aquatic animals, such as amphibians and fishes, the gills regenerate completely following resection or amputation; whereas in mammals, only partial, facultative regeneration of lung tissue occurs following injury. Given the homology between gills and lungs, the capacity of gill regeneration in aquatic species is of major interest in determining the underlying molecular or signalling pathways involved in respiratory organ regeneration. In the present study, we used adult zebrafish ( Danio rerio ) to characterize signalling pathways involved in the early stages of gill regeneration. Regeneration of the gills, including the gas exchange surfaces, was induced by resection of the gill filaments and observed over a period of up to 10 days. We screened for the effects of the drugs, SU5402, dorsomorphin, and LY411575, which inhibit FGF, BMP or Notch signalling, respectively, on development of the blastema. Exposure to each drug for 5 days significantly reduced blastema formation in regenerates, compared to unresected controls. In separate experiments, and under normal conditions of regeneration, we used quantitative real-time PCR and observed an increased expression of genes encoding for the bone morphogenetic factor, Bmp2b, fibroblast growth factor, Fgf8a, a transcriptional regulator (Her6) involved in Notch signalling, and Sonic Hedgehog (Shha), in regenerating gills at 10 day post-resection, compared to unresected controls. In situ hybridization confirmed that all four genes were expressed in regenerating gill tissue. This study implicates BMP, FGF, Notch and Shh signalling in gill regeneration in zebrafish. SUMMARY STATEMENT Gill regeneration in zebrafish is mediated by multiple signalling pathways, including BMP, FGF, Notch and Sonic Hedgehog.