The tight junction protein claudin-b regulates epithelial permeability and sodium handling in larval zebrafish, Danio rerio.
The functional role of the tight junction protein claudin-b in larval zebrafish (Danio rerio) was investigated. We showed that claudin-b protein is expressed at epithelial cell-cell contacts on the skin. Translational gene knockdown of claudin-b protein expression caused developmental defects, including edema in the pericardial cavity and yolk sac. Claudin-b morphants exhibited an increase in epithelial permeability to the paracellular marker polyethylene glycol (PEG-4000) and fluorescein isothiocyanate-dextran (FD-4). Accumulation of FD-4 was confined mainly to the yolk sac and pericardial cavity in the claudin-b morphants, suggesting these regions became particularly leaky in the absence of claudin-b expression. Additionally, Na(+) efflux was substantially increased in the claudin-b morphants, which contributed to a significant reduction in whole-body Na(+) levels. These results indicate that claudin-b normally acts as a paracellular barrier to Na(+). Nevertheless, the elevated loss of Na(+) in the morphants was compensated by an increase in Na(+) uptake. Notably, we observed that the increased Na(+) uptake in the morphants was attenuated in the presence of the selective Na(+)/Cl(-)-cotransporter (NCC) inhibitor metolazone, or during exposure to Cl(-)-free water. These results suggested that the increased Na(+) uptake in the morphants was, at least in part, mediated by NCC. Furthermore, treatment with an H(+)-ATPase inhibitor bafilomycin A1 was found to reduce Na(+) uptake in the morphants, suggesting that H(+)-ATPase activity was essential to provide a driving force for Na(+) uptake. Overall, the results suggest that claudin-b plays an important role in regulating epithelial permeability and Na(+) handling in zebrafish.
Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, Ontario, K1N 10 6N5 Canada. wkwong@uottawa.ca
Raymond W M
RW
Kwong
Steve F
SF
Perry
D000818:Animals; D002712:Chlorides / Q000378:metabolism; D057167:Claudins / Q000235:genetics / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000378:metabolism; D004848:Epithelium / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D055785:Gene Knockdown Techniques; D007814:Larva / Q000254:growth & development / Q000378:metabolism; D010539:Permeability; D020033:Protein Isoforms; D012964:Sodium / Q000378:metabolism*; D049992:Sodium Chloride Symporters; D019108:Tight Junctions / Q000378:metabolism*; D015027:Zebrafish / Q000196:embryology / Q000254:growth & development* / Q000378:metabolism
D002712:Chlorides; D057167:Claudins; D020033:Protein Isoforms; D049992:Sodium Chloride Symporters; D012964:Sodium