Gene expression after freshwater transfer in gills and opercular epithelia of killifish: insight into divergent mechanisms of ion transport.
We have explored the molecular basis for differences in physiological function between the gills and opercular epithelium of the euryhaline killifish Fundulus heteroclitus. These tissues are functionally similar in seawater, but in freshwater the gills actively absorb Na+ but not Cl-, whereas the opercular epithelium actively absorbs Cl- but not Na+. These differences in freshwater physiology are likely due to differences in absolute levels of gene expression (measured using real-time PCR), as several proteins important for Na+ transport, namely Na+,H+-exchanger 2 (NHE2), carbonic anhydrase 2 (CA2), Na+,HCO3- cotransporter 1, and V-type H+-ATPase, were expressed at 3- to over 30-fold higher absolute levels in the gills. In gills, transfer from 10% seawater to freshwater increased the activity of Na+,K+-ATPase by twofold (from 12 h to 7 days), increased the expression of NHE2 (at 12 h) and CA2 (from 12 h to 7 days), and decreased the expression of NHE3 (from 12 h to 3 days). In opercular epithelium, NHE2 was not expressed; furthermore, Na+,K+-ATPase activity was unchanged after transfer to freshwater, CA2 mRNA levels decreased, and NHE3 levels increased. Consistent with their functional similarities in seawater, killifish gills and opercular epithelium expressed Na+,K+-ATPase alpha 1a, Na+,K+,2Cl- cotransporter 1 (NKCC1), cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel and the signalling protein 14-3-3a at similar absolute levels. Furthermore, NKCC1 and CFTR were suppressed equally in each tissue after freshwater transfer, and 14-3-3a mRNA increased in both. These results provide insight into the mechanisms of ion transport by killifish gills and opercular epithelia, and demonstrate a potential molecular basis for the differences in physiological function between these two organs.
Scott
Graham R
GR
Department of Zoology, University of British Columbia, Vancouver BC, Canada V6T 1Z4. scott@zoology.ubc.ca
Claiborne
James B
JB
Edwards
Susan L
SL
Schulte
Patricia M
PM
Wood
Chris M
CM
D000704:Analysis of Variance; D000818:Animals; D001483:Base Sequence; D001693:Biological Transport, Active / Q000502:physiology; D024402:Carbonic Anhydrase II / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D003001:Cloning, Molecular; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D004848:Epithelium / Q000378:metabolism; D005618:Fresh Water; D023781:Fundulidae / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D015870:Gene Expression; D005880:Gills / Q000378:metabolism*; D017136:Ion Transport / Q000502:physiology; D008969:Molecular Sequence Data; D009674:Nova Scotia; D006180:Proton-Translocating ATPases / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D012964:Sodium / Q000378:metabolism*; D027982:Sodium-Bicarbonate Symporters / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism
D002712:Chlorides; D017931:DNA Primers; D018076:DNA, Complementary; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D012964:Sodium; D006180:Proton-Translocating ATPases; D024402:Carbonic Anhydrase II