Transport proteins NHA1 and NHA2 are essential for survival, but have distinct transport modalities.
The cation/proton antiporter (CPA) family includes the well-known sodium/proton exchanger (NHE; SLC9A) family of Na(+)/H(+) exchangers, and the more recently discovered and less well understood CPA2s (SLC9B), found widely in living organisms. In Drosophila, as in humans, they are represented by two genes, Nha1 (Slc9b1) and Nha2 (Slc9b2), which are enriched and functionally significant in renal tubules. The importance of their role in organismal survival has not been investigated in animals, however. Here we show that single RNAi knockdowns of either Nha1 or Nha2 reduce survival and in combination are lethal. Knockdown of either gene alone results in up-regulation of the other, suggesting functional complementation of the two genes. Under salt stress, knockdown of either gene decreases survival, demonstrating a key role for the CPA2 family in ion homeostasis. This is specific to Na(+) stress; survival on K(+) intoxication is not affected by sodium/hydrogen antiporter (NHA) knockdown. A direct functional assay in Xenopus oocytes shows that Nha2 acts as a Na(+)/H(+) exchanger. In contrast, Nha1 expressed in Xenopus oocytes shows strong Cl(-) conductance and acts as a H(+)-Cl(-) cotransporter. The activity of Nha1 is inhibited by chloride-binding competitors 4,4'-diiso-thiocyano-2,2'-disulfonic acid stilbene and 4,4'-dibenzamido-2,2'-stilbenedisulphonate. Salt stress induces a massive up-regulation of NHA gene expression not in the major osmoregulatory tissues of the alimentary canal, but in the crop, cuticle, and associated tissues. Thus, it is necessary to revise the classical view of the coordination of different tissues in the coordination of the response to osmoregulatory stress.
Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom;
Venkateswara R
VR
Chintapalli
Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905; Department of Biological Sciences, Tokyo Institute of Technology, Yokohama 226-8501, Japan;
Akira
http://orcid.org/0000-0002-9083-1443
A
Kato
Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom;
Louise
L
Henderson
Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905;
Taku
T
Hirata
Global Therapeutics Research-Parasitology, Zoetis Inc., Kalamazoo, MI 49007.
Debra J
DJ
Woods
Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom;
Gayle
G
Overend
Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom;
Shireen A
SA
Davies
Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905;
Michael F
MF
Romero
Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom; julian.dow@glasgow.ac.uk.
Julian A T
JA
Dow
D000483:Alleles; D000818:Animals; D001692:Biological Transport; D002470:Cell Survival; D003433:Crosses, Genetic; D029721:Drosophila Proteins / Q000502:physiology*; D004331:Drosophila melanogaster / Q000502:physiology*; D004848:Epithelium / Q000502:physiology; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins; D009865:Oocytes / Q000166:cytology; D034622:RNA Interference; D060888:Real-Time Polymerase Chain Reaction; D017923:Sodium-Hydrogen Exchangers / Q000502:physiology*; D014982:Xenopus laevis
D029721:Drosophila Proteins; D008565:Membrane Proteins; C532824:NHA1 protein, Drosophila; C532825:NHA2 protein, Drosophila; D017923:Sodium-Hydrogen Exchangers
Drosophila; exchanger; genetics; physiology; transport