title: A new role for a classical gene: white transports cyclic GMP.
abstract: Guanosine 3'-5' cyclic monophosphate (cGMP) and adenosine 3'-5' cyclic monophosphate (cAMP) are important regulators of cell and tissue function. However, cGMP and cAMP transport have received relatively limited attention, especially in model organisms where such studies can be conducted in vivo. The Drosophila Malpighian (renal) tubule transports cGMP and cAMP and utilises these as signalling molecules. We show here via substrate competition and drug inhibition studies that cAMP transport - but not cGMP transport - requires the presence of di- or tri-carboxylates; and that transport of both cyclic nucleotides occurs via ATP binding cassette sub-family G2 (ABCG2), but not via ABC sub-family C (ABCC), transporters. In Drosophila, the white (w) gene is known for the classic eye colour mutation. However, gene expression data show that of all adult tissues, w is most highly expressed in Malpighian tubules. Furthermore, as White is a member of the ABCG2 transporter class, it is a potential candidate for a tubule cGMP transporter. Assay of cGMP transport in w(-) (mutant) tubules shows that w is required for cGMP transport but not cAMP transport. Targeted over-expression of w in w(-) tubule principal cells significantly increases cGMP transport compared with that in w(-) controls. Conversely, treatment of wild-type tubules with cGMP increases w mRNA expression levels, implying that cGMP is a physiologically relevant substrate for White. Immunocytochemical localisation reveals that White is expressed in intracellular vesicles in tubule principal cells, suggesting that White participates in vesicular transepithelial transport of cGMP.
authors.affiliation: Division of Molecular Genetics, Faculty of Biomedical and Life Sciences, University of Glasgow, Glasgow G11 6NU, UK.
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Evans
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Day
authors.forename: Pablo
authors.initials: P
authors.lastname: Cabrero
authors.forename: Julian A T
authors.initials: JA
authors.lastname: Dow
authors.forename: Shireen-Anne
authors.initials: SA
authors.lastname: Davies
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D030801:Animals, Genetically Modified; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001693:Biological Transport, Active; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D029721:Drosophila Proteins / Q000235:genetics* / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics* / Q000378:metabolism*; D005136:Eye Proteins / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D017344:Genes, Insect; D007150:Immunohistochemistry; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D008317:Malpighian Tubules / Q000378:metabolism; D009154:Mutation; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014018:Tissue Distribution
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D017931:DNA Primers; D018076:DNA, Complementary; D029721:Drosophila Proteins; D005136:Eye Proteins; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; C059254:w protein, Drosophila; C054562:yellow fluorescent protein, Bacteria; D000242:Cyclic AMP; D006152:Cyclic GMP