title: Characterization of a type IIb sodium-phosphate cotransporter from zebrafish (Danio rerio) kidney.
abstract: Zebrafish (Danio rerio) express two isoforms of the type IIb Na-dependent P(i) cotransporter (NaPi). Type NaPi-IIb1 has previously been cloned and characterized. Here, we report the cloning of the NaPi-IIb2 transcript from zebrafish kidney, its localization, and its functional characterization. RT-PCR with renal RNA and degenerate NaPi-IIb-specific primers resulted in a specific fragment. 3'-Rapid amplification of cDNA ends yielded a product that contained typical NaPi-IIb characteristics such as a cysteine-rich COOH terminus and a PDZ (PSD95- Dlg-zona occludens-1) binding motif. Several approaches were unsuccessful at cloning the 5' end of the transcript; products lacked an in-frame start codon. The missing information was obtained from an EST (GenBank accession number ). The combined clone displayed a high degree of homology with published type IIb cotransporter sequences. Specific antibodies were raised against a COOH-terminal epitope of both NaPi-IIb1 and NaPi-IIb2 isoforms. Immunohistochemical mapping revealed apical expression of both isoforms in zebrafish renal and intestinal epithelia, as well as in bile ducts. The novel clone was expressed in oocytes, and function was assayed by the two-electrode voltage-clamp technique. The function of the new NaPi-IIb2 clone was found to be significantly different from NaPi-IIb1 despite strong structural similarities. NaPi-IIb2 was found to be strongly voltage sensitive, with higher affinities for both sodium and phosphate than NaPi-IIb1. Also, NaPi-IIb2 was significantly less sensitive to external pH than NaPi-IIb1. The strong structural similarity but divergent function makes these zebrafish transporters ideal models for the molecular mapping of functionally important regions in the type II NaPi-cotransporter family.
authors.affiliation: School of Cell and Molecular Biosciences, University of Newcastle, Newcastle upon Tyne, NE2 4HH, United Kingdom.
authors.forename: C
authors.initials: C
authors.lastname: Graham
authors.forename: P
authors.initials: P
authors.lastname: Nalbant
authors.forename: B
authors.initials: B
authors.lastname: Schölermann
authors.forename: H
authors.initials: H
authors.lastname: Hentschel
authors.forename: R K H
authors.initials: RK
authors.lastname: Kinne
authors.forename: A
authors.initials: A
authors.lastname: Werner
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D005260:Female; D005432:Flounder; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D007668:Kidney / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008845:Microinjections; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D009928:Organ Specificity; D018408:Patch-Clamp Techniques; D010710:Phosphates / Q000737:chemistry; D051381:Rats; D016415:Sequence Alignment; D012964:Sodium / Q000737:chemistry; D050608:Sodium-Phosphate Cotransporter Proteins; D050610:Sodium-Phosphate Cotransporter Proteins, Type II; D050614:Sodium-Phosphate Cotransporter Proteins, Type IIb; D027981:Symporters / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics*; D014982:Xenopus laevis; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics
chemical_list: D010710:Phosphates; C493558:Slc34a2 protein, mouse; C493559:Slc34a2 protein, rat; D050608:Sodium-Phosphate Cotransporter Proteins; D050610:Sodium-Phosphate Cotransporter Proteins, Type II; D050614:Sodium-Phosphate Cotransporter Proteins, Type IIb; D027981:Symporters; D029961:Zebrafish Proteins; C493560:slc34a2a protein, zebrafish; C493561:slc34a2b protein, zebrafish; D012964:Sodium