title: Two isoforms of aquaporin 2 responsive to hypertonic stress in the bottlenose dolphin.
abstract: This study investigated the expression of aquaporin 2 (AQP2) and its newly found alternatively spliced isoform (alternative AQP2) and the functions of these AQP2 isoforms in the cellular hyperosmotic tolerance in the bottlenose dolphin, ITALIC! Tursiops truncatus mRNA sequencing revealed that alternative AQP2 lacks the fourth exon and instead has a longer third exon that includes a part of the original third intron. The portion of the third intron, now part of the coding region of alternative AQP2, is highly conserved among many species of the order Cetacea but not among terrestrial mammals. Semi-quantitative PCR revealed that AQP2 was expressed only in the kidney, similar to terrestrial mammals. In contrast, alternative AQP2 was expressed in all organs examined, with strong expression in the kidney. In cultured renal cells, expression of both AQP2 isoforms was upregulated by the addition to the medium of NaCl but not by the addition of mannitol, indicating that the expression of both isoforms is induced by hypersalinity. Treatment with small interfering RNA for both isoforms resulted in a decrease in cell viability in hypertonic medium (500 mOsm kg(-1)) when compared with controls. These findings indicate that the expression of alternatively spliced AQP2 is ubiquitous in cetacean species, and it may be one of the molecules important for cellular osmotic tolerance throughout the body.
authors.affiliation: Department of Marine Science and Resources, College of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa, Kanagawa 252-0880, Japan suzuki.miwa@nihon-u.ac.jp.
authors.forename: Miwa
authors.initials: M
authors.lastname: Suzuki
authors.affiliation: Department of Marine Science and Resources, College of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa, Kanagawa 252-0880, Japan.
authors.forename: Hitomi
authors.initials: H
authors.lastname: Wakui
authors.affiliation: Nihon University Veterinary Research Center, Nihon University, 1866 Kameino, Fujisawa, Kanagawa 252-0880, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Itou
authors.affiliation: Nihon University Veterinary Research Center, Nihon University, 1866 Kameino, Fujisawa, Kanagawa 252-0880, Japan.
authors.forename: Takao
authors.initials: T
authors.lastname: Segawa
authors.affiliation: Cooperative Department of Veterinary Medicine, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Inoshima
authors.affiliation: Joint Faculty of Veterinary Medicine, Yamaguchi University, 1677-1 Yoshida, Yamaguchi 753-8515, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Maeda
authors.affiliation: Fisheries Laboratory, The University of Tokyo, 2941-4 Bentenjima, Maisaka, Nishi, Hamamatsu, Shizuoka 431-0214, Japan.
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Kikuchi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D051399:Aquaporin 2 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D050681:Bottle-Nosed Dolphin / Q000502:physiology; D016923:Cell Death / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D017124:Conserved Sequence / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics / Q000302:isolation & purification; D020869:Gene Expression Profiling; D055785:Gene Knockdown Techniques; D006982:Hypertonic Solutions / Q000494:pharmacology*; D007438:Introns / Q000235:genetics; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D008353:Mannitol / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D016366:Open Reading Frames / Q000235:genetics; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference / Q000187:drug effects; D012326:RNA Splicing / Q000187:drug effects / Q000235:genetics; D034741:RNA, Small Interfering / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology; D012984:Software; D013312:Stress, Physiological / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects; D014867:Water
chemical_list: D051399:Aquaporin 2; D018076:DNA, Complementary; D006982:Hypertonic Solutions; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D014867:Water; D008353:Mannitol; D012965:Sodium Chloride
keywords: Alternative splicing; Cellular osmoregulation; Cetacea; Osmotic tolerance