title: Upregulation of the mitochondrial phosphate carrier during freezing in the wood frog Rana sylvatica: potential roles of transporters in freeze tolerance.
abstract: Screening of a cDNA library prepared from liver of the freeze-tolerant wood frog (Rana sylvatica) identified a freeze-responsive clone containing a 1370-nt sequence with an open reading frame of 360 amino acids. Sequence analysis revealed 84-86% identity with the mammalian inorganic phosphate carrier (PiC) that spans the inner mitochondrial membrane. Northern blot analysis showed that pic transcript levels increased over a time course of freezing, reaching 60-fold upregulation after 24-h frozen. Transcript levels were also assessed under freezing-related stresses with results showing a strong increase in pic transcript levels in response to dehydration (elevated 9.0-fold in 40% dehydrated frogs) but not under anoxia. Western blotting revealed elevated PiC protein over a time course of freeze-thaw whereas other mitochondrial carriers (dicarboxylate carrier, oxoglutarate transporter) of the same family were not affected by freezing. This modulation of PiC protein levels may play a role in mitochondrial ionic and/or osmotic balance during freeze-induced cell volume reduction.
authors.affiliation: Institute of Biochemistry, College of Natural Sciences, Carleton University, Ottawa, Ontario, Canada. adecroos@mtsinai.on.ca
authors.forename: J N Amritha
authors.initials: JN
authors.lastname: De Croos
authors.forename: J Dayre
authors.initials: JD
authors.lastname: McNally
authors.forename: Ferdinando
authors.initials: F
authors.lastname: Palmieri
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Storey
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D017931:DNA Primers; D005615:Freezing; D015723:Gene Library; D008099:Liver / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D028061:Phosphate Transport Proteins / Q000235:genetics* / Q000378:metabolism; D011898:Ranidae / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D015854:Up-Regulation
chemical_list: D017931:DNA Primers; D024101:Mitochondrial Proteins; D028061:Phosphate Transport Proteins