title: Glycogen phosphorylase in glycogen-rich cells is involved in the energy supply for ion regulation in fish gill epithelia.
abstract: The molecular and cellular mechanisms behind glycogen metabolism and the energy metabolite translocation between mammal neurons and astrocytes have been well studied. A similar mechanism is proposed for rapid mobilization of local energy stores to support energy-dependent transepithelial ion transport in gills of the Mozambique tilapia (Oreochromis mossambicus). A novel gill glycogen phosphorylase isoform (tGPGG), which catalyzes the initial degradation of glycogen, was identified in branchial epithelial cells of O. mossambicus. Double in situ hybridization and immunocytochemistry demonstrated that tGPGG mRNA and glycogen were colocalized in glycogen-rich cells (GRCs), which surround ionocytes (labeled with a Na(+)-K(+)-ATPase antiserum) in gill epithelia. Concanavalin-A (a marker for the apical membrane) labeling indicated that GRCs and mitochondria-rich cells share the same apical opening. Quantitative real-time PCR analyses showed that tGPGG mRNA expression levels specifically responded to environmental salinity changes. Indeed, the glycogen content, glycogen phosphorylase (GP) protein level and total activity, and the density of tGPGG-expressing cells (i.e., GRCs) in fish acclimated to seawater (SW) were significantly higher than those in freshwater controls. Short-term acclimation to SW caused an evident depletion in the glycogen content of GRCs. Taken altogether, tGPGG expression in GRCs is stimulated by hyperosmotic challenge, and this may catalyze initial glycogen degradation to provide the adjacent ionocytes with energy to carry out iono- and osmoregulatory functions.
authors.affiliation: Institute of Cellular and Organismic Biology, Academia Sinica, Nankang, Taipei, Taiwan 11529, R.O.C.
authors.forename: Yung-Che
authors.initials: YC
authors.lastname: Tseng
authors.forename: Chang-Jen
authors.initials: CJ
authors.lastname: Huang
authors.forename: Joshua Chia-Hsi
authors.initials: JC
authors.lastname: Chang
authors.forename: Wen-Yuan
authors.initials: WY
authors.lastname: Teng
authors.forename: Otto
authors.initials: O
authors.lastname: Baba
authors.forename: Ming-Ji
authors.initials: MJ
authors.lastname: Fann
authors.forename: Pung-Pung
authors.initials: PP
authors.lastname: Hwang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001253:Astrocytes / Q000201:enzymology / Q000378:metabolism; D015153:Blotting, Western; D001921:Brain / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000096:biosynthesis / Q000235:genetics; D004734:Energy Metabolism / Q000502:physiology*; D004847:Epithelial Cells / Q000378:metabolism*; D005880:Gills / Q000166:cytology / Q000378:metabolism*; D006003:Glycogen / Q000378:metabolism*; D024981:Glycogen Phosphorylase / Q000378:metabolism*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007527:Isoenzymes / Q000378:metabolism; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012965:Sodium Chloride / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D017210:Tilapia / Q000378:metabolism*; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D018076:DNA, Complementary; D007527:Isoenzymes; D012333:RNA, Messenger; D012965:Sodium Chloride; D006003:Glycogen; D024981:Glycogen Phosphorylase; D000254:Sodium-Potassium-Exchanging ATPase