title: Mannosylinositol phosphorylceramide is a major sphingolipid component and is required for proper localization of plasma-membrane proteins in Schizosaccharomyces pombe.
abstract: In Saccharomyces cerevisiae, three classes of sphingolipids contain myo-inositol--inositol phosphorylceramide (IPC), mannosylinositol phosphorylceramide (MIPC) and mannosyldiinositol phosphorylceramide [M(IP)(2)C]. No fission yeast equivalent of Ipt1p, the inositolphosphotransferase that synthesizes M(IP)(2)C from MIPC, has been found in the Schizosaccharomyces pombe genome. Analysis of the sphingolipid composition of wild-type cells confirmed that MIPC is the terminal and most abundant complex sphingolipid in S. pombe. Three proteins (Sur1p, Csg2p and Csh1p) have been shown to be involved in the synthesis of MIPC from IPC in S. cerevisiae. The S. pombe genome has three genes (SPAC2F3.01, SPCC4F11.04c and SPAC17G8.11c) that are homologues of SUR1, termed imt1(+), imt2(+) and imt3(+), respectively. To determine whether these genes function in MIPC synthesis in S. pombe, single and multiple gene disruptants were constructed. Single imt disruptants were found to be viable. MIPC was not detected and IPC levels were increased in the triple disruptant, indicating that the three SUR1 homologues are involved in the synthesis of MIPC. GFP-tagged Imt1p, Imt2p and Imt3p localized to Golgi apparatus membranes. The MIPC-deficient mutant exhibited pleiotropic phenotypes, including defects in cellular and vacuolar morphology, and in localization of ergosterols. MIPC seemed to be required for endocytosis of a plasma-membrane-localized amino acid transporter, because sorting of the transporter from the plasma membrane to the vacuole was severely impaired in the MIPC-deficient mutant grown under nitrogen-limiting conditions. These results suggest that MIPC has multiple functions not only in the maintenance of cell and vacuole morphology but also in vesicular trafficking in fission yeast.
authors.affiliation: Department of Bioscience and Biotechnology, Faculty of Agriculture, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-8581, Japan.
authors.forename: Mai
authors.initials: M
authors.lastname: Nakase
authors.forename: Motohiro
authors.initials: M
authors.lastname: Tani
authors.forename: Tomotake
authors.initials: T
authors.lastname: Morita
authors.forename: Hiroko K
authors.initials: HK
authors.lastname: Kitamoto
authors.forename: Jun
authors.initials: J
authors.lastname: Kashiwazaki
authors.forename: Taro
authors.initials: T
authors.lastname: Nakamura
authors.forename: Akira
authors.initials: A
authors.lastname: Hosomi
authors.forename: Naotaka
authors.initials: N
authors.lastname: Tanaka
authors.forename: Kaoru
authors.initials: K
authors.lastname: Takegawa
mesh_terms: D000595:Amino Acid Sequence; D026905:Amino Acid Transport Systems / Q000378:metabolism; D002855:Chromatography, Thin Layer; D004705:Endocytosis / Q000187:drug effects; D004875:Ergosterol / Q000494:pharmacology; D005800:Genes, Fungal / Q000235:genetics; D006028:Glycosphingolipids / Q000378:metabolism*; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D008364:Mannosyltransferases / Q000172:deficiency / Q000235:genetics; D021962:Membrane Microdomains / Q000201:enzymology; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D021381:Protein Transport / Q000187:drug effects; D012568:Schizosaccharomyces / Q000166:cytology / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry / Q000378:metabolism*; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism
chemical_list: D026905:Amino Acid Transport Systems; D006028:Glycosphingolipids; D008565:Membrane Proteins; D029702:Schizosaccharomyces pombe Proteins; C479822:mannosylinositol phosphoylceramide; D008364:Mannosyltransferases; D004875:Ergosterol