title: Tortoise, a novel mitochondrial protein, is required for directional responses of Dictyostelium in chemotactic gradients.
abstract: We have identified a novel gene, Tortoise (TorA), that is required for the efficient chemotaxis of Dictyostelium discoideum cells. Cells lacking TorA sense chemoattractant gradients as indicated by the presence of periodic waves of cell shape changes and the localized translocation of cytosolic PH domains to the membrane. However, they are unable to migrate directionally up spatial gradients of cAMP. Cells lacking Mek1 display a similar phenotype. Overexpression of Mek1 in torA- partially restores chemotaxis, whereas overexpression of TorA in mek1- does not rescue the chemotactic phenotype. Regardless of the genetic background, TorA overexpressing cells stop growing when separated from a substrate. Surprisingly, TorA-green fluorescent protein (GFP) is clustered near one end of mitochondria. Deletion analysis of the TorA protein reveals distinct regions for chemotactic function, mitochondrial localization, and the formation of clusters. TorA is associated with a round structure within the mitochondrion that shows enhanced staining with the mitochondrial dye Mitotracker. Cells overexpressing TorA contain many more of these structures than do wild-type cells. These TorA-containing structures resist extraction with Triton X-100, which dissolves the mitochondria. The characterization of TorA demonstrates an unexpected link between mitochondrial function, the chemotactic response, and the capacity to grow in suspension.
authors.affiliation: Department of Cell Biology and Anatomy, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: S
authors.initials: S
authors.lastname: van Es
authors.forename: D
authors.initials: D
authors.lastname: Wessels
authors.forename: D R
authors.initials: DR
authors.lastname: Soll
authors.forename: J
authors.initials: J
authors.lastname: Borleis
authors.forename: P N
authors.initials: PN
authors.lastname: Devreotes
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D048429:Cell Size; D002633:Chemotaxis / Q000502:physiology*; D000242:Cyclic AMP / Q000378:metabolism*; D004023:Dictyostelium / Q000235:genetics / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure; D005456:Fluorescent Dyes / Q000378:metabolism; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D048369:MAP Kinase Kinase 1; D008928:Mitochondria / Q000737:chemistry / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009930:Organic Chemicals; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D012995:Solubility
chemical_list: D005456:Fluorescent Dyes; D008164:Luminescent Proteins; D009930:Organic Chemicals; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins; C426231:TorA protein, Dictyostelium; C107472:red dye CMXRos; D049452:Green Fluorescent Proteins; D000242:Cyclic AMP; D017346:Protein Serine-Threonine Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases