title: Sgt1, a co-chaperone of Hsp90 stabilizes Polo and is required for centrosome organization.
abstract: Sgt1 was described previously in yeast and humans to be a Hsp90 co-chaperone and required for kinetochore assembly. We have identified a mutant allele of Sgt1 in Drosophila and characterized its function. Mutations in sgt1 do not affect overall kinetochore assembly or spindle assembly checkpoint. sgt1 mutant cells enter less frequently into mitosis and arrest in a prometaphase-like state. Mutations in sgt1 severely compromise the organization and function of the mitotic apparatus. In these cells, centrioles replicate but centrosomes fail to mature, and pericentriolar material components do not localize normally resulting in highly abnormal spindles. Interestingly, a similar phenotype was described previously in Hsp90 mutant cells and correlated with a decrease in Polo protein levels. In sgt1 mutant neuroblasts, we also observe a decrease in overall levels of Polo. Overexpression of the kinase results in a substantial rescue of the centrosome defects; most cells form normal bipolar spindles and progress through mitosis normally. Taken together, these findings suggest that Sgt1 is involved in the stabilization of Polo allowing normal centrosome maturation, entry and progression though mitosis.
authors.affiliation: IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal.
authors.forename: Torcato
authors.initials: T
authors.lastname: Martins
authors.forename: André F
authors.initials: AF
authors.lastname: Maia
authors.forename: Soren
authors.initials: S
authors.lastname: Steffensen
authors.forename: Claudio E
authors.initials: CE
authors.lastname: Sunkel
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D002470:Cell Survival; D002502:Centrioles / Q000378:metabolism; D018385:Centrosome / Q000201:enzymology*; D029721:Drosophila Proteins / Q000737:chemistry / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000166:cytology* / Q000201:enzymology*; D004795:Enzyme Stability; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D018386:Kinetochores / Q000378:metabolism; D008938:Mitosis; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009474:Neurons / Q000166:cytology / Q000201:enzymology; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D021381:Protein Transport; D008941:Spindle Apparatus / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; D018841:HSP90 Heat-Shock Proteins; D018832:Molecular Chaperones; C538796:Sgt1 protein, Drosophila; C072004:polo protein, Drosophila; D017346:Protein Serine-Threonine Kinases