title: The mold-specific MS8 gene is required for normal hypha formation in the dimorphic pathogenic fungus Histoplasma capsulatum.
abstract: The dimorphic fungus Histoplasma capsulatum is the etiologic agent of one of the most common systemic mycoses of humans, histoplasmosis. In the environment, H. capsulatum grows in a differentiated mold form and shifts to an undifferentiated yeast form after mold fragments or spores are inhaled. This mold-to-yeast shift is required for disease. Little is known about the molecular biology of dimorphism in Histoplasma, and most studies have been directed toward yeast-specific genes. While it is important to examine the role of genes upregulated in the yeast morphotype, genes which are silenced in the yeast (i.e., mold-specific genes) may also play a critical role in dimorphism. To begin to examine this hypothesis, we report here the first misexpression and knockout analysis of a mold-specific gene in Histoplasma. The strongly expressed MS8 gene encodes a predicted 21-kDa protein extremely rich in glycine and glutamine. Forced expression of MS8 driven by the TEF1 promoter in yeast did not alter the yeast morphology at 37 degrees C or mold formation at 25 degrees C. Yeast expressing MS8 did exhibit clumping in liquid medium and formed "sticky" colonies on agar plates. Allelic replacement of MS8 was accomplished by a positive-negative selection procedure. ms8 knockout mutants formed apparently normal yeast at 37 degrees C but gave rise to aberrant mycelia at 25 degrees C. The mold colonies of the knockouts were less than half as large as normal, had a granular surface, produced a dark-red pigment, and formed short hyphae which were 40% wider with a distinctive twisted "zig-zag" shape.
authors.affiliation: Department of Biological Sciences, Center for Molecular and Cellular Biosciences, University of Southern Mississippi, Hattiesburg, Mississippi 39406-5018, USA.
authors.forename: Xianbin
authors.initials: X
authors.lastname: Tian
authors.forename: Glenmore
authors.initials: G
authors.lastname: Shearer
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D015870:Gene Expression; D005800:Genes, Fungal; D006658:Histoplasma / Q000254:growth & development* / Q000472:pathogenicity / Q000502:physiology; D006660:Histoplasmosis / Q000235:genetics / Q000378:metabolism; D025301:Hyphae / Q000254:growth & development; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D017422:Sequence Analysis, DNA; D020539:Sequence Analysis, Protein
chemical_list: D005656:Fungal Proteins; C440890:MS8 protein, Ajellomyces capsulata