The mold-specific MS8 gene is required for normal hypha formation in the dimorphic pathogenic fungus Histoplasma capsulatum.
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.
Tian
Xianbin
X
Department of Biological Sciences, Center for Molecular and Cellular Biosciences, University of Southern Mississippi, Hattiesburg, Mississippi 39406-5018, USA.
Shearer
Glenmore
G
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
D005656:Fungal Proteins; C440890:MS8 protein, Ajellomyces capsulata