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Antimicrobial Agents and Chemotherapy, February 2009, p. 476-482, Vol. 53, No. 2
0066-4804/09/$08.00+0 doi:10.1128/AAC.01154-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Department of Pediatrics, Duke University Medical Center, Durham, North Carolina,1 Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina,2 Department of Medicine, Duke University Medical Center, Durham, North Carolina3
Received 28 August 2008/ Returned for modification 30 September 2008/ Accepted 10 November 2008
Aspergillus fumigatus must be able to properly form hyphae and maintain cell wall integrity in order to establish invasive disease. Ras proteins and calcineurin each have been implicated as having roles in these processes. Here, we further delineate the roles of calcineurin and Ras activity in cell wall biosynthesis and hyphal morphology using genetic and pharmacologic tools. Strains deleted for three genes encoding proteins of these pathways, rasA (the Ras protein), cnaA (calcineurin), or crzA (the zinc finger transcription factor downstream of calcineurin), all displayed decreased cell wall 1,3-β-D-glucan content. Echinocandin treatment further decreased the levels of 1,3-β-D-glucan for all strains tested yet also partially corrected the hyphal growth defect of the
rasA strain. The inhibition of glucan synthesis caused an increase in chitin content for wild-type, dominant-active rasA, and
rasA strains. However, this important compensatory response was diminished in the calcineurin pathway mutants (
cnaA and
crzA). Taken together, our data suggest that the Ras and calcineurin pathways act in parallel to regulate cell wall formation and hyphal growth. Additionally, the calcineurin pathway elements cnaA and crzA play a major role in proper chitin and glucan incorporation into the A. fumigatus cell wall.
Published ahead of print on 17 November 2008.
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