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Targeted gene disruption reveals an adhesin indispensable for pathogenicity of Blastomyces dermatitidis
T T Brandhorst1, M Wüthrich, T Warner
1Department of Pediatrics, University of Wisconsin Medical School, Madison, Wisconsin 53792, USA.
Abstract:
Systemic fungal infections are becoming more common and difficult to treat, yet the pathogenesis of these infectious diseases remains poorly understood. In many cases, pathogenicity can be attributed to the ability of the fungi to adhere to target tissues, but the lack of tractable genetic systems has limited progress in understanding and interfering with the offending fungal products. In Blastomyces dermatitidis, the agent of blastomycosis, a respiratory and disseminated mycosis of people and animals worldwide, expression of the putative adhesin encoded by the WI-1 gene was investigated as a possible virulence factor. DNA-mediated gene transfer was used to disrupt the WI-1 locus by allelic replacement, resulting in impaired binding and entry of yeasts into macrophages, loss of adherence to lung tissue, and abolishment of virulence in mice; each of these properties was fully restored after reconstitution of WI-1 by means of gene transfer. These findings establish the pivotal role of WI-1 in adherence and virulence of B. dermatitidis yeasts. To our knowledge, they offer the first example of a genetically proven virulence determinant among systemic dimorphic fungi, and underscore the value of reverse genetics for studies of pathogenesis in these organisms.
Insights
Researchers identified the WI-1 gene in Blastomyces dermatitidis as crucial for fungal adherence and virulence. Disrupting WI-1 impaired fungal infection, while restoring it reversed these effects, proving its role in pathogenesis.
Area of Science:
- Mycology
- Infectious Diseases
- Molecular Biology
Background:
- Systemic fungal infections are increasing and challenging to treat.
- Fungal pathogenicity often involves tissue adherence, but understanding is limited by genetic tool constraints.
- Blastomyces dermatitidis causes blastomycosis, a significant human and animal mycosis.
Purpose of the Study:
- To investigate the role of the WI-1 gene product as a virulence factor in Blastomyces dermatitidis.
- To understand the contribution of fungal adherence to pathogenesis.
- To establish a genetically proven virulence determinant in systemic dimorphic fungi.
Main Methods:
- Utilized DNA-mediated gene transfer for allelic replacement to disrupt the WI-1 gene locus.
- Assessed yeast binding and entry into macrophages.
- Evaluated fungal adherence to lung tissue and virulence in a mouse model.
- Restored WI-1 gene function through gene transfer to confirm findings.
Main Results:
- Disruption of the WI-1 gene resulted in impaired yeast binding and macrophage entry.
- Loss of WI-1 expression led to reduced adherence to lung tissue.
- Mice infected with the WI-1 disrupted mutant showed abolished virulence.
- Reconstitution of WI-1 fully restored adherence and virulence properties.
Conclusions:
- The WI-1 gene product plays a pivotal role in the adherence and virulence of Blastomyces dermatitidis yeasts.
- This study provides the first genetically confirmed virulence determinant for systemic dimorphic fungi.
- Reverse genetics approaches are valuable for studying pathogenesis in these fungi.