Two new genes, palH and palI, where mutations mimic the effects of acidic growth pH have been ide... more Two new genes, palH and palI, where mutations mimic the effects of acidic growth pH have been identified in Aspergillus nidulans. A palH mutation is phenotypically indistinguishable from mutations in the palA, palB, palC, and palF genes, whereas palI mutations differ only in that they allow some growth at pH 8. Mutations in palA, B, C, F, and H are epistatic to a palI mutation and the significance of this epistasis is discussed. Additionally, palE and palB mutations have been shown to be allelic. Thus, a total of six genes where mutations mimic acidic growth conditions has been identified.
The capture of pathogen gene expression signatures directly from the host niche promises to fuel ... more The capture of pathogen gene expression signatures directly from the host niche promises to fuel our understanding of the highly complex nature of microbial virulence. However, obtaining and interpreting biological information from infected tissues presents multiple experimental and intellectual challenges, from difficulties in extracting pathogen RNA and appropriate choice of experimental design, to interpretation of the resulting infection transcriptome, itself a product of responses to multiple host-derived cues. The recent publication of several host-infecting fungal transcriptomes offers new opportunities to study the commonalities of animal and plant pathogeneses, which in turn might direct the rational design of new and broader spectrum antifungal agents. Here, we examine the transcriptional basis of modelled Aspergillus fumigatus, Candida albicans, Cryptococcus neoformans, Ustilago maydis and Magneporthe infections, placing our analysis of the published findings within the context of the various modelling procedures used, and the relevant pathogen lifestyles, to facilitate the first cross-species comparison of fungal transcription during infectious growth. Significant concordance was identified among infecting transcriptomes of the inhaled fungal pathogens C. neoformans and A. fumigatus. The significance of gene clustering and subtelomeric gene repertoires is also discussed.
The conserved family of fungal Ste11 mitogen activated protein kinase/kinases play important role... more The conserved family of fungal Ste11 mitogen activated protein kinase/kinases play important roles in several signalling cascades. We have cloned the STE11 homologue from the fungal pathogen Candida glabrata. The C. glabrata gene is present in a single copy in the genome, contains a well-conserved catalytic domain typical of the serine-threonine protein kinases and a sterile alpha motif widespread in signalling and nuclear proteins. Hypothetical translation of C. glabrata STE11 suggests that the protein has 64% identity and 77% similarity at the amino acid level to Saccharomyces cerevisiae Ste11. We have shown that C. glabrata STE11 can complement the mating defect and partially rescue the reduced nitrogen starvation induced filamentation of S. cerevisiae ste11 mutants. Functional analysis of a C. glabrata ste11 null mutant demonstrates that Ste11 is required for adaptation to hypertonic stress but is largely dispensable for maintenance of cell wall integrity. It also plays a role in C. glabrata nitrogen starvation induced filamentation. Survival analysis revealed that C. glabrata ste11 mutants, while still able to cause disease, are attenuated for virulence compared to reconstituted, STE11 cells. These data suggest that C. glabrata Ste11, in a similar fashion to the S. cerevisiae protein, functions in a number of different signalling modules.
The ability of a pathogen to adapt to the host environment is usually required for the initiation... more The ability of a pathogen to adapt to the host environment is usually required for the initiation of disease. Here we have investigated the importance of the Aspergillus nidulans PacC-mediated pH response in the pathogenesis of pulmonary aspergillosis. Using mutational analysis, we demonstrate that, in neutropenic mice, elimination of the A. nidulans pH-responsive transcription factor PacC, blocking the ambient pH signal transduction pathway or prevention of PacC proteolytic processing acutely attenuates virulence. Infections caused by these alkali-sensitive mutants are characterized by limited growth in vivo and a reduction of inflammatory cell infiltration. In stark contrast, constitutive activation of PacC causes increased mortality marked by extensive fungal invasive growth. PacC action is therefore required for, and able to enhance virulence, demonstrating that the A. nidulans pH-responsive transcription factor PacC plays a pivotal role in pulmonary pathogenesis.
The highly conserved fungal Ste12 transcription factor family of proteins play critical roles in ... more The highly conserved fungal Ste12 transcription factor family of proteins play critical roles in the regulation of many cellular processes including mating, cell wall biosynthesis, filamentation and invasive growth. They are also important mediators of fungal virulence. The Candida glabrata STE12 homologue was cloned. The encoded protein has a single DNA binding homeodomain but lacks both a C2H2 zinc finger DNA binding domain and an apparent Dig1/Dig2 regulatory motif. Candida glabrata STE12 can functionally complement the nitrogen starvation induced filamentation and mating defects of Saccharomyces cerevisiae ste12 mutants. We also show that C. glabrata STE12 is required for nitrogen starvation-induced filamentation as ste12 mutants rarely produce pseudohyphae on nitrogen depeleted media. Finally we describe a novel murine model of C. glabrata systemic disease and use this to demonstrate that C. glabrata ste12 mutants, although still able to cause disease, are attenuated for virulence compared with STE12 reconstituted strains. Candida glabrata STE12 is therefore the first virulence factor encoding gene to be described in this increasingly important fungal pathogen.
Two new genes, palH and palI, where mutations mimic the effects of acidic growth pH have been ide... more Two new genes, palH and palI, where mutations mimic the effects of acidic growth pH have been identified in Aspergillus nidulans. A palH mutation is phenotypically indistinguishable from mutations in the palA, palB, palC, and palF genes, whereas palI mutations differ only in that they allow some growth at pH 8. Mutations in palA, B, C, F, and H are epistatic to a palI mutation and the significance of this epistasis is discussed. Additionally, palE and palB mutations have been shown to be allelic. Thus, a total of six genes where mutations mimic acidic growth conditions has been identified.
The capture of pathogen gene expression signatures directly from the host niche promises to fuel ... more The capture of pathogen gene expression signatures directly from the host niche promises to fuel our understanding of the highly complex nature of microbial virulence. However, obtaining and interpreting biological information from infected tissues presents multiple experimental and intellectual challenges, from difficulties in extracting pathogen RNA and appropriate choice of experimental design, to interpretation of the resulting infection transcriptome, itself a product of responses to multiple host-derived cues. The recent publication of several host-infecting fungal transcriptomes offers new opportunities to study the commonalities of animal and plant pathogeneses, which in turn might direct the rational design of new and broader spectrum antifungal agents. Here, we examine the transcriptional basis of modelled Aspergillus fumigatus, Candida albicans, Cryptococcus neoformans, Ustilago maydis and Magneporthe infections, placing our analysis of the published findings within the context of the various modelling procedures used, and the relevant pathogen lifestyles, to facilitate the first cross-species comparison of fungal transcription during infectious growth. Significant concordance was identified among infecting transcriptomes of the inhaled fungal pathogens C. neoformans and A. fumigatus. The significance of gene clustering and subtelomeric gene repertoires is also discussed.
The conserved family of fungal Ste11 mitogen activated protein kinase/kinases play important role... more The conserved family of fungal Ste11 mitogen activated protein kinase/kinases play important roles in several signalling cascades. We have cloned the STE11 homologue from the fungal pathogen Candida glabrata. The C. glabrata gene is present in a single copy in the genome, contains a well-conserved catalytic domain typical of the serine-threonine protein kinases and a sterile alpha motif widespread in signalling and nuclear proteins. Hypothetical translation of C. glabrata STE11 suggests that the protein has 64% identity and 77% similarity at the amino acid level to Saccharomyces cerevisiae Ste11. We have shown that C. glabrata STE11 can complement the mating defect and partially rescue the reduced nitrogen starvation induced filamentation of S. cerevisiae ste11 mutants. Functional analysis of a C. glabrata ste11 null mutant demonstrates that Ste11 is required for adaptation to hypertonic stress but is largely dispensable for maintenance of cell wall integrity. It also plays a role in C. glabrata nitrogen starvation induced filamentation. Survival analysis revealed that C. glabrata ste11 mutants, while still able to cause disease, are attenuated for virulence compared to reconstituted, STE11 cells. These data suggest that C. glabrata Ste11, in a similar fashion to the S. cerevisiae protein, functions in a number of different signalling modules.
The ability of a pathogen to adapt to the host environment is usually required for the initiation... more The ability of a pathogen to adapt to the host environment is usually required for the initiation of disease. Here we have investigated the importance of the Aspergillus nidulans PacC-mediated pH response in the pathogenesis of pulmonary aspergillosis. Using mutational analysis, we demonstrate that, in neutropenic mice, elimination of the A. nidulans pH-responsive transcription factor PacC, blocking the ambient pH signal transduction pathway or prevention of PacC proteolytic processing acutely attenuates virulence. Infections caused by these alkali-sensitive mutants are characterized by limited growth in vivo and a reduction of inflammatory cell infiltration. In stark contrast, constitutive activation of PacC causes increased mortality marked by extensive fungal invasive growth. PacC action is therefore required for, and able to enhance virulence, demonstrating that the A. nidulans pH-responsive transcription factor PacC plays a pivotal role in pulmonary pathogenesis.
The highly conserved fungal Ste12 transcription factor family of proteins play critical roles in ... more The highly conserved fungal Ste12 transcription factor family of proteins play critical roles in the regulation of many cellular processes including mating, cell wall biosynthesis, filamentation and invasive growth. They are also important mediators of fungal virulence. The Candida glabrata STE12 homologue was cloned. The encoded protein has a single DNA binding homeodomain but lacks both a C2H2 zinc finger DNA binding domain and an apparent Dig1/Dig2 regulatory motif. Candida glabrata STE12 can functionally complement the nitrogen starvation induced filamentation and mating defects of Saccharomyces cerevisiae ste12 mutants. We also show that C. glabrata STE12 is required for nitrogen starvation-induced filamentation as ste12 mutants rarely produce pseudohyphae on nitrogen depeleted media. Finally we describe a novel murine model of C. glabrata systemic disease and use this to demonstrate that C. glabrata ste12 mutants, although still able to cause disease, are attenuated for virulence compared with STE12 reconstituted strains. Candida glabrata STE12 is therefore the first virulence factor encoding gene to be described in this increasingly important fungal pathogen.
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Papers by Elaine Bignell