Homozygosity at the MTL locus in clinical strains of Candida albicans: Karyotypic rearrangments and tetraploid formation

One hundred and twenty Candida albicans clinical isolates from the late 1980s and early 1990s were examined for homosygosity at the MTL locus. Of these, 108 were heterozygous (MTLa/MTLα), whereas seven were MTLa and five were MTLα. Five of the homozygous isolates were able to switch to the opaque cell morphology, while opaque cells were not detectable among the remaining seven. Nevertheless, all but one of the isolates homozygous at the MTL locus were shown to mate and to yield cells containing markers from both parents; the non-mater was found to have a frameshift in the MTLα1 gene. In contrast to Saccharomyces cerevisiae, C. albicans homozygotes with no active MTL allele failed to mate rather than mating as a cells. There was no correlation between homoxygosity and fluconazole resistance, mating and fluconazole resistance or switching and fluconazole resistance, in part because most of the strains were isolated before the widespread use of this antifungal agent, and only three were in fact drug resistant Ten of the 12 homozygotes had rearranged karyotypes involving one or more homologue of chromosomes 4, 5, 6 and 7. We suggest that karyotypic rearrangement, drug resistance and homozygosity come about as the result of induction of hyperrecombination during the infection process; hence, they tend to occur together, but each is the independent result of the same event. Furthermore, as clinical strains can mate and form tetraploids, mating and marker exchange are likely to be a significant part of the life cycle of C. albicans in vivo

Phenotypic screening, transcriptional profiling, and comparative genomic analysis of an invasive and non-invasive strain of Candida albicans

<p>Abstract</p> <p>Background</p> <p>Invasion of host tissue by the human fungal pathogen <it>Candida albicans </it>is an important step during the development of candidosis. However, not all <it>C. albicans </it>strains possess the same invasive and virulence properties. For example, the two clinical isolates SC5314 and ATCC10231 differ in their ability to invade host tissue and cause experimental infections. Strain SC5314 is invasive whereas strain ATCC10231 is non-invasive and strongly attenuated in virulence compared to SC5314. In this study we compare the <it>in vitro </it>phenotypic, transcriptional and genomic profiles of these two widely used laboratory strains in order to determine the principal biological and genetic properties responsible for their differential virulence.</p> <p>Results</p> <p>In all media tested, the two strains showed the same metabolic flexibility, stress resistance, adhesion properties and hydrolytic enzyme secretion <it>in vitro</it>. However, differences were observed in response to cell-surface disturbing agents and alkaline pH. Furthermore, reduced hyphal formation in strain ATCC10231 under certain conditions correlated with reduced invasive properties in an <it>in vitro </it>invasion assay and a reduced ability to invade epithelial tissue. Despite these diverse phenotypic properties, no substantial genomic differences were detected by comparative genome hybridisation within the open reading frames. However, <it>in vitro </it>transcriptional profiling displayed major differences in the gene expression of these two strains, even under normal <it>in vitro </it>growth conditions.</p> <p>Conclusion</p> <p>Our data suggest that the reason for differential virulence of <it>C. albicans </it>strains is not due to the absence of specific genes, but rather due to differences in the expression, function or activity of common genes.</p

A Ste6p/P-glycoprotein homologue from the asexual yeast Candida albicans transports the a-factor mating pheromone in Saccharomyces cerevisiae

NRC publication: Ye

A Ste6p/P-glycoprotein homologue from the asexual yeast Candida albicans transports the a-factor mating pheromone in Saccharomyces cerevisiae

NRC publication: Ye

Candida albicans Lacking the Gene Encoding the Regulatory Subunit of Protein Kinase A Displays a Defect in Hyphal Formation and an Altered Localization of the Catalytic Subunit

The fungal pathogen Candida albicans switches from a yeast-like to a filamentous mode of growth in response to a variety of environmental conditions. We examined the morphogenetic behavior of C. albicans yeast cells lacking the BCY1 gene, which encodes the regulatory subunit of protein kinase A. We cloned the BCY1 gene and generated a bcy1 tpk2 double mutant strain because a homozygous bcy1 mutant in a wild-type genetic background could not be obtained. In the bcy1 tpk2 mutant, protein kinase A activity (due to the presence of the TPK1 gene) was cyclic AMP independent, indicating that the cells harbored an unregulated phosphotransferase activity. This mutant has constitutive protein kinase A activity and displayed a defective germinative phenotype in N-acetylglucosamine and in serum-containing medium. The subcellular localization of a Tpk1-green fluorescent protein (GFP) fusion protein was examined in wild-type, tpk2 null, and bcy1 tpk2 double mutant strains. The fusion protein was observed to be predominantly nuclear in wild-type and tpk2 strains. This was not the case in the bcy1 tpk2 double mutant, where it appeared dispersed throughout the cell. Coimmunoprecipitation of Bcy1p with the Tpk1-GFP fusion protein demonstrated the interaction of these proteins inside the cell. These results suggest that one of the roles of Bcy1p is to tether the protein kinase A catalytic subunit to the nucleus

The two isoforms of the cAMP-dependent protein kinase catalytic subunit are involved in the control of dimorphism in the human fungal pathogen Candida albicans

We have cloned the Candida albicans TPK2 gene encoding a cAMP-dependent protein kinase (PKA) catalytic subunit and generated a tpk2 homozygous null mutant to assess its ability to germinate in liquid media. N-acetylglucosamine (GlcNAc)-induced germ-tube formation was attenuated in the tpk2 strain and enhanced by compounds that are known to increase the PKA activity in situ. Germination was completely blocked in the presence of the myristoylated derivative of the heat-stable PKA inhibitor (MyrPKI). These results indicate that TPK1 acts positively in regulating the morphogenetic transition in C. albicans in the absence of the TPK2 gene. We were able to identify an mRNA from this second form of PKA in both wild-type and tpk2 null mutant cells. We found that PKA activity measured in the mutant lacking the TPK2 gene was about 10% of that displayed by the wild-type. The finding that the germinative response of tpk2 null mutant to serum was severely diminished at low serum concentrations indicates that the level of PKA is an important determinant of filamentous growth at low serum concentrations. The extent of germination attained at higher serum concentrations (5%) was similar in the wild-type and in the tpk2 null mutant strains suggesting that under these conditions germination was triggered through a PKA-independent pathway.Fil: Cloutier, Monikca. GREB Laval University; CanadáFil: Castilla Lozano, Maria del Rocio. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Invetigaciones Bioquímicas y Fisiologicas; ArgentinaFil: Bolduc, Nathalie. GREB Laval University; CanadáFil: Zelada, Alicia Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Invetigaciones Bioquímicas y Fisiologicas; ArgentinaFil: Martineau, Philippe. GREB Laval University; CanadáFil: Bouillon, Marlène. GREB Laval University; CanadáFil: Magee, Beatrice B.. University of Minnesota; Estados UnidosFil: Di Bernardo, Maria Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Invetigaciones Bioquímicas y Fisiologicas; ArgentinaFil: Giasson, Luc. GREB Laval University; CanadáFil: Cantore, Maria Leonor. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Invetigaciones Bioquímicas y Fisiologicas; Argentin