MFα1 , the Gene Encoding the α Mating Pheromone of Candida albicans

Abstract

Candida albicans, the single most frequently isolated human fungal pathogen, was thought to be asexual until the recent discovery of the mating-type-like locus (MTL). Homozygous MTL strains were constructed and shown to mate. Furthermore, it has been demonstrated that opaque-phase cells are more efficient in mating than white-phase cells. The similarity of the genes involved in the mating pathway in Saccharomyces cerevisiae and C. albicans includes at least one gene (KEX2) that is involved in the processing of the ␣ mating pheromone in the two yeasts. Taking into account this similarity, we searched the C. albicans genome for sequences that would encode the ␣ pheromone gene. Here we report the isolation and characterization of the gene MF␣1, which codes for the precursor of the ␣ mating pheromone in C. albicans. Two active ␣-peptides, 13 and 14 amino acids long, would be generated after the precursor molecule is processed in C. albicans. To examine the role of this gene in mating, we constructed an mf␣1 null mutant of C. albicans. The mf␣1 null mutant fails to mate as MTL␣, while MTLa mf␣1 cells are still mating competent. Experiments performed with the synthetic ␣-peptides show that they are capable of inducing growth arrest, as demonstrated by halo tests, and also induce shmooing in MTLa cells of C. albicans. These peptides are also able to complement the mating defect of an MTL␣ kex2 mutant strain when added exogenously, thereby confirming their roles as ␣ mating pheromones.Candida albicans is the most common opportunistic fungal pathogen of humans and mostly infects immunosuppressed patients (3). It inhabits diverse niches, which include the gastrointestinal tract and the vagina, and causes infection of skin, mucous membranes, and the bloodstream. Since each of these sites of infection presumably requires differences in gene expression, a great deal of effort has been spent in looking at how such adaptation occurs in Candida. Much of this effort was predicated on the characterization of C. albicans as an asexual obligate diploid.That this fungus is asexual was disproved after the C. albicans genome sequencing project revealed the presence of sequences homologous to the Saccharomyces cerevisiae MAT (mating-type) loci. The C. albicans homologues of the MAT loci, the MTL (mating-type-like) loci, were found to be heterozygous in common laboratory strains tested (17). Strains homozygous for the MTL locus were generated either by a deletion strategy (18) or by loss, induced by growth on sorbose as the sole carbon source (19), of one homologue of chromosome 5, the site of the MTL loci (29). Strains thus constructed were able to mate both under laboratory conditions (29) and in the animal host (18). These studies set the stage for dissecting the mating pathway in C. albicans.Mating in fungi has been examined in both yeasts and molds of various sorts. Certain general parts of the process seem to hold across genera and indeed across the kingdom. These include dissimilar regulatory genes (mating-type loci), soluble phe...

Morphogenesis in Candida albicans

“…The identification of the single gene encoding the C. albicans α-factor peptide has allowed for the chemical synthesis of the pheromone and the analysis of the behavior of cells in the presence of this factor (17,83,102). C. albicans cells treated with pheromone modify their gene expression profiles (17,83), their cell cycle progression (102), and their cellular morphology (83). In keeping with the terminology established for the modified morphology developed by pheromone-treated cells in S. cerevisiae, C. albicans MTLa cells treated with α-factor have been termed shmoos (83), even though their actual shapes are unlike either the Al Capp creation or the characteristic forms of the budding yeast.…”

“…MATα cells of the budding yeast and MTLα cells from C. albicans produce simple peptide pheromones (17,83,97,102), and the MATa and MTLa cells from the two species produce pheromones that are either proven or predicted to be lipid-modified peptides (28,41). The identification of the single gene encoding the C. albicans α-factor peptide has allowed for the chemical synthesis of the pheromone and the analysis of the behavior of cells in the presence of this factor (17,83,102). C. albicans cells treated with pheromone modify their gene expression profiles (17,83), their cell cycle progression (102), and their cellular morphology (83).…”

The Same Receptor, G Protein, and Mitogen-activated Protein Kinase Pathway Activate Different Downstream Regulators in the Alternative White and Opaque Pheromone Responses ofCandida albicans

“…Cells were then pelleted, resuspended at 10 6 cells/ml in fresh medium containing 3 ϫ 10 Ϫ6 M synthetic 13-mer ␣-pheromone (Bennett et al, 2003;Panwar et al, 2003) and incubated at 25°C in a shaker (250 rpm). The 13-mer peptide (GFRLTNFGYFEPG), synthesized by Open Biosystems (Huntsville, AL), was dissolved in dimethyl sulfoxide (DMSO).…”

Nuclear fusion occurs during mating in Candida albicans and is dependent on the KAR3 gene

“…Several groups recently identified the gene ( MF a ) encoding the a -pheromone produced by a opaque cells (Lan et al ., 2002;Lockhart et al ., 2003b;Newport et al ., 2003;Panwar et al ., 2003). Addition of a synthetic peptide corresponding to the mature a -pheromone caused a opaque cells to form mating projections; concomitant with these morphological changes, 60-70 genes were upregulated .…”