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Chapter 7 : The Mating-Type Locus and Mating of Candida albicans and Candida glabrata
Category: Fungi and Fungal Pathogenesis
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In 1999, Hull and Johnson identified the emerging Candida albicans genome database a mating-type-like (MTL) locus. The configuration of this putative mating-type locus contrasted markedly with those of S. cerevisiae. Lachke and coworkers considered the possibility that rather than mating in the body, C. albicans might mate outside on the body surface. In this chapter, the mating systems of C. albicans and Candida glabrata have been compared to that of S. cerevisiae. Since the last of these has been so intensely studied over the past three decades and thus provides a contextual framework for interpreting the first two. Incorporation of both the white-opaque switching program and the filamentation program into the mating process may be due at least in part to the intimate relationship C. albicans has developed with its host. In contrast to C. albicans, the configuration and structure of mating-type genes and loci are highly similar to those of S. cerevisiae. One must wonder, for both C. albicans and C. glabrata, why complex mating systems are maintained, given the predominantly clonal population structure of both. Why devote so many genes, especially in C. albicans, to such a rare event? The answer is that it may be that mating and associated recombination, although rare, is essential for the continued survival of the species. Secondly, it may be that the mating process has become integral to pathogenesis.
Key Concept Ranking
- Gene Expression and Regulation
A comparison of mating-type loci of S. cerevisiae, C. glabrata, and C. albicans. For each species, the configuration of loci in the genome and the structure of genes in each locus are presented. The gray boxes within genes represent introns. Hatched regions represent identical protein sequences. Genes bordering the mating-type loci are presented. Arrows represent the directions of open reading frames. A putative diploid of C. glabrata is presented in panel D, although a/α strains have not been identified in nature. Note that the MAT a 2 and MTL a 2 sequences of S. cerevisiae and C. glabrata, respectively, are not related to MAT a 2 of C. albicans. The information for C. glabrata was obtained from references 116 and 134 . The information for C. albicans is from references 17 , 45 , and 127 .
A comparison of mating-type expression and the general steps in the mating process between S. cerevisiae(A, B) and C. albicans (C, D).
Cell biology of C. albicans mating. In each panel, a model of the cellular stage is presented at the top, a scanning electron micrograph of the stage is presented in the middle, and a diagram of the nuclear event is presented at the bottom. In conjugation bridges, a thin white line represents the point of tube fusion.
Both similarities and dissimilarities exist between S. cerevisiae (left-hand diagrams) and C. albicans (right-hand diagrams) in the roles played by mating-type genes in the regulation of mating. The dashed ellipsoids highlight differences between the two species. See reference 11 for details.
Transcription-profiling studies indicate that while a majority of genes associated with the mating process are regulated similarly by pheromone in C. albicans and S. cerevisiae , a minority of genes are regulated dissimilarly. (A) A model incorporating the transcription profiling data from references 11 , 65 , and 137a . Vertical arrows indicate up-regulation demonstrated by the three studies. Boxed genes represent dissimilar regulation between C. albicans and S. cerevisiae. (B) Comparison of the combined profiling data for C. albicans with that of Roberts et al. ( 101 ) for S. cerevisiae. Boxed genes represent dissimilar regulation between C. albicans and S. cerevisiae.
Skin facilitates the mating of C. albicans. (A) formation of a conjugation tube by C. albicans along skin of a newborn mouse. (B) Fusion between a C. albicans a/a and an α/α cell on skin. (C) Lower-magnification image reveals high frequency fusion of C. albicans a/a and α/α cells on skin. (D) Fusion between a C. albicans a/a and a C. dublin-iensis α/α cell on skin. Arrows point to fusions. t, long conjugation tube. Scale bars, 2μm.