Quantitative genetic approaches to Candida albicans oropharyngeal pathogenesis

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Abstract: Candida albicans is a polymorphic commensal yeast that also manifests as a prevalent opportunistic fungal pathogen. C. albicans infections manifest as oropharyngeal candidiasis (OPC), or thrush, in immunocompromised individuals. Here, we deploy quantitative trait loci (QTL) analysis to identify genes responsible for different forms of oral disease and to dissect regulatory networks governing the pathogenic process of filamentation in C. albicans. These experiments will develop quantitative genetic approaches for all parasexual Candida species. C. albicans has substantial phenotypic diversity among strains and is capable of residing stably in the oral cavity or inducing epithelial damage that leads to either clearance by the immune system or OPC. However, the genetic loci governing differences in these disease phenotypes between strains are not understood. To address this, two isolates 529L and SC5314, a stable colonizer and damager, respectively, were mated to generate parasexual progeny. Progeny genomes were sequenced at marker positions covering ~1% of the genome. High rates of recombination during parasex facilitated mapping of 19 QTL regions associated with epithelial damage phenotypes using a chromium release assay. Aim 1 will test specific loci from within those QTLs to identify genetic determinants of damage and clearance by the immune system or non-damaging persistence that differentiate strains. Furthermore, QTL analysis of filamentation will be performed, as hyphal formation and host cell damage were separable phenotypes in some progeny. C. albicans uses filamentation to disrupt epithelial surfaces and progress into a disseminated systemic infection. Current models of filamentation do not account for the substantial differences in filamentation among C. albicans isolates. To identify species-wide regulators of filamentation, we will employ QTL techniques using 4 strains with distinct filamentation phenotypes in Aim 2. QTLs from all pairwise matings will uncover genes regulating differences in filamentation phenotypes when grown on three different induction media at 30oC and 37oC to mimic the oral cavity and internal body temperature of the human host. Filamentation phenotyping will be scored with a novel high-throughput visual analysis procedure. Thus, establishment of quantitative genetic approaches in a parasexual species will greatly enhance identification of C. albicans pathogenesis regulators. My goal as a graduate student is to become a scientist whose research brings together multiple scientific disciplines. While pursuing these aims, I will develop my skills at the bench and at the computer to bridge the gap between informatics and biology, an increasingly important role in science. Throughout this project, I will develop my communication skills by presenting this work to scientific audiences locally and internationally, collaborating with other scientists, and writing my work for broader dissemination to the scientific and lay communities.