The Genetic Basis of Virulence in Cryptococcus Neoformans

Abstract Pathogenic fungi of the genus Cryptococcus contribute to nearly 200,000 deaths annually world- wide. However, not all Cryptococcus isolates cause lethal infections; some are relatively benign whereas others are hypervirulent. Differences in pathogenicity are often correlated with variation in specific morphological and physiological features such as the ability to grow at high tempera- tures, the size of the protective polysaccharide capsule surrounding the yeast cell, or resistance to antifungal drugs. To advance the understanding of Cryptococcus biology and cryptococcal disease, we seek to identify genetic differences between isolates and species that lead to changes in viru- lence and virulence-related traits, to disentangle the effects of genetic variants on gene networks and pathways that govern such traits, and to understand the ecological interactions that contribute to pathogenesis. We propose to apply population and quantitative genomic approaches and microbial experi- mental evolution to dissect the genetic basis of variation in virulence and virulence-related traits in Cryptococcus. We propose three inter-related specific aims: Aim 1) Build mapping populations and carry out Quantitative Trait Locus (QTL) mapping in Cryptococcus neoformans, Cryptococcus deneofor- mans, and Cryptococcus gattii to identify genes and alleles that contribute to differences in virulence traits and resistance to anti-fungal drugs; Aim 2) Employ a novel chemical epistasis approach to dissect the impact of natural variation on signaling pathways and transcriptional networks that control virulence traits; and Aim 3) Utilize trait mapping and experimental evolution to identify genetic variants that modulate interactions between Cryptococcus and phagocytic amoeba and test whether these variants correlate with virulence in cellular and animal models of fungal disease.