Fungi are a major source of clinical infections, especially among patients with compromised immune systems. The mechanisms fungi use to colonize human hosts are not fully understood, but are thought to often involve invasive growth. Specifically, many fungi are capable of attaching to and penetrating surfaces, such as those of human tissues. Saccharomyces cerevisiae, which is known to colonize immunocompromised humans, is a valuable model for understanding the environmental triggers and genetic mechanisms that underlie invasive growth in fungi. Although the S. cerevisiae reference strain S288C does not exhibit invasive growth, we have found that many ecologically and genetically diverse isolates can grow invasively, with expression of the trait often dependent on specific environmental conditions. In this proposal, (Aim 1) we use a combination of genetic mapping and genetic engineering to identify genes that cause variability in invasive growth among clinical isolates of S. cerevisiae. We conduct our genetic mapping studies in a panel of 2,880 segregants derived from the mating of 5 diverse strains in all 10 possible pairwise combinations. Once causal loci have been identified, we will use genetic engineering techniques to resolve these loci to specific genes and genetic variants.
(Aim 2) We then test the potential relevance of the identified causal variants by infecting wild isolates and engineered strains into an animal model. We will inoculate the strains into a large number of wax moth larvae, which are commonly used to study the virulence of microbes, and measure the extent to which the strains cause sickness or death. Completion of the proposed research will provide detailed information about the genetic and environmental causes of invasive growth, and will also shed light on the potential clinical relevance of the identified alleles. Relevance: Cases of fungal pathogenesis are on the rise, with more than 500 species of fungi identified in human infections to date. Genetic approaches provide powerful tools for identifying the molecular mechanisms underlying pathogenesis in fungi. However, common opportunistic pathogens, such as Candida albicans, suffer from major limitations as genetic systems due to their inability to sexually reproduce in th lab. Isolates of S. cerevisiae exhibit substantial variability in the types of pathogenicity traitsthey exhibit, as well as the conditions in which these traits are expressed. To determine genetic and environmental factors that are involved in fungi attaching to and penetrating surfaces, which is thought to contribute to pathogenesis, we will perform genetic mapping experiments using multiple isolates of S. cerevisiae that were sampled from immunocompromised humans. The proposed research will improve general understanding of fungal pathogenesis and may identify potential targets for new antifungal drugs.

Public Health Relevance

Fungi are a major source of clinical infections, especially among patients with compromised immune systems. How fungal pathogens colonize human hosts is not fully understood, but is thought to involve the ability to adhere to and penetrate surfaces in the body (generally referred to as 'invasive growth'). We are using natural genetic variation among Saccharomyces cerevisiae isolates to identify the genetic factors that cause fungi to grow invasively.

Agency
National Institute of Health (NIH)
Type
Exploratory/Developmental Grants (R21)
Project #
5R21AI108939-02
Application #
8776919
Study Section
Genetic Variation and Evolution Study Section (GVE)
Program Officer
Duncan, Rory A
Project Start
Project End
Budget Start
Budget End
Support Year
2
Fiscal Year
2015
Total Cost
Indirect Cost
Name
University of Southern California
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
072933393
City
Los Angeles
State
CA
Country
United States
Zip Code
90032
Taylor, Matthew B; Phan, Joann; Lee, Jonathan T et al. (2016) Diverse genetic architectures lead to the same cryptic phenotype in a yeast cross. Nat Commun 7:11669
Linder, Robert A; Seidl, Fabian; Ha, Kimberly et al. (2016) The complex genetic and molecular basis of a model quantitative trait. Mol Biol Cell 27:209-18
Lee, Jonathan T; Taylor, Matthew B; Shen, Amy et al. (2016) Multi-locus Genotypes Underlying Temperature Sensitivity in a Mutationally Induced Trait. PLoS Genet 12:e1005929
Ehrenreich, Ian M; Pfennig, David W (2016) Genetic assimilation: a review of its potential proximate causes and evolutionary consequences. Ann Bot 117:769-79
Taylor, Matthew B; Ehrenreich, Ian M (2015) Higher-order genetic interactions and their contribution to complex traits. Trends Genet 31:34-40
Taylor, Matthew B; Ehrenreich, Ian M (2015) Transcriptional Derepression Uncovers Cryptic Higher-Order Genetic Interactions. PLoS Genet 11:e1005606
Matsui, Takeshi; Linder, Robert; Phan, Joann et al. (2015) Regulatory Rewiring in a Cross Causes Extensive Genetic Heterogeneity. Genetics 201:769-77
Taylor, Matthew B; Ehrenreich, Ian M (2014) Genetic interactions involving five or more genes contribute to a complex trait in yeast. PLoS Genet 10:e1004324
Pfennig, David W; Ehrenreich, Ian M (2014) Towards a gene regulatory network perspective on phenotypic plasticity, genetic accommodation and genetic assimilation. Mol Ecol 23:4438-40