Using Genetics and Genomics to Dissect Coccidioides Spherulation

Investigator: Anita Sil, MD, PhD
Sponsor: NIH National Institute of Allergy and Infectious Disease

Location(s): United States


Coccidioides spp. are primary fungal pathogens that cause striking morbidity in healthy individuals in endemic areas. The proposed characterization of Coccidioides genes that affect the differentiation of the fungus into the pathogenic host form is critical for the development of new diagnostics and anti-fungal therapeutics to reduce the morbidity and mortality of infection.

Coccidioides spp. are major fungal pathogens endemic to Southern California, Arizona, Central America, and South America. In recent years, the incidence of coccidioidomycosis has continued to rise, resulting in hospitalization costs greater than $2 billion. Coccidioides infects, colonizes, and kills immunocompetent individuals when they inhale spores from soils. The ability of Coccidioides to cause disease depends on an elaborate developmental transition from saprophytic soil form to host form, which can be triggered in the laboratory by incubating fungal spores at elevated temperature and carbon dioxide conditions. Specifically, the hyphal form of the organism produces arthroconidia, which disperse easily and can be inhaled by mammalian hosts. Once inside the host lung, arthroconidia germinate, enlarge, and undergo nuclear division and segmentation to form large spherules filled with vegetative endospores. Rupture of the spherules allows release of endospores and dissemination of the fungus to other sites. Given the critical role of spherule development in disease progression, the focus of our proposal is the genomic and genetic dissection of this process, also known as spherulation. We will take advantage of two complementary approaches, high-resolution transcriptomics and genome-wide association studies (GWAS), to perform an innovative molecular dissection of spherulation in Coccidioides. Principal Investigator Sil has extensive experience working with Biosafety Level 3 pathogens and is well equipped to apply her expertise in transcriptional profiling of thermally dimorphic fungi to Coccidioides. PI Brem is an evolutionary and statistical geneticist with a track record of applying GWAS to fungi to identify genes that play a critical role in biologically important traits. Together, we will harness the tools of systems genetics to discover new gene functions on a genomic scale in Coccidioides. In Aim 1, we will identify a core set of spherulation-enriched transcripts by performing a high-resolution time-course analysis of the transcriptome of three Coccidioides strains undergoing spherulation. In Aim 2, we will apply GWAS analysis to identify genes that underlie variance of spherulation phenotypes, using 150 clinical isolates of Coccidioides posadasii. Taken together, these approaches will provide a rich dataset of spherulation-associated genes that will allow us to begin to elucidate critical molecular events that take place during spherule development in the context of infection.