Jon P. Woods, M.D., Ph.D.

Department of Medical Microbiology and Immunology

University of Wisconsin, Madison

Histoplasma capsulatum (Hc) is a thermally dimorphic fungus that is a significant cause of respiratory and systemic disease in humans and other mammals. Its clinical importance has increased along with the growing immunodeficiency of the human population associated with HIV/AIDS, cancer and its treatments, immunosuppressive therapy for transplants and inflammatory syndromes, aging, and hospitalization. Hc lives saprobically in the soil as a mold, which is a successful member of a competitive polymicrobial ecosystem. The host-adapted parasitic morphotype is a budding yeast which is a facultative intracellular pathogen of macrophages. This microbe faces a variety of different environments and must survive under harsh conditions or modulate its microenvironment to achieve success as a pathogen in a professionally antimicrobial host cell. We have used several molecular techniques to identify fungal genes that are differentially expressed during infection of host macrophages and/or mice, when Hc is subjected to a complex range of environmental conditions. These methods have included in vivo expression technology (IVET), differential display, and cDNA representational difference analysis (RDA). Such approaches do not provide exhaustive genomic surveys in this eukaryotic microorganism, but we have identified several interesting genes. One differentially expressed gene encodes a small transcript in antisense orientation to a homolog of a negative regulatory protein kinase gene from another fungus, which is important in mating and starvation responses. We are examining both upstream and downstream aspects of this potential regulatory system in Hc, such as the specific environmental stimuli influencing expression of the antisense transcript, whether expression of the antisense transcript affects sense transcript expression, whether the sense transcript encodes a protein kinase functional in Hc, what the downstream targets of the putative kinase are, and the role of this locus in Hc biology and pathogenesis. A second target gene is expressed specifically in the yeast morphotype and not in mold, and the predicted encoded protein displays significant sequence homology with epidermal growth factor (EGF) domains found in a variety of proteins from other organisms, that typically function in attachment or intercellular signaling. Finally, we have preliminarily identified homologs of genes in other organisms that are involved in iron uptake. This finding interfaces with our separate interest in iron acquistion and fungal responses to