Tamara L. Doering, M.D., Ph.D.

DEPARTMENT OF Molecular Microbiology
Keywords: pathogenic fungi, microbial pathogenesis, yeast, RNA interference, carbohydrate, biochemistry

Cryptococcus neoformans is a pathogenic fungus responsible for serious opportunistic infections in immunocompromised individuals. My lab studies unique aspects of cryptococcal biology that are of biological interest and may suggest targets for badly needed antifungal chemotherapy.

The main virulence factor of C. neoformans is its extensive polysaccharide capsule, a unique protective structure that is required for virulence. The chemical structure of the capsule is known, but almost nothing is known about its synthesis and assembly. We are taking several approaches to understanding capsule biosynthesis, and to investigating interactions of this pathogen with host cells.

One approach is biochemical. We develop assays for enzymes involved in capsule construction in order to purify and study them or to identify them genetically. We are also investigating the synthesis and intracellular transport of nucleotide sugar precursors that are required for the sugar transferase reactions that link capsule components. Another approach is genetic: generating and studying mutants with defects in capsule synthesis. In these studies we can take advantage of the well-sequenced cryptococcal genome for reverse genetic studies. (We also exploit this sequence information by using RNA interference to specifically down-regulate gene expression.) Taking a forward genetic strategy, we can also screen for mutants of interest after mutagenesis or exposure of cells to an RNA interference library.

Other experiments employ methods of cell biology to address the question of how new capsular material is incorporated into the existing structure, how capsule matures, and how capsular material associates with the cell. We hope in the future to address the molecular mechanisms of these fascinating processes. These and other studies in the lab will be aided by our recent development of RNA interference in this system and a 70-mer oligonucleotide microarray for studies of C. neoformans gene expression.