Rajendra Upadhya

My research focuses on fungal disease and virulence pathways in the model yeast Cryptococcus neoformans. During my initial training in Dr. Ian Willis' lab at the Albert Einstein College of Medicine, NY, I discovered a novel yeast protein that is a major regulator of RNA polymerase III transcription and consequently affects cell growth and proliferation. Later, I used this expertise to functionally characterize the genome of Toxoplasma gondii, where I created a number of genome-based methodologies to define the Toxoplasma genomeWe are primarily interested in the characterization of fungal cell walls and how they influence fungal virulence and disease. Fungal cell wall biosynthesis and architecture are good targets for creating new antifungals since the cell wall is important for the yeast but missing in the host. We revealed that cell wall chitosan is necessary for maintaining cell wall integrity in Cryptococcus and is also important for fungal virulence by applying several genomic, molecular biology, and cell biology approaches to the Cryptococcus genome.  Chitosan deficient mutants are avirulent in mice due to their good clearance from the host. This efficient clearance from the host is accompanied by the activation of a protective immunological response, which protects the mice from infection with a virulent wild-type strain later on. As a result, one of our primary goals is to better understand the biogenesis of chitosan in C. neoformans and C. gattii. We discovered that C. neoformans and C. gattii have different mechanisms for controlling chitosan synthesis. Cda1 and Cda2 are both engaged in fugal pathogenesis in C. neoformans, however Cda3 is the sole one implicated in C. gattii virulence. We have observed that different growth circumstances influence the amount of chitosan in the cell wall. In mice, these chitosan-deficient wild-type strains induced protective immunity against C. neoformans infection. Interestingly, the nature of the host immune response varied considerably between chitosan deficient mutants and wild-type that have been grown under different conditions to alter their chitosan levels. These mutants and wild-type strains with varied levels of chitosan allow us to explore the mechanisms of protective immunity evoked by C. neoformans cda1Δ2Δ3Δ.