F-024. A Novel Gene Is Correlated with Virulence in Cryptococcus neoformans

E. E. McClelland, A. Casadevall;
Albert Einstein Coll. of Med., Bronx, NY.

Background: Cryptococcus neoformans (Cn) is a pathogenic yeast that is the cause of cryptococcosis, a life-threatening fungal disease that often affects the central nervous system. The ability of Cn to infect a broad range of hosts, including immunocompetent individuals, makes the study of its virulence mechanisms crucial for much needed therapies. There are currently no data as to the type of mechanism that Cn may use to evolve virulence. Identification of such mechanisms could expose new virulence factors and important characteristics of Cn pathogenesis. One approach to studying the evolution of virulence experimentally is to serially passage a microbe in a host and then compare the pre- and post-passaged lines to identify traits that change virulence. Methods: A strain of Cn was passaged in mice resulting in passaged Cn strains with increased virulence in mice. Microarray analysis was used to compare two Cn passaged strains and the pre-passage strain. A novel gene was identified, sequenced in all passaged strains and the gene expression levels were evaluated both in vitro and in vivo using real time PCR. Results: Microarray analysis and real time-PCR identified a novel candidate gene (176-1) with an unknown function whose expression is negatively correlated with virulence. No sequence differences were seen when 176-1 was sequenced in all the passaged strains. 176-1 is 342 bp in length, is predicted to contain 3 exons and 2 introns and encode a 75 amino acid protein. It has similarly unknown homologs in a variety of human and plant pathogenic fungi. No known protein domains or homologous gene families exist for 176-1. Gene expression levels of 176-1 from real time PCR data are down-regulated both in vitro and in vivo in all passaged strains, with a significant correlation with virulence seen in vivo in the liver. Conclusions: The identification of a novel virulence factor involved in Cn virulence has important implications in the treatment of patients with cryptococcosis. The characterization of 176-1 may help determine how Cn has evolved virulence and could potentially lead to a fungal-specific drug target.