Biomolecular Chemistry

Faculty Advisor: Christina Hull

Cryptococcus neoformans is a clinically important fungal pathogen that has been utilized extensively to study molecular mechanisms that contribute to fungal pathogenesis. Immunocompromised patients, such as those with AIDS are most susceptible to infection by C. neoformans. In these patients, dissemination of C. neoformans from the lungs to the central nervous system can result in cryptococcal meningoencephalitis, a life-threatening disease. In healthy individuals, the infection is often asymptomatic and self-resolving.

The focus of my research in Dr. Christina Hull’s lab is to investigate the role of key regulators of C. neoformans sexual development in the production of spores, which are believed to be the infectious propagule. The most common infectious propagules produced by the pathogenic fungi are spores, which can result from the process of sexual development.   During sexual development, haploid cells of opposite mating type (a and a) fuse and form a binucleate cell that undergoes a transition from yeast-form to filamentous growth. The resulting filaments (known as dikaryons) ultimately differentiate into a specialized structure in which meiosis and spore formation occurs.

Sexual development in C. neoformans is regulated by the S e x I nducer genes SXI a and SXI2a, which are specific to a and a cells, respectively. Mating studies with sxi1aD and sxiaD mutant strains indicate that Sxi1a and Sxi2a are dispensable in haploid cells but are required for establishment of the dikaryon. The mechanisms by which Sxi1a and Sxi2a regulate sexual development are unknown. My goal is to use microarray analysis to elucidate the regulatory circuitry controlled by Sxi1a and Sxi2a. Whole genome C. neoformans spotted microarrays consisting of 70-mer oligos that represent 7738 predicted open reading frames will be used. We have established parameters that define early, mid, and late stages of sexual development. The rationale for looking at different stages within the developmental process is that Sxi1a and Sxi2a may have different roles in regulating sexual development relative to the stage of the developmental process. We anticipate that these experiments will elucidate the identity of constituents of the regulatory circuitry that are controlled by Sxi1a and Sxi2a. Preliminary results from a pilot microarray experiment have identified genes that were previously shown to be involved in regulating sexual development. Exploration of the regulatory circuitry that controls sexual development will provide insight into mechanisms that facilitate spore formation, which in turn is key to understanding the relationship between the biology of C. neoformans and pathogenesis.

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