| Cryptococcus neoformans is a free-living basidiomycete fungus that can infect animal hosts. Infection is believed to occur via a pulmonary route by small particles that can lodge deep within the lungs. One candidate particle for this route of infection is the fungal spore. C. neoformans can form spores by undergoing sexual development, a process that requires proper nuclear migration. All organisms require proper nuclear migration to maintain the faithful replication of genetic information during growth and sexual development, and this process has been well studied in ascomycetes. In basidiomycetes, however, the morphological stages of nuclear migration during sexual development are characterized, but little is known at the molecular level. My work in the Hull lab focused on characterizing the previously undefined molecular mechanisms that govern nuclear migration in C. neoformans.;The underlying hypothesis for this work is that C. neoformans will utilize similar cellular machinery that has been identified to be important for nuclear migration in ascomycetes, but will utilize this machinery in distinct ways to achieve the unique patterns of nuclear migration observed in basidiomycetes. To examine this hypothesis, I carried out a candidate gene analysis to identify sequence homologs in C. neoformans of genes known to be important for nuclear migration in other fungi. Four of thirteen identified target genes were deleted in both mating types, and two had observable phenotypes. BIM1 had the most intriguing phenotype and its role in C. neoformans was examined further.;BIM1 was originally identified in a microtubule-binding screen in S. cerevisiae. I identified a C. neoformans BIM1, and constructed deletion strains to characterize the role of BIM1 in C. neoformans. Sexual development assays revealed that bim1Delta x bim1Delta crosses displayed a severe defect in aerial filamentation. Further studies on Bim1 have lead to a model in which BIM1 is required for two distinct, but related functions: maintaining the structural integrity of filaments and facilitating nuclear congression via the microtubule cytoskeleton. These findings support the hypothesis that basidiomycetes have diverged such that selected proteins have acquired additional roles in the distinct developmental pathways that have evolved in this fungal phylum. |
