Cryptococcus neoformans Titanisation is an inducible and regulated morphotype underlying pathogenesis and drug resistance

Changes in fungal cell shape in response to environmental stimuli drive pathogenesis and niche adaptation. The basidiomycete Cryptococcus neoformans undergoes an unusual morphogenetic transition in the host lung from haploid yeast to large, highly polyploid cells termed Titan cells. Titan cells influence fungal interaction with host cells, including through increased drug resistance, altered cell size, and altered Pathogen Associated Molecular Pattern exposure. We recently described an in vitro induction system for these host-specific cells that provides new insight into the molecular mechanisms underlying Titan cell biology. In vitro Titan cells exhibit all the properties of in vivo-generated Titan cells, the current gold standard, including altered capsule, cell wall, size, high mother cell ploidy, and aneuploid progeny. In the current work, we investigate the role of Titanisation in transient antifungal resistance among clinical and environmental isolates. Specifically, we test the hypothesis that Titanisation is an intrinsic property of Cryptococcus neoformans var. grubbii isolates underlying pathogenesis and fluconazole resistance. We show that there is wide variation in the Titanisation capacity of C. neoformans var. grubbii isolates and link this to host response. Further, we test the role of Titanisation in drug resistance and virulence (capsule, melanin, thermotolerance) via experimental in vitro evolution. Finally, we begin to dissect the molecular mechanisms underlying Titanisation by investigating the role of the master regulator of pathogenesis, Usv101, in the yeast-to-Titan transition.