Phenotypic characterization ofHAM1, a novel mating regulator of the fungal pathogenCryptococcus neoformans

Abstract

AbstractCryptococcus neoformansis a fungal pathogen responsible for >200,000 yearly cases with a mortality as high as 81%. This burden results, in part, from an incomplete understanding of its pathogenesis and ineffective antifungal treatments, hence there is a pressing need to understand the biology and host interactions of this yeast to develop improved treatments. Characterization of genes of unknown function can provide a better understanding of cryptococcal biology and open possible avenues for more effective treatments. Protein palmitoylation is important for cryptococcal virulence, and we previously identified the substrates of its main palmitoyl transferase. One of these substrates was encoded by the uncharacterized gene CNAG_02129. This gene has a partially characterized homolog in the filamentous fungusNeurospora crassanamedHAM13,where it plays a role in proper cellular communication and filament fusion. InCryptococcus, cellular communication is essential during mating, therefore we hypothesized that CNAG_02129, which we namedHAM1,may play a role in mating. We found thatham1Δmutants produce more progeny during mating, filament more robustly, and exhibit competitive fitness defects under mating and non-mating conditions. Consistent with previous reports that have linked changes in mating to altered virulence capacity, we found several differences with the major virulence factor, the polysaccharide capsule. We observed thatham1Δmutants have decreased capsule attachment and transfer but exhibit higher amounts of exopolysaccharide shedding and biofilm production. Understanding the connection between mating and virulence inC. neoformansmay open new avenues of investigation into ways to improve the treatment of this disease.ImportanceFungal mating is a vital part of the lifecycle of the pathogenic yeastCryptococcus neoformans. More than just ensuring the propagation of the species, mating allows for genetic diversity as well as the generation of infectious particles that can invade mammalian hosts. Despite its importance in the biology of this pathogen, we still do not know all of the major players regulating the mating process and if they are involved or impact its pathogenesis. Here we identified a novel negative regulator of mating that also affect certain characteristics know to be important for virulence. This gene, which we callHAM1, is widely conserved across the cryptococcal family as well as in many pathogenic fungal species. This study will open new avenues of exploration regarding the function of uncharacterized but conserved genes in a variety of pathogenic fungal species, and specifically in serotype A ofC. neoformans.