A Family of Secretory Proteins Is Associated with Different Morphotypes in Cryptococcus neoformans

Abstract

Cryptococcus neoformans, an opportunistic human fungal pathogen, can undergo a yeast-to-hypha transition in response to environmental cues. This morphological transition is associated with changes in the expression of cell surface proteins. The Cryptococcus cell surface and secreted protein Cfl1 was the first identified adhesin in the Basidiomycota. Cfl1 has been shown to regulate morphology, biofilm formation, and intercellular communication. Four additional homologs of CFL1 are harbored by the Cryptococcus genome: DHA1, DHA2, CPL1, and CFL105. The common features of this gene family are the conserved C-terminal SIGC domain and the presence of an N-terminal signal peptide. We found that all these Cfl1 homolog proteins are indeed secreted extracellularly. Interestingly, some of these secretory proteins display cell type-specific expression patterns: Cfl1 is hypha specific, Dha2 is yeast specific, and Dha1 (delayed hypersensitivity antigen 1) is expressed in all cell types but is particularly enriched at basidia. Interestingly, Dha1 is induced by copper limitation and suppressed by excessive copper in the medium. This study further attests to the physiological heterogeneity of the Cryptococcus mating colony, which is composed of cells with heterogeneous morphotypes. The differential expression of these secretory proteins contributes to heterogeneity, which is beneficial for the fungus to adapt to changing environments. IMPORTANCE Heterogeneity in physiology and morphology is an important bethedging strategy for nonmobile microbes such as fungi to adapt to unpredictable environmental changes. Cryptococcus neoformans, a ubiquitous basidiomycetous fungus, is known to switch from the yeast form to the hypha form during sexual development. However, in a mating colony, only a subset of yeast cells switch to hyphae, and only a fraction of the hyphal subpopulation will develop into fruiting bodies, where meiosis and sporulation occur. Here, we investigated a basidiomycete-specific secretory protein family. We found that some of these proteins are cell type specific, thus contributing to the heterogeneity of a mating colony. Our study also demonstrates the importance of examining the protein expression pattern at the individual-cell level in addition to population gene expression profiling for the investigation of a heterogeneous community.KEYWORDS dimorphism, morphogenesis, morphotype, secretory proteins, sexual reproduction A dhesins are cell surface proteins that are required for microbes to adhere to the substrate as well as to other cells (1-3). Adhesins in pathogenic fungi play a role in a wide variety of functions, such as host-pathogen interactions, biofilm formation, filamentation, and mating (2, 4, 5). The expression of adhesins is responsive to environmental cues (1). For instance, adhesins of Saccharomyces (Flo proteins) are activated during nitrogen or carbon source starvation, and they are required for cell-cell adherence and cell-substrate adherence (6-8). Many fungal adhesins show a cell type-spec...

Elucidation of the determinant for orchestration of solo unisexual cycle in an important human fungal pathogen

“…To this end, the α-null mutant was quantitatively or semi-quantitatively examined for its ability to undergo sequential unisexual differentiation processes (Figures S1, and 1D-1H). Our results demonstrated that the removal of α identity genes did not markedly impair unisexual filamentation and the expression level of mCherry-tagged Cfl1 in unisexual communities, which is an indicator protein for filamentous development reported previously (Figure 1D) [35]. Similarly, in the α-null mutant, no detectable defect was identified during basidial maturation, based on the basidial maturation score (BMS) assay that allow us to quantitatively evaluate basidial maturation (Figure 1E) [16].…”

Pheromone independent unisexual development in Cryptococcus neoformans

“…The heterogeneity in the sexual mode in the community might reflect or be enforced by the stochastic expression of Mat2 within the population. Consistent with this idea, we noticed that not all cells responded to the calling of pheromone even under a strong mating-inducing condition [40]. Given that Cryptococcus is a ubiquitous environmental fungus and an opportunistic pathogen to a wide range of hosts, this fungus might have developed various tactics to propagate sexually under different conditions rather than the risky sole dependence on the pheromone pathway and the rare presence of a compatible mating partner.…”

Plant Homeodomain Genes Play Important Roles in Cryptococcal Yeast-Hypha Transition

“…Cfl1 is a hypha-specific protein downstream of Znf2, and the transcript level of CFL1 correlates with filamentation (6,11,12,43). In the bye1Δ mutant, the transcript level of CFL1 was approximately 16-fold higher than that of the wild type (Fig.…”