Candida albicans, a commensal organism and a pathogen of humans, can switch stochastically between a white phase and an opaque phase without an intermediate phase. The white and opaque phases have distinct cell shapes and gene expression programs. Once switched, each phase is stable for many cell divisions. White-opaque switching is under a1-␣2 repression and therefore only happens in a or ␣ cells. Mechanisms that control the switching are unknown. Here, we identify Wor1 (white-opaque regulator 1) as a master regulator of white-opaque switching. The deletion of WOR1 blocks opaque cell formation. The ectopic expression of WOR1 converts all cells to stable opaque cells in a or ␣ cells. In addition, the ectopic expression of WOR1 in a͞␣ cells is sufficient to induce opaque cell formation. Importantly, WOR1 expression displays an all-or-none pattern. It is undetectable in white cells, and it is highly expressed in opaque cells. The ectopic expression of Wor1 induces the transcription of WOR1 from the WOR1 locus, which correlates with the switch to opaque phase. We present genetic evidence for feedback regulation of WOR1 transcription. The feedback regulation explains the bistable and stochastic nature of white-opaque switching.feedback regulation ͉ a1-␣2 repression C andida albicans is associated with humans both as a harmless commensal organism and a pathogen. In most humans, it is a normal part of the microflora in the gastrointestinal tract and in other parts of the body. However, when the host immune system is compromised, it can cause mucosal infections and life-threatening disseminated infections. The ability of C. albicans to undergo a yeast-to-hypha transition and high-frequency phenotypic switching provides the organism with a high degree of phenotypic diversity and the adaptability that is necessary to survive in different host environments (1). One of the high-frequency switching systems is white-opaque switching. White-opaque switching was first identified in a clinical isolate, WO-1, in which cells switched spontaneously between white and opaque phases (2). White phase cells appear round and form hemispherical, white colonies on solid agar, and opaque phase cells are elongated in cell shape with pimples on the surface and form flat, opaque colonies. Several features of white-opaque switching are particularly interesting (1, 3): (i) the transition involves only two phases, and there is not an intermediate phase, (ii) the transition is stochastic, generating heterogeneity in a cell population, and (iii) the phase is stable for many cell divisions, with daughter cells inheriting the phase of their mother cells. White-opaque switching occurs at a frequency of 10 Ϫ4 to 10 Ϫ5 per cell division, and opaque-white switching happens at a frequency of 5 ϫ 10 Ϫ4 per cell generation (4). Opaque cells are stable at 25°C. Upon shifting the temperature to 37°C, they switch en masse to white cells (5).White-opaque switching is under a1-␣2 repression (6). In C. albicans, cell type is determined by the MTL (mating type-li...

The transcription factor Flo8 is essential for filamentous growth in Saccharomyces cerevisiae and is regulated under the cAMP/protein kinase A (PKA) pathway. To determine whether a similar pathway/regulation exists in Candida albicans, we have cloned C. albicans FLO8 by its ability to complement S. cerevisiae flo8. Deleting FLO8 in C. albicans blocked hyphal development and hypha-specific gene expression. The flo8/flo8 mutant is avirulent in a mouse model of systemic infection. Genome-wide transcription profiling of efg1/efg1 and flo8/flo8 using a C. albicans DNA microarray suggests that Flo8 controls subsets of Efg1-regulated genes. Most of these genes are hypha specific, including HGC1 and IHD1. We also show that Flo8 interacts with Efg1 in yeast and hyphal cells by in vivo immunoprecipitation. Similar to efg1/efg1, flo8/flo8 and cdc35/cdc35 show enhanced hyphal growth under an embedded growth condition. Our results suggest that Flo8 may function downstream of the cAMP/PKA pathway, and together with Efg1, regulates the expression of hypha-specific genes and genes that are important for the virulence of C. albicans.

SummaryCandida albicans had been thought to lack a mating process until the recent discovery of a mating typelike locus and mating between MTLa and MTL a a a a strains. To elucidate the molecular mechanisms that regulate mating in C. albicans , we examined the function of Cph1 and its upstream mitogen-activated protein (MAP) kinase pathway in mating, as they are homologues of the pheromone-responsive MAP kinase pathway in Saccharomyces cerevisiae . We found that overexpressing CPH1 in MTLa , but not in MTLa/ a a a a strains, induced the transcription of orthologues of S. cerevisiae pheromone-induced genes and also increased mating efficiency. Furthermore, cph1 and hst7 mutants were completely defective in mating, and cst20 and cek1 mutants showed reduced mating efficiency, as in S. cerevisiae . The partial mating defect in cek1 results from the presence of a functionally redundant MAP kinase, Cek2. CEK2 complemented the mating defect of a fus3 kss1 mutant of S. cerevisiae and was expressed only in MTLa or MTL a a a a , but not in MTLa/ a a a a cell types. Moreover, a cek1 cek2 double mutant was completely defective in mating. Our data suggest that the conserved MAP kinase pathway regulates mating in C. albicans . We also observed that C. albicans mating efficiency was greatly affected by medium composition, indicating the potential involvement of nutrient-sensing pathways in mating in addition to the MAP kinase pathway.

Highlights d Alterations in lung microbiota critically promote pulmonary fibrosis d Lung-microbiota-driven IL-17B is critical for pulmonary fibrosis d Three OMV-producing pulmonary microbes are identified to promote lung fibrosis d The microbe-derived OMVs induce IL-17B production through TLR-Myd88 signaling

Efg1 is essential for hyphal development and virulence in the human pathogenic fungus Candida albicans. How Efg1 regulates gene expression is unknown. Here, we show that Efg1 interacts with components of the nucleosome acetyltransferase of H4 (NuA4) histone acetyltransferase (HAT) complex in both yeast and hyphal cells. Deleting YNG2, a subunit of the NuA4 HAT module, results in a significant decrease in the acetylation level of nucleosomal H4 and a profound defect in hyphal development, as well as a defect in the expression of hypha-specific genes. Using chromatin immunoprecipitation, Efg1 and the NuA4 complex are found at the UAS regions of hypha-specific genes in both yeast and hyphal cells, and Efg1 is required for the recruitment of NuA4. Nucleosomal H4 acetylation at the promoters peaks during initial hyphal induction in an Efg1-dependent manner. We also find that Efg1 bound to the promoters of hypha-specific genes is critical for recruitment of the Swi/Snf chromatin remodeling complex during hyphal induction. Our data show that the recruitment of the NuA4 complex by Efg1 to the promoters of hypha-specific genes is required for nucleosomal H4 acetylation at the promoters during hyphal induction and for subsequent binding of Swi/Snf and transcriptional activation. INTRODUCTIONCandida albicans has emerged as one of the most prevalent opportunistic fungal pathogens in humans. It causes mucosal as well as systemic candidiasis, especially in immunocompromised patients. C. albicans can undergo reversible morphogenetic transitions between budding yeast, pseudohyphal, and hyphal growth forms. Its unique ability to switch from yeast to hyphal growth in response to various signals is essential for its pathogenicity.Central to the yeast-to-hypha transition is the transcription factor Efg1, a member of the Asm1p, Phd1p, Sok2p, Efg1p, and StuAp (APSES) family of fungal proteins that regulate cellular differentiation in ascomycetes. Members of this family share a conserved DNA binding domain. Efg1 is an essential regulator of hyphal development, chlamydospore formation, and white-opaque phenotypic switching in C. albicans (Lo et al., 1997;Stoldt et al., 1997;Sonneborn et al., 1999;Srikantha et al., 2000;Zordan et al., 2007). It is suggested to function downstream of the cAMP/protein kinase A (PKA) pathway in hyphal development (Sonneborn et al., 2000;Bockmuhl and Ernst, 2001), and both Efg1 and PKA are required for the induction of hypha-specific genes. However, Efg1 also regulates other genes that are not modulated by the cAMP pathway (Sohn et al., 2003;Doedt et al., 2004;Harcus et al., 2004;Setiadi et al., 2006). Numerous in vitro and in vivo studies with efg1 mutants have demonstrated that Efg1 is important for C. albicans virulence and for the interactions of C. albicans with endothelial and epithelia cells, as well as biofilm formation and catheter infection (Lo et al., 1997;Phan et al., 2000;Dieterich et al., 2002;Lewis et al., 2002;Ramage et al., 2002;Garcia-Sanchez et al., 2004). Despite its importance, molecula...

SUMMARYFungal infection stimulates the canonical C-type lectin receptors (CLRs) signaling pathway via Syk activation. Here we show that SHP-2 plays a crucial role in mediating CLRs-induced Syk activation. Genetic ablation of Shp-2 (Ptpn11) in dendritic cells (DCs) and macrophages impaired Syk-mediated signaling and abrogated pro-inflammatory gene expression following fungal stimulation. Mechanistically, SHP-2 operates as a scaffold facilitating the recruitment of Syk to dectin-1 or FcRγ, through its N-SH2 domain and a previously unrecognized C-terminal ITAM motif. We demonstrate that DC-derived SHP-2 is crucial for the induction of IL-1β, IL-6 and IL-23, and anti-fungal TH17 cell responses to control Candida albicans infection. Together, these data reveal a mechanism by which SHP-2 mediates Syk activation in response to fungal infections

a b s t r a c tA novel cyclin, CCNY, was identified as a PFTK1 interacting protein in a yeast two-hybrid screen. The cyclin box in CCNY and the PFTAIRE motif in PFTK1 are both required for the interaction which was confirmed by in vivo and in vitro assays. Two transcripts (4 and 2 kb), of CCNY were detected by Northern blot analysis and CCNY was enriched at the plasma membrane due to an N-terminal myristoylation signal. We propose that binding of CCNY to PFTK1 enhances PFTK1 kinase activity and changes its intracellular location.

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