Filamentation Involves Two Overlapping, but Distinct, Programs of Filamentation in the Pathogenic Fungus Candida albicans

The ability of the human pathogenic fungus Candida albicans to switch between yeast-like and filamentous forms of growth has long been linked to pathogenesis. Numerous environmental conditions, including growth at high temperatures, nutrient limitation, and exposure to serum, can trigger this morphological switch and are frequently used in in vitro models to identify genes with roles in filamentation. Previous work has suggested that differences exist between the various in vitro models both in the genetic requirements for filamentation and transcriptional responses to distinct filamentation-inducing media, but these differences had not been analyzed in detail. We compared 10 in vitro models for filamentation and found broad genetic and transcriptomic differences between model systems. The comparative analysis enabled the discovery of novel media-independent genetic requirements for filamentation as well as a core filamentation transcriptional profile. Our data also suggest that the physical environment drives distinct programs of filamentation in C. albicans, which has significant implications for filamentation in vivo

Morphology and Virulence in C. albicans

Candida albicans is a fungus capable of causing mucosal infections and life threatening disseminated invasive infections in susceptible individuals. Systemic infections with C. albicans have a 30-50% mortality rate depending on the underlying condition of the patient. The ability of C. albicans to switch between yeast and hyphal growth stages is vital for its ability to cause disseminated infection. EFG1 and HWP1 are key players in the filamentation pathway of C. albicans. EFG1 encodes a transcription factor that promotes filamentation and regulates filament-specific gene expression whereas HWP1 works as a filament-specific adhesion important for developmental regulation. Our understanding of filamentation, as with the majority of C. albicans research, has been almost exclusively carried out in the type strain, SC5314. However, wide variation exists between wild C. albicans strains that likely contribute to distinct pathogenic and antifungal sensitivity profiles. Indeed, critical mutations in EFG1 have been identified in the avirulent and nonfilamentous strain P94015. This study works to describe the morphology of 20 common C. albicans clinical strains and uses comparative analysis to determine key mutations in filamentation genes. EFG1 and HWP1 were selected as having potentially nonfunctional mutant versions of their genes in nonfilamentous strains

Analysis of gene expression in filamentous cells of Candida albicans grown on agar plates

Candida albicans (C. albicans) is a commensal organism of the human gastrointestinal and genitourinary tracts. C. albicans is also a major human pathogen, causing disease ranging from cutaneous infections to lethal systemic disease. The ability of this fungus to switch between yeast and filamentous forms of growth has long been linked to its pathogenesis. Filamentation can be induced by a variety of distinct environmental cues and can occur in either liquid or solid media. While some evidence suggests that there are differences between filamentation in solid and liquid media, gene expression analysis of filamentation in C. albicans has focused strictly on cells grown in liquid media. We have developed a method for analyzing gene expression of filamentous cells grown on solid induction media at early stages of filamentation, establishing cell plating densities, ideal collection times, and collection techniques. We have also demonstrated the utility of the approach not only in qRT-PCR assays, but high-throughput RNAseq assays as well. These assays will allow for comparison studies of C. albicans filamentation initiation in solid and liquid media