Virulence-related surface glycoproteins in the yeast pathogen Candida glabrata are encoded in subtelomeric clusters and subject to RAP1- and SIR-dependent transcriptional silencing

Abstract

Candida glabrata is an important opportunistic pathogen causing both mucosal and bloodstream infections. C. glabrata is able to adhere avidly to mammalian cells, an interaction that depends on the Epa1p lectin. EPA1 is shown here to be a member of a larger family of highly related genes encoded in subtelomeric clusters. Subtelomeric clustering of large families of surface glycoprotein-encoding genes is a hallmark of several pathogens, including Plasmodium, Trypanosoma, and Pneumocystis. In these other pathogens, a single surface glycoprotein is expressed, whereas other genes in the family are transcriptionally silent. Similarly, whereas EPA1 is expressed in vitro, EPA2-5 are transcriptionally repressed. This repression is shown to be due to regional silencing of the subtelomeric loci. In Saccharomyces cerevisiae, subtelomeric silencing is initiated by Rap1p binding to the telomeric repeats and subsequent recruitment of the Sir complex by protein-protein interaction. We demonstrate here that silencing of the subtelomeric EPA loci also depends on functional Sir3p and Rap1p. This identification and analysis of the EPA gene family provides a compelling example in an ascomycete of chromatin-based silencing of natural subtelomeric genes and provides for the first time in a pathogen, molecular insight into the transcriptional silencing of large subtelomeric gene families.[Keywords: Yeast; subtelomeric; GPI; virulence; fungal pathogen; adhesin] Supplemental material is available at http://www.genesdev.org.

The Chromatin and Transcriptional Landscape of NativeSaccharomyces cerevisiaeTelomeres and Subtelomeric Domains

“…But why would a cell want to simply lower the expression of genes in this way, as opposed to simply having a weaker promoter for such genes? Perhaps subtelomeric genes regulated by Sir proteins in S. cereivisiae, like those in C. glabrata (De Las Peñas et al 2003;Domergue et al 2005;Ma et al 2009), are involved in regulating the transcription of genes that are necessary only under certain conditions. In support of this model, seven genes encoding metabolic enzymes increased in expression in all three sir mutants: CHA1, AAD15, IMD2, FDH1, THI5, VBA3, and PAU4.…”

“…This selective expression of one antigen over all the other antigen genes is maintained by the epigenetic silencing of all var copies except the expressed one (Tonkin et al 2009;Guizetti and Scherf 2013). Similarly, in Candida glabrata, the EPA adhesion genes essential for colonization of the host urinary tract are located in subtelomeric regions, and their expression is regulated by a Sir-protein-based silencing mechanism that is responsive to the differences in niacin concentration in the bloodstream vs. the urinary track (De Las Peñas et al 2003;Domergue et al 2005). In S. cerevisiae, genes encoding cell wall components and genes required for the metabolism of certain nutrients tend to be located in subtelomeric regions and are expressed specifically under certain stressful conditions (Ai et al 2002).…”

Antigenic variation inPlasmodium falciparumis associated with movement ofvarloci between subnuclear locations

“…The subtelomeric grouping of virulence factors in such widely divergent groups suggests a convergent evolution of a feature whose significance is still puzzling. Suggested functions include control of antigen expression through telomeric silencing effects (1), expansion of virulence factor repertoire through duplication, and gene conversion after recombination between heterogeneously paired telomeres (2). In some of these organisms, subtelomerically encoded antigens are expressed in a mutually exclusive manner, with only a single representative expressed in any given individual.…”

Avoiding the Ends: Internal Epitope Tagging of Proteins Using Transposon Tn7

“…The demonstrate the generality of the tagging methodology, we used the same approach to mutagenize the SIR3 gene of Candida glabrata, which is required for silencing of sub-telomeric regions of the C. glabrata genome (De Las Penas et al 2003). Schematic diagrams of the Sir3 Gateway constructs are shown in Figure S2.…”

“…To demonstrate the generality of the method, we mutagenized a second gene, SIR3 from Candida glabrata. SIR3 is not an essential gene but is absolutely required for subtelomeric transcriptional silencing in C. glabrata (De Las Penas et al 2003). We used the transposon-based method to internally tag CgSIR3 with four different protein tags, including the fluorescent proteins GFP and mEOS2.…”