Halliwell Samantha C, Smith Matthew C A, Muston Philippa, Holland Sara L, Avery Simon V
School of Biology, University of Nottingham, University Park, Nottingham, United Kingdom.
Eukaryot Cell. 2012 Feb;11(2):141-50. doi: 10.1128/EC.05232-11. Epub 2011 Dec 2.
We investigated the relevance of gene expression heterogeneity to virulence properties of a major fungal pathogen, Candida glabrata. The organism's key virulence-associated factors include glycosylphosphatidylinositol-anchored adhesins, encoded subtelomerically by the EPA gene family. Individual-cell analyses of expression revealed very striking heterogeneity for Epa1, an adhesin that mediates ∼95% of adherence to epithelial cells in vitro. The heterogeneity in Epa1 was markedly greater than that known for other yeast genes. Sorted cells expressing high or low levels of Epa1 exhibited high and low adherence to epithelial cells, indicating a link between gene expression noise and potential virulence. The phenotypes of sorted subpopulations reverted to mixed phenotypes within a few generations. Variation in single-cell Epa1 protein and mRNA levels was correlated, consistent with transcriptional regulation of heterogeneity. Sir-dependent transcriptional silencing was the primary mechanism driving heterogeneous Epa1 expression in C. glabrata BG2, but not in CBS138 (ATCC 2001). Inefficient silencing in the latter strain was not due to a difference in EPA1 sequence or (sub)telomere length and was overcome by ectopic SIR3 expression. Moreover, differences between strains in the silencing dependence of EPA1 expression were evident across a range of clinical isolates, with heterogeneity being the greatest in strains where EPA1 was subject to silencing. The study shows how heterogeneity can impact the virulence-related properties of C. glabrata cell populations, with potential implications for microbial pathogenesis more broadly.
我们研究了基因表达异质性与主要真菌病原体光滑念珠菌毒力特性的相关性。该生物体的关键毒力相关因子包括糖基磷脂酰肌醇锚定黏附素，由EPA基因家族在亚端粒区域编码。对表达的单细胞分析显示，Epa1存在非常显著的异质性，Epa1是一种在体外介导约95%的上皮细胞黏附的黏附素。Epa1的异质性明显大于其他酵母基因。分选后表达高水平或低水平Epa1的细胞对上皮细胞的黏附能力分别为高和低，这表明基因表达噪声与潜在毒力之间存在联系。分选后的亚群表型在几代内恢复为混合表型。单细胞Epa1蛋白和mRNA水平的变化是相关的，这与异质性的转录调控一致。在光滑念珠菌BG2中，Sir依赖性转录沉默是驱动Epa1表达异质性的主要机制，但在CBS138（ATCC 2001）中并非如此。后一种菌株中沉默效率低下并非由于EPA1序列或（亚）端粒长度的差异，异位表达SIR3可克服这一问题。此外，在一系列临床分离株中，EPA1表达对沉默的依赖性在不同菌株之间存在明显差异，在EPA1受到沉默作用的菌株中异质性最大。该研究表明了异质性如何影响光滑念珠菌细胞群体的毒力相关特性，这对更广泛的微生物发病机制可能具有潜在影响。
