Data from: Decrease in ribosomal RNA in Candida albicans induced by serum exposure

Candida albicans is an important polymorphic human pathogen. It can switch from a unicellular yeast form to germinating hypha, which may play a role in making it the successful pathogen it is. This hyphal transformation can be triggered by various extracellular stimuli, the most potent one being serum from any source. We have previously reported that Candida albicans transiently polyadenylates portions of both the large and small subunits of ribosomal RNA, shortly after serum exposure. Northern blots at the same time suggested that serum might induce a decrease in total ribosomal RNA. We have carried out a number of experiments to carefully assess this possibility and now report that serum significantly reduces ribosomal RNA in Candida albicans. Fluorometric measurements, Northern blotting and quantitative RT-PCR, have all confirmed this decrease. Timed experiments show that serum induces this decrease rapidly, as it was seen in as early as five minutes. Cell mass is not decreased as total cellular protein content remains the same and metabolic activity does not appear to slow, as assessed by XTT assay, and by the observation that cells form hyphal structures robustly. Another hyphal inducer, N-acetylglucosamine, also caused RNA decrease, but to a lesser extent. We also observed it in non-germinating yeast, such as Candida glabrata. The reason for this decrease is unknown and overall our data suggests that decrease in rRNA does not play a causal role in hyphal transformation. Rapid and significant decrease in a molecule so central to the yeast’s biology is of some importance, and further studies, such as its effect on protein metabolism, will be required to better understand its purpose.白色念珠菌（Candida albicans）是一种重要的多态性人类致病菌。它可从单细胞酵母形态切换为萌发菌丝态，这一特性或许是其得以成为高效致病菌的关键因素。菌丝转化可被多种细胞外刺激物触发，其中活性最强的刺激物为任意来源的血清。 此前我们曾报道，在暴露于血清后不久，白色念珠菌会对核糖体RNA（ribosomal RNA, rRNA）的大亚基与小亚基的部分区域进行瞬时多腺苷酸化。同期开展的Northern印迹杂交实验结果提示，血清可能会诱导总核糖体RNA水平下降。 我们通过一系列实验对该可能性进行了严谨验证，如今证实血清可显著降低白色念珠菌内的核糖体RNA含量。荧光定量检测、Northern印迹杂交以及定量逆转录聚合酶链反应（quantitative RT-PCR）均验证了这一下调现象。 时序实验结果显示，血清可快速诱导该现象，暴露5分钟后即可观测到核糖体RNA水平下降。细胞总蛋白含量未发生改变，且通过XTT检测法以及细胞可高效形成菌丝结构的观测结果表明，细胞质量与代谢活性均未出现明显下降。 另一种菌丝诱导剂N-乙酰葡糖胺（N-acetylglucosamine）同样可引发RNA水平下降，但降幅相对较小。该现象在光滑念珠菌（Candida glabrata）这类非萌发酵母中也可被观测到。 目前该RNA水平下降的具体机制尚不明确，综合我们的实验数据来看，核糖体RNA含量下降并未在菌丝转化过程中发挥因果性作用。 对于这种在酵母生物学中处于核心地位的分子发生快速且显著的水平下降，其生物学意义值得关注，后续还需开展诸如其对蛋白质代谢影响等相关研究，以进一步阐明该现象的生理意义。