微RNA循环使用定量DNA结合染料化学和液滴的数字PCR
Summary
A sensitive and accurate method for cell-free microRNAs quantification using a dye-based chemistry and droplet digital PCR technology is described.
Abstract
循环微RNA（miRNA）（无细胞的），从细胞释放到血流中。在循环的特定微小RNA的量已与一种疾病状态，并具有被用作疾病的生物标志物的潜力。用于使用基于染料的化学和液滴数字PCR技术循环微RNA定量的灵敏和准确的方法最近已开发。具体而言，使用锁核酸（LNA）为基础的miRNA特异性引物用绿色荧光DNA结合染料在相容的液滴数字PCR系统能够获得特定miRNA的绝对定量。在这里，我们描述了如何执行此技术，以评估在生物流体，例如血浆和血清的miRNA量，是可行和有效的。
Introduction
MicroRNAs (miRNAs) are released into blood circulation by potentially all the cells of the organism, as a consequence of active release or necrotic and apoptotic processes. Cell-free miRNAs have been detected in the bloodstream either as free stable molecules or linked to lipoproteins or enveloped inside exosomes and microvesicles 1-3. They are believed to function as cell-to-cell communicators 4, and their amount changes in the presence of cancer, cardiac disorders or autoimmune diseases 5-7. Their accurate and reproducible quantification is the basis for their evaluation as disease biomarkers. However, for several reasons already described elsewhere 8,9, miRNA quantification in serum or plasma, as well as other body fluids, could be very challenging 10,11. We recently developed a method for the absolute quantification of circulating miRNAs, based on miRNA-specific LNA primers and DNA-binding dye droplet digital PCR (ddPCR) technology 12. This methodology has been applied to the validation of miRNA breast cancer biomarkers 13,14.
After the partitioning of each reverse-transcribed miRNA molecule inside a nanoliter-sized droplet, it is possible to count the copy number of each miRNA in each sample, basically counting the number of green, and therefore positive, fluorescent droplets. As soon as a PCR reaction occurs, a positive count is achieved, without the need to establish a standard curve or taking PCR efficiency into account in target amount calculation, as it happens with quantitative RT-PCR (RT-qPCR). In addition, ddPCR proved to be more sensitive and accurate than RT-qPCR in circulating miRNA quantification 15. In this article we present the detailed protocol of this methodology, discussing the most relevant steps andspecifically considering serum and plasma clinical samples.
Protocol
Representative Results
Discussion
循环miRNA是存在于血液中的浓度极低，而且可以从血浆和血清样品中提取的RNA的量是低的。因为这个原因，它们难以与其它技术，如微阵列和RNA测序量化。此外，还有在数据归一化的一般化缺乏协议和内源性“参考”微RNA在血液中的存在。在这种情况下，一个灵敏的技术，如微滴数字PCR，能够每毫升血清或血浆，即使非常低的计数的miRNA拷贝数的，是非常有吸引力的。我们配对该技术具有普遍性的…
Disclosures
The authors have nothing to disclose.
Acknowledgements
从意大利癌症研究协会（AIRC）为MF（MFAG 11676）和MN资金支持（特别节目分子临床肿瘤学 – 5千分数ñ9980，2010/15）和指令意大利教育部，大学和研究FIRB 2011年明尼苏达州（项目RBAPIIBYNP）。
Materials
| miRNeasy Mini Kit | Qiagen | 217004 | Columns for total RNA, including miRNA, extraction from serum/plasma |
| 100 nmole RNA oligo Cel-miR-39-3p | Integrated DNA Technologies | Custom | Sequence: UCACCGGGUGUAAAUCAGCUUG |
| Universal cDNA synthesis kit II, 8-64 rxns | Exiqon | 203301 | Kit for microRNA reverse transcription |
| MicroRNA LNA PCR primer set | Exiqon | 204000-206xxx and 2100000-21xxxxx | Primers for miRNA amplification inside droplets |
| QX200 droplet generator | BioRad | 186-4002 | Instrument used for droplet reading |
| QX200 droplet reader | BioRad | 186-4003 | Instrument used for droplet generation |
| QuantaSoft software | BioRad | 186-3007 | Software for data collection and analysis |
| PX1 PCR plate sealer | BioRad | 181-4000 | Plate sealer |
| DG8 droplet generator cartridges and gaskets | BioRad | 186-4008 | Cartridges used to mix sample and oil to generate droplets |
| QX200 ddPCR EvaGreen supermix | BioRad | 186-4033/36 | PCR supermix |
| QX200 droplet generator oil for EvaGreen dye | BioRad | 186-4005 | Oil for droplet generation |
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