Summary
Abstract
Introduction
Protocol
Representative Results
Discussion
Acknowledgements
Materials
References
Medicine
在这里,我们提出了一种用于测量单细胞中绝对线粒体(mt)DNA拷贝数和mtDNA缺失异质水平的方案。
哺乳动物线粒体(mt)DNA是一种小的环状双链线粒体内DNA分子,编码电子传递链的13个亚基。与二倍体核基因组不同,大多数细胞含有更多的mtDNA拷贝,根据细胞类型,从不到100个拷贝到超过20万个拷贝不等。MtDNA拷贝数越来越多地被用作许多与年龄相关的退行性疾病和疾病的生物标志物,因此,mtDNA拷贝数的准确测量正在成为研究和诊断环境中的关键工具。mtDNA中的突变通常以单核苷酸多态性(SNP)或缺失的形式发生,可以存在于细胞内mtDNA的所有拷贝中(称为同质),也可以作为突变和WT mtDNA拷贝的混合物(称为异质)。异质性mtDNA突变是临床线粒体病理学的主要原因,无论是在罕见疾病中还是在越来越多的常见迟发性疾病(如帕金森病)中。确定细胞中存在的异质性水平是诊断罕见线粒体疾病和旨在了解线粒体可能发挥作用的常见迟发性疾病的研究的关键步骤。传统上,MtDNA拷贝数和异质性通过基于定量(q)PCR的测定或深度测序来测量。然而,最近引入的ddPCR技术为测量这两个参数提供了一种替代方法。与现有方法相比,它具有几个优点,包括能够测量绝对mtDNA拷贝数和足够的灵敏度,即使在低拷贝数下也能从单个细胞进行准确测量。这里介绍的是描述使用ddPCR测量单细胞中mtDNA拷贝数的详细方案,此后称为液滴生成PCR,可以选择同时测量具有mtDNA缺失的细胞中的异质性。还讨论了扩展该方法以测量具有mtDNA SNP的细胞中的异质性的可能性。
哺乳动物线粒体 (mt)DNA 是一种小的(约 16.5 Kb)环状 DNA 基因组,存在于线粒体基质中,编码 37 个基因,包括两个 rRNA、22 个 tRNA 和 13 个蛋白质编码基因1。与每个细胞包含每个基因的一个(单倍体)或两个(二倍体)拷贝的核基因组不同,mtDNA存在于每个细胞的线粒体中有多个拷贝,范围从数十个拷贝(例如,成熟的精子细胞)到数十万个拷贝(例如,卵母细胞)2,3。这种多拷贝性质的结果是mtDNA基因组中的突变,可能以单核苷酸多态性(SNP),缺失或重复的形式存在,可以在任何给定细胞中以不同的水平存在,占细胞总mtDNA群体的0%至100%。同一细胞中野生型和突变型mtDNA基因组的存在称为异质性,致病性异质性mtDNA突变是线粒体疾病的主要原因,几种常见的神经系统综合征与潜在的异质性mtDNA突变有关4。
导致临床疾病的异质性mtDNA突变可能性的两个关键参数是异质水平和mtDNA拷贝数。许多异质突变表现出阈值效应,生化和临床表型仅在某个异质水平以上变得明显,通常约为80%5,随后随着异质性的进一步增加而恶化4。然而,考虑细胞中存在的mtDN....
Name | Company | Catalog Number | Comments |
50% Tween-20 solution | Novex | 3005 | |
Automated droplet-generating oil | Bio Rad | 1864110 | Commercial oil formulation used to generate the oil/droplet emulsion (used in Protocol Step 4.1) |
C1000 PCR machine with deep-well block | Bio Rad | 1851197 | PCR thermocycler equipped with a deep-well heating block, used for cell lysis (Protocol Step 2.1.2.) and PCR cycling (Protocol Step 5) |
Collection plate cooling block | Bio Rad | 12002819 | Cooling block that keeps samples chilled during droplet generation (used in Protocol step 4.3) |
ddPCR 96-well plates | Bio Rad | 12001925 | 96-well plates pipet tips designed for use in the QX200 AutoDG droplet generator, used for sample preparation (Protocol step 3.4) and droplet collection (Protocol step 4.3) |
ddPCR droplet reader oil | Bio Rad | 1863004 | Commercial oil formulation used by the droplet reader (used in Protocol step 6.1) |
ddPCR Supermix for Probes (no dUTP) | Bio Rad | 1863023 | Commercial supermix for use in ddPCR experiments utilising probes (used in Protocol Step 3.3) |
DG32 automated droplet generator cartridges | Bio Rad | 1864108 | Microfluidic cartridges used in the QX200 AutoDG droplet generator to generate the oil/droplet emulsion (used in Protocol Step 4.3) |
Fetal bovine serum | Gibco | 10270-106 | Qualified fetal bovine serum |
Foil plate covers | Bio Rad | 1814040 | Foil plate covers used to seal droplet collection plates after droplet generation (used in Protocol step 4.6) |
HEK 293T cells | Takara | 632180 | Commercial subclone of the transformed human embryonic kidney cell line, HEK 293, expressing the SV40 Large-T antigen |
HeLa cells | ECACC | 93021013 | Human cervix epitheloid carcinoma cells |
High glucose DMEM | Gibco | 13345364 | 4.5g/L D-Glucose, with L-glutamine and sodium pyruvate |
Human cybrids | University of Miami | ||
Mouse embryonic fibroblasts | Newcastle University | Immortalized from C57Bl/6 mice | |
Nuclease-free water | Ambion | AM9937 | |
PCR plate seals | Pierce | SP-0027 | Clear adhesive plate seals, only used pre-droplet generation (foil seal must be used in step 4.6) |
Pipet Tip Waste Bins | Bio Rad | 1864125 | Disposable collection bin used to collect discarded tips in the QX200 AutoDG droplet generator (used in Protocol step 4.3) |
Pipet tips for AutoDG system | Bio Rad | 1864120 | Filtered pipet tips designed for use in the QX200 AutoDG droplet generator (used in Protocol step 4.3) |
Primary human dermal fibroblast cells | Newcastle Biobank | ||
Primers/Probes | IDT | N/A | Exact primer/probe sequences will be assay dependent. Primers and probes used in this study are given in Table 1 |
Proteinase K 20 mg/mL solution | Ambion | AM2546 | |
PX1 PCR plate sealer | Bio Rad | 1814000 | Applies foil seals to ddPCR sample plates after droplet generation (used in Protocol Step 4.6) |
QX Manager software | Bio Rad | 12012172 | Droplet reader set up & analysis software (used in Protocol Steps 6 & 7) |
QX200 AutoDG droplet generator | Bio Rad | 1864101 | Automated microfluidic droplet generator (used in Protocol Step 4) |
QX200 droplet reader | Bio Rad | 1864003 | Droplet reader (used in Protocol Step 6) |
Trizma pre-set crystals pH 8.3 | Sigma | T8943-100G |
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