School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland, 1142, New Zealand.
Centre for Brain Research, The University of Auckland, Auckland, New Zealand.
Sci Rep. 2022 May 20;12(1):8572. doi: 10.1038/s41598-022-12613-7.
Rapid, cost-effective identification of genetic variants in small candidate genomic regions remains a challenge, particularly for less well equipped or lower throughput laboratories. The application of Oxford Nanopore Technologies' MinION sequencer has the potential to fulfil this requirement. We demonstrate a proof of concept for a multiplexing assay that pools PCR amplicons for MinION sequencing to enable sequencing of multiple templates from multiple individuals, which could be applied to gene-targeted diagnostics. A combined strategy of barcoding and sample pooling was developed for simultaneous multiplex MinION sequencing of 100 PCR amplicons. The amplicons are family-specific, spanning a total of 30 loci in DNA isolated from 82 human neurodevelopmental cases and family members. The target regions were chosen for further interrogation because a potentially disease-causative variant had been identified in affected individuals following Illumina exome sequencing. The pooled MinION sequences were deconvoluted by aligning to custom references using the minimap2 aligner software. Our multiplexing approach produced an interpretable and expected sequence from 29 of the 30 targeted genetic loci. The sequence variant which was not correctly resolved in the MinION sequence was adjacent to a five nucleotide homopolymer. It is already known that homopolymers present a resolution problem with the MinION approach. Interestingly despite equimolar quantities of PCR amplicon pooled for sequencing, significant variation in the depth of coverage (127×-19,626×; mean = 8321×, std err = 452.99) was observed. We observed independent relationships between depth of coverage and target length, and depth of coverage and GC content. These relationships demonstrate biases of the MinION sequencer for longer templates and those with lower GC content. We demonstrate an efficient approach for variant discovery or confirmation from short DNA templates using the MinION sequencing device. With less than 130 × depth of coverage required for accurate genotyping, the methodology described here allows for rapid highly multiplexed targeted sequencing of large numbers of samples in a minimally equipped laboratory with a potential cost as much 200 × less than that from Sanger sequencing.
快速、经济有效地鉴定小的候选基因组区域中的遗传变异仍然是一个挑战,特别是对于设备和通量较低的实验室。牛津纳米孔技术的 MinION 测序仪的应用具有满足这一需求的潜力。我们展示了一种用于多重分析的概念验证,该分析将 PCR 扩增子混合用于 MinION 测序,从而能够对来自多个个体的多个模板进行测序,这可应用于基因靶向诊断。开发了一种组合的条形码和样品混合策略,用于同时对 100 个 PCR 扩增子进行 MinION 多重测序。扩增子是家族特异性的,跨越从 82 个人类神经发育病例和家庭成员中分离的 DNA 中总共 30 个位点。选择这些靶区域进行进一步研究,是因为在受影响个体中进行 Illumina 外显子测序后发现了一个潜在的致病变异。通过使用 minimap2 比对软件将混合 MinION 序列比对到定制参考序列,对其进行解卷积。我们的多重方法从 30 个靶向遗传基因座中的 29 个产生了可解释和预期的序列。在 MinION 序列中未正确解析的序列变异位于 5 个核苷酸同源多聚体附近。已经知道,同源多聚体在 MinION 方法中存在分辨率问题。有趣的是,尽管用于测序的 PCR 扩增子等量混合,但观察到覆盖深度(127×-19,626×;平均值= 8321×,标准误差= 452.99)有显著差异。我们观察到覆盖深度与靶标长度和覆盖深度与 GC 含量之间的独立关系。这些关系表明 MinION 测序仪对较长模板和 GC 含量较低的模板存在偏倚。我们展示了一种使用 MinION 测序设备从短 DNA 模板中进行变体发现或确认的有效方法。对于准确的基因分型,所需的覆盖率不到 130×,这里描述的方法允许在设备最少的实验室中快速、高度多重化地对大量样本进行靶向测序,成本可能比 Sanger 测序低 200×。