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Molecular biology: Breaks in the brain

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发表于 2016-3-27 13:18:33 | 显示全部楼层 |阅读模式
Studies over the past decade have revealed a surprising degree of structural variation in human genomes. Structural variants (SVs) in germline DNA are now known to be a major factor in normal genomic variation and an important class of mutation in genomic disorders, and they arise frequently in cancers. Many SVs are thought to result from DNA-replication errors1, so they would be expected to occur at a high frequency in dividing somatic cells (those that do not undergo meiotic division). However, in contrast to heritable SVs in germline cells, little is known about somatic SVs and their impact on tissue function and disease. Writing in Cell, Wei et al.2 provide insight into these questions by examining the landscape of DNA double-strand breaks (DSBs) that arise in mouse neural cells.
过去十年的研究揭示了人类基因组结构变异的惊人程度。结构变异(SVS)在生殖细胞的DNA是目前已知是正常的基因组变异和疾病的一类重要的基因突变的主要因素,他们经常出现在癌症。多少个卫星基因被认为是导致DNA复制错误1,所以他们预计将发生在一个较高的频率分裂体细胞(那些不经过减数分裂)。然而,在对比中生殖细胞遗传的SVS,很少是关于体SVS和他们对组织的功能和疾病的影响。写在细胞、魏等人2提供洞察这些问题所研究的DNA双链断裂的情况(DSB)在小鼠神经细胞出现。

The difficulty in studying somatic SVs arises primarily from technical challenges in detecting rare events in cell populations. Sensitive sequencing technologies coupled with bioinformatic tools have begun to provide glimpses of somatic SVs in vivo, especially in the brain, where up to 40% of individual neurons have been found to contain megabase-scale copy-number variations (CNVs; a form of SV in which the number of copies of a genomic region varies between cells or individuals)3, 4. However, because of the low resolution of many approaches, the true prevalence of SVs in neurons or other cells, and the mechanisms by which they arise, are unknown.
在研究体SVS的困难主要来自于检测细胞群体的稀有事件的技术挑战。敏感的测序技术和生物信息学工具已开始提供躯体SVS体内的一瞥,特别是脑部,到单个神经元的40%被发现含有碱基规模的拷贝数变异(CNVs;一种SV的基因组区域的拷贝数变化的细胞或个体之间)3,4。然而,由于很多方法的分辨率低,SVS在神经元或其他细胞的真正流行,并通过它们产生的机制,是未知的。

Wei et al. used a sensitive, targeted assay known as high-throughput genomic translocation sequencing. This method allows genome-wide detection of naturally occurring 'prey' DSBs using experimentally induced 'bait' DSBs targeted elsewhere in the genome. The two DSBs are joined by cellular DNA-repair processes, leading to a translocation between the genomic regions. Sequencing of the resulting breakpoint junction allows mapping and characterization of the DSBs at nucleotide-level resolution.
wei,等。用敏感试验,针对known as高通量测序基因组的易位。这个方法允许全基因组检测自然发生的食饵”DNA双链断裂 使用实验性 '诱饵'诱导dsbs瞄准在其他地方的基因组。dsbs 参与两种细胞DNA修复过程,导致两个基因组区域异位。测序结果断点连接允许映射和表征dsbs在核苷酸水平分辨率。

The authors first created DSBs at bait loci on three mouse chromosomes in cultured neural stem/progenitor cells (NSPCs) that lacked the protein Xrcc4, which is essential for a DSB-repair process called non-homologous end-joining (NHEJ); preventing this joining enriches for cells with rearrangements. The cells also lacked the protein p53; this lack promotes cell survival. The researchers identified thousands of prey DSBs, with 61% located close to the bait DSBs and the rest spread across the genome (Fig. 1). Strikingly, many were found within three recurrent DSB clusters (RDCs); two of these were in the Lsamp and Npsa3 genes, which are unusually large genes that encode a neural-cell-specific adhesion molecule and a transcription factor, respectively. The third RDC reflected DSBs that occurred close to the bait.
作者首先建立在三个小鼠诱饵DSBs位点的染色体培养的神经干/祖细胞(NSPCs)缺乏蛋白质XRCC4,这是一个DSB修复的过程称为非同源末端连接(NHEJ);预防必不可少的加入丰富了细胞重排。这些细胞也缺乏蛋白质p53;缺乏促进细胞存活。研究人员发现猎物DSBs数以千计,61%位于靠近诱饵双链断裂和其他遍布整个基因组(图1)。引人注目的是,许多患者复发三DSB集群内发现(RDC);两个在LSAMP和npsa3基因,这是非常大的基因编码的神经细胞粘附分子和转录因子,分别。第三RDC反映DSBs发生接近诱饵。

图1:Wei et al.2 performed an unbiased genome-wide screen for DNA double-strand breaks (DSBs) in cultured mouse neural stem/progenitor cells (NSPCs). Their assay identifies prey DSBs that have joined with experimentally induced bait DSBs to generate inter-chromosomal translocations. The researchers found hotspots for recurrent DSBs in large, actively transcribed, late-replicating genes that function in synapses between neural cells or in neural adhesion. Many more recurrent DSB clusters were identified when the cells were subjected to replication stress. These DSBs could lead to genomic rearrangements that contribute to genetic heterogeneity in different cells of the brain or other tissues, giving rise to functional consequences in vivo.
Wei等人。对2对DNA双链断裂(DSBs)一个公正的全基因组筛选培养的小鼠神经干/祖细胞(NSPCs)。他们的方法识别猎物DSB已加入实验诱导诱饵DSBs生成间的染色体易位。研究人员发现在大,复发DSBs热点活跃的转录,晚期复制基因在神经粘附在神经细胞之间突触的功能或。许多反复DSB群当细胞进行复制的压力。这些双链断裂可能导致基因组重排导致的大脑或其他组织的不同细胞的遗传异质性,引起体内功能的影响。

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