Department of Medical Biology, Amsterdam University Medical Centers, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
Department of Clinical and Experimental Cardiology, Amsterdam University Medical Centers, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
Proc Natl Acad Sci U S A. 2020 Aug 4;117(31):18617-18626. doi: 10.1073/pnas.1919379117. Epub 2020 Jul 16.
Genome-wide association studies have identified noncoding variants near that are associated with PR interval and QRS duration, suggesting that subtle changes in expression affect atrioventricular conduction system function. To explore whether and to what extent the atrioventricular conduction system is affected by Tbx3 dose reduction, we first characterized electrophysiological properties and morphology of heterozygous mutant () mouse hearts. We found PR interval shortening and prolonged QRS duration, as well as atrioventricular bundle hypoplasia after birth in heterozygous mice. The atrioventricular node size was unaffected. Transcriptomic analysis of atrioventricular nodes isolated by laser capture microdissection revealed hundreds of deregulated genes in mutants. Notably, atrioventricular nodes showed increased expression of working myocardial gene programs (mitochondrial and metabolic processes, muscle contractility) and reduced expression of pacemaker gene programs (neuronal, Wnt signaling, calcium/ion channel activity). By integrating chromatin accessibility profiles (ATAC sequencing) of atrioventricular tissue and other epigenetic data, we identified Tbx3-dependent atrioventricular regulatory DNA elements (REs) on a genome-wide scale. We used transgenic reporter assays to determine the functionality of candidate REs near an up-regulated chamber-enriched gene, and in a down-regulated conduction system-specific gene. Using genome editing to delete candidate REs, we showed that a strong intronic bipartite RE selectively governs expression in the conduction system in vivo. Our data provide insights into the multifactorial Tbx3-dependent transcriptional network that regulates the structure and function of the cardiac conduction system, which may underlie the differences in PR duration and QRS interval between individuals carrying variants in the locus.
全基因组关联研究已经确定了 附近与 PR 间期和 QRS 持续时间相关的非编码变体，这表明 表达的微小变化会影响房室传导系统的功能。为了探索房室传导系统是否以及在何种程度上受到 Tbx3 剂量减少的影响，我们首先描述了杂合 突变（）小鼠心脏的电生理特性和形态。我们发现杂合子小鼠出生后 PR 间期缩短和 QRS 持续时间延长，房室束发育不良。房室结大小不受影响。通过激光捕获显微切割分离的房室结的转录组分析显示， 突变体中有数百个基因表达失调。值得注意的是， 房室结中工作心肌基因程序（线粒体和代谢过程、肌肉收缩力）表达增加，起搏基因程序（神经元、Wnt 信号、钙/离子通道活性）表达减少。通过整合房室组织的染色质可及性图谱（ATAC 测序）和其他表观遗传数据，我们在全基因组范围内鉴定了 Tbx3 依赖性房室调节 DNA 元件（REs）。我们使用转基因报告基因检测来确定候选 RE 附近一个上调的腔室富集基因和一个下调的传导系统特异性基因的功能。使用基因组编辑删除候选 REs，我们表明一个强的内含子二分 RE 选择性地在体内调节传导系统中的 表达。我们的数据提供了关于 Tbx3 依赖性转录网络的深入了解，该网络调节心脏传导系统的结构和功能，这可能是携带 基因座变体的个体之间 PR 间期和 QRS 间隔差异的基础。
