Fine Mapping of a Dravet Syndrome Modifier Locus on Mouse Chromosome 5 and Candidate Gene Analysis by RNA-Seq
Fine Mapping of a Dravet Syndrome Modifier Locus on Mouse Chromosome 5 and Candidate Gene Analysis by RNA-Seq
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DOI：
10.1371/journal.pgen.1006398
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发表时间：
2016-10-01
期刊：
影响因子：
4.5
通讯作者：
Kearney, Jennifer A.
中科院分区：
文献类型：
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作者：
Hawkins, Nicole A.;Zachwieja, Nicole J.;Kearney, Jennifer A.
在电压门控钠通道基因中发现了大量的突变，导致各种形式的人类癫痫。SCN 1A突变导致一系列严重程度，从轻度热性惊厥到Dravet综合征，一种婴儿发作的癫痫性脑病。Dravet综合征患者经历多种癫痫发作类型，这些类型通常难以治疗、发育迟缓和SUDEP风险升高。相同的钠通道突变可以产生不同临床严重程度的癫痫表型。这表明，其他因素，包括遗传，修改主要突变和改变疾病的严重程度。小鼠模型为研究癫痫的遗传基础提供了有用的工具。小鼠品系背景可以改变表型严重程度，支持遗传修饰剂在癫痫中的作用。Scn 1a（+/-）小鼠模型具有品系依赖性癫痫表型。129 S6/SvEvTac（129）品系的Scn 1a（+/-）小鼠具有正常的表型和寿命，而[129 xC 57 BL/6 J] F1-Scn 1a（+/-）小鼠出现自发性癫痫发作、高血压诱导的癫痫发作和高过早死亡率。我们假设表型差异是由于菌株特异性遗传修饰剂影响Scn 1a（+/-）表型的表达。Scn 1a（+/-）的低分辨率定位确定了几个Dravet综合征修饰基因（Dsm）位点，这些位点负责存活率的应变依赖性差异。使用间隔特异性同源基因，将位于5号染色体上的一个感兴趣基因座Dsm 1精确定位到9 Mb区域。然后利用RNA-Seq来鉴定该狭窄区域内的候选修饰基因。鉴定了129 S6/SvEvTac和[129 xC 57 BL/6 J]F1之间具有显著总基因表达差异的三个基因，包括GABA（A）受体亚基Gabra 2。进一步的分析表明Gabra 2的等位基因特异性表达。氯巴占（一种对GABRA 2受体具有优先亲和力的常见抗惊厥药）的药物操作显示，在Scn 1a（+/-）小鼠中对高血压诱导的癫痫发作具有剂量依赖性保护作用。这些发现支持Gabra 2作为Dravet综合征Scn 1a（+/-）小鼠模型的遗传修饰剂。
A substantial number of mutations have been identified in voltage-gated sodium channel genes that result in various forms of human epilepsy. SCN1A mutations result in a spectrum of severity ranging from mild febrile seizures to Dravet syndrome, an infant-onset epileptic encephalopathy. Dravet syndrome patients experience multiple seizures types that are often refractory to treatment, developmental delays, and elevated risk for SUDEP. The same sodium channel mutation can produce epilepsy phenotypes of varying clinical severity. This suggests that other factors, including genetic, modify the primary mutation and change disease severity. Mouse models provide a useful tool in studying the genetic basis of epilepsy. The mouse strain background can alter phenotype severity, supporting a contribution of genetic modifiers in epilepsy. The Scn1a(+/-) mouse model has a strain-dependent epilepsy phenotype. Scn1a(+/-) mice on the 129S6/SvEvTac (129) strain have a normal phenotype and lifespan, while [129xC57BL/6J] F1-Scn1a(+/-) mice experience spontaneous seizures, hyperthermia-induced seizures and high rates of premature death. We hypothesize the phenotypic differences are due to strain-specific genetic modifiers that influence expressivity of the Scn1a(+/-) phenotype. Low resolution mapping of Scn1a(+/-) identified several Dravet syndrome modifier (Dsm) loci responsible for the strain-dependent difference in survival. One locus of interest, Dsm1 located on chromosome 5, was fine mapped to a 9 Mb region using interval specific congenics. RNA-Seq was then utilized to identify candidate modifier genes within this narrowed region. Three genes with significant total gene expression differences between 129S6/SvEvTac and [129xC57BL/6J]F1 were identified, including the GABA(A) receptor subunit, Gabra2. Further analysis of Gabra2 demonstrated allele-specific expression. Pharmological manipulation by clobazam, a common anticonvulsant with preferential affinity for the GABRA2 receptor, revealed dose-dependent protection against hyperthermia-induced seizures in Scn1a(+/-) mice. These findings support Gabra2 as a genetic modifier of the Scn1a(+/-) mouse model of Dravet syndrome.