Generation of a mouse model of episodic ataxia type 2 (EA2)

描述(申请人提供)：发作性神经障碍的特征是发作衰弱的症状，其间穿插相对正常的功能周期。虽然症状可以是多样的，包括偏头痛、癫痫、瘫痪、共济失调和运动障碍，但在遗传病因和能够触发发作性疾病发作的因素方面都有显著的相似之处。许多发作性疾病与离子通道突变有关。此外，无论离子通道病的类别或表现出的症状，攻击的诱因最常见的是心理、物理或化学应激源，这表明存在发起攻击的共同机制。人们对这些触发因素在两次发作之间正常的个体中引发神经功能障碍的机制知之甚少。我们解决这个问题的方法是使用一种罕见的单基因紊乱作为模型系统。因为了解单基因发作性疾病的发病机制可能会为了解偏头痛和特发性癫痫等遗传复杂的发作性疾病提供洞察力。我们已经确定发作性共济失调2型(EA2)是在小鼠中模拟这类疾病的主要候选。EA2是由CACNA1A基因突变引起的，CACNA1A基因编码Cav2.1(P/Q型)电压门控钙通道的12.1亚基形成孔。这种疾病特别适合建模，因为已经有大量的基本信息可供建立，包括描述正常和突变的Cav2.1体外通道特性的大量工作。发作性共济失调2型患者经历了由情绪压力、运动、咖啡因或酒精引发的偏头痛、共济失调和其他神经体征的阵发性发作。虽然CACNA1a基因突变早在1996年就已被发现，但其致病机制仍不清楚。对异源系统中EA2突变的功能表达研究表明，正如预期的那样，Cav2.1电流减少。然而，有证据表明突变通道的单倍性不足和显性负面影响，表明即使是这个最基本的问题也需要突变在体内的天然系统中表达。在培养的神经元和小鼠突变体中的工作也表明，在体外评价突变通道的生物物理性质不太可能提供对表型的全面理解，因为体内神经元的代偿过程也可能起到作用。这些结果表明，需要一个行为完整的动物模型来充分了解疾病过程。因此，我们将开发并鉴定一种携带EA2突变的敲门小鼠。这项建议的具体目的是：1)建立和鉴定EA2敲门小鼠模型。2)研究EA2基因敲击小鼠的行为学特征。小鼠模型的发展将使我们处于检查病理生理学和洞察人类疾病的绝佳位置。发作性神经功能障碍的特征是发作衰弱的症状，包括偏头痛、癫痫、瘫痪、共济失调和运动障碍，并伴有相对正常的功能周期。人们对触发神经功能障碍的病理生理机制知之甚少。因此，我们将开发并鉴定一种携带发作性共济失调人类突变的敲门小鼠，这是一种罕见的单基因疾病，可能为偏头痛和特发性癫痫等遗传复杂的发作性疾病提供洞察。

DESCRIPTION (provided by applicant): Episodic neurological disorders are characterized by attacks of debilitating symptoms interspersed with periods of relatively normal function. Although the symptoms can be diverse, including migraine headache, epilepsy, paralysis, ataxia, and dyskinesia, there are marked similarities in both the genetic etiology and the factors capable of triggering attacks in episodic disorders. Many episodic disorders are associated with ion channel mutations. Further, regardless of the class of ion channelopathy or the expressed symptoms, the precipitants of attacks are most commonly psychological, physical or chemical stressors, suggesting the existence of a common mechanism for the initiation of the attacks. There is little understanding of the mechanisms by which these triggers precipitate neurological dysfunction in individuals who are otherwise normal between attacks. Our approach to this problem is to use a rare monogenic disorder as a model system. because understanding pathogenesis in a monogenic episodic disorder will likely provide insight into genetically complex episodic disorders such as migraine headache and idiopathic epilepsy. We have identified episodic ataxia type 2 (EA2), as a leading candidate for modeling this class of disorders in mice. EA2 is caused by mutations in the CACNA1A gene, which encodes the pore-forming a12.1 subunit of Cav2.1 (P/Q-type) voltage-gated calcium channels. This disorder is particularly amenable for modeling because there is already a wealth of basic information on which to build, including an enormous body of work describing normal and mutant Cav2.1 channel properties in vitro. Individuals with episodic ataxia type 2 experience paroxysmal attacks of migraine, ataxia, and other neurological signs that are triggered by emotional stress, exercise, caffeine or ethanol. Although the mutations in CACNA1A were first identified in 1996, the pathogenic mechanisms are still unknown. Functional expression studies of EA2 mutations in heterologous systems demonstrate reduced Cav2.1 currents, as expected. However, there is evidence for both haploinsufficiency and dominant negative effects of the mutant channel, demonstrating that even this most basic of questions requires expression of the mutants in a native in vivo system. Work in both cultured neurons and mouse mutants also demonstrates that an appreciation of the biophysical properties of the mutant channel in vitro is not likely to provide a comprehensive understanding of the phenotype because compensatory processes in neurons in vivo may also contribute. These results demonstrate the need for a behaviorally intact animal model to fully appreciate disease processes. Therefore, we will develop and characterize a knockin mouse bearing an EA2 mutation. The specific aims of this proposal are 1) To develop and characterize a knockin mouse model of EA2. 2) To behaviorally characterize the EA2 knockin mice. The development of a mouse model will place us in an excellent position to examine pathophysiology and provide insight into human disease. Episodic neurological disorders are characterized by attacks of debilitating symptoms, including migraine headache, epilepsy, paralysis, ataxia, and dyskinesia, interspersed with periods of relatively normal function. There is little understanding of the pathophysiological mechanisms that triggers neurological dysfunction. Therefore, we will develop and characterize a knockin mouse bearing a human mutation for episodic ataxia, a rare monogenic disorder that may provide insight into genetically complex episodic disorders such as migraine headache and idiopathic epilepsy.