Genetic Mechanisms of Muscular Dystrophy in Mice

描述(由申请人提供)：这项研究的长期目标是使用一种新的小鼠突变作为实验模型，更好地了解神经肌肉疾病背后的分子遗传机制。肌营养不良症包括一组不同的遗传异质性疾病，其特征是进行性肌肉无力和消瘦，导致严重残疾，往往过早死亡。有必要更多地了解这些疾病的发病机制，并将这些知识转化为有效的治疗方法。为了达到这一目标，我们建议研究MDM突变小鼠的发病机制，这是一种新的进行性肌营养不良模型，其功能上将巨大肌钙蛋白(TTN)基因与肢体带状2A型肌营养不良症(LGMD2A)半胱氨酸蛋白酶Calain 3(Capn3)联系起来。我们已经在基因上定位并鉴定了MDM突变是一种复杂的重排，导致了TTN推测的CAPN3相互作用结构域中的一个小的框内缺失。MDM小鼠也可能作为人类胫骨肌营养不良症(TMD)的遗传模型，该基因定位于2q31的TTN基因座。这是首次证明TTN突变与肌营养不良症有关，并提供了一种新的动物模型来测试这两种疾病基因之间的功能相互作用。 为了阐明肌动蛋白和钙蛋白3在肌肉细胞退变中的作用，我们将采取的步骤是：1)检验假设，即肌动蛋白与肌动蛋白的相互作用被MDM突变破坏，2)检验交替的假说，即进行性MDM肌营养不良是由于CAPN3水平降低或CAPN3蛋白酶异常激活所致，以及3)通过基因打靶产生TTN零等位基因，并使用敏化的ENU突变筛查TTN基因座上的一系列肌营养不良突变。因此，MDM突变小鼠为了解导致肌肉营养不良的分子途径提供了一个独特的工具，并可能揭示干预疾病过程的切入点。

DESCRIPTION (provided by applicant): The broad long term goals of this research are to better understand the molecular genetic mechanisms underlying neuromuscular disease using a novel mouse mutation as an experimental model. Muscular dystrophies include a diverse group of genetically heterogeneous disorders characterized by progressive muscle weakness and wasting that leads to severe disability and often premature death. There is a need to learn more about pathogenesis of the diseases and translate this knowledge into effective treatments. Toward this goal, we propose to study the mechanism of pathogenesis in the mdm mutant mouse, a novel model of progressive muscular dystrophy that functionally links the enormous Titin (Ttn) gene to the limb-girdle muscular dystrophy type 2A (LGMD2A) cysteine protease calpain 3 (Capn3). We have genetically mapped and identified the mdm mutation as a complex rearrangement that results in a small in-frame deletion within a putative CAPN3-interacting domain of TTN. The mdm mouse may also serve as a genetic model for human tibial muscular dystrophy (TMD) which maps to the TTN locus at 2q31. This is the first demonstration that mutations in Ttn are associated with muscular dystrophy and provides a novel animal model to test for functional interactions between these two disease genes. The steps we will take to elucidate the roles of titin and calpain 3 in muscle cell degeneration will be to 1) test the hypothesis that calpain 3 interactions with titin are disrupted by the mdm mutation, 2) test the alternate hypotheses that the progressive mdm muscular dystrophy is due to either reduced CAPN3 levels or aberrant activation of the CAPN3 protease, and 3) generate a Ttn-null allele by gene targeting and an allelic series of muscular dystrophy mutations at the Ttn locus using a sensitized ENU mutagenesis screen. Thus, the mdm mutant mouse provides a unique tool for understanding molecular pathways causing muscular dystrophy and may reveal entry points in which to intervene in the disease process.