Spinal Muscular Atrophy: Is it a motor axon disease?

脊髓性肌萎缩症：它是一种运动轴突疾病吗？

• 批准号: 7640696
• 负责人: CHRISTINE E BEATTIE
• 金额: $ 32.78万
• 依托单位: OHIO STATE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-09-15 至 2010-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7640696
• 关键词: Actins; Address; Affect; Animals; Automobile Driving; Axon; Behavioral; Biogenesis; Biological; Cell Death; Cells; Cessation of life; Complex; Data; Defect; Development; Disease; Embryo; Failure; Fishes; Genetic; Goals; Growth Cones; Individual; Infant Mortality; Intercostal Muscles; Label; Lead; Limb structure; Longevity; Messenger RNA; Modeling; Motor; Motor Neurons; Movement; Mus; Muscle; Muscular Atrophy; Mutant Strains Mice; Nerve; Neuromuscular Junction; Patients; Pattern; Phenotype; Proteins; RNA Splicing; RNA Transport; Respiratory Diaphragm; Role; SMN protein (spinal muscular atrophy); Small Nuclear RNA; Spinal Cord; Spinal Muscular Atrophy; Synapses; System; Testing; Tissues; Translations; Zebrafish; axon growth; beta Actin; in vivo; knock-down; motor neuron function; mouse model; particle; positional cloning; premature; promoter; research study; tool

Spinal muscular atrophy (SMA) is an autosomal recessive disease and one of the leading causes of infant mortality. To elucidate the biological mechanism underlying this motoneuron disease, SMA has been modeled in mice and zebrafish. Low levels of the Survival Motor Neuron (SMN) protein are the cause of SMA. The earliest phenotype associated with low SMN levels in zebrafish is motor axon defects (truncations and aberrant branching). These defects are specific and cell-autonomous for motor axons and occur in the absence of motoneuron cell death. This, and data from others showing that SMN is transported down axons to growth cones, indicates that SMA is a motor axon disease. The experiments outlined in this proposal directly test this possibility. First, the functional and behavioral consequences of ectopic motor axon branching in zebrafish will be addressed. Individual fish with defined motor axon defects will be analyzed for movement defects and decreased life span. To address directly whether defective motor axons lead to motoneuronal cell death, neuromuscular junctions, synaptic activity, and motoneuron survival will be analyzed for individual hemisegments with defective nerves. Secondly, whether SMN depletion in mice causes motor axon branching will be examined by analyzing axonal outgrowth into the intercostal, diaphragm, and limb muscles. In addition, it will be determined when in development SMN function is needed to rescue motor axon defects and the SMA phenotype. Lastly, SMN complexes have been implicated in RNA transport and are present in growth cones suggesting that SMN may function in localizing RNAs to growth cones for localized protein translation. Using a reverse genetic approach in zebrafish to deplete proteins shown to complex with SMN in motor axons will reveal whether decreasing these proteins also leads to motor axon defects and motoneuronal cell death. Zebrafish motor axons will also be used to directly test whether localized protein translation is affected when SMN levels are decreased using beta-actin as a candidate protein. Experiments outlined in this proposal will directly test the hypothesis that SMA is a motor axon disease and will reveal whether SMN functions in a complex crucial for localized protein translation in motor axon growth cones.

脊髓性肌萎缩症（SMA）是一种常染色体隐性遗传疾病，也是婴儿死亡的主要原因之一。为了阐明这种运动神经元疾病的生物学机制，我们在小鼠和斑马鱼中建立了 SMA 模型。运动神经元存活 (SMN) 蛋白水平低是 SMA 的原因。斑马鱼中与低 SMN 水平相关的最早表型是运动轴突缺陷（截断和异常分支）。这些缺陷对于运动轴突来说是特异性的和细胞自主的，并且在没有运动神经元细胞死亡的情况下发生。这一结果以及其他显示 SMN 沿着轴突运输到生长锥的数据表明 SMA 是一种运动轴突疾病。该提案中概述的实验直接测试了这种可能性。首先，将解决斑马鱼异位运动轴突分支的功能和行为后果。将分析具有明确运动轴突缺陷的个体鱼的运动缺陷和寿命缩短。为了直接解决有缺陷的运动轴突是否导致运动神经元细胞死亡、神经肌肉接头、突触活动和运动神经元存活，将对有缺陷神经的个体半节段进行分析。其次，通过分析肋间肌、膈肌和四肢肌肉的轴突生长来检查小鼠的 SMN 消耗是否会导致运动轴突分支。此外，将确定在开发过程中何时需要 SMN 功能来挽救运动轴突缺陷和 SMA 表型。最后，SMN 复合物与 RNA 运输有关，并且存在于生长锥中，这表明 SMN 可能在将 RNA 定位到生长锥上以实现局部蛋白质翻译方面发挥作用。在斑马鱼中使用反向遗传方法来消除与运动轴突中的 SMN 复合的蛋白质，将揭示减少这些蛋白质是否也会导致运动轴突缺陷和运动神经元细胞死亡。斑马鱼运动轴突也将用于直接测试当使用 β-肌动蛋白作为候选蛋白降低 SMN 水平时，局部蛋白翻译是否受到影响。该提案中概述的实验将直接检验 SMA 是一种运动轴突疾病的假设，并将揭示 SMN 是否在对运动轴突生长锥中的局部蛋白质翻译至关重要的复合体中发挥作用。