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: 7118976
• 负责人: CHRISTINE E BEATTIE
• 金额: $ 33.76万
• 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/7118976
• 关键词: actins; axon; cell death; congenital neuromuscular disorder; degenerative motor system disease; developmental neurobiology; genetic translation; genetically modified animals; green fluorescent proteins; growth cones; laboratory mouse; motor neurons; nerve /myelin protein; neurogenesis; neuromuscular junction; neuromuscular transmission; neuronal transport; progressive spinal muscular atrophy; protein localization; protein transport; zebrafish

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，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，SMA已在小鼠和斑马鱼中建模。低水平的运动神经元存活（SMN）蛋白是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（截短和异常分支）。这些缺陷是特定的和细胞自主的运动轴突和运动神经元细胞死亡的情况下发生。这一点，以及来自其他人的数据显示SMN沿着轴突运输到生长锥，表明SMA是一种运动轴突疾病。本提案中概述的实验直接测试了这种可能性。首先，在斑马鱼异位运动轴突分支的功能和行为后果将得到解决。将分析具有确定的运动轴突缺陷的个体鱼的运动缺陷和寿命缩短。为了直接解决是否有缺陷的运动轴突导致运动神经元细胞死亡，神经肌肉接头，突触活动，和运动神经元的生存将进行分析的个别半节段有缺陷的神经。其次，通过分析轴突长入肋间、横膈膜和肢体肌肉，检查小鼠中SMN耗竭是否导致运动轴突分支。此外，还将确定何时需要SMN功能来挽救运动轴突缺陷和SMA表型。最后，SMN复合物已被牵连在RNA运输和存在于生长锥中，这表明SMN可能在定位RNA到生长锥的定位蛋白质翻译中起作用。在斑马鱼中使用反向遗传方法来消除运动轴突中与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质降低SMN水平时，局部蛋白质翻译是否受到影响。本提案中概述的实验将直接测试SMA是运动轴突疾病的假设，并将揭示SMN是否在运动轴突生长锥中对局部蛋白质翻译至关重要的复合体中发挥作用。