Mammalian motor neuron SMN screens

脊髓性肌萎缩症(SMA)是一种常见的儿童常染色体隐性遗传病，由运动神经元存活1(SMN1)基因突变引起。SMA的主要特征之一是神经肌肉功能的进行性丧失，这往往是致命的，使SMA成为婴幼儿死亡的主要遗传原因。运动神经元死亡是这种疾病的一个重要特征，但最近的一些信息表明，肌肉功能障碍或畸形也可能发生。虽然SMN似乎具有多种细胞角色，目前尚不清楚哪些SMN支持神经肌肉发育和健康，但合理的患者信息表明，SMN表达水平较高与疾病较轻的病例相关。这表明了一个明确的治疗策略：即确定提高SMN水平的途径，并最终确定药物类别。然而，还有其他的策略，其中之一是寻找独立于SMN发挥作用的途径，并在SMN水平降低时进行纠正。为了做到这一点，我们和我们的合作者进行了两组筛选。第一组使用化学和生物文库来搜索能够增加小鼠运动神经元和其他细胞中SMN数量的化合物。第二组使用遗传方法在苍蝇和蠕虫模型中寻找可以改善SMA表型的基因。我们将建立一套关键的表型分析来测试所有来自筛查的化合物和基因。这些将包括小鼠运动神经元存活、骨骼肌发育和神经肌肉连接形成。此外，我们将在人类运动神经元上测试这些化合物和基因，这些细胞是从SMA患者的诱导多能干细胞(IPS)中产生的。从化学筛选中识别出的目标将在遗传模型中进行交叉验证。因此，所有屏幕上的点击量都将经过严格的评估和比较。最后，从这些屏幕中鉴定出的化合物将在小鼠SMA模型中进行测试。这项工作的最终结果应该是彻底表征化合物，这些化合物可能被用来开发这种儿童疾病的治疗方法。

Spinal muscular atrophy (SMA) is a common childhood autosomal recessive disease caused by mutations in the Survival of Motor Neuron 1 (SMN1) gene. One of the primary features of SMA is the progressive loss of neuromuscular function that is often fatal, making SMA the leading genetic cause of death in infants and young children. Motor neuron death is a significant feature of this disease, but some recent information suggests that muscle dysfunction or malformation may also occur. While SMN appears to have multiple cellular roles, and it is not yet clear which of them support neuromuscular development and health, a reasonable amount of patient information indicates that higher levels of SMN expression are associated with less severe cases of disease. This suggests a clear therapeutic strategy: namely, identifying the pathways and, ultimately, drug classes that increase SMN levels. However, there are alternate strategies, one of which is finding pathways that function independently of SMN and are corrective when SMN levels are reduced. To accomplish this, we and our collaborators have carried out two sets of screens. The first set used chemical and biological libraries to search for compounds that increase amounts of SMN in mouse motor neurons and other cells. The second set used genetic methods to find genes that can ameliorate SMA phenotypes in fly and worm models. We will establish a set of key phenotypic assays to test all of the compounds and genes that come out of the screens. These will include mouse motor neuron survival, skeletal muscle development and neuromuscular junction formation. In addition, we will test these compounds and genes on human motor neurons produced from induced pluripotent stem (iPS) cells made from an SMA patient. Targets identified from chemical screens will be cross-validated in genetic models. Thus, hits from all the screens will be evaluated and compared rigorously. Finally, compounds indentified from these screens will be tested in mouse SMA models. The end result of this work should be thoroughly characterized compounds that can potentially be used to develop therapeutics for this childhood disease.