The COPA vesicle protein and pathogenesis of spinal muscular atrophy

描述（由申请人提供）：我们发现SMN蛋白与七聚体COPI囊泡的最大成分α - cop结合。本项目要研究的假设是，SMA的发病机制是由于这种货物运输复合物无法维持运动神经元的功能完整性。我们探讨了SMN蛋白与α - cop相互作用在神经突发育和维持中的作用。重要的是，我们观察到α - cop的过表达可以恢复SMN缺失的NSC34细胞的神经突发育。新的数据显示，低水平的SMN会改变内质网-高尔基体运输的功能，这提示了一种以前未被认识到的对这种蛋白质加工途径的影响。我们最近报道了α - cop复合物包含来自分化的NSC-34细胞总转录组的约800个特异性rna。这些mrna的很大一部分在它们的3'非翻译区含有一个g -四重基序，该基序在神经突定位中起作用。我们的目标是鉴定依赖于SMN的mrna与COPI复合物的关联，从而研究α - cop和SMN在这些rna转运到轴突中的作用以及表征它们对神经元发育的需求。为了检验SMN与α - cop相互作用的生物学生理意义以及随后的机制研究，我们培育了α - cop蛋白水平降低的新型转基因小鼠，并预测这将导致运动单元功能障碍。我们还创造了一种转基因菌株，过度表达标记的人类α - COP。这些小鼠将与SMN水平较低的SMA模型小鼠杂交，以验证α - cop和COPI囊泡水平的增加是否促进SMN依赖性货物向轴突的输送，并恢复运动技能和延长寿命。这些实验小鼠模型将成为研究神经退行性变机制以及蛋白质和特异性rna向轴突和轴突内转运的重要资源。COPI途径的药物诱导可能是治疗SMA的一种新方法。

DESCRIPTION (provided by applicant): We discovered that the SMN protein binds to alpha-COP, the largest constituent of the heptameric COPI vesicle. The hypothesis to be investigated in this project is that pathogenesis of SMA results from inability of this cargo transport complex to sustain the functional integrity of motor neurons. We explore the role of the SMN protein's interaction with alpha-COP in neurite development and maintenance. Importantly, we observed that over-expression of alpha-COP restores neurite development in SMN depleted NSC34 cells. New data reveal that low levels of SMN alter the functionality of endoplasmic reticulum-Golgi trafficking, suggesting a previously unrecognized effect on this protein processing pathway. We recently reported that the alpha-COP complex incorporates ~800 specific RNAs from the total transcriptome of differentiated NSC-34 cells. A high fraction of these mRNAs contain in their 3' untranslated regions a G-quadruplex motif, which has been assigned a role in neurite localization. Our goal is to identify the mRNAs that depend on SMN for association with the COPI complex, enabling studies of the roles of alpha-COP and SMN in the trafficking of these RNAs into the axon and characterization of their requirement for neuronal development. To examine the biological physiologic significance of the interaction of SMN with alpha-COP and subsequent mechanistic studies, we generated novel transgenic mice with reduced levels of alpha-COP protein, with the prediction this will result in motor unit dysfunction. We also have created a transgenic strain that over-expresses tagged human alpha- COP. These mice will be crossed with SMA model mice with low levels of SMN to test the hypothesis that increased levels of alpha-COP and COPI vesicles promote SMN dependent cargo delivery to the axon and restore motor skills and increase lifespan. These experimental mouse models will be important resources to study the mechanism of neurodegeneration and the transport of proteins and specific RNAs to and within the axon. Pharmacologic induction of the COPI pathway may represent a novel means to treat SMA.