Spinal Muscular Atrophy: SMNs role in MRNA localization and local translation

描述（由申请人提供）： 脊髓性肌萎缩症（SMA）是一种常见的遗传性神经退行性疾病，由编码普遍存在的运动神经元存活蛋白（SMN）的SMN 1基因突变或缺失引起，该蛋白对所有细胞中剪接体snRNP复合物的组装至关重要。一个主要的未回答的问题是SMN的丢失如何导致神经元功能障碍和SMA。需要进一步的工作来确定神经元中SMN的功能。免疫组织化学研究显示SMN定位于脊髓切片的轴突和树突。使用高分辨率的免疫荧光培养的神经元，我们已经表明，SMN形成颗粒与RNA和核糖体在生长锥共定位。使用活细胞成像，我们发现EGFP-SMN颗粒在活神经元的神经元突起和生长锥中表现出快速和双向的运动。从SMA转基因小鼠模型培养的原代运动神经元显示轴突缺陷，包括生长锥中β-肌动蛋白mRNA的丢失，这表明SMN在mRNA定位机制中具有新的功能。我们的初步数据表明，SMN与mRNA结合蛋白，ZBP 1，ZBP 2和HuD，这是已知的参与神经元mRNA的定位和稳定性。我们假设，这些mRNA结合蛋白与SMN相互作用，以促进mRNA的定位过程和稳定的生长锥内。本文提出的实验将进一步表征SMN，HuD，ZBP和RNA转运颗粒内相关mRNA之间的关联，分子相互作用和动态调节。SMN缺陷型运动神经元将用于鉴定在其定位和翻译中改变的特定mRNA。我们将研究是否SMN缺陷神经元内的局部mRNA调控功能障碍有助于改变生长锥运动。这项研究将为SMN的神经元功能提供新的见解，其中mRNP复合物的组装，定位和/或翻译中可能存在的缺陷可能有助于SMA的疾病过程。

DESCRIPTION (provided by applicant): Spinal Muscular Atrophy (SMA) is a common inherited neurodegenerative disease caused by mutations or deletions in the SMN1 gene that encodes for the ubiquitous Survival of Motor Neuron Protein (SMN), which is essential for the assembly of spliceosomal snRNP complexes in all cells. A major unanswered question is how the loss of SMN leads to neuronal dysfunction and SMA. Further work is greatly needed to identify functions for SMN in neurons. Immunohistochemical studies have revealed localization of SMN to axons and dendrites from sections of spinal cord. Using high-resolution immunofluorescence of cultured neurons, we have shown that SMN forms granules which colocalize with RNA and ribosomes in growth cones. Using live cell imaging, we showed that EGFP-SMN granules exhibited rapid and bi-directional movements in neuronal processes and growth cones of live neurons. Primary motor neurons cultured from a transgenic mouse model of SMA displayed axonal defects that include loss of beta-actin mRNA from growth cones, suggesting a novel function for SMN in the mechanism of mRNA localization. Our preliminary data indicate that SMN associates with the mRNA binding proteins, ZBP1, ZBP2 and HuD, which are known to be involved in neuronal mRNA localization and stability. We hypothesize that these mRNA binding proteins interact with SMN to facilitate mRNA localization in processes and stabilization within growth cones. Experiments proposed here will further characterize the association, molecular interactions and dynamic regulation between SMN, HuD, ZBPs and associated mRNAs within RNA transport granules. SMN deficient motor neurons will be used to identify specific mRNAs that are altered in their localization and translation. We will investigate whether dysfunction of local mRNA regulation within SMN-deficient neurons contributes to altered growth cone motility. This research will provide new insight into neuronal functions for SMN, whereby possible defects in the assembly, localization and/or translation of mRNP complexes may contribute to the disease process in SMA.