Axnoal Transport and Cytoskeletal Incorporation of Neurofilaments

技术上的SUMMARYNeurons(大脑中的“思考”细胞)通过长长的延长线(“轴突”)相互连接，就像电话线一样，传递允许我们思考、感觉和移动的信号。一旦神经元以这种方式连接起来，它们的整体结构在整个一生中基本上保持不变。然而，这些轴突是活的，必须保持，甚至比我们的大多数细胞更容易受到压力。它们的形状和与下一个神经元保持连接的能力来自于沿其长度沉积的纤维蛋白组件。这种排列统称为“细胞骨架”，包括“神经丝”和“微管”。一个主要的复杂因素是轴突不能制造任何所需的蛋白质。相反，轴突中的一切，包括纤维本身，首先在细胞体中合成，然后通过一种被称为“轴突运输”的过程沿着轴突传递。某些蛋白质起到发动机的作用，并通过微管携带其他蛋白质和营养物质沿着轴突，基本上就像“铁轨”一样。调节神经细丝轴突运输的运动(S)尚不清楚。由于神经丝被认为为成熟的轴突提供结构支持，阐明其运输机制对于了解神经元的发育和再生具有重要意义。研究表明，神经丝作为运动蛋白的货物进行运输，它们也沿着微管轨道运输。拟议的研究将检查神经丝与这种运动蛋白相互作用的性质和程度，包括确定3-神经丝亚单位中的哪个亚基，以及亚单位的哪个区域(S)介导这种相互作用。一旦进入轴突，神经丝就会经历一系列的代谢修饰(“磷酸化”)，从而促进神经丝-神经丝的联系，并在此过程中形成细胞骨架的网状结构。还将确定这种神经丝-神经丝协会是否与神经丝-运动协会竞争。这些分析将通过在培养的神经元和转基因小鼠中表达外源基因来进行，这些小鼠缺乏一个或多个神经丝亚单位。这些后一种分析还将提供信息，说明早熟神经丝的磷酸化如何通过促进早熟的神经丝从其运输运动中解离，来促进它们在某些运动神经元障碍中的异常积累。

Tom Shea99-05123NON-TECHNICAL SUMMARYNeurons (the "thinking" cells of the brain) interconnect with each other by long extensions ("axons") that, like telephone wires, transmit the signals that allow us to think, feel and move. Once neurons have connected in this manner, their overall structure remains largely unchanged throughout an entire lifetime. These axons are, however, as alive, must be maintained, and are even more prone to stress than most of our cells. Their shape and ability to remain connected to the next neuron is derived from fibrous protein assemblies that are deposited along their length. This array, collectively referred to as the "cytoskeleton", includes "neurofilaments" and "microtubules". A major complicating factor is that the axon cannot manufacture any required proteins. Rather, everything in the axon, including the fibers themselves, is first synthesized in the cell body, and subsequently passed along the axon by a process referred to as "axonal transport." Certain proteins function as motors and carry other proteins and nutrients along the axon using microtubules essentially as "railroad tracks." The motor(s) that mediate axonal transport of neurofilaments are not known. Since neurofilaments are thought to provide structural support to the mature axon, elucidation of their transport mechanism is of great interest both for understanding neuronal development and for considerations of regeneration. Studies suggest that neurofilaments undergo transport as cargo of the motor protein "kinesin", and that they are also transported along microtubule tracks. The proposed studies will examine the nature and extent of interaction of neurofilaments with this motor protein, including determining which of the 3-neurofilament subunits, and moreover which region of the subunit(s), mediates this interaction. Once in the axon, neurofilaments undergo a series of metabolic modifications ("phosphorylation") which promote neurofilament-neurofilament associations, and, in doing so, form the latticework of the cytoskeleton. It will also be determined whether or not such neurofilament-neurofilament associations compete with neurofilament-motor associations. These analyses will be carried out by expressing foreign genes in cultured neurons and in mice that have been genetically engineered to lack one or more neurofilament subunits. These latter analyses will also provide information as to how precocious neurofilament phosphorylation, by fostering prematuredissociation from their transport motor, could contribute to their aberrant accumulation in certain motor neuron disorders.