SGER: Does Re-expression of Vimentin Induce Resumption of Axonal Elongation?

神经元延伸出长长的被称为轴突的过程，其本质上就像电话线一样，传递让我们思考、感觉和移动的信号。在胚胎发育过程中，轴突快速伸长，连接神经细胞和肌肉。然而，一旦轴突到达目标，它就会停止伸长并稳定其结构，因为它现在的任务是在个体的一生中保持连接。轴突内部由一系列纤维结构支撑，这些纤维结构统称为细胞骨架（即细胞骨架）。谢伊博士的实验室已经证明，发育过程中的快速伸长是由一种名为维门蛋白（vimentin）的蛋白质介导的，这种蛋白质形成柔韧的细丝，可以快速组装和拆卸。然而，一旦神经元到达目标，它就会停止产生波形蛋白，取而代之的是一组不同的蛋白质，称为神经丝。神经丝形成的纤维相互连接并结合在一起，形成一个稳定的基质，支撑着已经发育完全的轴突。不幸的是，如果轴突死亡或被切断，与神经元相连的部分就无法重新开始生长，从而无法与之前的目标重新连接。PI在神经母细胞瘤细胞中研究了这些事件；一种细胞系，由于易于操作和成本效益。他们的早期观察表明，在中间细丝（IFs）中存在发育等级。在轴突起始阶段，Vimentin （Vm）是主要的IF种类。在轴突伸长期间，Vm表达停止，神经元表达神经丝蛋白，增加轴突直径，稳定轴突发育。Shea博士的实验室已经通过细胞内传递中和抗体和反义寡核苷酸证明，Vm对于轴突的起始是必不可少的，但一旦轴突形成，则是必不可少的；相反，NFs不是轴突起始所必需的，而是轴突稳定所必需的。PI建议在体外生长的运动神经元（连接并刺激肌肉细胞的神经元）中进一步研究这种现象，以确定我们是否可以诱导轴突再次开始生长，以及当轴突到达目标时是否会停止生长。Shea博士的实验室精通所有所需的方法，该项目将为研究生和本科生提供丰富的培训机会。

Neurons, extend long processes called axons, that act essentially as telephone wires and transmit the signals that allow us to think, feel and move. During embryonic development, axons elongate at a rapid rate, connecting nerve cells and muscles. Once an axon reaches its target, however, it stops elongating and stabilizes its structure, since its task is now to remain connected for the lifetime of the individual. The axon is supported internally by a series of fibrous structures collectively referred to as the cytoskeleton (that is, the skeleton of the cell). Dr. Shea's laboratory has shown that the rapid elongation during development is mediated by a protein called vimentin, that forms pliable filaments that rapidly assemble and disassemble. Once the neuron reaches its target, however, it stops producing vimentin, and replaces it with a different group of proteins called neurofilaments. Neurofilaments make fibers that cross link and bind together, and form a stabilized matrix that supports the now fully-grown axon. Unfortunately, should an axon die or be severed, the portion that is connected to the neuron is unable to start growing again to allow reconnection to its previous target. The PI has studied these events in neuroblastoma cells; a cell line, due to ease of manipulation and cost-effectiveness. Their early observations indicated a developmental heirarchy in intermediate filaments (IFs). Vimentin (Vm) is the predominant IF species during axonal initiation. During axonal elongation, Vm expression ceases and neurons express neurofilament (NF) proteins, which increase axonal caliber and stabilize the developing axon. Dr. Shea's laboratory has demonstrated by intracellular delivery of neutralizing antibodies and antisense oligonucleotides that Vm is essential for axon initiation but is dispensable once the axon has formed; conversely, NFs are not required for axonal initiation but are essential for axonal stabilization. The PI proposes to examine further this phenomenon in motor neurons (neurons that connect to and stimulate muscle cells) grown outside the body, to determine whether or not we can induce axons to start growing again and whether or not such axons stop growing when they reach their targets. Dr. Shea's laboratory is proficient in all of the required methodologies, and this project will provide rich training opportunities for graduate and undergraduate students.