Guidance of Oligodendrocyte Processes: The Role of Local Protein Synthesis

描述（由申请人提供）：在中枢神经系统（CNS）的发育过程中，来自神经元和少突胶质细胞的迁移后细胞发出在实质中导航的过程，以寻找诱导其成熟的目标信号，即神经元的突触形成和少突胶质细胞的髓鞘形成。这种过程导航的调节已经在神经元细胞中得到了很好的表征，其中感觉运动结构，神经元生长锥，位于过程尖端，是感知环境信号的“细胞器”。相比之下，我们对少突胶质过程的寻路和靶向却知之甚少。我们的初步数据表明，少突胶质过程在其远端具有在结构和功能上类似于神经元生长锥的“细胞器”，我们将其称为少突胶质生长锥样结构（olg -生长锥）。在神经元中，生长锥内的mRNA转运和局部限制性蛋白合成被认为是轴突/神经突寻路和靶向的主要调节因子。我们的初步数据表明，类似的调控机制可能对少突胶质细胞过程的寻路和靶向很重要。因此，我们提出了一个中心假设，即髓鞘形成前、迁移后的少突胶质细胞拥有含有mrna的olg生长锥，其局部受限的翻译对于少突胶质过程寻路和靶向的调节至关重要，即髓鞘形成。这一假设将在两个具体目标中得到检验。1)我们将确定局部限制性蛋白合成在olg生长锥寻路中的作用，特别是在响应非允许信号的趋化转向中。在这组实验中，局部限制性蛋白质合成在寻路的olg生长锥中发生的程度将被确定。此外，分离过程的趋化转向将在抑制蛋白质合成后进行分析。预计局部限制性蛋白合成的抑制将干扰OLG-生长锥的趋化反应。2)使用微阵列方法，我们将识别存在于olg生长锥中特异性响应轴突靶向信号的mrna。这组实验有望揭示对olg生长锥靶向（即髓鞘形成的起始）很重要的候选蛋白。在基于本提案发现的持续研究中，我们计划进一步表征这些蛋白质。因此，提出的研究代表了进入一系列旨在更好地了解少突胶质细胞过程寻路和靶向调节的实验的第一步。这种知识的进步是特别令人感兴趣的，因为过程生长和轴突识别的缺陷似乎是患有人类主要脱髓鞘疾病多发性硬化症的CMS患者中病变修复的主要限制因素之一。

DESCRIPTION (provided by applicant): During development of the central nervous system (CNS) post-migratory cells of both neuronal and oligodendroglial origin send out processes that navigate through the parenchyma in search for a target signal that induces their maturation, i.e. synapse formation for neuronal and myelin sheath formation for oligodendroglial cells. The regulation of this process navigation has been well characterized for neuronal cells, where a sensorimotor structure, the neuronal growth cone, located at the process tip is the "organelle" that senses environmental cues. In contrast, surprisingly little is known about oligodendroglial process pathfinding and targeting. Our preliminary data demonstrate that oligodendrocyte processes possess at their distal ends "organelles" that structurally and functionally resemble neuronal growth cones and that we will refer to as oligodendroglial growth cone-like structures (OLG-growth cones). In neurons, mRNA transport and locally restricted protein synthesis within the growth cone are considered main regulators of axon/neurite pathfinding and targeting. Our preliminary data suggest that similar regulatory mechanisms may be important for the pathfinding and targeting of oligodendrocyte processes. Thus, we formulate the central hypothesis that premyelinating, post-migratory oligodendrocytes possess OLG-growth cones that contain mRNAs, the locally restricted translation of which is critical for the regulation of oligodendroglial process pathfinding and targeting, i.e. myelination. This hypothesis will be tested in two specific aims. 1) We will determine the role of locally restricted protein synthesis for OLG-growth cone pathfinding and in particular for chemotropic turning in response to non-permissive cues. In this set of experiments the extent to which locally restricted protein synthesis occurs in pathfinding OLG-growth cones will be determined. In addition, chemotropic turning of separated processes will be analyzed after inhibition of protein synthesis. It is expected that inhibition of locally restricted protein synthesis will perturb OLG- growth cone chemotropic turning responses. 2) Using a microarray approach, we will identify mRNAs that are present in OLG-growth cones specifically in response to axonal targeting signals. This set of experiments is expected to reveal candidate proteins that are important for OLG-growth cone targeting, i.e. the initiation of myelin sheath formation. In continuing studies based on the findings of the present proposal, we are planning to further characterize these proteins. The proposed studies thus represent a first step into a set of experiments designed to better understand the regulation of oligodendrocyte process pathfinding and targeting. Such advancement in knowledge is of particular interest since deficiencies in process outgrowth and axon recognition appear to be among the main limiting factors for repair of lesions present in the CMS of patients suffering from the major demyelinating disease in humans, Multiple Sclerosis.