Pathfinding of Ganglion Cell Axons and Ocular Albinism

描述：(申请者摘要)眼白化病(OA)患者缺乏 立体视觉是由于大脑的同侧部分减少 视束和视网膜色素上皮中黑色素水平不足 (RPE)。导致这种X连锁形式的这种疾病的基因0A1已经被 确定和表征的。它编码一个G蛋白偶联受体。 定位在黑素体膜上的未知功能。 黑素合成发生在这些细胞器中，酪氨酸酶是关键酶。 参与了这一过程。黑色素存在于黑素细胞中。 皮肤和RPE中。 这项提议的目的是研究轴突的分子机制。 导致脑内异常突触连接形成的引导 受骨性关节炎影响的人的大脑。小鼠白化病突变体，携带一种 酪氨酸酶基因突变导致未交叉视网膜数目减少 轴突提供了一种遗传模型来解释为什么黑色素缺乏会导致 骨性关节炎患者视交叉的异常。我们建议使用一种基因 一种识别酪氨酸酶、RPE细胞和OAL提供的提示的方法 视交叉处视网膜轴突的直接发散及其机制 视网膜神经节细胞对这些提示作出反应的规范。最初，我们 将对具有Cre重组酶的小鼠进行基因工程。这些动物将允许 美国控制特定基因表达的时间。CRE-MICE将是 与表达酪氨酸酶或白喉毒素的转基因白化小鼠杂交， 以及携带条件等位基因0al的转基因小鼠。诱导性 酪氨酸酶对黑色素的修复将使我们能够确定 色素沉着在轴突寻路中起作用。诱导性的表达 白喉毒素消融RPE会表明这些细胞是否会影响 神经节细胞的分化和轴突的发现。这个 在翻转OAL编码序列的过程中引入“开/关”开关将使我们能够 为了确定轴突交叉的阶段是否可以被 野生型基因的重新表达。使用这些工具获得的信息 学习会的。加深对白化病发病机制的认识 并将帮助我们。揭开视神经寻路的分子机制 交叉，一个生长锥体导航到相同或相反的“选择点” 大脑的一侧。了解RPE中的色素沉着缺陷是如何引起的 轴突引导和视网膜发育的异常可能提供 适用于未来治疗的见解。

DESCRIPTION: (Applicant's Abstract) Individuals with ocular albinism (OA) lack stereoscopic vision due to a reduction of the ipsilateral component of the optic tract and have deficient melanin levels in the retinal pigment epithelium (RPE). The gene that causes the X-linked form of this disease, 0A1, has been identified and characterized. It encodes a G-protein coupled-receptor of unknown function that is localized on the membrane of melanosomes. Melanogenesis occurs in these organelles and tyrosinase is the key enzyme involved in this process. Melanosornes are present in the melanocytes, of the skin and in the RPE. The goal of this proposal is to investigate the molecular mechanisms of axon guidance that lead to the formation of abnormal synaptic connections in the brain of individuals affected with OA. The mouse albino mutant, that carries a point mutation in tyrosinase leading to decreased numbers of uncrossed retinal axons, offers a genetic model to address why the deficiency in melanin results in the abnormality at the optic chiasm seen in OA. We propose to use a genetic approach to identify the cues provided by tyrosinase, RPE cells and Oal that direct retinal axon divergence at the chiasm, and the mechanisms underlying specification of retinal ganglion cells to respond to these cues. Initially, we will genetically engineer mice having Cre-recombinase. These animals will allow us to control the timing of expression of specific genes. The Cre-mice will be crossed with transgenic albino mice expressing tyrosinase or diphteria toxin, and with transgenic mice carrying a conditional allele of 0al. The inducible restoration of melanine by tyrosinase will allow us to determine whether pigmentation has a role in axonal pathfinding. The inducible expression of diphteria toxin to ablate the RPE will indicate whether these cells influence both the differentiation of ganglion cells and their axonal pathfinding. The introduction of an "on/off" switch to flip Oal coding sequences will allow us to determine whether the stages of axonal crossing can be reversed by the re-expression of the wild type gene. The information obtained with these studies will. increase our understanding of the pathology of ocular albinism and will help us . to unravel molecular mechanisms of pathfinding in the optic chiasm, a "choice point" where growth cones navigate to the same or opposite side of the brain. Finding how pigmentation defects in the RPE cause abnormalities in axonal guidance and in retinal development may provide insights applicable to future therapy.