Pathfinding of Ganglion Cell Axons and Ocular Albinism

描述：（申请人的摘要）患有眼白化病（OA）的个体缺乏 立体视觉由于减少同侧组成部分的 视网膜色素上皮细胞中黑色素水平不足 （RPE）。导致这种疾病的X连锁形式的基因，0A 1， 识别和表征。它编码一种G蛋白偶联受体， 定位于黑素体膜上的未知功能。 黑素生成发生在这些细胞器中，酪氨酸酶是关键酶 参与这个过程。黑素体存在于黑素细胞中， 皮肤和RPE中。 本研究的目的是探讨轴突的分子机制， 引导，导致形成异常的突触连接，在 大脑受OA影响的个体。一种小鼠白化病突变体， 酪氨酸酶的点突变导致非交叉视网膜 轴突，提供了一个遗传模型，以解决为什么缺乏黑色素的结果 OA视交叉的异常。我们建议使用基因 一种鉴定酪氨酸酶、RPE细胞和Oal提供的信号的方法， 视交叉处的直接视网膜轴突发散及其机制 视网膜神经节细胞对这些线索的反应。最初我们 将用基因工程改造小鼠体内的Cre重组酶。这些动物将允许 我们控制特定基因表达的时间。克里老鼠会 与表达酪氨酸酶或白喉毒素的转基因白化病小鼠杂交， 以及携带条件等位基因α 1的转基因小鼠。诱导型 酪氨酸酶对黑色素的恢复将使我们能够确定 色素沉着在轴突寻路中起作用。的诱导表达 白喉毒素消融RPE将表明这些细胞是否影响 神经节细胞的分化及其轴突寻路。的 引入“开/关”开关来翻转Oal编码序列将允许我们 为了确定轴突穿越的阶段是否可以通过逆转， 野生型基因的再表达。通过这些获得的信息 研究会。增加我们对眼白化病病理学的理解 会帮助我们来解开视觉中寻路的分子机制 交叉，一个“选择点”，生长锥导航到相同或相反的方向， 大脑的一侧。发现RPE中的色素沉着缺陷如何导致 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.