Identification of factors controlling the genesis of cone photoreceptors

描述（由申请人提供）：本文描述的研究旨在阐明产生特定类别神经元-视网膜视锥光感受器的分子机制。控制这种特化细胞类型发育的因素还不清楚。使用微阵列分析小鼠突变产生多余的锥细胞，我们的实验室已经确定了一些基因上调伴随着这种细胞效应。这些基因中的两个是视锥细胞转导素亚基：Gnat 2，一个G蛋白α亚基，和Gnb 3，一个G蛋白β亚基。在成年脊椎动物视网膜中，Gnat 2仅在视锥光感受器中表达，而Gnb 3在双极细胞和视锥中发现。在这里，它们的功能是在视蛋白下游的信号转导级联中抑制光刺激，视蛋白是G蛋白偶联受体。初步证据表明，Gnat 2和Gnb 3都在小鼠和鸡的早期感光层中特异性表达，通过RNA原位杂交检测。与其他转导途径组分相比，这种表达是早熟的，其中大多数直到发育后期才表达。该提案将测试这些G蛋白亚基是否在发育早期起作用以指定视锥命运或允许视锥光感受器的适当分化。将在鸡视网膜中进行功能丧失和功能获得研究，以测试这些基因在视锥细胞产生中的必要性和/或充分性。在发育早期可以在Gnat 2和Gnb 3的上游起作用的候选G蛋白偶联受体家族是受体的Frizzled家族。Gnat 2已显示响应于WntSa（Frizzled受体的分泌配体）而与Frizzled 2受体偶联。实验将被设计为扩展以前的发现，Wnt信号参与锥发育。最终的目标将是转录配置文件的早期锥感光细胞谱系，以确定其他候选基因的功能，以产生完全分化的锥。我们设想这些研究提供了新的见解，如何在人类视觉中使用的主要感光体，锥，是在发展过程中产生的。将被测试的候选光感受器发生基因之一（Gnat 2）已被确定为色盲（无色觉）的遗传原因，该提案将解决这种疾病的机制。至少有2000万至2500万人患有遗传性疾病，导致光感受器退化和视力下降。对产生光感受器的正常机制的基本理解将为用新的功能性光感受器取代这些细胞提供基础。

DESCRIPTION (provided by applicant): The studies described here are designed to elucidate the molecular mechanisms underlying the production of a specific class of neurons - cone photoreceptors of the retina. The factors controlling the development of this specialized cell type are not well understood. Using microarray analysis of a mouse mutant that produces excess cones, our lab has identified a number of genes upregulated concommitantly with this cellular effect. Two of these genes are the cone transducin subunits: Gnat2, a G-protein alpha subunit, and Gnb3, a G-protein beta subunit. In the adult vertebrate retina, Gnat2 is expressed exclusively in cone photoreceptors, while Gnb3 is found in bipolar cells and cones. Here they function to transduce light stimulus in a signal transduction cascade downstream of opsins, which are G-protein coupled receptors. Preliminary evidence presented in this proposal shows that Gnat2 and Gnb3 are both expressed specifically in the early photoreceptor layer in both mice and chickens as assayed by RNA in situ hybridizations. This expression is precocious as compared to the other transduction pathway components, most of which are not expressed until much later in development. This proposal will test whether these G-protein subunits function early in development to specify the cone fate or allow for the proper differentiation of cone photoreceptors. Loss-of-function and gain-of-function studies will be used in the chicken retina to test the necessity and/or sufficiency of these genes in the production of cones. A candidate G-protein coupled receptor family that could function upstream of Gnat2 and Gnb3 early in development is the Frizzled family of receptors. Gnat2 has been shown to couple to Frizzled2 receptor in response to WntSa, a secreted ligand for Frizzled receptors. Experiments will be designed to extend previous findings that Wnt signaling is involved in cone development. The final aim will be to transcriptionally profile the early cone photoreceptor lineage to identify other candidate genes that function to generate fully differentiated cones. We envision these studies providing new insights into how the primary photoreceptor used in human vision, the cone, is derived during development. One of the candidate photoreceptor-genesis genes that will be tested (Gnat2) has been identified as a genetic cause of achromatopsia (no color vision) and this proposal will address the mechanism for this disease. At least 20 to 25 million people are afflicted with genetic diseases that cause the degeneration of photoreceptors and a decrease in their vision. A basic understanding of the normal mechanisms that generate photoreceptors will provide the basis for replacing these cells with new functional photoreceptors.