Patterning the retina for color vision

描述(申请人提供)：为了获得真彩色视觉，动物需要比较对不同颜色敏感的光感受器的输出。人类是三色动物，使用中心凹的蓝色(S)、绿色(M)和红色(L)视锥感光器来辨别颜色。在果蝇中，两个内部的光感受器R7和R8之间进行了比较，它们指向每个小眼(单位眼)的同一方向。事实上，苍蝇的视网膜由两类不同的小眼组成，它们随机分布在视网膜各处，专门区分不同的颜色。30%的小眼是p，在R7细胞中含有紫外光敏感的视紫红质光色素(Rh3)，在R8细胞中含有蓝色Rh5，能够最好地区分短波长。在其余70%的y小眼中，R7含有UV-Rh4，而R8含有绿色-Rh6；它们专门识别较长的波长。由于Rh3总是与Rh5联系在一起，Rh4与Rh6联系在一起，这表明在R7和R8之间存在着协调视紫红质表达的信号。这一提议提出研究一种三步路径，该路径导致对p和yR8两类的精确说明。首先，来自PR7的BMP/DPP信号指示PR8表达Rh5。该信号是由另一个相关的生长控制途径的受体-激活素受体介导的，这表明BMP和激活素途径存在交叉作用。其次，双稳定循环确保做出明确的决定来表示Rh6(Y)或Rh5(P)。有趣的是，这个环路涉及河马/疣肿瘤抑制途径和生长调节剂熔化，这是胰岛素/TOR途径的一部分。因此，这些肿瘤抑制通路在有丝分裂后的光感受器中被重新利用，因为它们不再需要控制增殖。最后，维持这两种截然不同的命运是由视紫红质分子本身调节的，这些分子可以避免不同敏感度的视紫红质的共同表达。这一建议提供了研究BMP/DPP和激活素通路之间的非正则相互作用的机会。它还将剖析稳定R8决定的肿瘤抑制途径，以及视紫红质参与维持每个光感受器一个视紫红质基因的排他性表达。最后，使用RNAi系的遗传筛选将识别介导这些信号通路功能的转录因子，并允许视紫红质的精确表达。这项工作与我们对视网膜模式的理解有明显的相关性，但也与河马/沃茨肿瘤抑制途径有关，该途径的上游成分和转录效应器尚不清楚。遗传学为识别这些新成分提供了最好的机会。公共卫生相关性：该项目解决了几个基本问题，不仅涉及视网膜模式，还涉及肿瘤抑制因子和生长控制途径的功能。我们预计，我们将能够提供这些途径的上游和下游组件的关键识别，特别是它们在基因表达水平上的输出，以及对它们交叉相互作用的理解。

DESCRIPTION (provided by applicant): In order to achieve true color vision, animals need to compare the outputs of photoreceptors that are sensitive to different colors. Humans are trichromats who use Blue (S), Green (M) and Red (L) cone photoreceptors in the fovea to discriminate colors. In Drosophila, comparison occurs between the two inner photoreceptors, R7 and R8, which point in the same direction in each ommatidium (unit eye). In fact, the fly retina is composed of two classes of distinct ommatidia, which are distributed randomly throughout the retina and specialize in discriminating among different colors. 30% of ommatidia are p, which contain a UV-sensitive Rhodopsin photopigment (Rh3) in the R7 cell and blue-Rh5 in R8 and can best discriminate among short wavelengths. In the remaining 70% y ommatidia, R7 contains UV-Rh4 while R8 contains green-Rh6; they specialize in the discrimination of longer wavelengths. Because Rh3 is always associated with Rh5 and Rh4 with Rh6, this indicates that there is a signal between R7 and R8 that coordinates Rhodopsin expression. This proposal offers to study a three-step pathway that leads to the precise specification of the two classes of p and y R8. First, a BMP/Dpp signal from pR7 instructs pR8 to express Rh5. The signal is mediated by the receptor for another related growth control pathway, the Activin receptor, suggesting that the BMP and Activin pathways cross-interact. Second, a bi-stable loop insures that an unambiguous decision is made to express either Rh6 (y) or Rh5 (p). Interestingly, this loop involves the Hippo/Warts tumor suppressor pathway and the growth regulator Melted, which is part of the Insulin/TOR pathway. Thus, these tumor suppressor pathways are re-utilized in post-mitotic photoreceptors after they are no longer needed to control proliferation. Finally, maintenance of the two distinct fates is mediated by the Rhodopsin molecules themselves that act to avoid co-expression of Rhodopsins of different sensitivity. This proposal offers to study the non-canonical interaction between the BMP/Dpp and Activin pathways. It will also dissect the tumor suppressor pathway that stabilizes the decision in R8 and the involvement of Rhodopsins in maintaining the exclusive expression of one Rhodopsin gene per photoreceptor. Finally, a genetic screen using RNAi lines will identify the transcription factors that mediate the function of these signaling pathways and allow precise expression of Rhodopsins. This work has clear relevance to our understanding of retinal patterning but also of the Hippo/Warts tumor suppressor pathway whose upstream components and transcriptional effectors remain unknown. Genetics offers the best chance to identify these new components. PUBLIC HEALTH RELEVANCE: This project addresses several fundamental questions, not only about retinal patterning but also about the function of tumor suppressor and growth control pathways. We anticipate that we will be able to provide critical identification of upstream and downstream components of these pathways, in particular their output at the level of gene expression, as well as an understanding of their cross-interactions.