多年以来科学家一直努力研究动物视觉系统的机理，譬如动物如何在不同的情况下，包括黑夜与强烈日光下侦测光，及人类眼睛如何于不同的光度环境下作出反应及调控光的接收。
近期来自香港科技大学研究人员以果蝇的感光细胞作为模型系统，发现了动物的感光细胞如何以极高的速度侦测强度差距极大的光信号的机理，这对于视网膜色素变性（人群中每3，000人就有一人会患上此病，其早期病症表现为夜盲）及其他人类视觉障碍的研究大有裨益。也对于了解人类的癌症、神经退化及免疫力障碍等疾病的生物信号转导过程亦有帮助，因为蛋白氧化与这些生物过程有关。
研究人员发现在暗光的环境下，还原的INAD蛋白处于还原状态，让果蝇的视觉系统可以保持对光侦测的高敏感度，而随着光线强度的逐渐增加，INAD蛋白进入氧化状态，从而降低了感光细胞对光线的敏感度。因此，INAD支架蛋白在动物视觉侦测系统内，起了‘变阻器’的作用：感光细胞将随着侦测到的光线强弱而调整输出的神经信号强弱。
这些说明动物眼睛内称为INAD的支架蛋白会跟随光线的强弱而发生分子结构的改变，从而调控光信号的侦测速度与信号输出的大小。INAD蛋白这种倚赖光的分子结构变化，乃是由动物眼睛的快速氧化还原所致。
另外一篇文章中，来自纽约大学等处的研究人员通过对果蝇视网膜上的光感细胞进行分析，发现了调解视觉系统基因表达的重要机制。
果蝇的视紫质（视网膜光感受器）至少有13种表达模式，科学家们对于这项基因如何相互影响的并不清楚，而这对于了解眼睛的作用机制具有重要的意义。
在这篇文章中，研究人员通过对比正常和变异的视觉系统，发现转录因子基因dve在调解视紫质表达的网络中是个关键点。在dve的变异体中，正常存在于色彩视觉光感受器中的视紫质会在感受运动的光感受器中表达。这种变异会导致果蝇在略微的光线变化时对光的检测缺陷。
dve基因是两个相反连锁前馈回路（FFLs）的共享成分。FFLs是网络中控制基因表达的重要基序。dve在其中一个FFL中的作用是抑制感受运动光感受器中的视紫质表达。而在色觉光感受器中，另一个FFL通过dve基因解除抑制，激活视紫质的表达。因此，这个网络的作用既限制又导致特定细胞的表达。这个连锁FFL基序有可能是控制基因表达的一个总的机制。
原文摘要：
Interlocked Feedforward Loops Control Cell-Type-Specific Rhodopsin Expression in the Drosophila Eye
Highlights
Dve is a key transcription factor in the network regulating Rhodopsins in the fly eye
Dve is a shared component of two opposing, interlocked feedforward loops (FFLs)
An incoherent FFL represses expression of Rhodopsins in outer photoreceptors
A coherent FFL relieves Dve repression and activates Rhodopsins in inner photoreceptors
Summary
How complex networks of activators and repressors lead to exquisitely specific cell-type determination during development is poorly understood. In the Drosophila eye, expression patterns of Rhodopsins define at least eight functionally distinct though related subtypes of photoreceptors. Here, we describe a role for the transcription factor gene defective proventriculus (dve) as a critical node in the network regulating Rhodopsin expression. dve is a shared component of two opposing, interlocked feedforward loops (FFLs). Orthodenticle and Dve interact in an incoherent FFL to repress Rhodopsin expression throughout the eye. In R7 and R8 photoreceptors, a coherent FFL relieves repression by Dve while activating Rhodopsin expression. Therefore, this network uses repression to restrict and combinatorial activation to induce cell-type-specific expression. Furthermore, Dve levels are finely tuned to yield cell-type- and region-specific repression or activation outcomes. This interlocked FFL motif may be a general mechanism to control terminal cell-fate specification.
The INAD Scaffold Is a Dynamic, Redox-Regulated Modulator of Signaling in the Drosophila EyeHighlights
PDZ domains 4 and 5 of Drosophila scaffold protein INAD form a supramodule
Coupling between PDZ4 and 5 elevates the redox potential of the PDZ5 disulfide bond
The release of protons by PIP2 hydrolysis regulates the coupling of PDZ4 and 5
The redox potential cycle of the PDZ5 disulfide bond regulates fly visual signaling
Summary
INAD is a scaffolding protein that regulates signaling in Drosophila photoreceptors. One of its PDZ domains, PDZ5, cycles between reduced and oxidized forms in response to light, but it is unclear how light affects its redox potential. Through biochemical and structural studies, we show that the redox potential of PDZ5 is allosterically regulated by its interaction with another INAD domain, PDZ4. Whereas isolated PDZ5 is stable in the oxidized state, formation of a PDZ45 supramodule locks PDZ5 in the reduced state by raising the redox potential of its Cys606/Cys645 disulfide bond by 330 mV. Acidification, potentially mediated via light and PLCβ-mediated hydrolysis of PIP2, disrupts the interaction between PDZ4 and PDZ5, leading to PDZ5 oxidation and dissociation from the TRP Ca2+ channel, a key component of fly visual signaling. These results show that scaffolding proteins can actively modulate the intrinsic redox potentials of their disulfide bonds to exert regulatory roles in signaling.
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