School of Life Science and Technology, the Key Laboratory of Developmental Genes and Human Disease, Southeast University, Nanjing, Jiangsu 210096, China.
School of Life Science and Technology, the Key Laboratory of Developmental Genes and Human Disease, Southeast University, Nanjing, Jiangsu 210096, China; Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu 226001, China.
J Biol Chem. 2020 Apr 24;295(17):5554-5563. doi: 10.1074/jbc.RA120.012764. Epub 2020 Mar 20.
Heterotrimeric G proteins mediate a variety of signaling processes by coupling G protein-coupled receptors to intracellular effector molecules. In the α gene encodes several Gαq splice variants, with the Gαq1 isoform protein playing a major role in fly phototransduction. However, α null mutant flies still exhibit a residual light response, indicating that other Gαq splice variants or additional Gq α subunits are involved in phototransduction. Here, we isolated a mutant fly with no detectable light responses, decreased rhodopsin (Rh) levels, and rapid retinal degeneration. Using electrophysiological and genetic studies, biochemical assays, immunoblotting, real-time RT-PCR, and EM analysis, we found that mutations in the α gene disrupt light responses and demonstrate that the Gαq3 isoform protein is responsible for the residual light response in α null mutants. Moreover, we report that Gαq3 mediates rhodopsin synthesis. Depletion of all Gαq splice variants led to rapid light-dependent retinal degeneration, due to the formation stable Rh1-arrestin 2 (Arr2) complexes. Our findings clarify essential roles of several different Gαq splice variants in phototransduction and retinal integrity in and reveal that Gαq3 functions in rhodopsin synthesis.
三聚体 G 蛋白通过将 G 蛋白偶联受体与细胞内效应分子偶联来介导各种信号转导过程。α 基因编码几种 Gαq 剪接变体，其中 Gαq1 同工型蛋白在果蝇光转导中起主要作用。然而，α 缺失突变体果蝇仍表现出残余光反应，表明其他 Gαq 剪接变体或其他 Gqα 亚基参与光转导。在这里，我们分离到一种突变体果蝇，其对光没有可检测到的反应，视紫红质（Rh）水平降低，视网膜迅速退化。通过电生理学和遗传学研究、生化分析、免疫印迹、实时 RT-PCR 和 EM 分析，我们发现 α 基因的突变破坏了光反应，并证明 Gαq3 同工型蛋白负责α 缺失突变体中的残余光反应。此外，我们报告 Gαq3 介导视紫红质合成。由于形成稳定的 Rh1-抑制素 2（Arr2）复合物，所有 Gαq 剪接变体的耗竭导致快速光依赖性视网膜退化。我们的研究结果阐明了几种不同的 Gαq 剪接变体在果蝇光转导和视网膜完整性中的重要作用，并揭示了 Gαq3 在视紫红质合成中的功能。
