Division of Molecular and Developmental Biology, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
PLoS One. 2013 Aug 23;8(8):e72065. doi: 10.1371/journal.pone.0072065. eCollection 2013.
Cone photopigments (opsins) are crucial elements of, and the first detection module in, color vision. Individual opsins have different wavelength sensitivity patterns, and the temporal and spatial expression patterns of opsins are unique and stringently regulated. Long and middle wavelength-sensitive (L/M) opsins are of the same phylogenetic type. Although the roles of thyroid hormone/TRß2 and COUP-TFs in the transcriptional regulation of L/M opsins have been explored, the detailed mechanisms, including the target sequence in the enhancer of L/M opsins, have not been revealed. We aimed to reveal molecular mechanisms of L/M opsins in vertebrates. Using several human red opsin enhancer/promoter-luciferase reporter constructs, we found that TRß2 increased luciferase activities through the 5'-UTR and intron 3-4 region, whereas the presence of T3 affected only the intron 3-4 region-dependent luciferase activity. Furthermore, COUP-TFII suppressed intron 3-4 region-dependent luciferase activities. However, luciferase expression driven by the mouse M opsin intron 3-4 region was only slightly increased by TRß2, and rather enhanced by COUP-TFII. To determine whether these differential responses reflect differences between primates and rodents, we examined the enhancer/promoter region of the red opsin of the common marmoset. Interestingly, while TRß2 increased 5'-UTR- or intron 3-4 region-driven luciferase expression, as observed for the human red opsin, expression of the latter luciferase was not suppressed by COUP-TFII. In fact, immunostaining of common marmoset retinal sections revealed expression of COUP-TFII and red opsin in the cone cells.
视锥感光色素（opsin）是色觉的关键组成部分和第一检测模块。单个 opsin 具有不同的波长敏感性模式，而 opsin 的时空表达模式是独特且严格调控的。长波和中波敏感（L/M）opsin 属于同一进化类型。尽管甲状腺激素/TRß2 和 COUP-TFs 在 L/M opsin 的转录调控中的作用已经被探索，但详细的机制，包括 L/M opsin 增强子中的靶序列，尚未被揭示。我们旨在揭示脊椎动物 L/M opsin 的分子机制。使用几种人红视蛋白增强子/启动子-荧光素酶报告基因构建体，我们发现 TRß2 通过 5'-UTR 和内含子 3-4 区域增加荧光素酶活性，而 T3 的存在仅影响内含子 3-4 区域依赖性荧光素酶活性。此外，COUP-TFII 抑制内含子 3-4 区域依赖性荧光素酶活性。然而，由小鼠 M opsin 内含子 3-4 区域驱动的荧光素酶表达仅被 TRß2 轻度增加，而被 COUP-TFII 显著增强。为了确定这些差异反应是否反映灵长类动物和啮齿动物之间的差异，我们检查了普通狨猴的红视蛋白的增强子/启动子区域。有趣的是，虽然 TRß2 增加了 5'-UTR 或内含子 3-4 区域驱动的荧光素酶表达，就像人红视蛋白一样，但后者的荧光素酶表达不受 COUP-TFII 的抑制。事实上，对普通狨猴视网膜切片的免疫染色显示 COUP-TFII 和红视蛋白在视锥细胞中表达。
