Kojima Keiichi, Matsutani Yuki, Yanagawa Masataka, Imamoto Yasushi, Yamano Yumiko, Wada Akimori, Shichida Yoshinori, Yamashita Takahiro
Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700-8530, Japan.
Sci Adv. 2021 Oct;7(40):eabj1316. doi: 10.1126/sciadv.abj1316. Epub 2021 Oct 1.
Vertebrates generally have a single type of rod for scotopic vision and multiple types of cones for photopic vision. Noteworthily, nocturnal geckos transmuted ancestral photoreceptor cells into rods containing not rhodopsin but cone pigments, and, subsequently, diurnal geckos retransmuted these rods into cones containing cone pigments. High sensitivity of scotopic vision is underlain by the rod’s low background noise, which originated from a much lower spontaneous activation rate of rhodopsin than of cone pigments. Here, we revealed that nocturnal gecko cone pigments decreased their spontaneous activation rates to mimic rhodopsin, whereas diurnal gecko cone pigments recovered high rates similar to those of typical cone pigments. We also identified amino acid residues responsible for the alterations of the spontaneous activation rates. Therefore, we concluded that the switch between diurnality and nocturnality in geckos required not only morphological transmutation of photoreceptors but also adjustment of the spontaneous activation rates of visual pigments.
脊椎动物通常具有一种用于暗视觉的视杆细胞和多种用于明视觉的视锥细胞。值得注意的是，夜行性壁虎将祖先的光感受器细胞转变为含有视锥色素而非视紫红质的视杆细胞，随后，日行性壁虎又将这些视杆细胞重新转变为含有视锥色素的视锥细胞。暗视觉的高灵敏度是由视杆细胞的低背景噪声决定的，这种低背景噪声源于视紫红质的自发激活率远低于视锥色素。在这里，我们发现夜行性壁虎的视锥色素降低了它们的自发激活率以模仿视紫红质，而日行性壁虎的视锥色素恢复了与典型视锥色素相似的高自发激活率。我们还确定了负责自发激活率改变的氨基酸残基。因此，我们得出结论，壁虎昼夜习性的转变不仅需要光感受器的形态转变，还需要调整视觉色素的自发激活率。
