Isayama Tomoki, Chen Ying, Kono Masahiro, Fabre Eduard, Slavsky Michael, DeGrip Willem J, Ma Jian-Xing, Crouch Rosalie K, Makino Clint L
Department of Ophthalmology, Massachusetts Eye and Ear Infirmary and Harvard Medical School, Boston, Massachusetts, 02114.
J Comp Neurol. 2014 Jul 1;522(10):2249-65. doi: 10.1002/cne.23531.
Although more than one type of visual opsin is present in the retina of most vertebrates, it was thought that each type of photoreceptor expresses only one opsin. However, evidence has accumulated that some photoreceptors contain more than one opsin, in many cases as a result of a developmental transition from the expression of one opsin to another. The salamander UV-sensitive (UV) cone is particularly notable because it contains three opsins (Makino and Dodd [1996] J Gen Physiol 108:27-34). Two opsin types are expressed at levels more than 100 times lower than the level of the primary opsin. Here, immunohistochemical experiments identified the primary component as a UV cone opsin and the two minor components as the short wavelength-sensitive (S) and long wavelength-sensitive (L) cone opsins. Based on single-cell recordings of 156 photoreceptors, the presence of three components in UV cones of hatchlings and terrestrial adults ruled out a developmental transition. There was no evidence for multiple opsin types within rods or S cones, but immunohistochemistry and partial bleaching in conjunction with single-cell recording revealed that both single and double L cones contained low levels of short wavelength-sensitive pigments in addition to the main L visual pigment. These results raise the possibility that coexpression of multiple opsins in other vertebrates was overlooked because a minor component absorbing at short wavelengths was masked by the main visual pigment or because the expression level of a component absorbing at long wavelengths was exceedingly low.
尽管大多数脊椎动物的视网膜中存在不止一种视觉视蛋白，但人们曾认为每种光感受器仅表达一种视蛋白。然而，越来越多的证据表明，一些光感受器含有不止一种视蛋白，在许多情况下，这是由于从一种视蛋白的表达向另一种视蛋白表达的发育转变所致。蝾螈的紫外线敏感（UV）视锥细胞尤为显著，因为它含有三种视蛋白（牧野和多德[1996]《普通生理学杂志》108:27 - 34）。两种视蛋白的表达水平比主要视蛋白的水平低100多倍。在这里，免疫组织化学实验确定主要成分是一种UV视锥视蛋白，两种次要成分是短波长敏感（S）和长波长敏感（L）视锥视蛋白。基于对156个光感受器的单细胞记录，幼体和成体陆地蝾螈的UV视锥细胞中存在三种成分排除了发育转变的可能性。在视杆细胞或S视锥细胞中没有证据表明存在多种视蛋白类型，但免疫组织化学以及结合单细胞记录的部分漂白显示，单L视锥细胞和双L视锥细胞除了主要的L视觉色素外，还含有低水平的短波长敏感色素。这些结果增加了一种可能性，即其他脊椎动物中多种视蛋白的共表达被忽视了，原因要么是吸收短波长的次要成分被主要视觉色素掩盖，要么是吸收长波长的成分表达水平极低。
