Exploration of human trichromatic origin by studying visual pigment genes of nocturnal primates and zebrafish

脊椎动物的视色素可分为5类：RH 1、SWS 1、SWS 2、RH 2和LWS。只有灵长类动物和硬骨鱼被认为有亚类的色素，大概反映了他们的光环境适应。然而，关于灵长类和鱼类视色素的基因组结构、光谱特性和表达调控的研究还很有限，我们发现，高等灵长类中唯一的夜行猴--枭猴在Y染色体和X染色体上都有LWS色素基因，而其他哺乳动物的X染色体上都有。我们还发现，加拉戈斯和洛里斯，夜间原猴的SWS 1基因，在编码区有多个插入和缺失，是非功能化的。与昼行动物相比，盔形目LWS色素的吸收光谱发生了蓝移。结果表明，斑马鱼基因组中含有2个红色（LWS-1和LWS-2）、4个绿色（RH 2 -1、RH 2 -2、RH 2 -3和RH 2 -4）以及1个蓝色（SWS 2）和1个紫外（SWS 1）视蛋白基因，其中LWS-2、RH 2 -2和RH 2 -3是新发现的。SWS 2、LWS-1和LWS-2串联定位，RH 2 -1、RH 2 -2、RH 2 -3和RH 2 -4形成另一个串联基因簇。从视蛋白cDNA重构的色素的峰吸收光谱在它们之间显著不同。定量RT-PCR结果显示，不同的视蛋白基因在视网膜中的表达水平存在显著差异。我们还发现RH 1基因上游1 kb的区域可以导致GFP在视杆细胞特异性表达，其时空模式与内源性RH 1基因的时空模式没有区别。

Vertebrate visual pigments can be classified into five classes : RH1, SWS1, SWS2, RH2, and LWS. Only primates and bony fish are known to have sub-categories of pigments under the classes, presumably reflecting their photo-environmental adaptation. However, the information regarding genomic organization, spectral properties and expressional regulation of the visual pigments of primates and fish is limited.We found that owl monkey, the only nocturnal monkey among higher primates, has LWS pigment gene(s) on Y chromosome as well as on X chromosome, while all the other mammals have been believed to have it on X chromosome. We also found that SWS1 genes of galagos and loris, nocturnal prosimians, have multiple insertions and deletions in the coding region and are non-functionalized. Absorption spectrum of galago's LWS pigment was shown to be blue-shifted compared to those of diurnal animals. These results indicate that visual pigments of nocturnal primates have evolved in their own way to adapt to nocturnal light environment.We showed that zebrafish has two red (LWS-1 and LWS-2), four green (RH2-1, RH2-2, RH2-3 and RH2-4) and single blue (SWS2) and ultraviolet (SWS1) opsin genes in the genome, among which LWS-2, RH2-2 and RH2-3 are novel. SWS2, LWS-1 and LWS-2 are located in tandem and RH2-1, RH2-2, RH2-3 and RH2-4 form another tandem gene cluster. The peak absorption spectra of the reconstituted photopigments from the opsin cDNAs differed markedly among them. The quantitative RT-PCR revealed a considerable difference among the opsin genes in the expression level in the retina. We also found that 1 kb upstream of RH1 can lead to rod cell-specific expression of GFP in the spatio-temporal pattern indistinguishable from that of endogenous RH1 gene.