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

脊椎动物视色素可分为5类：RH1、SWS1、SWS2、RH2和LWS。已知只有灵长类动物和硬骨鱼在类下有色素亚类，可能反映了它们对光环境的适应。然而，关于灵长类动物和鱼类视觉色素的基因组组织、光谱特性和表达调控的信息有限。我们发现猫头鹰猴是高等灵长类动物中唯一的夜行猴，它在Y染色体和X染色体上都有LWS色素基因，而其他所有哺乳动物都认为它在X染色体上。我们还发现加拉戈斯和懒猴的SWS1基因在编码区有多个插入和缺失，并且是非功能化的。与白天活动的动物相比，galago的LWS色素的吸收光谱显示出蓝移。这些结果表明，夜行性灵长类动物的视色素以自己的方式进化以适应夜间光环境。结果表明，斑马鱼基因组中存在2个红色视蛋白基因（LWS-1和LWS-2）、4个绿色视蛋白基因（RH2-1、RH2-2、RH2-3和RH2-4）和1个蓝色视蛋白基因（SWS2）和紫外视蛋白基因（SWS1），其中LWS-2、RH2-2和RH2-3是新发现的。SWS2、LWS-1和LWS-2串联在一起，RH2-1、RH2-2、RH2-3和RH2-4构成另一个串联基因簇。重组光色素的峰吸收光谱在不同的视蛋白dna中有明显的差异。定量RT-PCR显示不同视蛋白基因在视网膜中的表达水平存在较大差异。我们还发现，在RH1上游1kb处，可以导致杆状细胞特异性表达GFP，其时空模式与内源性RH1基因没有区别。

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.