A second visual rhodopsin gene, rh1-2, is expressed in zebrafish photoreceptors and found in other ray-finned fishes
A second visual rhodopsin gene, rh1-2, is expressed in zebrafish photoreceptors and found in other ray-finned fishes
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DOI：
10.1242/jeb.145953
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发表时间：
2017-01-01
影响因子：
2.8
通讯作者：
Chang, Belinda S. W.
中科院分区：
文献类型：
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作者：
Morrow, James M.;Lazic, Savo;Chang, Belinda S. W.
视紫红质 (rh1) 是脊椎动物视杆感光细胞中表达的视觉色素，负责启动弱光视觉的关键第一步。视紫红质通常是单拷贝基因；然而，我们之前发现了一种在斑马鱼视网膜中表达的新型视紫红质样基因 rh1-2，我们将其鉴定为一种功能性光敏色素，可结合 11-cis 视网膜并响应光而激活。在这里，我们将斑马鱼视网膜中 rh1-2 的表达定位于周围感光细胞的一个子集，这表明与 rh1 的表达模式部分重叠。我们还表达、纯化和表征了 Rh1-2，包括研究生物活性中间体的稳定性。使用荧光光谱法，我们发现光活化后 Rh1-2 的视网膜释放速率的半衰期与视色素视紫红质的半衰期更相似，而不是非视色素外视紫红质 (exorh)，后者释放视网膜的速度大约快 5 倍。系统发育和分子进化分析表明，rh1-2 在硬骨鱼中具有古老的起源，与 rh1 处于相似的选择压力下，并且在与 rh1 复制和分化后可能经历了一次正选择的爆发。这些发现表明，rh1-2 是另一种功能性视觉视紫红质基因，这与视觉视紫红质主要在射线鳍鱼类中作为单拷贝基因被发现的普遍观点相矛盾。讨论了保留该重复基因的原因，以及视觉系统可能的功能后果。
Rhodopsin (rh1) is the visual pigment expressed in rod photoreceptors of vertebrates that is responsible for initiating the critical first step of dim-light vision. Rhodopsin is usually a single copy gene; however, we previously discovered a novel rhodopsin-like gene expressed in the zebrafish retina, rh1-2, which we identified as a functional photosensitive pigment that binds 11-cis retinal and activates in response to light. Here, we localized expression of rh1-2 in the zebrafish retina to a subset of peripheral photoreceptor cells, which indicates a partially overlapping expression pattern with rh1. We also expressed, purified and characterized Rh1-2, including investigation of the stability of the biologically active intermediate. Using fluorescence spectroscopy, we found the half-life of the rate of retinal release of Rh1-2 following photoactivation to be more similar to that of the visual pigment rhodopsin than to the non-visual pigment exo-rhodopsin (exorh), which releases retinal around 5 times faster. Phylogenetic and molecular evolutionary analyses show that rh1-2 has ancient origins within teleost fishes, is under similar selective pressure to rh1, and likely experienced a burst of positive selection following its duplication and divergence from rh1. These findings indicate that rh1-2 is another functional visual rhodopsin gene, which contradicts the prevailing notion that visual rhodopsin is primarily found as a single copy gene within ray-finned fishes. The reasons for retention of this duplicate gene, as well as possible functional consequences for the visual system, are discussed.