Romero Ricardo D, de Souza Flávio S J
Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE-UBA-CONICET), Buenos Aires, Argentina.
Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires (FBMC-FCEyN-UBA), Buenos Aires, Argentina.
Genome Biol Evol. 2025 Apr 30;17(5). doi: 10.1093/gbe/evaf058.
Many lizards (Squamata), as well as the tuatara (Rhynchocephalia), are distinguished among vertebrate groups for the presence of the parietal eye, or "third eye", a structure derived from the pineal complex containing a simplified retina with photoreceptor cells. The parietal eye expresses nonvisual opsins that differ from the visual opsin repertoire of the lateral eyes. These are pinopsin (OPNP), parapinopsin (OPNPP), and parietopsin (OPNPT), all being evolutionary close to visual opsins. Here, we searched over 60 lepidosaurian genomes for pineal nonvisual opsins to check for the evolutionary trajectory of these genes in reptiles. Unexpectedly, we identified a novel opsin gene, which we termed "lepidopsin" (OPNLEP), that is present solely in the genomes of the tuatara and most lizard groups but absent from other vertebrates. Remnants of the gene are found in the coelacanth and some ray-finned fishes, implying that OPNLEP is an ancient opsin that has been repeatedly lost during vertebrate evolution. We found that the tuatara and most lizards of the Iguania, Anguimorpha, Scincoidea, and Lacertidae clades, which possess a parietal eye, harbor all pineal opsin genes. Lizards missing the parietal eye, like geckos, teiids, and a fossorial amphisbaenian, lack most or all pineal nonvisual opsins. In summary, our survey of pineal nonvisual opsins reveals (i) the persistence of a previously unknown ancient opsin gene-OPNLEP-in lepidosaurians; (ii) losses of nonvisual opsins in specific lizard clades; and (iii) a correlation between the presence of a parietal eye and the genomic repertoire of pineal nonvisual opsins.
许多蜥蜴（有鳞目）以及喙头蜥（喙头目）在脊椎动物群体中因顶眼（即“第三只眼”）的存在而与众不同，顶眼是一种源自松果体复合体的结构，包含一个带有感光细胞的简化视网膜。顶眼表达的非视觉视蛋白与侧眼的视觉视蛋白种类不同。这些视蛋白包括视锥视蛋白（OPNP）、副视锥视蛋白（OPNPP）和顶视蛋白（OPNPT），它们在进化上都与视觉视蛋白密切相关。在这里，我们在60多个鳞龙类基因组中搜索松果体非视觉视蛋白，以检查这些基因在爬行动物中的进化轨迹。出乎意料的是，我们鉴定出了一个新的视蛋白基因，我们将其命名为“鳞龙视蛋白”（OPNLEP），它仅存在于喙头蜥和大多数蜥蜴类群的基因组中，而在其他脊椎动物中不存在。在腔棘鱼和一些辐鳍鱼类中发现了该基因的残余，这意味着OPNLEP是一种古老的视蛋白，在脊椎动物进化过程中多次丢失。我们发现，拥有顶眼的喙头蜥以及鬣蜥亚目、蛇蜥亚目、石龙子超科和蜥蜴科分支中的大多数蜥蜴都含有所有松果体视蛋白基因。像壁虎、美洲蜥蜴和一种穴居蚓蜥这样没有顶眼的蜥蜴，则缺少大多数或所有松果体非视觉视蛋白。总之，我们对松果体非视觉视蛋白的调查揭示了：（i）鳞龙类中一个以前未知的古老视蛋白基因——OPNLEP的存在；（ii）特定蜥蜴类群中非视觉视蛋白的丢失；以及（iii）顶眼的存在与松果体非视觉视蛋白的基因组种类之间的相关性。
