Department of Neurobiology, Faculty of Life Sciences, University of Vienna, Vienna, Austria.
BMC Evol Biol. 2013 Sep 8;13:186. doi: 10.1186/1471-2148-13-186.
Opsins have been found in the majority of animals and their most apparent functions are related to vision and light-guided behaviour. As an increasing number of sequences have become available it has become clear that many opsin-like transcripts are expressed in tissues other than the eyes. Opsins can be divided into three main groups: rhabdomeric opsins (r-opsins), ciliary opsins (c-opsins) and group 4 opsins. In arthropods, the main focus has been on the r-opsins involved in vision. However, with increased sequencing it is becoming clear that arthropods also possess opsins of the c-type, group 4 opsins and the newly discovered arthropsins but the functions of these opsins are unknown in arthropods and data on their localisation is limited or absent.
We identified opsins from the spider Cupiennius salei and the onychophoran Euperipatoides kanangrensis and characterised the phylogeny and localisation of these transcripts. We recovered all known visual opsins in C. salei, and in addition found a peropsin, a c-opsin and an opsin resembling Daphnia pulex arthropsin. The peropsin was expressed in all eye types except the anterior median eyes. The arthropsin and the c-opsin were expressed in the central nervous system but not the eyes. In E. kanangrensis we found: a c-opsin; an opsin resembling D. pulex arthropsins; and an r-opsin with high sequence similarity to previously published onychophoran onychopsins. The E. kanangrensis c-opsin and onychopsin were expressed in both the eyes and the brain but the arthropsin only in the brain.
Our novel finding that opsins of both the ciliary and rhabdomeric type are present in the onychophoran and a spider suggests that these two types of opsins were present in the last common ancestor of the Onychophora and Euarthropoda. The expression of the c-opsin in the eye of an onychophoran indicates that c-opsins may originally have been involved in vision in the arthropod clade. The lack of c-opsin expression in the spider retina suggests that the role for c-opsin in vision was lost in the euarthropods. Our discovery of arthropsin in onychophorans and spiders dates the emergence of arthropsin to the common ancestor of Onychophora and Euarthropoda and their expression in the brain suggests a non-visual function.
opsins 存在于大多数动物中，其最明显的功能与视觉和光引导行为有关。随着越来越多的序列可用，很明显许多类似 opsin 的转录本在眼睛以外的组织中表达。opsins 可分为三大类：视杆 opsins（r-opsins）、纤毛 opsins（c-opsins）和第 4 组 opsins。在节肢动物中，主要关注的是参与视觉的 r-opsins。然而，随着测序的增加，越来越清楚的是，节肢动物也具有 c 型、第 4 组 opsins 和新发现的 arthropsins 的 opsins，但这些 opsins 的功能在节肢动物中尚不清楚，其定位数据有限或不存在。
我们从蜘蛛 Cupiennius salei 和有爪动物 Euperipatoides kanangrensis 中鉴定出 opsins，并对这些转录本的系统发育和定位进行了特征描述。我们在 C. salei 中回收了所有已知的视觉 opsins，此外还发现了一个 peropsin、一个 c-opsin 和一个类似于 Daphnia pulex arthropsin 的 opsin。peropsin 在除前正中眼以外的所有眼型中均有表达。arthropsin 和 c-opsin 在中枢神经系统中表达，但不在眼睛中表达。在 E. kanangrensis 中，我们发现了：一个 c-opsin；一个类似于 D. pulex arthropsins 的 opsin；和一个与先前发表的有爪动物onychopsin 具有高序列相似性的 r-opsin。E. kanangrensis 的 c-opsin 和 onychopsin 均在眼睛和大脑中表达，但 arthropsin 仅在大脑中表达。
我们的新发现表明，纤毛和视杆型 opsins 均存在于有爪动物和蜘蛛中，这表明这两种类型的 opsins存在于有爪动物和真节肢动物的最后共同祖先中。有爪动物的 c-opsin 在眼睛中的表达表明，c-opsin 最初可能参与了节肢动物类群的视觉。蜘蛛视网膜中缺乏 c-opsin 的表达表明，c-opsin 在真节肢动物中失去了在视觉中的作用。我们在有爪动物和蜘蛛中发现的 arthropsin 将 arthropsin 的出现追溯到有爪动物和真节肢动物的共同祖先，其在大脑中的表达表明其具有非视觉功能。
