Department of Biology, University of South Dakota, Vermillion, SD 57069, USA.
Integr Comp Biol. 2013 Jul;53(1):39-49. doi: 10.1093/icb/ict060. Epub 2013 May 31.
Stomatopod crustaceans have complex visual systems containing up to 16 different spectral classes of photoreceptors, more than described for any other animal. A previous molecular study of this visual system focusing on the expression of opsin genes found many more transcripts than predicted on the basis of physiology, but was unable to fully document the expressed opsin genes responsible for this diversity. Furthermore, questions remain about how other components of phototransduction cascades are involved. This study continues prior investigations by examining the molecular function of stomatopods' visual systems using new whole eye 454 transcriptome datasets from two species, Hemisquilla californiensis and Pseudosquilla ciliata. These two species represent taxonomic diversity within the order Stomatopoda, as well as variations in the anatomy and physiology of the visual system. Using an evolutionary placement algorithm to annotate the transcriptome, we identified the presence of nine components of the stomatopods' G-protein-coupled receptor (GPCR) phototransduction cascade, including two visual arrestins, subunits of the heterotrimeric G-protein, phospholipase C, transient receptor potential channels, and opsin transcripts. The set of expressed transduction genes suggests that stomatopods utilize a Gq-mediated GPCR-signaling cascade. The most notable difference in expression between the phototransduction cascades of the two species was the number of opsin contigs recovered, with 18 contigs found in retinas of H. californiensis, and 49 contigs in those of P. ciliata. Based on phylogenetic placement and fragment overlap, these contigs were estimated to represent 14 and 33 expressed transcripts, respectively. These data expand the known opsin diversity in stomatopods to clades of arthropod opsins that are sensitive to short wavelengths and ultraviolet wavelengths and confirm the results of previous studies recovering more opsin transcripts than spectrally distinct types of photoreceptors. Many of the recovered transcripts were phylogenetically placed in an evolutionary clade of crustacean opsin sequences that is rapidly expanding as the visual systems from more species are investigated. We discuss these results in relation to the emerging pattern, particularly in crustacean visual systems, of the expression of multiple opsin transcripts in photoreceptors of the same spectral class, and even in single photoreceptor cells.
十足目甲壳动物拥有复杂的视觉系统，其中包含多达 16 种不同光谱类别的光感受器，比任何其他动物都要多。之前对该视觉系统的分子研究主要集中在视蛋白基因的表达上，结果发现的转录本比基于生理学预测的要多得多，但仍无法完全记录负责这种多样性的表达视蛋白基因。此外，关于其他光转导级联的组成部分如何参与的问题仍然存在。本研究通过使用来自两种十足目物种（加利福尼亚鲜明虾和中国明对虾）的全新整体眼 454 转录组数据集，继续之前的研究，检查十足目视觉系统的分子功能。这两个物种在十足目目中代表了分类多样性，以及视觉系统的解剖和生理学变化。使用进化定位算法注释转录组，我们鉴定出了十足目 G 蛋白偶联受体（GPCR）光转导级联的九个组成部分，包括两种视觉 arrestin、异三聚体 G 蛋白亚基、磷脂酶 C、瞬时受体电位通道和视蛋白转录本。表达的转导基因表明，十足目利用 Gq 介导的 GPCR 信号级联。这两个物种的光转导级联之间最显著的表达差异是回收的视蛋白基因数量，加利福尼亚鲜明虾的视网膜中发现了 18 个基因，而中国明对虾中则有 49 个基因。基于系统发育定位和片段重叠，这些基因估计分别代表 14 个和 33 个表达转录本。这些数据将十足目已知的视蛋白多样性扩展到对短波长和紫外线敏感的节肢动物视蛋白的进化枝，并证实了之前研究的结果，即回收的视蛋白转录本比光谱上不同类型的光感受器更多。回收的许多转录本在系统发育上被定位在一个甲壳动物视蛋白序列的进化枝中，随着更多物种的视觉系统被研究，这个进化枝正在迅速扩张。我们将这些结果与新兴模式进行了讨论，特别是在甲壳动物视觉系统中，相同光谱类别的光感受器中表达多种视蛋白转录本，甚至在单个光感受器细胞中也表达多种视蛋白转录本。
