Abstract
This study was carried out to identify and estimate physiological function of a new type of opsin subfamily present in the retina and whole brain tissues of Japanese eel using RNA–Seq transcriptome method. A total of 18 opsin subfamilies were identified through RNA–seq. The visual opsin family included Rh2, SWS2, FWO, DSO, and Exo-Rhod. The non-visual opsin family included four types of melanopsin subfamily (Opn4x1, Opn4x2, Opn4m1, and Opn4m2), peropsin, two types of neuropsin subfamily (Opn5-like, Opn5), Opn3, three types of TMT opsin subfamily (TMT1, 2, 3), VA-opsin, and parapinopsin. In terms of changes in photoreceptor gene expression in the retina of sexually mature and immature male eels, DSO mRNA increased in the maturation group. Analysis of expression of opsin family gene in male eel brain before and after maturation revealed that DSO and SWS2 expression in terms of visual opsin mRNA increased in the sexually mature group. In terms of non-visual opsin mRNA, parapinopsin mRNA increased whereas that of TMT2 decreased in the fore-brain of the sexually mature group. The mRNA for parapinopsin increased in the mid-brain of the sexually mature group, whereas those of TMT1 and TMT3 increased in the hind-brain of the sexually mature group. DSO mRNA also increased in the retina after sexual maturation, and DSO and SWS2 mRNA increased in whole brain part, suggesting that DSO and SWS2 are closely related to sexual maturation.
Highlights
Living organisms recognize various environmental information according to their specific ecology and have ecologically evolved based on the information
We investigated the opsin subfamily present in the retina and whole brain tissues of Japanese eel inhabiting Northeast Asia using the RNA-Seq transcriptome
We examined the opsin subfamily mRNA levels in sexually immature and mature eels using Quantitative real-time RT-PCR (qPCR) method. These results identify the physiological role of photoreceptors in the maturation process of Japanese eels and, can be used as a basic material for studies on photoreceptor mechanisms including the effect of environmental factors on maturation and visual adaptation
Summary
Living organisms recognize various environmental information (light, water temperature, salinity, etc.) according to their specific ecology and have ecologically evolved based on the information. A photoreceptor is a visual sensory cell capable of recognizing light of a specific wavelength. Photoreceptors refer to an opsin protein receptor that absorbs light and converts it into chemical energy. Vertebrate photoreceptors are regulated by opsin, a superfamily of G-protein-coupled receptor (GPCR), opsin, with an inverse agonist 11–cis retinal chromophore, covalently bound. Retinal molecules selectively absorb various spectrum of light depending on the formation of binding with the opsin protein (reviewed in Pugh & Lamb, 2000). Absorption of light at a specific wavelength leads to conversion into all-trans form that binds the opsin and transducing proteins, thereby activating a series of visual sensitive-related cellular signal transduction processes (Terakita, 2005). Opsin superfamily is broadly divided into visual and non–visual opsins. Visual opsin initiates the visual transduction cascade, whereas non-visual opsin is involved in circadian entrainment (Doyle et al, 2008) and retinal metabolism (Bellingham et al, 2003)
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