Rhodopsin in the Dark Hot Sea: Molecular Analysis of Rhodopsin in a Snailfish, Careproctus rhodomelas, Living near the Deep-Sea Hydrothermal Vent

Abstract

Visual systems in deep-sea fishes have been previously studied from a photobiological aspect; however, those of deep-sea fish inhabiting the hydrothermal vents are far less understood due to sampling difficulties. In this study, we analyzed the visual pigment of a deep-sea snailfish, Careproctus rhodomelas, discovered and collected only near the hydrothermal vents of oceans around Japan. Proteins were solubilized from the C. rhodomelas eyeball and subjected to spectroscopic analysis, which revealed the presence of a pigment characterized by an absorption maximum (λmax) at 480 nm. Immunoblot analysis of the ocular protein showed a rhodopsin-like immunoreactivity. We also isolated a retinal cDNA encoding the entire coding sequence of putative C. rhodomelas rhodopsin (CrRh). HEK293EBNA cells were transfected with the CrRh cDNA and the proteins extracted from the cells were subjected to spectroscopic analysis. The recombinant CrRh showed the absorption maximum at 480 nm in the presence of 11-cis retinal. Comparison of the results from the eyeball extract and the recombinant CrRh strongly suggests that CrRh has an A1-based 11-cis-retinal chromophore and works as a photoreceptor in the C. rhodomelas retina, and hence that C. rhodomelas responds to dim blue light much the same as other deep-sea fishes. Because hydrothermal vent is a huge supply of viable food, C. rhodomelas likely do not need to participate diel vertical migration and may recognize the bioluminescence produced by aquatic animals living near the hydrothermal vents.

Insights into the vision of the hadal snailfish Pseudoliparis swirei through proteomic analysis of the eye

“…Four different sites between PsRho and CrRho were marked with ① to ④ in green. Blue triangles indicate nine amino acid sites for spectral tuning reported in a previous study [19]. Purple asterisks indicate functionally important residues in visual pigment: [19] Cys110 and Cys187: formation of disulphide bond, Glu113: serving as the retinylidene Schiff's base counterion, Glu134: providing stabilizing negative charge for inactive opsin, Lys296: retinal binding site, Cys322 and Cys323: for palmitoylation eye or a kind of adaptation needs further investigations.…”

“…Blue triangles indicate nine amino acid sites for spectral tuning reported in a previous study [19]. Purple asterisks indicate functionally important residues in visual pigment: [19] Cys110 and Cys187: formation of disulphide bond, Glu113: serving as the retinylidene Schiff's base counterion, Glu134: providing stabilizing negative charge for inactive opsin, Lys296: retinal binding site, Cys322 and Cys323: for palmitoylation eye or a kind of adaptation needs further investigations. As the most advanced organism living in the hadal trench, hadal snailfish should have evolved a sophisticated regulatory network consisting of different kinds of proteins to adapt to the extreme environment cooperatively.…”

“…The protein sequence of PsRho has a 98.8% similarity to that of CrRho, the rhodopsin of snailfish Careproctus rhodomelas inhabiting hydrothermal vents at a depth of 1480-1530 m. It has four different amino acid sites, which are neither functionally important residues nor spectral tuning sites (Figure 3) [19]. CrRho has a λ max value of 480 nm with the presence of 11-cis retinal, which is sensitive to dim blue light [19].…”

Redescription of the Snailfish <i>Careproctus rhodomelas</i> (Cottoidei: Liparidae), with Ontogenetic and Distributional Notes

“…6 mm in maximum diameter. Sakata et al (2015) subsequently reported on the visual systems of C. rhodomelas from the Hatoma Knoll by the molecular analysis of rhodopsin, and showed that the eyesight of the specimens appeared sufficiently developed to recognize bioluminescence produced by other animals living near the hydrothermal vents. However, those records of C. rhodomelas from the Hatoma Knoll without showing any supporting evidence for species identification or museum deposition of the specimens for re-examination.…”

Gene expression patterns of novel visual and non-visual opsin families in immature and mature Japanese eel males

“…The light conditions of these habitats are different in terms of turbidity, color, and brightness (Bowmaker et al, 1994;Bowmaker, 2008). For example, in the case of deep-sea snailfish inhabiting relatively deep-water areas, the spectral sensitivities of the rod and cone photoreceptors react to the blue light (Sakata et al, 2015). In contrast, in the case of black bream, shallow-sea fish, cone photoreceptors (Rh2 or MWS), have maximal light absorbance wavelength (λmax) at 545 to 575 nm, which is the dominant light in their habitat (Shand et al, 2002).…”