Dataset Information

Unexpected molecular diversity of vertebrate nonvisual opsin Opn5.

ABSTRACT: Animals depend on light from their external environment to provide information for physiological functions such as vision, photoentrainment of circadian and circannual rhythms, photoperiodism, and background adaptation. Animals have a variety of photoreceptor cells that perform these functions, not only in the retina but also in other tissues, including brain tissue. In these cells, opsins function as universal photoreceptive proteins responsible for both visual and nonvisual photoreception. All opsins identified thus far bind either 11-cis or all-trans retinal as a chromophore and are classified into several groups based on their amino acid sequences. Opn5 forms an independent group that has diversified among vertebrate species. Most mammals only have one Opn5 gene, Opn5m, while nonmammalian vertebrates have two additional Opn5 subtypes, Opn5L1 and Opn5L2. Among these subtypes, Opn5m and Opn5L2 are UV-sensitive pigments in the dark. UV irradiation converts them into the visible light-sensitive active state, which converts back to the dark state by visible light irradiation. Opn5m and Opn5L2 therefore behave as bistable pigments. By contrast, Opn5L1 exclusively binds all-trans retinal to form the active state in the dark. Opn5L1 is converted to the resting state by light irradiation and subsequently reverts to the active state by a thermal process. Thus, Opn5L1 is categorized as a unique reverse photoreceptor whose activity is regulated by its photocyclic reaction. In this review, I introduce the diversity of molecular properties that have been described for vertebrate Opn5 subtypes and their physiological relevance.

SUBMITTER: Yamashita T

PROVIDER: S-EPMC7242584 | biostudies-literature | 2020 Apr

REPOSITORIES: biostudies-literature

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Unexpected molecular diversity of vertebrate nonvisual opsin Opn5.

Yamashita Takahiro T

Biophysical reviews 20200309 2

Animals depend on light from their external environment to provide information for physiological functions such as vision, photoentrainment of circadian and circannual rhythms, photoperiodism, and background adaptation. Animals have a variety of photoreceptor cells that perform these functions, not only in the retina but also in other tissues, including brain tissue. In these cells, opsins function as universal photoreceptive proteins responsible for both visual and nonvisual photoreception. All ...[more]

PMID: 32152922

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Project description:Most animals possess multiple opsins which sense light for visual and non-visual functions. Here, we show spectral characteristics of non-visual opsins, vertebrate Opn3s, which are widely distributed among vertebrates. We successfully expressed zebrafish Opn3 in mammalian cultured cells and measured its absorption spectrum spectroscopically. When incubated with 11-cis retinal, zebrafish Opn3 formed a blue-sensitive photopigment with an absorption maximum around 465 nm. The Opn3 converts to an all-trans retinal-bearing photoproduct with an absorption spectrum similar to the dark state following brief blue-light irradiation. The photoproduct experienced a remarkable blue-shift, with changes in position of the isosbestic point, during further irradiation. We then used a cAMP-dependent luciferase reporter assay to investigate light-dependent cAMP responses in cultured cells expressing zebrafish, pufferfish, anole and chicken Opn3. The wild type opsins did not produce responses, but cells expressing chimera mutants (WT Opn3s in which the third intracellular loops were replaced with the third intracellular loop of a Gs-coupled jellyfish opsin) displayed light-dependent changes in cAMP. The results suggest that Opn3 is capable of activating G protein(s) in a light-dependent manner. Finally, we used this assay to measure the relative wavelength-dependent response of cells expressing Opn3 chimeras to multiple quantally-matched stimuli. The inferred spectral sensitivity curve of zebrafish Opn3 accurately matched the measured absorption spectrum. We were unable to estimate the spectral sensitivity curve of mouse or anole Opn3, but, like zebrafish Opn3, the chicken and pufferfish Opn3-JiL3 chimeras also formed blue-sensitive pigments. These findings suggest that vertebrate Opn3s may form blue-sensitive G protein-coupled pigments. Further, we suggest that the method described here, combining a cAMP-dependent luciferase reporter assay with chimeric opsins possessing the third intracellular loop of jellyfish opsin, is a versatile approach for estimating absorption spectra of opsins with unknown signaling cascades or for which absorption spectra are difficult to obtain.

Project description:BACKGROUND: In metazoans, opsins are photosensitive proteins involved in both vision and non-visual photoreception. Echinoderms have no well-defined eyes but several opsin genes were found in the purple sea urchin (Strongylocentrotus purpuratus) genome. Molecular data are lacking for other echinoderm classes although many species are known to be light sensitive. RESULTS: In this study focused on the European brittle star Amphiura filiformis, we first highlighted a blue-green light sensitivity using a behavioural approach. We then identified 13 new putative opsin genes against eight bona fide opsin genes in the genome of S. purpuratus. Six opsins were included in the rhabdomeric opsin group (r-opsins). In addition, one putative ciliary opsin (c-opsin), showing high similarity with the c-opsin of S. purpuratus (Sp-opsin 1), one Go opsin similar to Sp-opsins 3.1 and 3.2, two basal-branch opsins similar to Sp-opsins 2 and 5, and two neuropsins similar to Sp-opsin 8, were identified. Finally, two sequences from one putative RGR opsin similar to Sp-opsin 7 were also detected. Adult arm transcriptome analysis pinpointed opsin mRNAs corresponding to one r-opsin, one neuropsin and the homologue of Sp-opsin 2. Opsin phylogeny was determined by maximum likelihood and Bayesian analyses. Using antibodies designed against c- and r-opsins from S. purpuratus, we detected putative photoreceptor cells mainly in spines and tube feet of A. filiformis, respectively. The r-opsin expression pattern is similar to the one reported in S. purpuratus with cells labelled at the tip and at the base of the tube feet. In addition, r-opsin positive cells were also identified in the radial nerve of the arm. C-opsins positive cells, expressed in pedicellariae, spines, tube feet and epidermis in S. purpuratus were observed at the level of the spine stroma in the brittle star. CONCLUSION: Light perception in A. filiformis seems to be mediated by opsins (c- and r-) in, at least, spines, tube feet and in the radial nerve cord. Other non-visual opsin types could participate to the light perception process indicating a complex expression pattern of opsins in this infaunal brittle star.

Dataset Information

Unexpected molecular diversity of vertebrate nonvisual opsin Opn5.

Publications

Unexpected molecular diversity of vertebrate nonvisual opsin Opn5.

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