Dataset Information

Extraocular, rod-like photoreceptors in a flatworm express xenopsin photopigment.

ABSTRACT: Animals detect light using opsin photopigments. Xenopsin, a recently classified subtype of opsin, challenges our views on opsin and photoreceptor evolution. Originally thought to belong to the G?i-coupled ciliary opsins, xenopsins are now understood to have diverged from ciliary opsins in pre-bilaterian times, but little is known about the cells that deploy these proteins, or if they form a photopigment and drive phototransduction. We characterized xenopsin in a flatworm, Maritigrella crozieri, and found it expressed in ciliary cells of eyes in the larva, and in extraocular cells around the brain in the adult. These extraocular cells house hundreds of cilia in an intra-cellular vacuole (phaosome). Functional assays in human cells show Maritigrella xenopsin drives phototransduction primarily by coupling to G?i. These findings highlight similarities between xenopsin and c-opsin and reveal a novel type of opsin-expressing cell that, like jawed vertebrate rods, encloses the ciliary membrane within their own plasma membrane.

SUBMITTER: Rawlinson KA

PROVIDER: S-EPMC6805122 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Publications

Extraocular, rod-like photoreceptors in a flatworm express xenopsin photopigment.

Rawlinson Kate A KA Lapraz Francois F Ballister Edward R ER Terasaki Mark M Rodgers Jessica J McDowell Richard J RJ Girstmair Johannes J Criswell Katharine E KE Boldogkoi Miklos M Simpson Fraser F Goulding David D Cormie Claire C Hall Brian B Lucas Robert J RJ Telford Maximilian J MJ

eLife 20191022

Animals detect light using opsin photopigments. Xenopsin, a recently classified subtype of opsin, challenges our views on opsin and photoreceptor evolution. Originally thought to belong to the Gαi-coupled ciliary opsins, xenopsins are now understood to have diverged from ciliary opsins in pre-bilaterian times, but little is known about the cells that deploy these proteins, or if they form a photopigment and drive phototransduction. We characterized xenopsin in a flatworm, <i>Maritigrella crozier ...[more]

PMID: 31635694

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Project description:The two basic animal photoreceptor types, ciliary and microvillar, use different light-transduction schemes: their photopigments couple to Gt versus Gq proteins, respectively, to either mobilize cyclic nucleotides or trigger a lipid signaling cascade. A third class of photoreceptors has been described in the dual retina of some marine invertebrates; these present a ciliary morphology but operate via radically divergent mechanisms, prompting the suggestion that they comprise a novel lineage of light sensors. In one of these organisms, an uncommon putative opsin was uncovered that was proposed to signal through Go Orthologues subsequently emerged in diverse phyla, including mollusks, echinoderms, and chordates, but the cells in which they express have not been identified, and no studies corroborated their function as visual pigments or their suggested signaling mode. Conversely, in only one invertebrate species, Pecten irradians, have the ciliary photoreceptors been physiologically characterized, but their photopigment has not been identified molecularly. We used the transcriptome of Pecten retina to guide the cloning by polymerase chain reaction (PCR) and rapid amplification of cDNA ends (RACE) extensions of a new member of this group of putative opsins. In situ hybridization shows selective transcription in the distal retina, and specific antibodies identify a single band of the expected molecular mass in Western blots and distinctly label ciliary photoreceptors in retina sections. RNA interference knockdown resulted in a reduction in the early receptor current-the first manifestation of light transduction-and prevented the prolonged aftercurrent, which requires a large buildup of activated rhodopsin. We also obtained a full-length clone of the ?-subunit of a Go from Pecten retina complementary DNA and localized it by in situ hybridization to the distal photoreceptors. Small interfering RNA targeting this Go caused a specific depression of the photocurrent. These results establish this novel putative opsin as a bona fide visual pigment that couples to Go to convey the light signal.

Dataset Information

Extraocular, rod-like photoreceptors in a flatworm express xenopsin photopigment.

Publications

Extraocular, rod-like photoreceptors in a flatworm express xenopsin photopigment.

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