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1 November 2006 Origin of the Vertebrate Visual Cycle: III. Distinct Distribution of RPE65 and β-carotene 15,15′-Monooxygenase Homologues in Ciona intestinalis
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Abstract

We previously identified three genes that encode putative visual cycle proteins that are homologues of retinal G-protein coupled receptor (Ci-opsin3), cellular retinaldehyde-binding protein (Ci-CRALBP) and β-carotene 15,15′-monooxygenase (Ci-BCO) in the ascidian Ciona intestinalis. Ci-opsin3 and Ci-CRALBP are localized in both ocellus photoreceptor cells and surrounding non-photoreceptor cells in the brain vesicle of the larva. In the present study, we investigated the possible role and evolutionary origin of the BCO/RPE65 family in the visual cycle by analyzing Ci-BCO localization by immunohistochemistry and by identifying a novel gene that encodes a homologue of retinal pigment epithelium–specific 65 kDa protein (Ci-RPE65) in C. intestinalis. In situ hybridization and expressed sequence tag (EST) profiles consistently suggest that Ci-RPE65 is not significantly expressed in the ocellus and brain vesicle of the larva. Ci-RPE65 is expressed in the neural complex, a photoreceptor organ of the adult ascidian, at a level comparable to that of Ci-opsin3 and Ci-CRALBP. Ci-RPE65 is also expressed in various adult tissues, including the gill, body wall and intestine, suggesting that Ci-RPE65 plays a role in addition to that in the visual cycle. In contrast, Ci-BCO is predominantly localized in ocellus photoreceptor cells of the larva. The larval visual cycle seems to use Ci-opsin3 as a photoisomerase. Our results also suggest that the RPE65-dependent visual cycle is used in the adult photoreceptors of a primitive chordate.

Noriko Takimoto, Takehiro Kusakabe, Takeo Horie, Yuki Miyamoto, and Motoyuki Tsuda "Origin of the Vertebrate Visual Cycle: III. Distinct Distribution of RPE65 and β-carotene 15,15′-Monooxygenase Homologues in Ciona intestinalis," Photochemistry and Photobiology 82(6), 1468-1474, (1 November 2006). https://doi.org/10.1562/2006-01-14-RA-775
Received: 14 January 2006; Accepted: 1 March 2006; Published: 1 November 2006
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