Origin of the vertebrate visual cycle: III. Distinct distribution of RPE65 and beta-carotene 15,15'-monooxygenase homologues in Ciona intestinalis.
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 beta-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 photo-isomerase. Our results also suggest that the RPE65-dependent visual cycle is used in the adult photoreceptors of a primitive chordate.
Department of Life Science, Graduate School of Life Science, University of Hyogo, 3-2-1 Kouto, Kamigori, Ako-gun, Hyogo 678-1297, Japan.
Noriko
N
Takimoto
Takehiro
T
Kusakabe
Takeo
T
Horie
Yuki
Y
Miyamoto
Motoyuki
M
Tsuda
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002938:Ciona intestinalis / Q000201:enzymology*; D017124:Conserved Sequence; D017931:DNA Primers; D020224:Expressed Sequence Tags; D006801:Humans; D008969:Molecular Sequence Data; D010802:Phylogeny; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014714:Vertebrates / Q000145:classification / Q000235:genetics; D014785:Vision, Ocular; D050559:beta-Carotene 15,15'-Monooxygenase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D017931:DNA Primers; D050559:beta-Carotene 15,15'-Monooxygenase