A novel Go-mediated phototransduction cascade in scallop visual cells.
Scallop retinas contain ciliary photoreceptor cells that respond to light by hyperpolarization like vertebrate rods and cones, but the response is generated by a different phototransduction cascade from those of rods and cones. To elucidate the cascade, we investigated a visual pigment and a G-protein functioning in the hyperpolarizing cell. Sequencing of cDNAs and in situ hybridization experiments showed that the hyperpolarizing cells express a novel subtype of visual pigment, which showed significant differences in amino acid sequence from other visual pigments. Cloning cDNA genes of G-protein and immunohistochemical analysis revealed the presence of an alpha subunit of a Go type G-protein, 83% identical in amino acid sequence to mammalian Go(alpha) in the nervous system, in the photoreceptive region of the cells. The results demonstrate that a novel, Go-mediated, phototransduction cascade is present in the hyperpolarizing cells. The phototransduction cascade in the scallop hyperpolarizing cell provides an alternative system to investigate Go-mediated transduction pathways in the nervous system. Molecular phylogenetic analysis strongly suggests that the Go-mediated phototransduction system emerged before the divergence of animals into vertebrate and invertebrate in the course of evolution.
Kojima
D
D
Department of Biophysics, Faculty of Science, Kyoto University, Kyoto 606-01, Japan.
Terakita
A
A
Ishikawa
T
T
Tsukahara
Y
Y
Maeda
A
A
Shichida
Y
Y
D000595:Amino Acid Sequence; D000818:Animals; D018076:DNA, Complementary / Q000235:genetics; D019143:Evolution, Molecular; D005136:Eye Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D017403:In Situ Hybridization; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D008974:Mollusca / Q000378:metabolism*; D017956:Photoreceptor Cells, Invertebrate / Q000166:cytology / Q000378:metabolism*; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014018:Tissue Distribution; D014785:Vision, Ocular
D018076:DNA, Complementary; D005136:Eye Proteins; D008565:Membrane Proteins; C108077:SCOP2 protein, Patinopecten yessoensis