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N. Artemyev, H. Muradov, K. Boyd, V. Kerov; Phototransduction Components in Photoreceptors of Lamprey Petromyzon Marinus. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1660. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Lampreys represent the earliest known vertebrate class of jawless fish. In order to understand the evolution of vertebrate phototransduction proteins, we cloned and expressed transducin-α subunits from the lamprey Petromyzon marinus.
Partial sequences of lamprey transducin-α (Gαt) subunits were identified in the Ensemble genomic database. The full-length transducin sequences were obtained by targeted PCR-amplification and 5’-RACE amplification of lamprey retinal cDNA, and subcloned into the pET15b vector for bacterial expression. Retinal localization of lamprey Gαt subunits was investigated by immunofluorescence using custom-made and commercial antibodies.
Two transducin-α subunits were identified in the sea lamprey Petromyzon marinus retina. The phylogenetic analysis suggests that both Gαt subunits, termed Gat-s and Gat-l, belong to a class of rod-like transducins. Nonetheless, the sequences of Gαt-s and Gαt-l share several unique features of cone-like transducins, including 4-residue inserts in the N-terminal regions. Immunofluorescence analysis demonstrated cell specific expression of Gαt-s and Gαt-l in the short and long photoreceptors of sea lamprey, respectively. In addition to the previously characterized Rh1 opsin, a second opsin was identified in lamprey Petromyzon marinus. This long wave-length sensitive pigment is expressed in the long photoreceptors where it colocalizes with Gαt-l.
Except for the PDE6 catalytic subunit, duplicate opsin, transducin, and PDE6γ genes are present in lamprey Petromyzon marinus. The products of these genes are selectively expressed in long and short photoreceptor cells in the lamprey retina and may underlie known mixed rod/cone physiology of these cells. The lamprey transducin-α subunits display features of both rod- and cone-type G-proteins, and thus, may serve as a model for understanding the mechanism of light-dependent transducin translocation occurring exclusively in rods.
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