The Visual Cycle in the Inner Retina of Chicken and the involvement of Retinal G-Protein-coupled Receptor (RGR)

NICOLÁS M. DÍAZ; LUIS P. MORERA; TOMAS TEMPESTI; MARIO E. GUIDO

MOLECULAR NEUROBIOLOGY

HUMANA PRESS INC

Lugar: Oregon; Año: 2016

0893-7648

Abstract The vertebrate retina contains typical photoreceptor(PR) cones and rods responsible for day/night vision, respectively,and intrinsically photosensitive retinal ganglion cells(ipRGCs) involved in the regulation of non-image-formingtasks. Rhodopsin/cone opsin photopigments in visual PRs ormelanopsin (Opn4) in ipRGCs utilizes retinaldehyde as achromophore. The retinoid regeneration process denominatedas Bvisual cycle^ involves the retinal pigment epithelium(RPE) or Müller glial cells. Opn4, on the contrary, has beencharacterized as a bi/tristable photopigment, in which a photonof one wavelength isomerizes 11-cis to all-trans retinal(Ral), with a second photon re-isomerizing it back.However, it is unknown how the chromophore is further metabolizedin the inner retina. Nor is it yet clear whether analternative secondary cycle occurs involving players such asthe retinal G-protein-coupled receptor (RGR), a putativephotoisomerase of unidentified inner retinal activity. Here,we investigated the role of RGR in retinoidphotoisomerization in Opn4x (Xenopus ortholog) (+) RGCprimary cultures free of RPE and other cells from chickenembryonic retinas. Opn4x (+) RGCs display significant photicresponses by calcium fluorescent imaging and photoisomerizeexogenous all-trans to 11-cis Ral and other retinoids. RGRwas found to be expressed in developing retina and in primarycultures; when its expression was knocked down, the levels of11-cis, all-trans Ral, and all-trans retinol in cultures exposedto light were significantly higher and those in all-trans retinylesters lower than in dark controls. The results support a novelrole for RGR in ipRGCs to modulate retinaldehyde levels inlight, keeping the balance of inner retinal retinoid pools.