Molecular Neurobiology

, Volume 54, Issue 4, pp 2507–2517 | Cite as

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


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-forming tasks. Rhodopsin/cone opsin photopigments in visual PRs or melanopsin (Opn4) in ipRGCs utilizes retinaldehyde as a chromophore. The retinoid regeneration process denominated as “visual cycle” involves the retinal pigment epithelium (RPE) or Müller glial cells. Opn4, on the contrary, has been characterized as a bi/tristable photopigment, in which a photon of 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 metabolized in the inner retina. Nor is it yet clear whether an alternative secondary cycle occurs involving players such as the retinal G-protein-coupled receptor (RGR), a putative photoisomerase of unidentified inner retinal activity. Here, we investigated the role of RGR in retinoid photoisomerization in Opn4x (Xenopus ortholog) (+) RGC primary cultures free of RPE and other cells from chicken embryonic retinas. Opn4x (+) RGCs display significant photic responses by calcium fluorescent imaging and photoisomerize exogenous all-trans to 11-cis Ral and other retinoids. RGR was found to be expressed in developing retina and in primary cultures; when its expression was knocked down, the levels of 11-cis, all-trans Ral, and all-trans retinol in cultures exposed to light were significantly higher and those in all-trans retinyl esters lower than in dark controls. The results support a novel role for RGR in ipRGCs to modulate retinaldehyde levels in light, keeping the balance of inner retinal retinoid pools.


Retinoids Inner retina Melanopsin Retinal ganglion cells Retinal G-protein-coupled receptor Photoisomerization Visual cycle 



This work has been supported by the Agencia Nacional de Promoción Científica y Técnica (FONCyT, PICT 2010 No. 647 and PICT 2013 No. 021), Consejo Nacional de Investigaciones Científicas y Tecnológicas de la República Argentina (CONICET; PIP 2011 and 2014), and Secretaría de Ciencia y Tecnología de la Universidad Nacional de Córdoba (SeCyT-UNC). The authors are grateful to Dr. Andrew Tsin and Mrs. Brandy Betts for their excellent assistance in retinoid purification and identification in control retinal samples, and for the gift of the RGR antibody.


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Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  • Nicolás M. Díaz
    • 1
  • Luis P. Morera
    • 1
  • Tomas Tempesti
    • 2
  • Mario E. Guido
    • 1
  1. 1.CIQUIBIC—Departamento de Química Biológica, Facultad de Ciencias QuímicasUniversidad Nacional de Córdoba-CONICET, Ciudad UniversitariaCórdobaArgentina
  2. 2.Departamento de Química Orgánica, Facultad de Ciencias QuímicasUniversidad Nacional de Córdoba (UNC)CórdobaArgentina

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