Fig. (8) KEGG scheme of phototransduction reactions during dark and light adaptation. The whole phototransduction reactions could be divided in two main phases, regarding dark and light adaptation, and involving selected genes. During phototransduction, photoreceptor cells convert light into electrical signals. The vertebrate cascade starts with the absorption of photons by the photoreceptive pigments, the rhodopsins, isomerizing 11-cis-retinal to all-trans-retinal and inducing a structural change that activates the opsin. Such biochemical reaction triggers hydrolysis of cGMP by activating a transducinphosphodiesterase 6 (PDE6) cascade, resulting in membrane cGMP-gated cation channels (CNG) closure. This event implies photoreceptor membrane hyperpolarization, modulating the release of neurotransmitters to downstream cells. Recovery from light involves photolyzed rhodopsin phosphorilation by rhodopsin kinase (RK) and subsequent capping off by arrestin. Finally, GTP-binding transducin alpha subunit is deactivated by RGS9.