Figure 7.

Phototransduction and GUCY2D. Absorption of light by rhodopsin in the rod photoreceptor outer segment activates rhodopsin and starts the cascade of reactions that successively include activation of transducin and cGMP phosphodiesterase (PDE), which hydrolyzes cGMP. Reduction in the concentration of cGMP leads to closure of cGMP-gated channels (CNG). The recovery response occurs as there is continued decrease of intracellular Ca²⁺ and activation of guanylyl cyclase (retGC) by GCAP (guanylyl cyclase activating protein). This replenishes cGMP and causes reopening of CNG. GUCY2D, the gene encoding retGC, is key to response recovery. Redrawn and reprinted with permission from Boye SE. Insights gained from gene therapy in animal models of retGC1 deficiency. Front Mol Neurosci. 2014:7:43. © 2014 Boye.