Photoreceptor guanylate cyclases and cGMP phosphodiesterases in zebrafish.

Tightly regulated control of cGMP levels is critical for proper functioning of photoreceptors, and mutations in cGMP synthesis or degradation factors can lead to various forms of retinal disorder. Here we review heterogenous human retinal disorders associated with mutant retinal guanylate cyclases (RetGCs) and phosphodiesterase 6 (PDE6), and describe how zebrafish are being used to examine phototransduction components and their roles in these diseases. Though mutations in RetGCs and PDE6 lead to retinal disorders, there is a lack of molecular and biochemical data on routes of subsequent photoreceptor degeneration and visual impairment. Use of animal model systems provides important information to connect in vitro biochemical analyses of mutant genes with clinically observed pathologies of human retinal diseases. Zebrafish are an excellent in vivo system to generate animal models of human retinal disorders and study photoreceptor components, and have already provided valuable data on retinal diseases caused by phototransduction component mutations.