Abstract
Purpose: :
The visual system of vertebrates is functioning over a wide rage of light intensities. To adjust properly to ambient light levels, different types of photoreceptors, the rods and the cones, have evolved. Rod photoreceptors are highly sensitive to light and, therefore, responsible for vision at dim light (scotopic) conditions. Cone photoreceptors, in contrast, are less sensitive to light, but fail to saturate even at maximal light levels.Although cones are functional over the widest range of the visual light, most studies on adaptation are performed in rods. Since cones differ functionally from rods, regulation of the adaptation mechanism used by cone photoreceptors may well be different. From rods, it is known that binding of arrestin to phosphorylated photopigment quenches signal transduction of the receptor.In order to study the effect of arrestins on adaptation we used the cone dominant retina of the zebrafish (Danio rerio) to determine the role of cone arrestins on vision and adaptation in particular.
Methods: :
Zebrafish arrestins were cloned by a combined cDNA and bioinformatics strategy. Genomic localization was determined by radiation hybrid mapping. Expression was assessed by RNA in situ hybridization. Functional studies were performed on morpholino antisense injection larvae using electroretinography and visually mediated optokinetic response behavior.
Results: :
We have identified two rod-specific and two cone-specific full length arrestin clones in zebrafish. Specific expression in their respective photoreceptor cell types have been confirmed by in situ hybridization. Chromosomal location of these genes has been determined by radiation hybrid mapping. The depletion of cone arrestin affects rapid cone response inactivation.
Keywords: photoreceptors • retinal development • signal transduction