Knockdown of Cone Specific Kinase GRK7 in Larval Zebrafish Leads to Impaired Cone-Reponse Recovery and Delayed Dark Adaptation

Purpose: To investigate the function of cone specific kinase GRK7 in photoresponse recovery Methods: A paralogue of GRK7 (Grk7a) was cloned and sequenced from the zebrafish genome. Gene expression during development was assessed by in situ hybridization. A polyclonal antibody was raised and used to study protein expression during larval development. Gene knockdowns were performed by morpholino antisense nucleotide injection and visual function was assessed by optokinetic response measurements and electroretinography. Results: Grk7a is expressed in cone photoreceptors and the photosensitive pineal organ. Morpholino antisense nucleotides targeted against the translational start site reduced the amounts of GRK7A below 5% at 4 days post fertilization in Western blots. The functional characterisation of these larvae revealed a delay in photoresponse recovery in electroretinographic measurements. After cone bleaching dark adaptation is prolonged. Psychophysical temporal contrast sensitivity is reduced, particularly under bright light conditions. Conclusions: These results show that function of a cone specific kinase is essential for cone vision in the zebrafish retina, arguing that that pigment regeneration alone is not sufficient for rapid cone response inactivation