Dual Knockout Models of the Spatially and Functionally Conserved rgra and rgrb Zebrafish Genes Reveal the Requirement of RGR for the Integrity of Cone‐Mediated Photopic Vision, the Photopic Visual Cycle and Bruch's Membrane Morphology

The retinal G protein‐coupled receptor (RGR) is a visual cycle photoisomerase that photopically regenerates 11‐ cis ‐retinal (11cRAL). It plays a crucial role in sustaining vision. Here, we investigated the in vivo role of RGR in the cone photoreceptor‐dominant, zebrafish retina, focusing predominantly on how visual function is impacted in the absence of RGR. There are two zebrafish RGR paralogs, rgra and rgrb, both with predominant expression in retinal pigment epithelium (RPE) and Müller glia cells. Under standard light rearing conditions, bespoke rgrb −/− ; rgra −/− double knockout zebrafish present with a ~21% reduction in optokinetic response (OKR) saccades per minute relative to wild‐type (WT). This impaired visual behavior worsens in higher photopic conditions ranging from 20 000–81 000 lx. In contrast, no significant OKR defect is observed under dark‐adapted conditions, consolidating the light‐dependent role of RGR in vision. Retinoid profiling of rgrb −/− ; rgra −/− zebrafish larvae demonstrated significant decreases in 11cRAL levels under standard and brighter light rearing conditions. Proteomic profiling validated the successful generation of rgrb −/− ; rgra −/− zebrafish and revealed an unanticipated upregulation in ocular extracellular matrix proteins. From polarized light microscopy, increased collagen fiber abundance with dysregulated organization in Bruch's membrane at the interface between the retina and choroid was observed. These novel findings demonstrate the role of RGR in sustaining visual function under cone‐mediated photopic conditions, a concomitant deficit in the photopic visual cycle and a novel role in maintaining the integrity of Bruch's membrane.