Visual Arrestin 1 Contributes to Cone Photoreceptor Survival and Light Adaptation

Abstract

Purpose To evaluate morphologic and functional contributions of Arrestin 1 (Arr1) and Arrestin 4 (Arr4) in cone photoreceptors, the authors examined the phenotypes of visual arrestin knockout mice (Arr1−/−, Arr4−/−, Arr1−/− Arr4−/− [Arr-DKO]) reared in darkness. Methods Retinal rods and cones were evaluated in wild-type (WT), Arr1−/−, Arr4−/−, and Arr-DKO mice using quantitative morphologic analysis, immunoblot, immunohistochemistry, TUNEL, and electroretinographic (ERG) techniques. Results Compared with either Arr4−/− or WT, Arr1−/− and Arr-DKO mice had increased apoptotic nuclei in their retinal outer nuclear layer (ONL) at postnatal day (P) 22. By P60, cone density was significantly diminished, but the ONL appeared normal. After 1 minute of background illumination, cone ERG b-wave amplitudes were similar in WT and all Arr KO mice. However, by 3 minutes and continuing through 15 minutes of light adaptation, the cone b-wave amplitudes of WT and Arr4−/− mice increased significantly over those of the Arr1−/− and Arr-DKO mice, which demonstrated no cone b-wave amplitude increase. In contrast, ERG flicker analysis after the 15-minute light adaptation period demonstrated no loss in amplitude for either Arr1−/− or Arr4−/− mice, whereas Arr-DKO demonstrated significantly lower amplitudes. When Arr1 expression was restored in Arr1−/− mice (p48Arr1−/−), normal cone density and light-adapted ERG b-wave amplitudes were observed. Conclusions In the adult dark-reared Arr1−/− and Arr-DKO mice, viable cones diminish over time. Arr1 expression is essential for cone photoreceptor survival and light adaptation, whereas either Arr1 or Arr4 is necessary for maintaining normal flicker responses.

Differences in RDS trafficking, assembly and function in cones versus rods: insights from studies of C150S-RDS

“…S4). Rabbit polyclonal antibodies against M-opsin and cone arrestin (mCAR) were generously shared by Dr Cheryl Craft (Keck School of Medicine, University of Southern California) (42)(43)(44)(45). M-opsin was used at 1 : 20 000 for IF and 1 : 10 000 for WB while mCAR was used at 1 : 2000 for IF.…”

Arrestin 1 and Cone Arrestin 4 Have Unique Roles in Visual Function in an All-Cone Mouse Retina

“…21 In addition, visual defects in Arr4 À/À mice compared to WT, including decreases in contrast sensitivity, visual acuity, and a slow age-related cone dystrophy, have been reported. 20 These phenotypes are distinct from those observed in Arr1 À/À mice, 7,12,14,15 indicating that ARR4 performs a unique role in cones, the mechanisms of which have yet to be discovered. Based on these results, we hypothesized that ARR1 and ARR4 perform differing roles aside from phototransduction shutoff in mouse cones.…”

“…The phenotype of Arr1 À/À mice has demonstrated clearly the necessity of this protein for rod phototransduction shutoff 12,14 and light adaptation, 15 though single-cell cone photoreceptor electrophysiological shutoff is normal in these mice. 7 Furthermore, ARR1 is highly expressed in mouse cones and it can substitute for ARR4 in the cone phototransduction shutoff pathway, 7 although transgenic mice with ARR4 expressed in rods lacking ARR1 display deficits in the known functions of ARR1, 16 including phototransduction shutoff, 12 light adaptation, 15 and synaptic function.…”

“…7 Furthermore, ARR1 is highly expressed in mouse cones and it can substitute for ARR4 in the cone phototransduction shutoff pathway, 7 although transgenic mice with ARR4 expressed in rods lacking ARR1 display deficits in the known functions of ARR1, 16 including phototransduction shutoff, 12 light adaptation, 15 and synaptic function. 17 The concentration of ARR4 in mouse cones is approximately 2% of the total arrestin concentration while the other 98% is arrestin 1, yet at the single-cell level, cone shutoff 7 This indicates that ARR4 has a much higher affinity for cone opsins than ARR1, and has an important role in the termination of the light-activated signal that originates with the cone opsins.…”

“…Mice lacking both ARR1 and ARR4 display a lack of rod and cone phototransduction shutoff and are unable to light-adapt normally. 7,15 The evolutionary conservation of ARR4 7,18,19 suggests that it has an important role in maintenance of cone structure and function that is not redundant with that of ARR1, and recent evidence clearly supports this idea. 20 The zebrafish ortholog of ARR4 in red/green cones was shown to be essential for normal contrast sensitivity in zebrafish larvae.…”