Visual Cone Arrestin 4 Contributes to Visual Function and Cone Health

Abstract

Our study demonstrates that Arr4-/- mice display distinct phenotypic differences when compared to controls, suggesting that ARR4 modulates essential functions in high acuity vision and downstream cellular signaling pathways that are not fulfilled or substituted by the coexpression of ARR1, despite its high expression levels in all mouse cones. Without normal ARR4 expression levels, cones slowly degenerate with increasing age, making this a new model to study age-related cone dystrophy.

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.…”

“…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. 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.…”

“…20,39 Reflexive head movements in the same direction as the rotating gratings were considered positive responses. Spatial frequency thresholds were determined with an increasing staircase paradigm starting at 0.042 cycles/deg (c/d) with 100% contrast.…”

“…15,20 Each mouse was anesthetized and flash stimuli of 10 ls duration (from 0.2-20 Hz) was delivered to the eye of the mouse from which recordings were taken. For photopic cone readings, continuous white background light of 8 foot candles (fc; 200 cd-s/m 2 ) was delivered to the recorded eye for 1 minute before the first flash was administered and light adaptation recordings began.…”

“…15,20,33 Briefly, after dissection, each mouse retina was flash frozen and homogenized in 50 mM Tris buffer with cOmplete Protease Inhibitor Cocktail (Hoffman-La Roche, Basel, Switzerland). A total of 60 lg of protein per retina was resolved on replicate 10% SDS-PAGE (each lane containing a portion of total retinal homogenate from a different mouse), transferred to nitrocellulose membranes (Li-Cor, Lincoln, NE, USA), and incubated sequentially with antibodies for either S-opsin (1:5000) or M-opsin (1:5000), 33 followed by loading control, b-actin (1:4000).…”