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B. M. Brown, L. Rife, L. Fu, F. Zuniga, C. M. Craft; Cone Dystrophy in Visual Arrestin Knockout Mice. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4644.
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Cone photoreceptors express not only the 43 kDa cone arrestin (CARR), but also the 48 kDa arrestin1 (ARR1/S-antigen) first identified in rods and at a concentration similar to that in rods. To evaluate CARR and ARR1 function in cones, knockout (KO) mice were created that lack either one or both visual arrestins (Carr-/-, Arr1-/-, and Carr-/-/Arr1-/-).1
Photopic ERG a- and b-wave amplitudes were measured in dark reared control and KO mice at 2 min intervals during 15 min of light adaptation. A full power Grass Xenon flash stimulus was delivered through a fiberoptic cable to ~3mm from the eye. Immunohistochemistry (IHC), TUNEL, and immunoblot techniques were used to evaluate morphology, apoptosis, and retinal proteins.
After 1 min of a rod-saturating background illumination, adult controls and KOs had similar photopic b-wave amplitudes of ~265µV; however, continued light adaptation to elicit a maximum cone response revealed distinct phenotypes: Arr1-/- b-wave amplitudes did not change, while Carr-/-Arr1-/- increased to ~300µV, controls to ~435µV, and Carr-/- to ~515µV. Photopic a-wave amplitudes did not increase but were much higher in controls (~180µV) compared to Arr1-/- (~65µV). Knocking out CARR had little effect on a-wave amplitudes. At postnatal day 60 (p60), immunoblot analysis showed a significant decrease in CARR in Arr1-/- mice compared to controls, and IHC revealed a decrease in cone density with reduced CARR and peanut agglutinin (PNA) staining, but no increase in TUNEL staining. However, at p22, when morphology and ERGs are not as compromised in Arr1-/- mice compared to controls, TUNEL staining revealed an increased number of positive cells in the outer nuclear layer.
Knocking out CARR expression increased photopic b-wave but had little effect on a-wave amplitudes, suggesting a downstream synaptic function for CARR. Although light exposure leads to rod photoreceptor degeneration in Arr-/- mice, no significant decrease in the outer nuclear layer thickness occurs when the mice are dark reared.2 Although the rods survive, our data suggest that by p22, cones are metabolically compromised and dying even in dark reared Arr-/- mice and by p60 the reduction in cone density and ERG response suggests ARR1 is essential for normal cone survival.1 Craft, CM, et al., IOVS 2006; 47: ARVO E-abstract 43152 Chen, J, et al., IOVS 1999; 40:2978
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