TY - JOUR T1 - An S-Opsin Knock-In Mouse (F81Y) Reveals a Role for the Native Ligand 11-<em>cis</em>-Retinal in Cone Opsin Biosynthesis JF - The Journal of Neuroscience JO - J. Neurosci. SP - 8094 LP - 8104 DO - 10.1523/JNEUROSCI.0131-12.2012 VL - 32 IS - 23 AU - Christine Insinna AU - Lauren L. Daniele AU - Jason A. Davis AU - DeLaine D. Larsen AU - Colleen Kuemmel AU - Jinhua Wang AU - Sergei S. Nikonov AU - Barry E. Knox AU - Edward N. Pugh, Jr. Y1 - 2012/06/06 UR - http://www.jneurosci.org/content/32/23/8094.abstract N2 - In absence of their natural ligand, 11-cis-retinal, cone opsin G-protein-coupled receptors fail to traffic normally, a condition associated with photoreceptor degeneration and blindness. We created a mouse with a point mutation (F81Y) in cone S-opsin. As expected, cones with this knock-in mutation respond to light with maximal sensitivity red-shifted from 360 to 420 nm, consistent with an altered interaction between the apoprotein and ligand, 11-cis-retinal. However, cones expressing F81Y S-opsin showed an ∼3-fold reduced absolute sensitivity that was associated with a corresponding reduction in S-opsin protein expression. The reduced S-opsin expression did not arise from decreased S-opsin mRNA or cone degeneration, but rather from enhanced endoplasmic reticulum (ER)-associated degradation of the nascent protein. Exogenously increased 11-cis-retinal restored F81Y S-opsin protein expression to normal levels, suggesting that ligand binding in the ER facilitates proper folding. Immunohistochemistry and electron microscopy of normal retinas showed that Mueller cells, which synthesize a precursor of 11-cis-retinal, are closely adjoined to the cone ER, so they could deliver the ligand to the site of opsin synthesis. Together, these results suggest that the binding of 11-cis-retinal in the ER is important for normal folding during cone opsin biosynthesis. ER -