Abstract
Abstract: :
Purpose: Cone and rod physiology and survival are differentially affected in the GC1 –/– mouse retina. The purpose of this study was to examine the function of rod and cone cells in the GC1 –/– retina at the biochemical level to better resolve these differences. Here we provide direct evidence that light–driven arrestin translocation in rod cells is maintained in the absence of GC1 signaling but that in cone cells this process is disrupted. Methods: WT and GC1 –/– mice were light adapted by dilating their pupils with atropine and exposing them to bright light for 30 min or were dark adapted by placing them in complete darkness for 2 h. Eyes were then removed under light or dark conditions, fixed in 4% PFA, cryoprotected in 30% sucrose, and sectioned using a cryostat. Sections at the level of the optic nerve head were analyzed using arrestin immunohistochemistry and fluorescence microscopy. Immunolabeling was performed using rabbit pAbs that recognize either cone arrestin (LUMIJ, kind gift from C. Craft) or rod+cone arrestin and goat anti–rabbit IgGs tagged with Alexa–488. Sections were counterstained using PNA tagged with Alexa–594 and DAPI. Results: In WT retinas, arrestins were concentrated in rod and cone photoreceptor outer segments (OS) following light adaptation and shifted to the inner segment (IS) and outer nuclear layer (ONL) compartments of rod and cone cells following dark adaptation. These results were consistent with previous reports showing that rod and cone arrestins are localized to the OS in the light and translocate to the IS and ONL in the dark. In GC1 –/– retinas, the translocation of arrestin in rod cells was indistinguishable from that observed in WT retinas. In contrast, arrestin failed to translocate in cone photoreceptors. In these cells arrestin was localized to the cone OS and OPL in both dark– and light–adapted retinas, the same position observed following light adaptation in WT retinas. Conclusions: Our results show that light–driven translocation of arrestin in cone cells is disrupted in GC1 –/– retinas, a result suggesting that GC1–mediated cGMP synthesis is essential for translocation in these cells. Our finding that translocation of arrestin was unaffected in GC1 –/– rod cells is consistent with previous analyses showing that these cells remain functional in the GC1 –/– mouse and support the hypothesis that GC2 is capable of maintaining rod cell function in the absence of GC1. Together, these data provide important insight into the relative importance of GC1 in rod and cone physiology.
Keywords: photoreceptors • signal transduction • transgenics/knock–outs