Abstract
Human cone phototropism is a key mechanism underlying the Stiles-Crawford effect, a psychophysiological phenomenon according to which photoreceptor outer/inner segments are aligned along with the direction of incoming light. However, such photomechanical movements of photoreceptors remain elusive in mammals. We first show here that primate cone photoreceptors have a planar polarity organized radially around the optical center of the eye. This planar polarity, based on the structure of the cilium and calyceal processes, is highly reminiscent of the planar polarity of the hair cells and their kinocilium and stereocilia. Secondly, we observe under super-high resolution expansion microscopy the cytoskeleton and Usher proteins architecture in the photoreceptors, which appears to establish a mechanical continuity between the outer and inner segments. Taken together, these results suggest a comprehensive cellular mechanism consistent with an active phototropism of cones toward the optical center of the eye, and thus with the Stiles-Crawford effect.
Highlights
Human cone phototropism is a key mechanism underlying the Stiles-Crawford effect, a psychophysiological phenomenon according to which photoreceptor outer/inner segments are aligned along with the direction of incoming light
We investigated the macroscopic distribution of Usher proteins and cytoskeletal proteins on the retina, both using classical immunohistochemistry and to a very high 3D resolution, using expansion microscopy (ExM)[23], with a protocol adapted for the retina
We first investigated the structural organization of these proteins by localizing the USHER 1 (USH1) protein, protocadherin 15 (Pcd15), relative to the actin cytoskeleton
Summary
Human cone phototropism is a key mechanism underlying the Stiles-Crawford effect, a psychophysiological phenomenon according to which photoreceptor outer/inner segments are aligned along with the direction of incoming light. Usher proteins are localized in calyceal processes, a structure extending around the OS from the OS/IS junction, in both the rod and cone photoreceptors and of unknown function[19].
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