The Photoreceptor Protein RP1 Is Not Detected in the Axonemes of Motile or Primary Cilia

Abstract

Abstract: : Purpose: Mutations in RP1 are a common cause of autosomal dominant retinitis pigmentosa. We recently reported that the RP1 protein is localized in the axoneme of the connecting cilia and outer segments of rod and cone photoreceptors (IOVS, 1/2002). While previous data has shown RP1 to be photoreceptor-specific, a focused evaluation of RP1 expression in tissues with motile and primary cilia has not been reported. The goal of this study was to evaluate non-ocular cilia for RP1 protein expression. Methods: Tissues with motile (brain, lung, oviduct, trachea) and primary (kidney) cilia were isolated from C57BL/6 mice, and frozen sections prepared. Retinal sections were used as a positive controls. Tissue sections were immunostained with antibodies to acetylated α-tubulin to identify axonemal microtubules. Adjacent sections were stained with anti-Rp1 antibodies. Fluorescence microscopy was performed with a Nikon TE300 microscope, and a Zeiss LSM 510 confocal microscope. Results: The axonemes of cilia in different tissues were readily detected with the anti-acetylated α-tubulin antibodies. Control sections demonstrated little to no non-specific background. No specific staining was detected with the anti-Rp1 antibodies in any tissue except the retina. Conclusions: The RP1 protein does not appear to be expressed at detectable levels in motile or primary cilia. This is consistent with prior data indicating that RP1 is photoreceptor-specific, and the lack of know systemic manifestations in patients with RP1 disease. It also implies that RP1 contributes to a unique function of the photoreceptor axoneme.

Keywords: photoreceptors • retinal degenerations: hereditary • retinal degenerations: cell biology