EYS Is a Protein Associated with the Ciliary Axoneme in Rods and Cones

Mutations in the EYS gene are a common cause of autosomal recessive retinitis pigmentosa (arRP), yet the role of the EYS protein in humans is presently unclear. The aim of this study was to investigate the isoform structure, expression and potential function of EYS in the mammalian retina in order to better understand its involvement in the pathogenesis of arRP. To achieve the objective, we examined the expression of mRNA transcripts of EYS isoforms in human tissues and cell lines by RT-PCR. We also investigated the localisation of EYS in cultured cells and retinal cryo-sections by confocal fluorescence microscopy and Western blot analysis. RT-PCR analysis confirmed that EYS has at least four isoforms. In addition to the previously reported EYS isoforms 1 and 4, we present the experimental validation of two smaller variants referred to as EYS isoforms 2 and 3. All four isoforms are expressed in the human retina and Y79 cells and the short variants were additionally detected in the testis. Immunofluorescent confocal microscopy and Western blot analysis revealed that all EYS isoforms preferentially localise to the cytoplasm of Y79 and HeLa cells. Moreover, an enrichment of the endogenous protein was observed near the centrosomes in Y79 cells. Interestingly, EYS was observed at the ciliary axoneme in Y79 ciliated cells. In macaque retinal cryosections, EYS was found to localise in the region of the photoreceptor ciliary axoneme in both rods and cones as well as in the cytoplasm of the ganglion cells. The results obtained in this study lead us to speculate that, in photoreceptor cells, EYS could be a protein involved in maintaining the stability of the ciliary axoneme in both rods and cones. The variability of its isoform structure suggests that other roles are also possible and yet to be established.