Ablation of EYS in zebrafish causes mislocalisation of outer segment proteins, F-actin disruption and cone-rod dystrophy

Abstract

Mutations in EYS are associated with autosomal recessive retinitis pigmentosa (arRP) and autosomal recessive cone-rod dystrophy (arCRD) however, the function of EYS and the molecular mechanisms of how these mutations cause retinal degeneration are still unclear. Because EYS is absent in mouse and rat, and the structure of the retina differs substantially between humans and Drosophila, we utilised zebrafish as a model organism to study the function of EYS in the retina. We constructed an EYS-knockout zebrafish-line by TALEN technology which showed visual impairment at an early age, while the histological and immunofluorescence assays indicated the presence of progressive retinal degeneration with a cone predominately affected pattern. These phenotypes recapitulate the clinical manifestations of arCRD patients. Furthermore, the EYS−/− zebrafish also showed mislocalisation of certain outer segment proteins (rhodopsin, opn1lw, opn1sw1, GNB3 and PRPH2), and disruption of actin filaments in photoreceptors. Protein mislocalisation may, therefore, disrupt the function of cones and rods in these zebrafish and cause photoreceptor death. Collectively, these results point to a novel role for EYS in maintaining the morphological structure of F-actin and in protein transport, loss of this function might be the trigger for the resultant cellular events that ultimately lead to photoreceptor death.

A frequent variant in the Japanese population determines quasi-Mendelian inheritance of rare retinal ciliopathy

“…In primates, the EYS protein has been shown to physically co-localize with RP1 in the ciliary axoneme of photoreceptors and is thought to play a role in the structural organization and maintenance of these cells' apical part, the outer segment (OS) 51 . This functional role is further supported by studies in zebrafish, where EYS knockouts show progressive retinal degeneration due to mis-localization of specific OS proteins and the disruption of F-actin filaments 52,53 , a key component not only for the integrity, but also for the morphogenesis of the OS 54 . In a similar fashion, targeted disruption of the RP1 gene in mice leads to defects of the OS, because of the incorrect stacking of its discs 55 .…”

Zebrafish Photoreceptor Degeneration and Regeneration Research to Understand Hereditary Human Blindness

“…Since eys is absent from several rodent genomes, including mice, zebrafish hold promise as a model for EYS-deficient patients. Several groups established an eys knock-out zebrafish model using CRISPR/Cas9 and TALEN technology [50][51][52]. Embryos and adult retinas showed disorganization of photoreceptor OSs.…”

Systematic detection of Mendelian and non-Mendelian variants associated with retinitis pigmentosa by genome-wide association study

“…Among mammals, only primates have EYS gene. And zebrafish (Danio rerio) is the only model in which loss-of-function mutations in the homologous eys has been shown to recapitulate photoreceptor degeneration observed in RP patients with EYS mutations 27,28,29 .…”