Knockout ofRP2decreases GRK1 and rod transducin subunits and leads to photoreceptor degeneration in zebrafish

Abstract

Retinitis pigmentosa (RP) affects about 1.8 million individuals worldwide. X-linked retinitis pigmentosa (XLRP) is one of the most severe forms of RP. Nearly 85% of XLRP cases are caused by mutations in the X-linked retinitis pigmentosa 2 (RP2) and RPGR. RP2 has been considered to be a GTPase activator protein for ARL3 and to play a role in the traffic of ciliary proteins. The mechanism of how RP2 mutations cause RP is still unclear. In this study, we generated an RP2 knockout zebrafish line using transcription activator-like effector nuclease technology. Progressive retinal degeneration could be observed in the mutant zebrafish. The degeneration of rods' outer segments (OSs) is predominant, followed by the degeneration of cones' OS. These phenotypes are similar to the characteristics of RP2 patients, and also partly consistent with the phenotypes of RP2 knockout mice and morpholino-mediated RP2 knockdown zebrafish. For the first time, we found RP2 deletion leads to decreased protein levels and abnormal retinal localizations of GRK1 and rod transducin subunits (GNAT1 and GNB1) in zebrafish. Furthermore, the distribution of the total farnesylated proteins in zebrafish retina is also affected by RP2 ablation. These molecular alterations observed in the RP2 knockout zebrafish might probably be responsible for the gradual loss of the photoreceptors' OSs. Our work identified the progression of retinal degeneration in RP2 knockout zebrafish, provided a foundation for revealing the pathogenesis of RP caused by RP2 mutations, and would help to develop potential therapeutics against RP in further studies.

Eyes shut homolog is required for maintaining the ciliary pocket and survival of photoreceptors in zebrafish

“…Knockdown of Ift172 results in the loss of photoreceptors as well (Bujakowska et al, 2015). Reverse genetic mutations in the CC/TZ protein CC2D2A (Bachmann-Gagescu et al, 2011), axoneme protein RP2 (Liu et al, 2015), and myosin 7A (Wasfy et al, 2014) result in photoreceptor degeneration in zebrafish, indicating that zebrafish are an excellent model for the study of photoreceptor diseases associated with ciliopathies. In the case of EYS, it is difficult to model RP25 in the mouse due to the lack of an EYS gene.…”

Loss of retinitis pigmentosa 2 (RP2) protein affects cone photoreceptor sensory cilium elongation in mice

“…Recently, a gene-trap mouse model of Rp2 ablation was reported to have a relatively delayed defect in both cones and rods and associated with defective trafficking of prenylated proteins [Zhang et al, 2015]. Moreover, a zebrafish model of rp2 ablation was recently reported [Liu et al, 2015]. This model develops an early rod and cone dysfunction but a preservation of the morphology of the retina up to 7 months of age.…”

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

“…Notably, Drosophila possesses a compound eye, however, humans lack this compound eye structure. Because zebrafish has a similar retinal structure and a cone-dominant vision like in humans2223, and is a widely used animal model in biological research242526, it confers advantages to better interpret the pathological and molecular mechanisms of EYS mutations. Very recently, an independent study with EYS -knockout zebrafish was reported by Yu et al 27…”