CRISPR/Cas9-Mediated Models of Retinitis Pigmentosa Reveal Differential Proliferative Response of Müller Cells between Xenopus laevis and Xenopus tropicalis

Karine Parain,Muriel Perron,Albert Chesneau,Odile Bronchain,Alicia Donval,Sophie Lourdel,Morgane Locker,Caroline Borday

doi:10.3390/cells11050807

Abstract

Retinitis pigmentosa is an inherited retinal dystrophy that ultimately leads to blindness due to the progressive degeneration of rod photoreceptors and the subsequent non-cell autonomous death of cones. Rhodopsin is the most frequently mutated gene in this disease. We here developed rhodopsin gene editing-based models of retinitis pigmentosa in two Xenopus species, Xenopus laevis and Xenopus tropicalis, by using CRISPR/Cas9 technology. In both of them, loss of rhodopsin function results in massive rod cell degeneration characterized by progressive shortening of outer segments and occasional cell death. This is followed by cone morphology deterioration. Despite these apparently similar degenerative environments, we found that Müller glial cells behave differently in Xenopus laevis and Xenopus tropicalis. While a significant proportion of Müller cells re-enter into the cell cycle in Xenopus laevis, their proliferation remains extremely limited in Xenopus tropicalis. This work thus reveals divergent responses to retinal injury in closely related species. These models should help in the future to deepen our understanding of the mechanisms that have shaped regeneration during evolution, with tremendous differences across vertebrates.

Highlights

The degeneration of photoreceptors in retinal diseases, such as age-related macular degeneration or retinitis pigmentosa, is irreversible in humans and leads to visual impairment
Efficient CRISPR/Cas9-mediated editing of the rhodopsin gene was previously reported in both Xenopus laevis [11] and zebrafish [15] and was shown to generate features of retinitis pigmentosa
In order to develop a similar model in X. tropicalis, a diploid Xenopus species displaying a single rho gene, we designed a specific single guide RNA targeting exon 1 (Figure 1A)

Summary

Introduction

The degeneration of photoreceptors in retinal diseases, such as age-related macular degeneration or retinitis pigmentosa, is irreversible in humans and leads to visual impairment. Müller cells are the major glial cell type of the retina that provide homeostatic, metabolic and structural support to retinal neurons [1] These glial cells were identified as the cellular source of retinal regeneration in zebrafish [2]. Contrasting with their mammalian counterparts, whose regenerative properties are limited, zebrafish Müller glia behave as genuine multipotent stem cells, able to replace all retinal cell types upon injury. We recently discovered that this holds true in the frog Xenopus laevis (X. laevis) as well [3] In this species, mechanical injury or conditional rod cell ablation triggers Müller cells to re-enter into the cell cycle and regenerate lost photoreceptors. Much progress has been made these past few years in identifying genes and signalling pathways sustaining Müller cell regeneration [5,6], the molecular bases that account for interspecies differential potential are still largely unknown

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