Conditional Dicer1 depletion using Chrnb4-Cre leads to cone cell death and impaired photopic vision

Eduardo Zabala Aldunate,Juan Pedro Martinez-Barbera,Laura Abelleira Hervas,Fabiana Di Marco,Aara Patel,Dorothy A Thompson,Tommaso B Jannini,Robin R Ali,Rachael A Pearson,Valentina Di Foggia,Daniel L Holder,Joana Claudio Ribeiro,Jane C Sowden

doi:10.1038/s41598-018-38294-9

Abstract

Irreversible photoreceptor cell death is a major cause of blindness in many retinal dystrophies. A better understanding of the molecular mechanisms underlying the progressive loss of photoreceptor cells remains therefore crucial. Abnormal expression of microRNAs (miRNAs) has been linked with the aetiology of a number of retinal dystrophies. However, their role during the degenerative process remains poorly understood. Loss of cone photoreceptors in the human macula has the greatest impact on sight as these cells provide high acuity vision. Using a Chrnb4-cre; Dicerflox/flox conditional knockout mouse (Dicer CKO) to delete Dicer1 from cone cells, we show that cone photoreceptor cells degenerate and die in the Dicer-deleted retina. Embryonic eye morphogenesis appeared normal in Dicer CKO mice. Cone photoreceptor abnormalities were apparent by 3 weeks of age, displaying either very short or absent outer segments. By 4 months 50% of cones were lost and cone function was impaired as assessed by electroretinography (ERG). RNAseq analysis of the Dicer CKO retina revealed altered expression of genes involved in the visual perception pathway. These data show that loss of Dicer1 leads to early-onset cone cell degeneration and suggest that Dicer1 is essential for cone photoreceptor survival and homeostasis.

Highlights

Vision relies on the proper function of two types of light-sensitive photoreceptor cells: rods and cones
In this study we investigated the effect of conditional Dicer[1] knockout in developing cones using a neuronal acetylcholine receptor subunit beta-4 (Chrnb4)-cre driver to elucidate directly whether DICER processing of miRNAs is needed for cone photoreceptor survival
Analysis of earlier embryonic stages showed that at E12, when the retina is mainly comprised of retinal progenitor cells (RPCs), a small subset of CHX10-positive, YFP-positive RPCs was observed (Fig. 1J, white arrows) with a variable distribution between embryos, suggesting that the YFP positive inner retinal cells observed in adult mice derive from these RPCs, as Chrnb4GFP expression was not detected in adult inner nuclear layer (INL) cells (Fig. 1A)

Summary

Introduction

Vision relies on the proper function of two types of light-sensitive photoreceptor cells: rods and cones. Photoreceptor cells are metabolically highly active, needing high rates of protein synthesis and trafficking from the inner to the outer segments via the connecting cilium to maintain visual cycle function[1] They are constantly under photo-oxidative stress and their lipid-enriched outer segments are vulnerable to oxidative stress. Cone ERGs were abnormal and RNAseq transcriptome analysis of the Dicer[1] CKO retina revealed gene dysregulation These data suggest that loss of Dicer[1] function in cones leads to cone cell degeneration in a process that is reminiscent of a cone dystrophy, in which cones are primarily affected and rods remain unaffected

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Results

Conclusion