Let-7 MicroRNA-Mediated Regulation of Shh Signaling and the Gene Regulatory Network Is Essential for Retina Regeneration

Simran Kaur,Shivangi Gupta,Mansi Chaudhary,Mohammad Anwar Khursheed,Soumitra Mitra,Akshai Janardhana Kurup,Rajesh Ramachandran

doi:10.1016/j.celrep.2018.04.002

Simran Kaur, Shivangi Gupta + Show 5 more

Open Access

https://doi.org/10.1016/j.celrep.2018.04.002

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Abstract

SummaryUpon injury, Müller glia cells of the zebrafish retina reprogram themselves to progenitor cells with stem cell characteristics. This necessity for retina regeneration is often compromised in mammals. We explored the significance of developmentally inevitable Sonic hedgehog signaling and found its necessity in MG reprogramming during retina regeneration. We report on stringent translational regulation of sonic hedgehog, smoothened, and patched1 by let-7 microRNA, which is regulated by Lin28a, in Müller glia (MG)-derived progenitor cells (MGPCs). We also show Shh-signaling-mediated induction of Ascl1 in mouse and zebrafish retina. Moreover, Shh-signaling-dependent regulation of matrix metalloproteinase9, in turn, regulates Shha levels and genes essential for retina regeneration, such as lin28a, zic2b, and foxn4. These observations were further confirmed through whole-retina RNA-sequencing (RNA-seq) analysis. This mechanistic gene expression network could lead to a better understanding of retina regeneration and, consequently, aid in designing strategies for therapeutic intervention in human retinal diseases.

Highlights

In contrast to mammals, zebrafish retina possesses remarkable regenerative capacity after an acute injury, leading to functional restoration of vision (Sherpa et al, 2008)
The Shh protein is expressed in Mu€ller glia (MG) cells of wild-type (WT) injured retina marked by glutamine synthetase (GS) at 4 dpi (Figure S1D)
Using tuba1a1016:GFP transgenic zebrafish (Fausett and Goldman, 2006), we showed the expression of Shh and its signaling components in proliferating MG-derived progenitor cells (MGPCs) marked by GFP

Summary

Introduction

Zebrafish retina possesses remarkable regenerative capacity after an acute injury, leading to functional restoration of vision (Sherpa et al, 2008). While the mechanism of retina regeneration is histologically well described, only a subset of the involved genes/proteins has been identified and characterized functionally (Goldman, 2014; Wan and Goldman, 2016). We identified expression pattern of several important genes induced by Shh signaling and vice versa that reveal the robust regulatory network associated with retina regeneration. These include the interplay of Shh/Notch signaling components, transcription factors (namely, Ascl1a, Zic2b, Foxn, and Insm1a), the matrix metalloproteinase Mmp, the RNA-binding protein Lin28a, and microRNA let-7. The findings from this study add clarity to the enigmatic process of retina regeneration lacking in mammals

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