Loss of CPEB3 Upregulates MEGF10 to Impair Mosaic Development of ON Starburst Amacrine Cells.

Yin-Peng Chen,Yi-Shuian Huang,Chuan-Chin Chiao,Meng-Fang Wu,Geng-Shuo Bai

doi:10.3389/fnmol.2016.00105

Abstract

Cytoplasmic polyadenylation element binding protein 3 (CPEB3) regulates target RNA translation in neurons. Here, we examined CPEB3 distribution and function in the mouse retina. CPEB3 is expressed in retinal neurons, including those located in the inner nuclear layer (INL) and ganglion cell layer (GCL) but not in cone and rod photoreceptors in the outer nuclear layer (ONL). A previous study found CPEB3 expressed in cholinergic starburst amacrine cells (SACs). We first examined these cells and observed aberrant SAC mosaicism in CPEB3-knockout (KO) retinas. Retinal neurons showed orderly spatial arrangements. Many individual subtypes are organized non-randomly in patterns called mosaics. Despite CPEB3 being expressed in both populations of SACs, OFF SACs in the INL and ON SACs in the GCL, aberrant mosaic regularity was observed in only ON SACs of CPEB3-KO retinas. Molecular characterization revealed that translation of multiple epidermal growth factor 10 (Megf10) RNA is suppressed by CPEB3 during the first week of postnatal development, when MEGF10 is primarily expressed in SACs and mediates homotypic repulsive interactions to define intercellular spacing of SACs. Thus, elevated MEGF10 expression in the absence of the translational repressor CPEB3 may account for the defective spatial organization of ON SACs. Our findings uncover for the first time that translational control plays a role in shaping retinal mosaic arrangement.

Highlights

The cytoplasmic polyadenylation element binding (CPEB) family of RNA-binding proteins in vertebrates contains CPEB1, CPEB2, Cytoplasmic polyadenylation element binding protein 3 (CPEB3) and CPEB4
The cell bodies are located in the outer nuclear layer (ONL), inner nuclear layer (INL) and ganglion cell layer (GCL), and the processes are located in the outer plexiform layer (OPL) and inner plexiform layer (IPL)
This study demonstrates that CPEB3-controlled translation regulates retinal mosaic development

Summary

Introduction

The cytoplasmic polyadenylation element binding (CPEB) family of RNA-binding proteins in vertebrates contains CPEB1, CPEB2, CPEB3 and CPEB4. They all share sequence similarity in their RNA-binding domains (Huang et al, 2006) and regulate target RNA translation in various tissues (see review in Ivshina et al, 2014). CPEB3-regulated translation is important for synaptic plasticity and memory (Chao et al, 2013; Huang et al, 2014; Fioriti et al, 2015). We uncovered the role of CPEB3 in shaping retinal mosaic development

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Results

Conclusion