Polycomb repressive complex PRC2 regulates Xenopus retina development downstream of Wnt/β-catenin signaling

Abstract

The histone methyltransferase complex PRC2 controls key steps in developmental transitions and cell fate choices; however, its roles in vertebrate eye development remain unknown. Here, we report that in Xenopus, PRC2 regulates the progression of retinal progenitors from proliferation to differentiation. We show that the PRC2 core components are enriched in retinal progenitors and downregulated in differentiated cells. Knockdown of the PRC2 core component Ezh2 leads to reduced retinal progenitor proliferation, in part due to upregulation of the Cdk inhibitor p15Ink4b. In addition, although PRC2 knockdown does not alter eye patterning, retinal progenitor gene expression or expression of the neural competence factor Sox2, it does cause suppression of proneural bHLH gene expression, indicating that PRC2 is crucial for the initiation of neural differentiation in the retina. Consistent with this, knocking down or blocking PRC2 function constrains the generation of most retinal neural cell types and promotes a Müller glial cell fate decision. We also show that Wnt/β-catenin signaling acting through the receptor Frizzled 5, but independent of Sox2, regulates expression of key PRC2 subunits in the developing retina. This is consistent with a role for this pathway in coordinating proliferation and the transition to neurogenesis in the Xenopus retina. Our data establish PRC2 as a regulator of proliferation and differentiation during eye development.

Ezh2 maintains retinal progenitor proliferation, transcriptional integrity, and the timing of late differentiation

“…In the developing Xenopus retina, Ezh2 is enriched in retinal progenitors and downregulated in differentiated cells (Aldiri et al, 2013). To determine where Ezh2 is expressed during mouse retinal development we performed in situ hybridization and found expression in progenitor cells throughout the optic cup at e9.5 (Figure 1A), and in retinal progenitors at e12.5 (not shown).…”

“…Since blocking Ezh2 in the Xenopus retina results in increased Müller glial cell differentiation (Aldiri et al, 2013), we assessed whether these cells would be affected with loss of Ezh2 in the mouse retina. We found that at P3 there was increased Müller glial differentiation in the peripheral retina of both Ezh2 fl/ − and Ezh2 fl/fl CKO mice as detected by CRALBP expression (Figure 5A–C).…”

“…Furthermore, genome-wide H3K27me3 histone modification has been characterized at several key stages of mouse retinal development (Popova et al, 2012). In Xenopus , we previously found that knocking down or blocking the PRC2 core component Ezh2 reduces retinal neurogenesis and promotes Müller glial cell differentiation (Aldiri et al, 2013). We also observed reduced retinal progenitor proliferation, in part due to upregulation of the Cdk inhibitor p15 ( Ink4b; Cdkn2b ), which is a direct target of EZH2-mediated repression in multiple tissues (Popov and Gil, 2010).…”

“…We also observed reduced retinal progenitor proliferation, in part due to upregulation of the Cdk inhibitor p15 ( Ink4b; Cdkn2b ), which is a direct target of EZH2-mediated repression in multiple tissues (Popov and Gil, 2010). Conditional disruption of Ezh2 in the mouse retina using Dkk-Cre showed that Ezh2 is also required to repress cdkn2a and maintain progenitor proliferation and the normal timing of retinal differentiation (Aldiri et al, 2013; Iida et al, 2014). …”

Histone demethylase Jmjd3 is required for the development of subsets of retinal bipolar cells

“…The importance of histone methylation during retinal development has been discussed in previous studies (details are provided in SI Note 1). Recently, it was reported that loss of function of ezh2 in Xenopus causes defective proliferation of retinal progenitor cells and repression of proneural gene expression (15). Xenopus ezh2 was expressed in the ganglia cell layer (GCL) and inner nuclear layer (INL) in the developing retina, and low-level expression of jmjd3 in these layers has been reported (16).…”