Polycomb Group Protein Pcgf6 Acts as a Master Regulator to Maintain Embryonic Stem Cell Identity.

Chao-Shun Yang,Kung-Yen Chang,Jason Dang,Tariq M Rana

doi:10.1038/srep26899

Chao-Shun Yang, Kung-Yen Chang + Show 2 more

Open Access

https://doi.org/10.1038/srep26899

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Abstract

The polycomb repressive complex 1 (PRC1) is a multi-subunit complex that plays critical roles in the epigenetic modulation of gene expression. Here, we show that the PRC1 component polycomb group ring finger 6 (Pcgf6) is required to maintain embryonic stem cell (ESC) identity. In contrast to canonical PRC1, Pcgf6 acts as a positive regulator of transcription and binds predominantly to promoters bearing active chromatin marks. Pcgf6 is expressed at high levels in ESCs, and knockdown reduces the expression of the core ESC regulators Oct4, Sox2, and Nanog. Conversely, Pcgf6 overexpression prevents downregulation of these factors and impairs differentiation. In addition, Pcgf6 enhanced reprogramming in both mouse and human somatic cells. The genomic binding profile of Pcgf6 is highly similar to that of trithorax group proteins, but not of PRC1 or PRC2 complexes, suggesting that Pcgf6 functions atypically in ESCs. Our data reveal novel roles for Pcgf6 in directly regulating Oct4, Nanog, Sox2, and Lin28 expression to maintain ESC identity.

Highlights

The two key characteristics of embryonic stem cells (ESCs) are self-renewal and pluripotency[1,2]
Oct4-EGFP ESCs were transfected with non-targeting control (NTC) or polycomb group ring finger 6 (Pcgf6)-specific siRNA for 3–5 h, and EGFP signal was detected four days later by flow cytometry
Whereas Oct4-EGFP ESCs treated with control siRNA retained the typical colony morphology of ESCs and expressed high levels of Oct[4] (EGFP signal), we observed that Pcgf[6] KD induced differentiation, as indicated by the flat cell morphology and concomitant loss of Oct4-EGFP expression (Figure S1A). mRNA knockdown efficiency was examined by RT-qPCR at day 4 post siRNA transfection (Figure S1B)

Summary

Introduction

The two key characteristics of embryonic stem cells (ESCs) are self-renewal and pluripotency[1,2]. The 5 Cbx homolog proteins have been shown to confer nonoverlapping target specificity on PRC1 complexes[27], resulting in repression of unique gene sets during ESC self-renewal and differentiation[25]. Pcgf[6] has been shown to play a repressive role in modulating mesodermal-specific lineage genes, maintaining embryonic stem cell pluripotency and facilitating iPSC reprogramming. Consistent with previous works, we found that Pcgf[6] is a positive regulator of ESC self-renewal It remains unclear how Pcgf[6] modulates the mRNA expression level of core ESC transcriptional regulators (e.g. Oct[4], Sox[2], Nanog). This prompted us to further investigate the functions of Pcgf[6] in ESC self-renewal and differentiation

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