Abstract
Factor induced reprogramming of fibroblasts is an orchestrated but inefficient process. At the epigenetic level, it results in drastic chromatin changes to erase the existing somatic “memory” and to establish the pluripotent state. Accordingly, alterations of chromatin regulators including Ezh2 influence iPSC generation. While the role of individual transcription factors in resetting the chromatin landscape during iPSC generation is increasingly evident, their engagement with chromatin modulators remains to be elucidated. In the current study, we demonstrate that histone methyl transferase activity of Ezh2 is required for mesenchymal to epithelial transition (MET) during human iPSC generation. We show that the H3K27me3 activity favors induction of pluripotency by transcriptionally targeting the TGF-β signaling pathway. We also demonstrate that the Ezh2 negatively regulates the expression of pro-EMT miRNA's such as miR-23a locus during MET. Unique association of Ezh2 with c-Myc was required to silence the aforementioned circuitry. Collectively, our findings provide a mechanistic understanding by which Ezh2 restricts the somatic programme during early phase of cellular reprogramming and establish the importance of Ezh2 dependent H3K27me3 activity in transcriptional and miRNA modulation during human iPSC generation.
Highlights
Factor induced reprogramming of fibroblasts is an orchestrated but inefficient process
We demonstrate that histone methyl transferase activity of Ezh[2] is required for mesenchymal to epithelial transition (MET) during human iPSC generation
In the current study we investigated the requirement of Ezh[2] and its methyltransferase activity in human iPSC generation using gain/loss of function approaches and by using specific small molecular inhibitor of H3K27 activity
Summary
Radhika Arasala Rao1,2*, Narendra Dhele1*, Sabna Cheemadan[3], Alhad Ketkar[1], Giridhara R. This widespread remodeling of histone modifications acts as an immediate response and is consistent with the fact that the perturbation of somatic gene expression is a prerequisite for cellular reprogramming[10] To accomplish such massive epigenomic changes, pluripotency transcription factors direct the recruitment of chromatin modulators to repress the fibroblast specific programme. Genome-wide binding of PRC2 in human and mouse pluripotent cells demonstrated binding overlap with pluripotency factors on the promoters of genes encoding developmental regulators that are required for lineage specification later during development[15] These genes are enriched for the domains containing repressive H3K27me[3] and activating H3K4me[3] that are deposited by polycomb (PcG) and trithorax (Trx) complexes, to hold the promoters of developmental regulators in a poised state[16]. Our data provides a mechanistic understanding by which Ezh[2] overcomes the initial impediments of cellular reprogramming
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