Extended self-renewal and accelerated reprogramming in the absence of Kdm5b

KDM5B focuses H3K4 methylation near promoters and enhancers during embryonic stem cell self-renewal and differentiation

Background

Pluripotency of embryonic stem (ES) cells is controlled in part by chromatin-modifying factors that regulate histone H3 lysine 4 (H3K4) methylation. However, it remains unclear how H3K4 demethylation contributes to ES cell function.

Results

Here, we show that KDM5B, which demethylates lysine 4 of histone H3, co-localizes with H3K4me3 near promoters and enhancers of active genes in ES cells; its depletion leads to spreading of H3K4 methylation into gene bodies and enhancer shores, indicating that KDM5B functions to focus H3K4 methylation at promoters and enhancers. Spreading of H3K4 methylation to gene bodies and enhancer shores is linked to defects in gene expression programs and enhancer activity, respectively, during self-renewal and differentiation of KDM5B-depleted ES cells. KDM5B critically regulates H3K4 methylation at bivalent genes during differentiation in the absence of LIF or Oct4. We also show that KDM5B and LSD1, another H3K4 demethylase, co-regulate H3K4 methylation at active promoters but they retain distinct roles in demethylating gene body regions and bivalent genes.

Conclusions

Our results provide global and functional insight into the role of KDM5B in regulating H3K4 methylation marks near promoters, gene bodies, and enhancers in ES cells and during differentiation.

Regulatory factors of induced pluripotency: current status

Somatic cells can be reprogrammed to induced pluripotent stem cells (iPSCs) through enforced expression of four transcription factors [Oct4, Sox2, Klf4, and c-Myc (OSKM)]; however, the reprogramming efficiency is extremely low. This finding raises fundamental questions about the regulators that influence the change in epigenetic stability and endowment of dedifferentiation potential during reprogramming. Identification of such regulators is critical to removing the roadblocks impeding the efficient generation of safe iPSCs and their successful translation into clinical therapies. In this review, we summarize the current progress that has been made in understanding cellular reprogramming, with an emphasis on the molecular mechanisms of epigenetic regulators in induced pluripotency.

Efficient library preparation for next-generation sequencing analysis of genome-wide epigenetic and transcriptional landscapes in embryonic stem cells

Gene expression in embryonic stem (ES) cells is regulated in part by a network of transcription factors, epigenetic regulators, and histone modifications that influence the underlying chromatin in a way that is conducive or repressive for transcription. Advances in next-generation sequencing technology have allowed for the genome-wide analysis of chromatin constituents and protein-DNA interactions at high resolution in ES cells and other stem cells. While many studies have surveyed genome-wide profiles of a few factors and expression changes at a fixed time point in undifferentiated ES cells, few have utilized an integrative approach to simultaneously survey protein-DNA interactions, histone modifications, and expression programs during ES cell self-renewal and differentiation. To identify transcriptional networks that regulate pluripotency and differentiation, it is important to generate high-quality genome-wide maps of transcription factors, chromatin factors, and histone modifications and to survey global gene expression profiles. Here, to interrogate genome-wide profiles of chromatin features and to survey global gene expression programs in ES cells, we describe protocols for efficient library construction for next-generation sequencing of ChIP-Seq and RNA-Seq samples.

The epigenomics of embryonic stem cell differentiation

Embryonic stem cells (ESCs) possess an open and highly dynamic chromatin landscape, which underlies their plasticity and ultimately maintains ESC pluripotency. The ESC epigenome must not only maintain the transcription of pluripotency-associated genes but must also, through gene priming, facilitate rapid and cell type-specific activation of developmental genes upon lineage commitment. Trans-generational inheritance ensures that the ESC chromatin state is stably transmitted from one generation to the next; yet at the same time, epigenetic marks are highly dynamic, reversible and responsive to extracellular cues. Once committed to differentiation, the ESC epigenome is remodeled and resolves into a more compact chromatin state. A thorough understanding of the role of chromatin modifiers in ESC fate and differentiation will be important if they are to be used for therapeutic purposes.

Recent technical advances, particularly in next-generation sequencing technologies, have provided a genome-scale view of epigenetic marks and chromatin modifiers. More affordable and faster sequencing platforms have led to a comprehensive characterization of the ESC epigenome and epigenomes of differentiated cell types. In this review, we summarize and discuss the recent progress that has highlighted the central role of histone modifications, histone variants, DNA methylation and chromatin modifiers in ESC pluripotency and ESC fate. We provide a detailed and comprehensive discussion of genome-wide studies that are pertinent to our understanding of mammalian development.