Dynamic regulation of chromatin accessibility by pluripotency transcription factors across the cell cycle [MD-OCT4 ChIP-seq]
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ABSTRACT: The pioneer activity of transcription factors allows for opening of inaccessible regulatory elements and has been extensively studied in the context of cellular differentiation and reprogramming. In contrast, the function of pioneer activity in self-renewing cell divisions and across the cell cycle is poorly understood. Here we assessed the interplay between OCT4 and SOX2 in controlling chromatin accessibility of mouse embryonic stem cells. We found that OCT4 and SOX2 operate in a largely independent manner even at co-occupied sites, and that their cooperative binding is mostly mediated indirectly through regulation of chromatin accessibility. Controlled protein degradation strategies revealed that the uninterrupted presence of OCT4 is required for post-mitotic re-establishment and interphase maintenance of chromatin accessibility, and that highly OCT4-bound enhancers are particularly vulnerable to transient loss of OCT4 expression. Our study sheds light on the constant pioneer activity required to maintain the dynamic pluripotency regulatory landscape in an accessible state.
Project description:The pioneer activity of transcription factors allows for opening of inaccessible regulatory elements and has been extensively studied in the context of cellular differentiation and reprogramming. In contrast, the function of pioneer activity in self-renewing cell divisions and across the cell cycle is poorly understood. Here we assessed the interplay between OCT4 and SOX2 in controlling chromatin accessibility of mouse embryonic stem cells. We found that OCT4 and SOX2 operate in a largely independent manner even at co-occupied sites, and that their cooperative binding is mostly mediated indirectly through regulation of chromatin accessibility. Controlled protein degradation strategies revealed that the uninterrupted presence of OCT4 is required for post-mitotic re-establishment and interphase maintenance of chromatin accessibility, and that highly OCT4-bound enhancers are particularly vulnerable to transient loss of OCT4 expression. Our study sheds light on the constant pioneer activity required to maintain the dynamic pluripotency regulatory landscape in an accessible state.
Project description:The pioneer activity of transcription factors allows for opening of inaccessible regulatory elements and has been extensively studied in the context of cellular differentiation and reprogramming. In contrast, the function of pioneer activity in self-renewing cell divisions and across the cell cycle is poorly understood. Here we assessed the interplay between OCT4 and SOX2 in controlling chromatin accessibility of mouse embryonic stem cells. We found that OCT4 and SOX2 operate in a largely independent manner even at co-occupied sites, and that their cooperative binding is mostly mediated indirectly through regulation of chromatin accessibility. Controlled protein degradation strategies revealed that the uninterrupted presence of OCT4 is required for post-mitotic re-establishment and interphase maintenance of chromatin accessibility, and that highly OCT4-bound enhancers are particularly vulnerable to transient loss of OCT4 expression. Our study sheds light on the constant pioneer activity required to maintain the dynamic pluripotency regulatory landscape in an accessible state.
Project description:The pioneer activity of transcription factors allows for opening of inaccessible regulatory elements and has been extensively studied in the context of cellular differentiation and reprogramming. In contrast, the function of pioneer activity in self-renewing cell divisions and across the cell cycle is poorly understood. Here we assessed the interplay between OCT4 and SOX2 in controlling chromatin accessibility of mouse embryonic stem cells. We found that OCT4 and SOX2 operate in a largely independent manner even at co-occupied sites, and that their cooperative binding is mostly mediated indirectly through regulation of chromatin accessibility. Controlled protein degradation strategies revealed that the uninterrupted presence of OCT4 is required for post-mitotic re-establishment and interphase maintenance of chromatin accessibility, and that highly OCT4-bound enhancers are particularly vulnerable to transient loss of OCT4 expression. Our study sheds light on the constant pioneer activity required to maintain the dynamic pluripotency regulatory landscape in an accessible state.
Project description:The pioneer activity of transcription factors allows for opening of inaccessible regulatory elements and has been extensively studied in the context of cellular differentiation and reprogramming. In contrast, the function of pioneer activity in self-renewing cell divisions and across the cell cycle is poorly understood. Here we assessed the interplay between OCT4 and SOX2 in controlling chromatin accessibility of mouse embryonic stem cells. We found that OCT4 and SOX2 operate in a largely independent manner even at co-occupied sites, and that their cooperative binding is mostly mediated indirectly through regulation of chromatin accessibility. Controlled protein degradation strategies revealed that the uninterrupted presence of OCT4 is required for post-mitotic re-establishment and interphase maintenance of chromatin accessibility, and that highly OCT4-bound enhancers are particularly vulnerable to transient loss of OCT4 expression. Our study sheds light on the constant pioneer activity required to maintain the dynamic pluripotency regulatory landscape in an accessible state.
Project description:Pioneer transcription factors are able to recognise and bind their motif sequences in inaccessible or closed chromatin, and their ability to achieve this is required to establish new regulatory elements and transcriptional networks during development and cellular reprogramming. An essential feature of this pioneering activity is the transition from inaccessible chromatin to a nucleosome-depleted and accessible chromatin state typical of normal regulatory elements, and this is believed to facilitate further transcription factor binding events. However, the mechanisms by which many pioneer transcription factors achieve this remarkable feat remain elusive. Here we reveal that the pluripotency-associated pioneer factor OCT4 binds inaccessible chromatin to shape the chromatin accessibility, transcription factor co-binding and regulatory potential of thousands of distal regulatory elements in mouse embryonic stem cells, demonstrating that its pioneering activity is a feature of normal pluripotency, and not just reprogramming. The accessible chromatin formed at OCT4 binding sites relies on the chromatin remodelling factor BRG1, which is recruited to these sites by OCT4. The occupancy of BRG1 is then required to support OCT4/SOX2 co-binding and normal expression of the pluripotency-associated transcriptome, and this reliance on BRG1 reflects OCT4 binding dynamics during cellular reprograming and early mouse development. Together these observations reveal a distinct requirement for the chromatin remodelling factor BRG1 in shaping the pioneering activity of OCT4 and regulating the pluripotency network in embryonic stem cells.
Project description:Pioneer transcription factors are able to recognise and bind their motif sequences in inaccessible or closed chromatin, and their ability to achieve this is required to establish new regulatory elements and transcriptional networks during development and cellular reprogramming. An essential feature of this pioneering activity is the transition from inaccessible chromatin to a nucleosome-depleted and accessible chromatin state typical of normal regulatory elements, and this is believed to facilitate further transcription factor binding events. However, the mechanisms by which many pioneer transcription factors achieve this remarkable feat remain elusive. Here we reveal that the pluripotency-associated pioneer factor OCT4 binds inaccessible chromatin to shape the chromatin accessibility, transcription factor co-binding and regulatory potential of thousands of distal regulatory elements in mouse embryonic stem cells, demonstrating that its pioneering activity is a feature of normal pluripotency, and not just reprogramming. The accessible chromatin formed at OCT4 binding sites relies on the chromatin remodelling factor BRG1, which is recruited to these sites by OCT4. The occupancy of BRG1 is then required to support OCT4/SOX2 co-binding and normal expression of the pluripotency-associated transcriptome, and this reliance on BRG1 reflects OCT4 binding dynamics during cellular reprograming and early mouse development. Together these observations reveal a distinct requirement for the chromatin remodelling factor BRG1 in shaping the pioneering activity of OCT4 and regulating the pluripotency network in embryonic stem cells.
Project description:Pioneer transcription factors are able to recognise and bind their motif sequences in inaccessible or closed chromatin, and their ability to achieve this is required to establish new regulatory elements and transcriptional networks during development and cellular reprogramming. An essential feature of this pioneering activity is the transition from inaccessible chromatin to a nucleosome-depleted and accessible chromatin state typical of normal regulatory elements, and this is believed to facilitate further transcription factor binding events. However, the mechanisms by which many pioneer transcription factors achieve this remarkable feat remain elusive. Here we reveal that the pluripotency-associated pioneer factor OCT4 binds inaccessible chromatin to shape the chromatin accessibility, transcription factor co-binding and regulatory potential of thousands of distal regulatory elements in mouse embryonic stem cells, demonstrating that its pioneering activity is a feature of normal pluripotency, and not just reprogramming. The accessible chromatin formed at OCT4 binding sites relies on the chromatin remodelling factor BRG1, which is recruited to these sites by OCT4. The occupancy of BRG1 is then required to support OCT4/SOX2 co-binding and normal expression of the pluripotency-associated transcriptome, and this reliance on BRG1 reflects OCT4 binding dynamics during cellular reprograming and early mouse development. Together these observations reveal a distinct requirement for the chromatin remodelling factor BRG1 in shaping the pioneering activity of OCT4 and regulating the pluripotency network in embryonic stem cells.
Project description:SOX2 and OCT4 are pioneer transcription factors playing a key role in embryonic stem (ES) cell self-renewal and differentiation. How temporal fluctuations in their expression levels bias lineage commitment is unknown. Here we generated knock-in reporter fusion ES cell lines allowing to monitor endogenous SOX2 and OCT4 protein fluctuations in living cells and to determine their impact on mesendodermal and neuroectodermal commitment. We found that small differences in SOX2 and OCT4 levels impact cell fate commitment in G1 but not in S phase. Elevated SOX2 levels modestly increased neuroectodermal commitment and decreased mesendodermal commitment upon directed differentiation. In contrast, elevated OCT4 levels strongly biased ES cells towards both neuroectodermal and mesendodermal fates. Using ATAC-seq on ES cells gated for different endogenous SOX2 and OCT4 levels, we found that high OCT4 levels increased chromatin accessibility at differentiation-associated enhancers. This suggests that small endogenous fluctuations of pioneer transcription factors can bias cell fate decisions by concentration-dependent priming of differentiation-associated enhancers.
Project description:The nucleosome is a fundamental unit of chromatin in eukaryotes, and generally prevents the binding of transcription factors to genomic DNA. Pioneer transcription factors overcome the nucleosome barrier, and bind their target DNA sequences in chromatin. OCT4 is a representative pioneer transcription factor that plays a role in stem cell pluripotency. In the present study, we biochemically analyzed the nucleosome binding by OCT4. Crosslinking mass spectrometry showed that OCT4 binds the nucleosome.
Project description:Genome-wide transcriptional activity involves the binding of many transcription factors to thousands of sites in the genome. Determining which sites are directly driving transcription remains a challenge. Here we use acute protein depletion of the pioneer transcription factor SOX2 to establish its functionality in maintaining chromatin accessibility. We show that thousands of accessible sites are lost within an hour of protein depletion, indicating rapid turnover of these sites in the absence of pioneer factors. To understand the relationship with transcription we performed nascent transcription analysis and found that open chromatin sites that are maintained by SOX2 are highly predictive of gene expression, in contrast to all other SOX2 binding sites. We use CRISPR-Cas9 genome editing in the Klf2 locus to functionally validate a predicted regulatory element. We conclude that the regulatory activity of SOX2 is exerted largely at sites where it maintains accessibility and that other binding sites are largely dispensable for gene regulation.