Project description:Reactivation of the pluripotency network during somatic cell reprogramming by exogenous transcription factors involves chromatin remodeling and the recruitment of RNA polymerase II (Pol II) to target loci. Here, we report that Pol II is engaged at pluripotency promoters in reprogramming but remains paused and inefficiently released. We also show that bromodomain-containing protein 4 (BRD4) stimulates productive transcriptional elongation of pluripotency genes by dissociating the pause release factor P-TEFb from an inactive complex containing HEXIM1. Consequently, BRD4 overexpression enhances reprogramming efficiency and HEXIM1 suppresses it, whereas Brd4 and Hexim1 knockdown do the opposite. We further demonstrate that the reprogramming factor KLF4 helps recruit P-TEFb to pluripotency promoters. Our work thus provides a mechanism for explaining the reactivation of pluripotency genes in reprogramming and unveils an unanticipated role for KLF4 in transcriptional pause release. Pol II ChIP-seq for MEFs, ESCs and bulk populations of OSKM reprogramming intermediates at two time points.
Project description:C/EBPα induces transdifferentiation of B cells into macrophages at high efficiencies and enhances reprogramming into induced pluripotent stem cells (iPSCs) when co-expressed with Oct4, Sox2, Klf4 and Myc (OSKM). However, how C/EBPα accomplishes these effects is unclear. We now found that transient C/EBPα expression followed by OSKM activation induces a 100 fold increase in iPSC reprogramming efficiency, involving 95% of the cells. During this conversion pluripotency and epithelial-mesenchymal transition genes become dramatically up-regulated and 60% of the cells express Oct4 within 2 days. C/EBPα acts as a pathbreaker since it transiently makes the chromatin of pluripotency genes more accessible to DNase I. It also induces the expression of the dioxygenase Tet2 and promotes its translocation to the nucleus where it binds to regulatory regions of pluripotency genes that become demethylated following OSKM induction. In line with these findings, overexpression of Tet2 enhances OSKM‐induced B cell reprogramming. Since the enzyme is also required for efficient C/EBPα-induced immune cell conversion, our data suggest that Tet2 provides a mechanistic link between iPSC reprogramming and B cell transdifferentiation. The rapid iPS reprogramming approach described should help to fully elucidate the process and has potential clinical applications. Change in Cebpa genome binding/occupancy, comparing primary B-cells treated with estradiol for 18h to induce C/EBPa to untreated cells.
Project description:C/EBPM-NM-1 induces transdifferentiation of B cells into macrophages at high efficiencies and enhances reprogramming into induced pluripotent stem cells (iPSCs) when co-expressed with Oct4, Sox2, Klf4 and Myc (OSKM). However, how C/EBPM-NM-1 accomplishes these effects is unclear. We now found that transient C/EBPM-NM-1 expression followed by OSKM activation induces a 100 fold increase in iPSC reprogramming efficiency, involving 95% of the cells. During this conversion pluripotency and epithelial-mesenchymal transition genes become dramatically up-regulated and 60% of the cells express Oct4 within 2 days. C/EBPM-NM-1 acts as a pathbreaker since it transiently makes the chromatin of pluripotency genes more accessible to DNase I. It also induces the expression of the dioxygenase Tet2 and promotes its translocation to the nucleus where it binds to regulatory regions of pluripotency genes that become demethylated following OSKM induction. In line with these findings, overexpression of Tet2 enhances OSKMM-bM-^@M-^Pinduced B cell reprogramming. Since the enzyme is also required for efficient C/EBPM-NM-1-induced immune cell conversion, our data suggest that Tet2 provides a mechanistic link between iPSC reprogramming and B cell transdifferentiation. The rapid iPS reprogramming approach described should help to fully elucidate the process and has potential clinical applications. Refer to individual Series
Project description:Reactivation of the pluripotency network during somatic cell reprogramming by exogenous transcription factors involves chromatin remodeling and the recruitment of RNA polymerase II (Pol II) to target loci. Here, we report that Pol II is engaged at pluripotency promoters in reprogramming but remains paused and inefficiently released. We also show that bromodomain-containing protein 4 (BRD4) stimulates productive transcriptional elongation of pluripotency genes by dissociating the pause release factor P-TEFb from an inactive complex containing HEXIM1. Consequently, BRD4 overexpression enhances reprogramming efficiency and HEXIM1 suppresses it, whereas Brd4 and Hexim1 knockdown do the opposite. We further demonstrate that the reprogramming factor KLF4 helps recruit P-TEFb to pluripotency promoters. Our work thus provides a mechanism for explaining the reactivation of pluripotency genes in reprogramming and unveils an unanticipated role for KLF4 in transcriptional pause release. Refer to individual Series
Project description:Reactivation of the pluripotency network during somatic cell reprogramming by exogenous transcription factors involves chromatin remodeling and the recruitment of RNA polymerase II (Pol II) to target loci. Here, we report that Pol II is engaged at pluripotency promoters in reprogramming but remains paused and inefficiently released. We also show that bromodomain-containing protein 4 (BRD4) stimulates productive transcriptional elongation of pluripotency genes by dissociating the pause release factor P-TEFb from an inactive complex containing HEXIM1. Consequently, BRD4 overexpression enhances reprogramming efficiency and HEXIM1 suppresses it, whereas Brd4 and Hexim1 knockdown do the opposite. We further demonstrate that the reprogramming factor KLF4 helps recruit P-TEFb to pluripotency promoters. Our work thus provides a mechanism for explaining the reactivation of pluripotency genes in reprogramming and unveils an unanticipated role for KLF4 in transcriptional pause release. Examination of differential gene expression after overexpression of Cdk9-DN at 4 time points of somatic cell reprogramming
Project description:Pluripotent stem cells are derived from culture of early embryos or the germline, and can be induced by reprogramming of somatic cells. Barriers to reprogramming are expected to exist that stabilize the differentiated state and have tumor suppression functions. However, we have a limited understanding of what such barriers might be. To find novel barriers to reprogramming to pluripotency, we compared the transcriptional profiles of the mouse germline to pluripotent and somatic cells, in vivo and in vitro. There is a remarkable global expression of the transcriptional program for pluripotency in Primordial Germ Cells (PGCs). We identify parallels between PGCs reprogramming to pluripotency and human germ cell tumorigenesis, including the loss of LATS2, a tumor suppressor kinase of the Hippo pathway. We show that knockdown of LATS2 increases the efficiency of induction of pluripotency in human cells. LATS2 RNAi, unlike p53 RNAi, specifically enhances the generation of fully reprogrammed iPS cells without accelerating cell proliferation. We further show that LATS2 represses reprogramming in human cells by post-transcriptionally antagonizing TAZ but not YAP, two downstream effectors of the Hippo pathway. These results reveal transcriptional parallels between germ cell transformation and the generation of iPS cells, and indicate that the Hippo pathway constitutes a barrier to cellular reprogramming. Mouse pluripotent cells isolated directly from embryos or cultured in vitro as stem cells were analyzed using Affymetrix expression microarrays, together with several non-pluripotent cell controls, in 2-6 replicates per sample.
Project description:Changing the somatic cell transcriptome to a pluripotent state using exogenous reprogramming factors needs transcriptional co-regulators that help activate or suppress gene expression and rewrite the epigenome. Here, we show that reprogramming-specific engagement of the NCoR/SMRT co-repressor complex at key pluripotency loci creates an epigenetic block to reprogramming. HDAC3 executes the repressive function of NCoR/SMRT in reprogramming by inducing histone deacetylation at these loci. Recruitment of NCoR/SMRT-HDAC3 to pluripotency genes is facilitated by all 4 Yamanaka factors (OCT4, SOX2, KLF4 and c-MYC) but mostly by c-MYC. Class IIa HDACs further potentiate this recruitment by interacting with both the reprogramming factors and NCoR/SMRT. Consequently, depleting NCoR/SMRT-HDAC3 function enables high efficiency of reprogramming, while elevating NCoR/SMRT-HDAC3 recruitment at pluripotency loci by over-expressing constitutively active class IIa HDACs derails it. Our findings thus uncover an unexpected epigenetic mechanism involving c-MYC, whose manipulation greatly enhances reprogramming efficiency.
Project description:Embryonic stem (ES) cells derived from the inner cell mass (ICM) of blastocysts are characterised by their ability to self-renew and their potential to differentiate into many different cell types. Recent studies have shown that zinc finger proteins are crucial for maintaining pluripotent ES cells. Mouse zinc finger protein 322a (Zfp322a) is expressed in the ICM of early mouse embryos. However, little is known regarding the role of Zfp322a in the pluripotentcy maintenance of ES cells. Here, we report that Zfp322a is required for ES cell identity since depletion of Zfp322a directs ES cells towards differentiation. Chromatin immunoprecipitation (ChIP) and dual-luciferase reporter assays revealed that Zfp322a binds to Oct4 and Nanog promoters and regulates their transcription. These data along with the results obtained from our ChIP-seq experiment showed that Zfp322a is an essential component of the ES cell transcription regulatory network. Targets which are directly regulated by Zfp322a were identified by correlating the gene expression profile of Zfp322a RNAi-treated ES cells with the ChIP-seq results. These experiments revealed that Zfp322a inhibits ES cell differentiation by suppressing MAPK pathway. Additionally, Zfp322a is found to be a novel reprogramming factor that can replace Sox2 in the classical Yamanaka’s factors (OSKM). It can be even used in combination with Yamanaka’s factors and that addition leads to a higher reprogramming efficiency and to acceleration of the onset of the reprogramming process. Together, our results demonstrate that Zfp322a is a novel essential component of the transcription factor network which maintains the identity of ES cells. E14 mES cells were immunoprecipitated with Zfp322a antibody or IgG from rabbit.