Project description:The Wnt3a/?-catenin and Activin/Smad2,3 signaling pathways synergize to induce endodermal differentiation of human embryonic stem cells, however the mechanism is not well-understood. Using ChIP-seq and GRO-seq analyses, we report here that hESC enhancers, including Wnt3a/LEF-1 sites, hold enhancer RNAPII complexes (eRNAPII) containing high levels of Ser5P and low Ser7P. In Wnt3a signaling, ?-catenin recruits cohesin to the LEF-1:eRNAPII sites to induce enhancer-promoter looping and activate transcription of mesoendodermal (ME) genes. However, paused Ser5P-RNAPII complexes accumulate at these genes, indicating that elongation remains limiting. Subsequent Activin/Smad2,3 signaling increases P-TEFb occupancy, CTD-Ser7P, and productive elongation at ME genes. Additionally, ME genes, including EOMES and MIXL1, are repressed by the Hippo regulator, Yap1, an essential pluripotency factor. GRO-seq experiments indicate that Yap1 blocks nascent transcription and controls NELF occupancy on ME genes. Thus, Wnt3a/?-catenin and Activin/Smad2,3 pathways up-regulate transcription initiation and elongation, respectively, to overcome Yap1 repression during early hESC differentiation ChIP-seq and GROseq experiments in H1 hESCs. Cells were treated with Wnt3a (200ng/ml), Activin A (100ng/ml) or Wnt3a+Activin A (W200ng/ml+A100ng/ml) for 4h (ChIP-seq) or 6h (GRO-seq). GRO-seq in YAP depleted cells were carried out following transfection with control or YAP siRNAs . After 48h transfection, cells were left untreated or treated with Wnt3a+Activin (W200ng/ml+A100ng/ml) for additional 6h.
Project description:The Wnt3a/β-catenin and Activin/Smad2,3 signaling pathways synergize to induce endodermal differentiation of human embryonic stem cells, however the mechanism is not well-understood. Using ChIP-seq and GRO-seq analyses, we report here that hESC enhancers, including Wnt3a/LEF-1 sites, hold enhancer RNAPII complexes (eRNAPII) containing high levels of Ser5P and low Ser7P. In Wnt3a signaling, β-catenin recruits cohesin to the LEF-1:eRNAPII sites to induce enhancer-promoter looping and activate transcription of mesoendodermal (ME) genes. However, paused Ser5P-RNAPII complexes accumulate at these genes, indicating that elongation remains limiting. Subsequent Activin/Smad2,3 signaling increases P-TEFb occupancy, CTD-Ser7P, and productive elongation at ME genes. Additionally, ME genes, including EOMES and MIXL1, are repressed by the Hippo regulator, Yap1, an essential pluripotency factor. GRO-seq experiments indicate that Yap1 blocks nascent transcription and controls NELF occupancy on ME genes. Thus, Wnt3a/β-catenin and Activin/Smad2,3 pathways up-regulate transcription initiation and elongation, respectively, to overcome Yap1 repression during early hESC differentiation
Project description:Specifying the primitive streak (PS) guides stem cell differentiation in vitro, however much remains to be learned about the transcription networks that direct anterior and posterior PS cells (APS and PPS, respectively) to differentiate to distinct mesendodermal subpopulations. Here, we show that APS genes are predominantly induced in YAP1-/- hESCs in response to ACTIVIN. This finding establishes the Hippo effector YAP1 as a master regulator of PS specification, functioning to repress ACTIVIN-regulated APS genes in hESCs. Moreover, transient exposure of wild-type hESCs to dasatinib, a potent C-SRC/YAP1 inhibitor, enables differentiation to APS-derived endoderm and cardiac mesoderm in response to ACTIVIN. Importantly, these cells can differentiate efficiently to normal beating cardiomyocytes without the cytoskeletal defect seen in YAP1-/- hESC-derived cardiomyocytes. Overall, we uncovered an induction mechanism to generate APS cells using a cocktail of ACTIVIN and YAP1i molecules that holds practical implications for hESC and iPSC differentiation into distinct mesendodermal lineages.
Project description:We have previously shown that RNA polymerase II (Pol II) pause release and transcriptional elongation involve phosphorylation of the factor TRIM28 by the DNA damage response (DDR) kinases ATM and DNA-PK. Here, we report a significant role for DNA breaks and DDR signaling in the mechanisms of transcriptional elongation in stimulus-inducible genes in humans. Our data show the enrichment of TRIM28 and γH2AX on serum-induced genes and the important function of DNA-PK for Pol II pause release and transcriptional activation-coupled DDR signaling on these genes. γH2AX accumulation decreases when P-TEFb is inhibited, confirming that DDR signaling results from transcriptional elongation. In addition, transcriptional elongation-coupled DDR signaling involves topoisomerase II because inhibiting this enzyme interferes with Pol II pause release and γH2AX accumulation. Our findings propose that DDR signaling is required for effective Pol II pause release and transcriptional elongation through a novel mechanism involving TRIM28, DNA-PK, and topoisomerase II 42 samples in total. IP targets were gammaH2ax, s2-pol-II, pol-II, pTRIM28, DNA-pk, topo-IIB. Experimental conditions included DMSO treatment (control), pTEFb, topoII-i, dnapk-i. Matched non-specific IP samples used for control in peak calling.
Project description:We have previously shown that RNA polymerase II (Pol II) pause release and transcriptional elongation involve phosphorylation of the factor TRIM28 by the DNA damage response (DDR) kinases ATM and DNA-PK. Here, we report a significant role for DNA breaks and DDR signaling in the mechanisms of transcriptional elongation in stimulus-inducible genes in humans. Our data show the enrichment of TRIM28 and γH2AX on serum-induced genes and the important function of DNA-PK for Pol II pause release and transcriptional activation-coupled DDR signaling on these genes. γH2AX accumulation decreases when P-TEFb is inhibited, confirming that DDR signaling results from transcriptional elongation. In addition, transcriptional elongation-coupled DDR signaling involves topoisomerase II because inhibiting this enzyme interferes with Pol II pause release and γH2AX accumulation. Our findings propose that DDR signaling is required for effective Pol II pause release and transcriptional elongation through a novel mechanism involving TRIM28, DNA-PK, and topoisomerase II
Project description:In vitro studies identified various factors including P-TEFb, SEC, SPT6, PAF1, DSIF, and NELF functioning at different stages of transcription elongation driven by RNA polymerase II (RNA Pol II). What remains unclear is how these factors cooperatively regulate pause/release and productive elongation in the context of living cells. Using an acute 5 protein-depletion approach, prominent release and a subsequent increase in mature transcripts, whereas long genes fail to yield mature transcripts due to a loss of processivity. Mechanistically, loss of SPT6 results in loss of PAF1 complex (PAF1C) from RNA Pol II, leading to NELF-bound RNA Pol II release into the gene bodies. Furthermore, SPT6 and/or PAF1 depletion impairs heat shock-induced pausing, pointing to a role for SPT6 in regulating RNA Pol II pause/release through the recruitment of PAF1C during the early elongation.
Project description:Genome-wide analysis of miRNA expression was performed in Activin A and Wnt3a-treated mouse ESCs during the different stages of DE differentiation to identify candidate miRNAs likely to be involved in Wnt3a and Activin A induced DE formation. Our analysis exhibited a distinct miRNA expression finger print. Furthermore, we found that forced expression of a subset of synergistically regulated miRNAs could partially mimic the roles of Wnt3a and Activin A. Pathway analyses also revealed the involvement of histone acetylation in Activin A/Wnt3a-driven DE differentiation, which is further confirmed by treating the cells with small molecular weight HDAC inhibitors as well as ChIP experiments. Our study established a regulatory cascade from extracellular cytokine treatment to miRNA expression to histone modification in cell nucleus during DE differentiation. ESCs were treated with 100ng/ml Activin A, or 50ng/ml Wnt3a, or 100ng/ml Activin A plus 50ng/ml Wnt3a, and the samples were collected at 1 day, 3 days, and 5 days after treatment, respectively. Cells treated with the same medium without growth factors were used as the negative controls for each time point.
Project description:The pause-release model of transcription proposes that pol II pauses 40-100 bases from the start site resulting in a pile-up that is relieved by subsequent release into productive elongation. Pause release is facilitated by PTEFb phosphorylation of the pol II elongation factor, Spt5. We mapped paused polymerases by eNETseq and found frequent pausing in zones that extend ~0.3-3kb into genes, even when PTEFb is inhibited. The fraction of paused polymerases or “pausiness” declines gradually over several kb, and not abruptly as predicted for a discrete pause release event. Spt5 depletion extends pausing zones suggesting that it promotes maturation of elongation complexes to a low-pausing state. Expression of mutants after Spt5 depletion showed that phosphomimetic substitutions in the Spt5 CTR1 domain diminished pausing throughout genes. In contrast mutants that prevent phosphorylation of the Spt5 RNA-binding domain strengthened pausing. Thus distinct Spt5 phospho-isoforms set the balance between pausing and elongation.
Project description:Genome-wide analysis of miRNA expression was performed in Activin A and Wnt3a-treated mouse ESCs during the different stages of DE differentiation to identify candidate miRNAs likely to be involved in Wnt3a and Activin A induced DE formation. Our analysis exhibited a distinct miRNA expression finger print. Furthermore, we found that forced expression of a subset of synergistically regulated miRNAs could partially mimic the roles of Wnt3a and Activin A. Pathway analyses also revealed the involvement of histone acetylation in Activin A/Wnt3a-driven DE differentiation, which is further confirmed by treating the cells with small molecular weight HDAC inhibitors as well as ChIP experiments. Our study established a regulatory cascade from extracellular cytokine treatment to miRNA expression to histone modification in cell nucleus during DE differentiation.