MEK and GSK3β inhibition drives ES cells into a naive pluripotent state irrespective of their global methylation status
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ABSTRACT: Mouse embryonic stem cells (mESCs) can convert to a ground state by dual inhibition of MEK and GSK3β signalling in defined media in the presence of LIF (2i). The cellular transition in 2i leads to uniform expression of pluripotency markers and global DNA hypomethylation. Whether hypomethylation is required for achieving ground state or is an outcome of the conversion process is still not clear. Here we show that J1 wild type and hypomethylated mESCs (dnmt3a-/-, dnmt3b-/-, dnmt1-/- [TKO]) lacking DNA methyltransferases undergo similar morphological and expression changes upon culturing in 2i that are consistent with conversion of both to a more naive state. Maintenance of global DNA methylation levels in 2i media by constitutive expression of de novo methyltransferases is also not a barrier to conversion. Hence, signalling pathways in mES cells regulate pluripotency networks and cell state independently of their global DNA methylation status. Indicated mESCs were cultured in 2i/LIF for 2 weeks and then harvested along with serum/LIF counterparts for microarray analysis. 1ug of total RNA was used to prepare Cy3 labelled aRNA using an Amino Allyl MessageAmp II aRNA kit (Ambion) following manufacturers protocol. The samples were hybridised to SurePrint G3 mouse GE 8x60k microarrays (Agilent) and were scanned using NimbleGen MS 200 (Roche). Results were analysed with custom-written scripts implemented in the statistical programming language R (http://www.R-project.org).
Project description:We compare gene expression changes in mESCs culture in serum/LIF or 2i/LIF which favour the ground state pluripotency. Published RNASeq data where compared with newly generated data set in order to indentify transciptional signatures associated with pluripotency of mouse ES cells
Project description:The self-renewing pluripotent state was first captured in mouse embryonic stem cells (mESCs) over two decades ago. The standard condition requires the presence of serum and LIF, which provide growth promoting signals for cell expansion. However, there are pro-differentiation signals which destabilize the undifferentiated state of mESCs. The dual inhibition (2i) of the pro-differentiation Mek/Erk and Gsk3/Tcf3 pathways in mESCs is sufficient to establish an enhanced pluripotent “ground state” which bears features resembling the pre-implantation mouse epiblast. Gsk3 inhibition alleviates the repression of Esrrb, a transcription factor that can substitute for Nanog function in mESCs. The molecular mechanism that is mediated by Mek inhibition is however not clear. In this study, we investigate the pathway through which Mek inhibition operates to maintain ground state pluripotency. We have found that in mESCs, Kruppel-like factor 2 (Klf2) is a protein target of the Mek/Erk pathway; and that Klf2 protein is phosphorylated by Erk2 and subsequently degraded through the proteosome. It is therefore by Mek-inhibition through PD0325901 or 2i that enables the stabilization and accumulation of Klf2 to sustain ground state pluripotency. Importantly, we found that Klf2-null mESCs, while viable under LIF/Serum conditions, cannot be maintained and eventually gradually die within a few passages. Our result thus demonstrates that Klf2 is an essential factor of ground state pluripotency. Collectively, our study defines the Mek/Klf2 axis that cooperates with the Gsk3/Esrrb pathway in mediating ground state pluripotency.
Project description:The self-renewing pluripotent state was first captured in mouse embryonic stem cells (mESCs) over two decades ago. The standard condition requires the presence of serum and LIF, which provide growth promoting signals for cell expansion. However, there are pro-differentiation signals which destabilize the undifferentiated state of mESCs. The dual inhibition (2i) of the pro-differentiation Mek/Erk and Gsk3/Tcf3 pathways in mESCs is sufficient to establish an enhanced pluripotent “ground state” which bears features resembling the pre-implantation mouse epiblast. Gsk3 inhibition alleviates the repression of Esrrb, a transcription factor that can substitute for Nanog function in mESCs. The molecular mechanism that is mediated by Mek inhibition is however not clear. In this study, we investigate the pathway through which Mek inhibition operates to maintain ground state pluripotency. We have found that in mESCs, Kruppel-like factor 2 (Klf2) is a protein target of the Mek/Erk pathway; and that Klf2 protein is phosphorylated by Erk2 and subsequently degraded through the proteosome. It is therefore by Mek-inhibition through PD0325901 or 2i that enables the stabilization and accumulation of Klf2 to sustain ground state pluripotency. Importantly, we found that Klf2-null mESCs, while viable under LIF/Serum conditions, cannot be maintained and eventually gradually die within a few passages. Our result thus demonstrates that Klf2 is an essential factor of ground state pluripotency. Collectively, our study defines the Mek/Klf2 axis that cooperates with the Gsk3/Esrrb pathway in mediating ground state pluripotency.
Project description:Mouse embryonic stem cells (mESCs) fluctuate between a naïve inner cell mass (ICM)-like state and a primed epiblast-like state of pluripotency in serum, but are harnessed exclusively in a distinctive, apparently more naïve state of pluripotency (the ground state) with inhibitors for mitogen-activated protein kinase (MAPK) and glycogen synthase kinase 3 pathways (2i). Understanding the mechanism ensuring a naïve state of pluripotency would be critical in realizing a full potential of ESCs. We show here that PRDM14, a PR domain-containing transcriptional regulator, ensures a naïve pluripotency by a dual mechanism: Antagonizing fibroblast growth factor receptor (FGFR) signaling that is activated paradoxically by the core transcriptional circuitry for pluripotency and directs a primed state and repressing de novo DNA methyltransferases that create a primed epiblast-like epigenome. PRDM14 exerts these functions by recruiting polycomb repressive complex 2 (PRC2) specifically to key targets and repressing their expression. Mouse Embryonic Stem Cells (mESCs) or mESC-like cells with different Prdm14 genotypes {Prdm14(+/+), Prdm14(-/-), and Prdm14(-/-) rescued with Avitag-EGFP-Prdm14 transgene [Prdm14(-/-)+AGP14]} are cultured on MEF in different medium [2i, Serum(day 2), Serum+MEK inhibitor (PD0325901) (day 2), Serum without LIF (day2)].
Project description:WT J1 and 3B3L cells (in which Dnmt3B and Dnm3L are constitutively expressed from an exogenous construct) were cultured under both serum/LIF and 2i/LIF conditions. 3B3L cells do not show ground state-associated hypomethylation phenotype. This experiment sought to analyse the gene expression changes between the two conditions.
Project description:Mouse embryonic stem cells (mESCs) cultured in 2i (MEK and GSK3 kinase inhibitor)/LIF and serum/LIF that we called 2i-ESCs and serum-ESCs represent ground and confused pluripotent states, respectively. However, the transcription factors that regulate ground pluripotency through chromatin-associated characteristics are not yet fully understood. By mapping chromatin accessibility and transcription factor regulatory networks during the interconversion of 2i-ESCs and serum-ESCs, we have identified TEAD2 as highly enriched in 2i-specific peaks. While Tead2 knockout did not affect the pluripotency or differentiation ability of either 2i-ESCs or serum-ESCs, it did prevent the establishment of the 2i-specific state and the exit from the serum-specific state. TEAD2 binds to active regions in 2i-specific genes and activates their expression by regulating enhancer-promoter (EP) interactions during serum-to-2i transition. Remarkably, TEAD2-mediated EP interactions were independent of chromatin architecture proteins YY1 and CTCF, but instead appear to be facilitated by TEAD2 homodimer formation.
Project description:The pluripotent ground state is defined as a basal state free of epigenetic restrictions, which influence lineage specification. While naive embryonic stem cells (ESCs) can be maintained in a hypomethylated state with open chromatin when grown using two small-molecule inhibitors (2i)/leukemia inhibitory factor (LIF), in contrast to serum/LIF-grown ESCs that resemble early post-implantation embryos, broader features of the ground-state pluripotent epigenome are not well understood. We identified epigenetic features of mouse ESCs cultured using 2i/LIF or serum/LIF by proteomic profiling of chromatin-associated complexes and histone modifications. Polycomb-repressive complex 2 (PRC2) and its product H3K27me3 are highly abundant in 2i/LIF ESCs, and H3K27me3 is distributed genome-wide in a CpG-dependent fashion. Consistently, PRC2-deficient ESCs showed increased DNA methylation at sites normally occupied by H3K27me3 and increased H4 acetylation. Inhibiting DNA methylation in PRC2-deficient ESCs did not affect their viability or transcriptome. Our findings suggest a unique H3K27me3 configuration protects naive ESCs from lineage priming, and they reveal widespread epigenetic crosstalk in ground-state pluripotency.
Project description:Derivation of naive state of mouse embryonic stem cells (mESCs) in LIF+serum (LS) culture condition is strain dependent, whereas derivation of ground state mESCs is readily possible from all strains tested so far in “2i” culture condition. ESCs can be derived from the post-implantation stage mouse embryos (EpiSCs), showing primed characteristics. In the present study, we characterized and compared the transcriptional profile of naïve, primed and ground state mESCs. Considering the importance of genetic background of mouse model for ESCs derivation in conventional culture conditions, all ESCs lines used in the study were derived from the same strain of mice. We found distinct transcriptional profiles between naive, primed and ground state mESCs. Primed state mESCs exhibit lower expression of pluripotency markers along with higher expression of lineage specific markers compared to naive and ground state mESCs. We also demonstrate that the differentiation propensity of ESCs to specific germ layer varies depending on the pluripotency state of ESCs.
Project description:Mouse embryonic stem cells (mESCs) represent an exceptional model for understanding how transcriptional responses are regulated by signalling pathways during development. Treatment with a cocktail of MEK and GSK3β inhibitors (“2i”) induces ground state pluripotency, characterized by increased self-renewal, reduced DNA methylation, and uniformly high expression of pluripotency markers. Polycomb Repressive Complex 2 (PRC2) is a key developmental regulator controlling stem cell self-renewal and differentiation decisions, and altered expression of PRC2 target genes is a signature of 2i-mediated ground state conversion. Here, we generated a comprehensive RNA sequencing dataset from mESCs subjected to 2i conversion time-course across five time points, representing six population doublings. We analysed two independently derived wild type lines, and two isogenic Cas9-edited lines carrying loss-of-function mutations in core PRC2 subunits Enhancer of Zeste Homolog 2 (Ezh2) or Embryonic Ectoderm Development (Eed). These data may provide a comprehensive resource to understand the temporal patterns of transcriptional responses to MEK and GSK3β inhibitors and explore the role of PRC2 function in regulation of pluripotency circuit.
Project description:Mouse embryonic stem cells (mESCs) cultured under serum/LIF conditions exhibit heterogeneous expression of pluripotency-associated factors that can be overcome by two inhibitors (2i) of the MEK and GSK3 pathway, respectively. Several studies have shown that the “ground state” induced by 2i is characterized by global hypomethylation and specific transcriptional profiles, but little is known about the contributing effectors. Here we show that 2i conditions rapidly alter the global binding landscape of OCT4, SOX2 and NANOG. The dynamic binding influences enhancer activity and shows enrichment for regulators linked to Wnt and Erk signaling. Epigenomic characterization provided limited insights to the immediate transcriptional dynamics suggesting these are likely more secondary effects. Likewise, knock-out of the PRC2 component EED to prevent H3K27me3 deposition had minimal effect on the transcriptome, rendering it largely dispensable for continued repression of bivalent genes and de novo silencing in 2i.