Pluripotency reprogramming by competent and incompetent POU factors uncovers temporal dependency for Oct4 and Sox2 [RNA-Seq]
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ABSTRACT: Oct4, along with Sox2 and Klf4 (SK), can induce pluripotency but structurally similar factors like Oct6 cannot. To decode why Oct4 has this unique ability, we compare Oct4-binding, accessibility patterns and transcriptional waves with Oct6 and an Oct4 mutant defective in the dimerization with Sox2 (Oct4defSox2). We find that initial silencing of the somatic program proceeds indistinguishably with or without Oct4. Oct6 mitigates the mesenchymal-to-epithelial transition and derails reprogramming. These effects are a consequence of differences in genome-wide binding, as the early binding profile of Oct4defSox2 resembles Oct4, whilst Oct6 does not bind pluripotency enhancers. Nevertheless, in the Oct6-SK condition many otherwise Oct4-bound locations become accessible but chromatin opening is compromised when Oct4defSox2 occupies these sites. We find that Sox2 predominantly facilitates chromatin opening, whilst Oct4 serves an accessory role. Formation of Oct4/Sox2 heterodimers is essential for pluripotency establishment; however, reliance on Oct4/Sox2 heterodimers declines during pluripotency maintenance.
Project description:Oct4, along with Sox2 and Klf4 (SK), can induce pluripotency but structurally similar factors like Oct6 cannot. To decode why Oct4 has this unique ability, we compare Oct4-binding, accessibility patterns and transcriptional waves with Oct6 and an Oct4 mutant defective in the dimerization with Sox2 (Oct4defSox2). We find that initial silencing of the somatic program proceeds indistinguishably with or without Oct4. Oct6 mitigates the mesenchymal-to-epithelial transition and derails reprogramming. These effects are a consequence of differences in genome-wide binding, as the early binding profile of Oct4defSox2 resembles Oct4, whilst Oct6 does not bind pluripotency enhancers. Nevertheless, in the Oct6-SK condition many otherwise Oct4-bound locations become accessible but chromatin opening is compromised when Oct4defSox2 occupies these sites. We find that Sox2 predominantly facilitates chromatin opening, whilst Oct4 serves an accessory role. Formation of Oct4/Sox2 heterodimers is essential for pluripotency establishment; however, reliance on Oct4/Sox2 heterodimers declines during pluripotency maintenance.
Project description:Oct4, along with Sox2 and Klf4 (SK), can induce pluripotency but structurally similar factors like Oct6 cannot. To decode why Oct4 has this unique ability, we compare Oct4-binding, accessibility patterns and transcriptional waves with Oct6 and an Oct4 mutant defective in the dimerization with Sox2 (Oct4defSox2). We find that initial silencing of the somatic program proceeds indistinguishably with or without Oct4. Oct6 mitigates the mesenchymal-to-epithelial transition and derails reprogramming. These effects are a consequence of differences in genome-wide binding, as the early binding profile of Oct4defSox2 resembles Oct4, whilst Oct6 does not bind pluripotency enhancers. Nevertheless, in the Oct6-SK condition many otherwise Oct4-bound locations become accessible but chromatin opening is compromised when Oct4defSox2 occupies these sites. We find that Sox2 predominantly facilitates chromatin opening, whilst Oct4 serves an accessory role. Formation of Oct4/Sox2 heterodimers is essential for pluripotency establishment; however, reliance on Oct4/Sox2 heterodimers declines during pluripotency maintenance.
Project description:Oct4, along with Sox2 and Klf4 (SK), can induce pluripotency but structurally similar factors like Oct6 cannot. To decode why Oct4 has this unique ability, we compare Oct4-binding, accessibility patterns and transcriptional waves with Oct6 and an Oct4 mutant defective in the dimerization with Sox2 (Oct4defSox2). We find that initial silencing of the somatic program proceeds indistinguishably with or without Oct4. Oct6 mitigates the mesenchymal-to-epithelial transition and derails reprogramming. These effects are a consequence of differences in genome-wide binding, as the early binding profile of Oct4defSox2 resembles Oct4, whilst Oct6 does not bind pluripotency enhancers. Nevertheless, in the Oct6-SK condition many otherwise Oct4-bound locations become accessible but chromatin opening is compromised when Oct4defSox2 occupies these sites. We find that Sox2 predominantly facilitates chromatin opening, whilst Oct4 serves an accessory role. Formation of Oct4/Sox2 heterodimers is essential for pluripotency establishment; however, reliance on Oct4/Sox2 heterodimers declines during pluripotency maintenance.
Project description:Somatic cells can be reprogrammed into pluripotent stem cells by the ectopic expression of OCT4, SOX2, KLF4, and c-MYC. Although SOX2, KLF4, and c-MYC (SKM) can be substituted by their respective family members, OCT4 is considered to not be interchangeable with any octamer-binding POU proteins. Through a screening with 102 candidate genes, here we have identified that the POU protein OCT6 (also known as SCIP, TST-1, and POU3F1), in conjunction with SKM, is capable of functionally replacing OCT4 and inducing pluripotency. OCT6-mediated reprogramming works with any human cell type, but not with mouse cells. The reprogramming process involving OCT6 is relatively inefficient and slow. This is mainly due to either inefficient formation of OCT6-SOX2 heterodimers onto canonical SOX-OCT sites or lower transactivation activity of OCT6. We demonstrate that modulating either the DNA-binding propensity or the transactivation activity of OCT6 enhances iPSC generation to the efficiency of OCT4. These results thus provide the first evidence that a POU factor other than OCT4 can induce human pluripotency.
Project description:Pioneer transcription factors (TFs), such as OCT4 and SOX2, play crucial roles in pluripotency regulation. However, the master TF-governed pluripotency regulatory circuitry was largely inferred from cultured cells. In this work, we investigated SOX2 binding from embryonic day 3.5 (E3.5) to E7.5 in the mouse. In E3.5 inner cell mass (ICM), SOX2 regulates the ICM-trophectoderm program but is dispensable for opening global enhancers. Instead, SOX2 occupies preaccessible enhancers in part opened by early-stage expressing TFs TFAP2C and NR5A2. SOX2 then redistributes when cells adopt naive and formative pluripotency by opening enhancers or poising them for further rapid activation. Hence, multifaceted pioneer TF–enhancer interaction underpins pluripotency progression in embryos, including a state in E3.5 ICM that bridges totipotency and pluripotency.
Project description:In this study, we set out to identify those molecular features of the POU transcription factor Oct4 that are responsible for inducing pluripotency in somatic cells. Oct4 is known to have a strong preference to cooperate with Sox2 on heterodimeric SoxOct elements predominantly found in enhancers of genes expressed in embryonic stem cells (ESCs). To test whether this partnership is specific to Oct4, we compared its DNA recognition and reprogramming activities to the paralogous transcription factor Oct6, which cannot induce and maintain pluripotency in mouse cells. By analyzing ChIP-Seq data and performing quantitative dimerization assays, we found that in somatic cells, instead of heterodimerzing with Sox-factors, Oct6 more potently homodimerizes on OctOct elements. We identified that a single amino acid is crucial in directing binding to the respective composite DNA element. As a consequence, just changing this one amino acid hampers Oct4 in generating induced pluripotent stem cells (iPSCs). In contrast, the reverse mutation in Oct6 did not augment its reprogramming activity. This was achieved with at least two additional exchanges. In summary, we demonstrate that cell-type specific POU factor function is determined by a limited set of residues that affect DNA and partner factor interactions. Such relatively minor changes lead to a pronounced impact on regulatory function and reprogramming activity.
Project description:Embryonic stem cell (ESCs) identity is orchestrated by co-operativity between the transcription factors (TFs) Sox2 and the class V POU-TF, Oct4 at composite Sox/Oct motifs. Neural stem cells (NSCs) lack Oct4 but express Sox2 and class III POU-TFs. This raises the question of how Sox2 interacts with POU-TFs to transcriptionally specify ESCs or NSCs. Here we show that Oct4 alone binds the Sox/Oct motif and the octamer-containing palindromic MORE equally well. Sox2 binding selectively increases the affinity of Oct4 for the Sox/Oct motif. In contrast, Oct6 binds preferentially to the MORE, and is unaffected by Sox2. ChIP-seq in NSCs shows the MORE to be the most enriched motif for class III POU-TFs, with MORE sub-types apparent, but no Sox/Oct motif enrichment. These results suggest that in NSCs, co-operativity between Sox2 and class III POU-TFs may not occur and that POU-TF driven transcription uses predominantly the MORE cis architecture. Thus, distinct interactions between Sox2 and POU-TF subclasses distinguish pluripotent ESCs from multipotent NSCs, providing molecular insight into how Oct4 alone can convert NSCs to pluripotency.
Project description:Protein-protein proximity of core pluripotency transcription factors plays an important role during cell reprogramming. Pluripotent embryonic stem (ES) cell identity is controlled by a trio of transcription factors: Sox2, Oct4, and Nanog. These proteins often bind to closely localized genomic sites. The precise mode by which Sox2, Oct4, and Nanog interact with DNA is likely to make a crucial contribution to their function. Here, a detailed protocol for in vivo detection and quantitative analysis of protein-protein proximity of Sox2 and Oct4 using Proximity Utilizing Biotinylation (PUB) method based on the use of the BAP/BirA (target/enzyme) system is described. The method includes design and cloning of DNA plasmid construct, transient transfection of HEK293T cells, Western blot analysis of nuclei fraction and LC-MS/MS analysis. Experiments with coexpression of BAP-X+BirA-Y (X, Y=Sox2, Oct4 and GFP as control) revealed strong biotinylation level of target proteins when X and Y were pluripotency transcription factors compared with control when X=GFP. Since mass spectrometry provides both high sensitivity and more accurate quantification of data a modified workflow was used, in which SDS-PAGE step was eliminated and His-tagged BAP-fused proteins from cell lysate were purified in 6M guanidine HCl buffer, washed, propionylated, digested directly on the Ni sepharose beads using trypsin and analysed on Q-TOF Impact II instrument. Using mass spectrometry allows making quantitative estimation of in vivo interaction of BAP-Sox2 and BirA-Oct4 which was demonstrated by measuring ratios of biotinylation levels of BAP fused either with Sox2 or GFP at different biotin pulse times. After vector preparation this protocol can be completed in seven working days.
Project description:Octamer-binding Pit-Oct-Unc (POU) family members have distinct reprogramming competences. OCT4 induces pluripotency, whereas POU III factors (OCT6, OCT7, OCT8, and OCT9) lack this ability, but are prone to inducing neural identities. However, which specific features of these proteins render the distinct reprograming competences remains unknown. Here, we present that OCT6 can also induce pluripotency. But, it works only with human cells, indicating its species-dependent reprogramming activity. Functional readouts with a series of reciprocal mutants uncover that the central role of OCT4 and its strong reprogramming competence to pluripotency arise from its C-terminal transactivation domain. Furthermore, we identify intrinsic properties of OCT7, OCT8, and OCT9 that are detrimental for inducing pluripotency. A chemical screen reveals that their persistent deficiency for inducing pluripotency can be surmounted by reducing H3K79 methylation in donor cells. Our findings delineate that intrinsic properties of POU factors and their responsive donor-cell epigenome state are tightly linked to the reprogramming competence.