Project description:During the first lineage segregation, mammalian embryos generate the inner cell mass (ICM) and trophectoderm (TE). ICM gives rise to the epiblast (EPI) that forms all cell types of the body, an ability referred to as pluripotency. The molecular mechanisms that induce pluripotency in embryos remain incompletely elucidated. Using knockout (KO) mouse models in conjunction with low-input ATAC-seq and RNA-seq, we found that Oct4 and Sox2 gradually come into play in the early ICM, coinciding with the initiation of Sox2 expression. Oct4 and Sox2 directly activate the pluripotency-related genes through the corresponding OCT-SOX enhancers in the early ICM. Furthermore, we observed a substantial reorganization of chromatin landscape and transcriptome from the morula to the early ICM stages, which was partially driven by Oct4 and Sox2, highlighting their pivotal role in promoting the developmental trajectory towards the ICM. Our study provides new insights into the establishment of the pluripotency network in mouse preimplantation embryos.
Project description:During the first lineage segregation, mammalian embryos generate the inner cell mass (ICM) and trophectoderm (TE). ICM gives rise to the epiblast (EPI) that forms all cell types of the body, an ability referred to as pluripotency. The molecular mechanisms that induce pluripotency in embryos remain incompletely elucidated. Using knockout (KO) mouse models in conjunction with low-input ATAC-seq and RNA-seq, we found that Oct4 and Sox2 gradually come into play in the early ICM, coinciding with the initiation of Sox2 expression. Oct4 and Sox2 directly activate the pluripotency-related genes through the corresponding OCT-SOX enhancers in the early ICM. Furthermore, we observed a substantial reorganization of chromatin landscape and transcriptome from the morula to the early ICM stages, which was partially driven by Oct4 and Sox2, highlighting their pivotal role in promoting the developmental trajectory towards the ICM. Our study provides new insights into the establishment of the pluripotency network in mouse preimplantation embryos.
Project description:The pluripotency control regions (PluCRs) are defined as genomic regions that are bound by Oct4, Sox2, and Nanog in vivo. We utilized a high-throughput binding assay to record more than 270,000 different DNA/protein binding measurements along incrementally tiled windows of DNA within these PluCRs. This high-resolution binding map is then used to systematically define the context of Oct factor binding and reveals patterns of cooperativity and competition in the pluripotency network. The most prominent pattern is a pervasive binding competition between Oct4 and the forkhead transcription factors. Like many transcription factors, Oct4 is co-expressed with a paralog, Oct1, that shares an apparently identical binding specificity. By analyzing thousands of binding measurements we discover context effects that discriminate Oct1 from Oct4 binding. Proximal Nanog binding promotes Oct4 binding, whereas nearby Sox2 binding favors Oct1. We demonstrate by cross-species comparison and by chromatin immunoprecipitation (ChIP) that the contextual sequence determinants learned in vitro are sufficient to predict Oct1 binding in vivo.
Project description:The pluripotency control regions (PluCRs) are defined as genomic regions that are bound by Oct4, Sox2, and Nanog in vivo. We utilized a high-throughput binding assay to record more than 270,000 different DNA/protein binding measurements along incrementally tiled windows of DNA within these PluCRs. This high-resolution binding map is then used to systematically define the context of Oct factor binding and reveals patterns of cooperativity and competition in the pluripotency network. The most prominent pattern is a pervasive binding competition between Oct4 and the forkhead transcription factors. Like many transcription factors, Oct4 is co-expressed with a paralog, Oct1, that shares an apparently identical binding specificity. By analyzing thousands of binding measurements we discover context effects that discriminate Oct1 from Oct4 binding. Proximal Nanog binding promotes Oct4 binding, whereas nearby Sox2 binding favors Oct1. We demonstrate by cross-species comparison and by chromatin immunoprecipitation (ChIP) that the contextual sequence determinants learned in vitro are sufficient to predict Oct1 binding in vivo. An oligonucleotide pool that tiles through 316 PluCR regions ( a region of simulataneous in vivo Oct4, Sox2 and Nanog ChIP enrichement in human ES cells - Boyer et al. 2005) was incubated in embryonic stem cell extract. Complexes were allowed to form and oligonucletide:protein complexes were immunoprecipitated with one of four antidodies (against Oct4 , Sox2, Nanog, Oct1). The enrichment of oligonucleotides in co-precipitate was analyzed by two color (Cy3/Cy5) microarray strategy using an Agilent custom oligonucleotide array. MEGAshift (microarray evaluation of genomic aptamers by shift) binding assay protocol based on Tantin et. Al, 2008 and Reid et. Al, 2009. There are two internal technical replicates.
Project description:Sox2 is a transcription factor involved in the regulatory network maintaining the pluripotency of embryonic stem cells in culture as well as in early embryos. In addition, Sox2 plays a pivotal role in neural stem cell formation and neurogenesis. How Sox2 can serve both processes has remained elusive. Here we identified a set of Sox2-dependent neural associated enhancers (SONAE) activated immediately following neural induction and required in neural gene activation. SONAE are a distinct subgroup (1898) of 8531 Oct4/Sox2/Nanog (OSN) bound enhancers, characterized by enhanced Sox2 binding and chromatin accessibility. SONAE activation is triggered by neural induction via Retinoic Acid treatment of wild type cells and is antagonized by mesodermal transcription factors repressing Sox2 following mesoderm induction. Neural differentiation is also set off by default in Smad4 ablated cells resistant to mesodermal induction. Our data provide mechanistic insight into the regulation of early neural versus mesodermal induction in ESCs and embryos.
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: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.