Project description:We performed 3 single-cell RNAseq experiments to identify the mechanisms of definitive endoderm formation during gastrulation. To enrich for the rare endoderm and endoderm progenitor populations we used the FVF reporter mouse line. 103 homozygous FVF embryos were isloated at two consecutive days: 40 early to mid streak stage embryos at day 1, 39 early to mid streak embryos at day 2 , 24 mid streak to late streak embryos at day 2 . Embryonic compartments from each sample were FACS sorted according to Foxa2-Venus fluorescence intensity into FVF negative, FVF low and FVF high cell populations. Using the FVF-sorted cell populations we could identify FVF low endoderm progenitors and their continous transition into FVF high anterior defintive endoderm.
Project description:It is generally accepted that epiblast cells ingress into the primitive streak by epithelial-to-mesenchymal transition (EMT) to give rise to the mesoderm; however, it is less clear how the endoderm acquires an epithelial fate. Here, we used embryonic stem cell and mouse embryo knock‐in reporter systems to combine time-resolved lineage labelling with high-resolution single-cell transcriptomics. This allowed us to resolve the morphogenetic programs that segregate the mesoderm from the endoderm germ layer. Strikingly, while the mesoderm is formed by classical EMT, the endoderm is formed independent of the key EMT transcription factor Snail1 by mechanisms of epithelial cell plasticity. Importantly, forkhead box transcription factor A2 (Foxa2) acts as an epithelial gatekeeper and EMT suppressor to shield the endoderm from undergoing a mesenchymal transition. Altogether, these results not only establish the morphogenetic details of germ layer formation, but also have broader implications for stem cell differentiation and cancer metastasis.
Project description:It is generally accepted that epiblast cells ingress into the primitive streak by epithelial-to-mesenchymal transition (EMT) to give rise to the mesoderm; however, it is less clear how the endoderm acquires an epithelial fate. Here, we used embryonic stem cell and mouse embryo knock-in reporter systems to combine time-resolved lineage labelling with high-resolution single-cell transcriptomics. This allowed us to resolve the morphogenetic programs that segregate the mesoderm from the endoderm germ layer. Strikingly, while the mesoderm is formed by classical EMT, the endoderm is formed independent of the key EMT transcription factor Snail1 by mechanisms of epithelial cell plasticity. Importantly, forkhead box transcription factor A2 (Foxa2) acts as an epithelial gatekeeper and EMT suppressor to shield the endoderm from undergoing a mesenchymal transition. Altogether, these results not only establish the morphogenetic details of germ layer formation, but also have broader implications for stem cell differentiation and cancer metastasis.
Project description:Mammalian blastocyst formation involves the sequential specification of trophectoderm and the differentiation of inner cell mass into either epiblast or primitive endoderm. During this time, the embryo maintains a window of plasticity and able to redirect its cellular fate when challenged experimentally. In this context, we found that the primitive endoderm alone was capable of regenerating a complete blastocyst and continue normal postimplantation development. We identify an in vitro population similar to the early primitive endoderm in vivo that exhibits plasticity, forms three dimensional embryoid structures and exhibits multilineage competence in chimera assays. Here, we find OCT4 as the main player in collaborating with endodermal transcription factors to maintain pluripotent enhancers in a state that is primed for activation mediated by JAK/STAT signalling. Our observations support the notion that transcription factor persistence underlies plasticity in regulative development and highlights the importance of primitive endoderm in perturbed development.
Project description:Mammalian blastocyst formation involves the sequential specification of trophectoderm and the differentiation of inner cell mass into either epiblast or primitive endoderm. During this time, the embryo maintains a window of plasticity and able to redirect its cellular fate when challenged experimentally. In this context, we found that the primitive endoderm alone was capable of regenerating a complete blastocyst and continue normal postimplantation development. We identify an in vitro population similar to the early primitive endoderm in vivo that exhibits plasticity, forms three dimensional embryoid structures and exhibits multilineage competence in chimera assays. Here, we find OCT4 as the main player in collaborating with endodermal transcription factors to maintain pluripotent enhancers in a state that is primed for activation mediated by JAK/STAT signalling. Our observations support the notion that transcription factor persistence underlies plasticity in regulative development and highlights the importance of primitive endoderm in perturbed development.
Project description:Cellular differentiation requires the proper interpretation of multiple signalling cues which vary in concentration. How exactly the combination and history of signals a cell is exposed to influences a fate decision remains poorly understood. In this study we use hESCs as a tractable model system to explore how combinations of cues guide state transitions during gastrulation. Using single-cell transcriptomics and live-cell imaging of engineered hESCs expressing endogenous cell state reporters, we reconstructed developmental lineages and obtained single-cell measurements of fate specification dynamics during gastrulation. We found that definitive endoderm, one of the three germ layers, arises from two distinct developmental trajectories: a direct route from pluripotency, and an indirect route via a mesoderm progenitor state. Furthermore, by modulating the signalling input we found that the relative concentration of Activin and BMP4 controls the choice between alternate trajectories to endoderm. These findings reveal a lineage convergence event during human gastrulation with multiple routes existing to definitive endoderm dictated by the combination of signalling cues presented. This work shows that the combination cues a cell is exposed to not only directs the final fate outcome it assumes, but the developmental route taken.
Project description:Cellular differentiation requires the proper interpretation of multiple signalling cues which vary in concentration. How exactly the combination and history of signals a cell is exposed to influences a fate decision remains poorly understood. In this study we use hESCs as a tractable model system to explore how combinations of cues guide state transitions during gastrulation. Using single-cell transcriptomics and live-cell imaging of engineered hESCs expressing endogenous cell state reporters, we reconstructed developmental lineages and obtained single-cell measurements of fate specification dynamics during gastrulation. We found that definitive endoderm, one of the three germ layers, arises from two distinct developmental trajectories: a direct route from pluripotency, and an indirect route via a mesoderm progenitor state. Furthermore, by modulating the signalling input we found that the relative concentration of Activin and BMP4 controls the choice between alternate trajectories to endoderm. These findings reveal a lineage convergence event during human gastrulation with multiple routes existing to definitive endoderm dictated by the combination of signalling cues presented. This work shows that the combination cues a cell is exposed to not only directs the final fate outcome it assumes, but the developmental route taken.
Project description:Cellular differentiation requires the proper interpretation of multiple signalling cues which vary in concentration. How exactly the combination and history of signals a cell is exposed to influences a fate decision remains poorly understood. In this study we use hESCs as a tractable model system to explore how combinations of cues guide state transitions during gastrulation. Using single-cell transcriptomics and live-cell imaging of engineered hESCs expressing endogenous cell state reporters, we reconstructed developmental lineages and obtained single-cell measurements of fate specification dynamics during gastrulation. We found that definitive endoderm, one of the three germ layers, arises from two distinct developmental trajectories: a direct route from pluripotency, and an indirect route via a mesoderm progenitor state. Furthermore, by modulating the signalling input we found that the relative concentration of Activin and BMP4 controls the choice between alternate trajectories to endoderm. These findings reveal a lineage convergence event during human gastrulation with multiple routes existing to definitive endoderm dictated by the combination of signalling cues presented. This work shows that the combination cues a cell is exposed to not only directs the final fate outcome it assumes, but the developmental route taken.
Project description:Anterior mesoderm (AM) and definitive endoderm (DE) progenitors represent the earliest embryonic cell types that are specified during germ layer formation at the primitive streak (PS) of the mouse embryo. Genetic experiments indicate that both lineages segregate from Eomes expressing progenitors in response to different NODAL signaling levels. However, the precise spatiotemporal pattern of the emergence of these cell types and molecular details of lineage segregation remain unexplored. We combined genetic fate labeling and imaging approaches with single cell RNA sequencing (scRNA-seq) to follow the transcriptional identities and define lineage trajectories of Eomes dependent cell types. Accordingly, all cells moving through the PS during the first day of gastrulation express Eomes AM and DE specification occurs before cells leave the PS from Eomes positive progenitors in a distinct spatiotemporal pattern. ScRNA-seq analysis further suggest the immediate and complete separation of AM and DE lineages from Eomes expressing cells as last common bipotential progenitor.