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: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.
Project description:A conserved molecular pathway has emerged controlling endoderm formation in Xenopus zebrafish and mice. Key genes in this pathway include Nodal ligands and transcription factors of the Mix-like paired homeodomain class, Gata4-6 zinc finger factors and Sox17 HMG domain proteins. While a linear epistatic pathway has been proposed, the precise hierarchical relationships between these factors and their downstream targets are largely unresolved. Here we used a combination of microarray analysis and loss-of-function experiments to examine the global regulatory network controlling Xenopus endoderm formation. We identified over 300 transcripts enriched in the gastrula endoderm, including most of the known endoderm regulators as well as over a hundred uncharacterized genes. Surprisingly only 10% of the endoderm transcriptome is regulated as predicted by the current linear model. We find that Nodals, Mixer and Sox17 have both shared and distinct sets of downstream targets and that a number of unexpected autoregulatory loops exist between Sox17 and Gata4-6, Sox17 and Bix1, 2, 4 and between Sox17 and Xnr4. We find that Mixer does not function primarily via Sox17 as previously proposed. This data provides a new insight into the complexity of endoderm formation and will serve as valuable resource for establishing a complete endoderm gene regulatory network. Keywords: Embryonic, Development. Endoderm, Xenopus, nodal, Sox17, Mixer, microarray, gene regulatory network