Project description:Single cell technologies hold promise for resolving complex early developmental phenotypes. Here we define a novel Hedgehog (Hh)-Fibroblast Growth Factor (FGF) signaling axis for the formation of anterior mesoderm lineages during gastrulation. Single-cell transcriptome analysis of Hh-deficient mesoderm revealed selective deficits in anterior mesoderm populations—culminating in defects to anterior embryonic structures including the pharyngeal arches, heart, and anterior somites. Transcriptional profiling of Hh-deficient mesoderm during gastrulation revealed disruptions to both transcriptional patterning of the mesoderm and FGF signaling for mesoderm migration. Mesoderm-specific Fgf4/Fgf8 double mutants recapitulated anterior mesoderm defects and Hh-dependent GLI transcription factors modulated enhancers at FGF gene loci. Cellular migration defects during gastrulation induced by Hh pathway antagonism were mitigated by FGF4 protein. These findings implicate a multicomponent signaling hierarchy activated by Hh ligands from the embryonic node and executed by FGF signals in nascent mesoderm to control anterior mesoderm patterning.
Project description:The mesodermal precursor populations for different internal organ systems are specified during gastrulation by the combined activity of extracellular signaling systems such as BMP, Wnt, Nodal, and FGF. The BMP, Wnt and Nodal signaling requirements for the differentiation of specific mesoderm subtypes in mammals have been mapped in detail, but which mesodermal cell types depend on FGF signaling is not precisely known. It is also not clear how FGF signaling modulates the activity of orthogonal signaling systems involved in mesoderm differentiation. Here, we address these questions by analyzing the effects of targeted signaling manipulations in differentiating stem cell populations with single cell resolution. We identify opposing functions of BMP and FGF, and map the boundary between FGF-dependent and -independent mesodermal lineages. Stimulation with exogenous FGF boosts the expression of endogenous Fgfs while repressing Bmp ligands. This intercellular positive autoregulation of FGF signaling coupled to the repression of BMP signaling may contribute to the specification of reproducible and coherent cohorts of cells with the same identity via a community effect, both in the embryo and in synthetic embryo-like systems.
Project description:Single-cell technology was used to investigate dynamic transcriptional changes in the blastula and gastrula of Drosophila embryos. Cells from embryo of stages 5 to 9 were isolated and subjected to library construction. Mesoderm cells were labeled with mCD8-GFP utilizing the GAL/UAS system. PCA identified 12 unique cell clusters that represent the blastoderm, mesoderm, endoderm and ectoderm anlage, primordia, and a sampling of differentiating cell types. In the cellular blastoderm, we found that the major wave of zygotic gene activation consists of two steps, which is supported by sub-clustering analysis. Trajectory analysis of stage 6-8 mesoderm cells suggested that transcription factors, previously linked to ectodermal segment polarity, also control mesoderm segmentation, patterning and differentiation. With the cells originating from the posterior ventral region of the blastoderm, trajectory analysis identified a group of cells that are multipotent progenitors giving rise to visceral muscles, Malpighian tubules as well as a new cell type. In summary, this single-cell study of gastrulation demonstrates early patterning involves trunk- versus pole-centered programs, the mesoderm is segmentally patterned, and a new cell type arises from the caudal mesoderm.
Project description:The transition from progenitor to differentiated cells is critical for successful organogenesis; subtle alterations in this process can lead to developmental disorders. The anterior heart field (AHF) encompasses a niche in which cardiac progenitors maintain their multipotent and undifferentiated nature by signals from the surrounding tissues, which thus far have been poorly defined. Using systems biology approaches and perturbations of signaling molecules in chick embryos, we revealed a tight crosstalk between the bone morphogenic protein (BMP) and fibroblast growth factor (FGF) signaling pathways within the AHF: BMP4 promotes myofibrillar gene expression and cardiomyocyte contractions, by blocking FGF signaling. Furthermore, inhibition of the FGF-ERK pathway is both sufficient and necessary for these processes, suggesting that FGF signaling blocks premature differentiation of cardiac progenitors in the AHF. Investigating the molecular mechanisms downstream to BMP signaling revealed that BMP4 induced a set of neural crest-related genes; including MSX1, which was sufficient to induce cardiomyocyte differentiation. We suggest that BMP and FGF signaling pathways act via inter- and intra-regulatory loops in multiple tissues, to coordinate the balance between proliferation and differentiation of cardiac progenitors. Splanchnic mesoderm (AHF) explants were dissected and cultured for 0, 3, 12 or 24 hrs on a collagen drop covered with 0.5 ml of dissection medium (10% Fetal Calf Serum, chick embryo extract 2.5% and pen/strep 0.5% in MEM medium). 12 hour time point was used as a duplicate. In all samples, there was control plus BMP4: human recombinant BMP4 (Sigma, 200 ng/mL), which was added to the explant dissection medium.
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:The transition from progenitor to differentiated cells is critical for successful organogenesis; subtle alterations in this process can lead to developmental disorders. The anterior heart field (AHF) encompasses a niche in which cardiac progenitors maintain their multipotent and undifferentiated nature by signals from the surrounding tissues, which thus far have been poorly defined. Using systems biology approaches and perturbations of signaling molecules in chick embryos, we revealed a tight crosstalk between the bone morphogenic protein (BMP) and fibroblast growth factor (FGF) signaling pathways within the AHF: BMP4 promotes myofibrillar gene expression and cardiomyocyte contractions, by blocking FGF signaling. Furthermore, inhibition of the FGF-ERK pathway is both sufficient and necessary for these processes, suggesting that FGF signaling blocks premature differentiation of cardiac progenitors in the AHF. Investigating the molecular mechanisms downstream to BMP signaling revealed that BMP4 induced a set of neural crest-related genes; including MSX1, which was sufficient to induce cardiomyocyte differentiation. We suggest that BMP and FGF signaling pathways act via inter- and intra-regulatory loops in multiple tissues, to coordinate the balance between proliferation and differentiation of cardiac progenitors.
Project description:KMT2D is required in the cardiac mesoderm, anterior heart field precursors and cardiomyocytes. Kmt2d deletion in cardiac mesoderm (Mesp1Cre) is embryonic lethal at E10.5 and mutants have hypoplastic hearts; Kmt2d deletion in anterior heart field precursors (Mef2cAHF::Cre) deletion is embryonic lethal at E13.5 and mutants have defects in septation of outflow tract and interventricular septum (IVS); Kmt2d deletion in cardiomyocytes (Tnnt2::Cre) deletion is embryonic lethal at E14.5 and mutants have defects in IVS septation and compact myocardium. The goal of this study is to compare changes in gene expression in these Kmt2d conditional deletion mutants and understand common or distinct pathways dysregulated in absence of KMT2D. Whole genome gene expression analysis was performed on RNA isolated from control and mutant embryonic hearts (or right ventricles and outflow tract for anterior heart field deletion samples). Libraries were prepared using Illumina TruSeq Paired-End Cluster Kit v3, and sequenced with the Illumina HiSeq 2500 system for pair-ended 100 base pairs (PE 100 bp).
Project description:KMT2D is required in the cardiac mesoderm, anterior heart field precursors and cardiomyocytes. Kmt2d deletion in cardiac mesoderm (Mesp1Cre) is embryonic lethal at E10.5 and mutants have hypoplastic hearts; Kmt2d deletion in anterior heart field precursors (Mef2cAHF::Cre) deletion is embryonic lethal at E13.5 and mutants have defects in septation of outflow tract and interventricular septum (IVS); Kmt2d deletion in cardiomyocytes (Tnnt2::Cre) deletion is embryonic lethal at E14.5 and mutants have defects in IVS septation and compact myocardium. The goal of this study is to compare changes in gene expression in these Kmt2d conditional deletion mutants and understand common or distinct pathways dysregulated in absence of KMT2D.