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: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:The heart integrates diverse cell lineages into a functional unit, including the pericardium, a mesothelial sac that supports heart movement, homeostasis, and immune responses. However, despite its critical roles, the developmental origins of the pericardium remain uncertain due to disparate models. Here, using live imaging, lineage tracking, and single-cell transcriptomics in zebrafish, we find the pericardium forms within the lateral plate mesoderm from dedicated anterior mesothelial progenitors and distinct from the classic heart field. Imaging of transgenic reporters in zebrafish documents lateral plate mesoderm cells that emerge lateral of the classic heart field and among a continuous mesothelial progenitor field. Single-cell transcriptomics and trajectories of hand2-expressing lateral plate mesoderm reveal distinct populations of mesothelial and cardiac precursors, including pericardial precursors that are distinct from the cardiomyocyte lineage. The mesothelial gene expression signature is conserved in mammals and carries over to postnatal development. Light sheet-based live-imaging and machine learning-supported cell tracking documents that during heart tube formation, pericardial precursors that reside at the anterior edge of the heart field migrate anteriorly and medially before fusing, enclosing the embryonic heart to form a single pericardial cavity. Pericardium formation proceeds even upon genetic disruption of heart tube formation, uncoupling the two structures. Canonical Wnt/β-catenin signaling modulates pericardial cell number, resulting in a stretched pericardial epithelium with reduced cell number upon canonical Wnt inhibition. We connect the pathological expression of secreted Wnt antagonists of the SFRP family found in pediatric dilated cardiomyopathy to increased pericardial stiffness: sFRP1 in the presence of increased catecholamines causes cardiomyocyte stiffness in neonatal rats as measured by atomic force microscopy. Altogether, our data integrate pericardium formation as an independent process into heart morphogenesis and connect disrupted pericardial tissue properties such as pericardial stiffness to pediatric cardiomyopathies.
Project description:Development of the vertebrate heart requires the appropriate integration of temporally-distinct differentiating progenitor populations. While factors that promote accrual of later-differentiating second heart field (SHF)-derived cells to the outflow tract (OFT) have been intensively investigated, few signals are understood that specifically restrict the size of the vertebrate OFT. Here, we show that improper specification and proliferation of SHF progenitors in zebrafish lazarus (lzr) mutants, which lack the transcription factor Pbx4, produces enlarged hearts with a specific increase in ventricular cardiomyocytes and smooth muscle cells within the OFT. Specifically, optogenetic lineage-tracing demonstrates Pbx4 initially promotes the proper partitioning of the SHF into anterior progenitors, which contribute to the OFT, and adjacent endothelial cell progenitors, which contribute to posterior pharyngeal arch arteries. Subsequently, Pbx4 also limits the size of the SHF through repressing SHF progenitor proliferation. Single-cell RNA sequencing of nkx2.5+ cells revealed that the enlarged SHF progenitor population within Pbx4-deficient embryos assimilates characteristics of normally distinct proliferative and more anterior, differentiated cardiomyocyte populations. Therefore, the generation of proper OFT size and great arteries in vertebrates requires Pbx-dependent stratification of unique progenitor differentiation states to facilitate homeotic-like transformations and limit progenitor production within the SHF.
Project description:Normal developmental progression relies on a close crosstalk between the embryonic and extraembryonic lineages in the pre- and peri-gastrulation conceptus. This has been demonstrated in the mouse where epiblast-derived FGF and NODAL signals are required to maintain a stem-like state in trophoblast cells of the extraembryonic ectoderm, while visceral endoderm signals are pivotal to pattern the anterior region of the epiblast. These developmental stages also coincide with the specification of the first heart precursors. Here, we established a robust differentiation protocol of mouse embryonic stem cells (ESCs) into cardiomyocytes that we used to test the impact of trophoblast on this key developmental process. Using trophoblast stem cells (TSCs) to produce trophoblast-conditioned medium (TCM), we show that TCM profoundly slows down the cardiomyocyte differentiation dynamics and specifically delays the emergence of cardiac mesoderm progenitors. TCM also strongly promotes the retention of pluripotency transcription factors. By applying TCM from various mutant TSCs, we further show that specifically those mutations that cause a trophoblast-mediated effect on early heart development alter the normal cardiomyocyte differentiation trajectory. Our approaches provide a meaningful deconstruction of the intricate crosstalk between the embryonic and the extraembryonic compartments. They demonstrate that trophoblast helps prolong a pluripotent state in embryonic cells by delaying early differentiative processes, likely through secretion of leukemia inhibitory factor (LIF). These data expand our knowledge of the multifaceted signalling interactions between distinct compartments of the early conceptus that ensure normal embryogenesis, insights that will also be of great importance for the field of synthetic embryo research.
Project description:Approximately 60-70% of patients with 22q11.2 deletion syndrome (22q11.2DS; velo-cardio-facial syndrome/DiGeorge syndrome) have cardiac outflow tract anomalies including persistent truncus arteriosus (PTA) as the most severe defect. Among the genes in the 22q11.2 region, TBX1, encoding a T-box transcription factor is a major candidate for cardiovascular malformations and its inactivation in mice results in a PTA. To identify novel signaling mechanisms that function downstream, we found that Tbx1 restricts canonical Wnt signaling in the pharyngeal apparatus. To test for tissue specificity within the pharyngeal apparatus, we inactivated Tbx1 in the anterior portion of the secondary heart field (AHF) mesoderm using the Mef2c-AHF-Cre allele and observed a full penetrant PTA (n = 30). Tbx1 promotes progenitor cells but restricts differentiation whereas Wnt signaling, in the AHF, promotes cardiomyocyte differentiation. To determine whether Tbx1 and canonical Wnt signaling act in opposing pathways, both alleles of Tbx1 and one β-catenin allele were inactivated in the AHF and 85% of them (n = 35) showed partial or complete rescue. The antagonistic function of the two pathways was further confirmed by gene expression profiling, indicating that these two pathways provide a key balance in the AHF to prevent premature differentiation of progenitor cells prior to reaching the cardiac outflow tract. We inactivatedTbx1 and beta-catenin allele to identify function of Tbx1 and beta-catenin in the anterior portion of the secondary heart field (AHF) mesoderm. We also inactivated both alleles of Tbx1 and one β-catenin alleles (rescue design) to determine whether Tbx1 and canonical Wnt signaling act in opposing pathways
Project description:Heart formation requires input from two populations of progenitor cells - the first and second heart fields - that differentiate at distinct times and create different cardiac components. The cardiac outflow tract (OFT) is built through recruitment of late-differentiating, second heart field (SHF) -derived cardiomyocytes to the arterial pole of the heart. Mechanisms responsible for selection of an appropriate number of OFT cells from the SHF remain unclear, although several lines of evidence emphasize the importance of FGF signaling in promoting this process. Here, we examine the impact of inhibition of FGF signaling on cardiac transcription profiles in an effort to identify genes operating downstream of FGF during OFT development. We compared hearts from embryos treated with the FGFR inhibitor SU5402 to the hearts from sibling embryos treated with DMSO. Two replicates were performed.
Project description:Heart formation requires input from two populations of progenitor cells - the first and second heart fields - that differentiate at distinct times and create different cardiac components. The cardiac outflow tract (OFT) is built through recruitment of late-differentiating, second heart field (SHF) -derived cardiomyocytes to the arterial pole of the heart. Mechanisms responsible for selection of an appropriate number of OFT cells from the SHF remain unclear, although several lines of evidence emphasize the importance of FGF signaling in promoting this process. Here, we examine the impact of inhibition of FGF signaling on cardiac transcription profiles in an effort to identify genes operating downstream of FGF during OFT development.
Project description:Dynamic gene expression programs determine multipotent cell states and fate choices during development. Multipotent progenitors for cardiomyocytes and branchiomeric head muscles populate the pharyngeal mesoderm of vertebrate embryos, but the mechanisms underlying cardiopharyngeal multipotency and heart vs. head muscle fate choices remain elusive. The tunicate Ciona emerged as a simple chordate model to study cardiopharyngeal development with unprecedented spatio-temporal resolution. We analyzed the transcriptome of single cardiopharyngeal lineage cells isolated at successive time points encompassing the transitions from multipotent progenitors to distinct first and second heart, and pharyngeal muscle precursors. We reconstructed the three cardiopharyngeal developmental trajectories, and characterized gene expression dynamics and regulatory states underlying each fate choice. Experimental perturbations and bulk transcriptome analyses revealed that ongoing FGF/MAPK signaling maintains cardiopharyngeal multipotency and promotes the pharyngeal muscle fate, whereas signal termination permits the deployment of a full pan-cardiac program and heart fate specification. We identified the Dach1/2 homolog as a novel evolutionarily conserved second-heart-field-specific factor and demonstrate, through lineage tracing and CRISPR/Cas9 perturbations, that it operates downstream of Tbx1/10 to actively suppress the first heart lineage program. This data indicates that the regulatory state of multipotent cardiopharyngeal progenitors determines the first vs. second heart lineage choice, and that Tbx1/10 acts as a bona fide regulator of cardiopharyngeal multi potency. We performed bulk RNAseq to profile the FACS purified Ciona Robusta Truck Ventral Cells (TVCs) with FGF-MAPK perturbation conditions to address the question- What is the role of FGF signaling pathway during early cardiopharyngeal specification. we performed bulk RNA sequencing of FACS-purified cardiopharyngeal lineage cells isolated from embryos and larvae expressing either a dominant negative form the fibroblast growth factor receptor (dnFGFR), or a constitutively active form of M-Ras (caM-Ras), the sole Ras homolog in Ciona, under the control of TVC-specific enhancers.