Project description:Smooth muscle guides morphogenesis of epithelia during development of several organs, including the mammalian lung. However, it remains unclear how airway smooth-muscle differentiation is spatiotemporally patterned and whether it originates from distinct mesenchymal progenitors. Using single-cell RNA-sequencing of embryonic mouse lungs, we show that the pulmonary mesenchyme contains a continuum of cell identities, but no distinct progenitors. Transcriptional variability correlates with sub-epithelial and sub-mesothelial mesenchymal compartments that are regulated by Wnt signaling. Live-imaging and tension sensors reveal patterned migratory behaviors and cortical forces in each compartment, and show that sub-epithelial mesenchyme gives rise to airway smooth muscle. Differentiation trajectory reconstruction reveals that cytoskeleton, adhesion, and Wnt signaling pathways are activated early in differentiation. Finally, we show that Wnt activation stimulates the earliest stages of differentiation and induces local accumulation of mesenchymal F-actin, which influences epithelial morphology. Our work provides the first single-cell view of pulmonary mesenchymal patterning during branching morphogenesis.
Project description:Smooth muscle differentiation has been proposed to sculpt airway epithelial branches in mammalian lungs. Serum response factor (SRF) acts with its cofactor myocardin to promote the expression of contractile smooth muscle markers. However, smooth muscle cells exhibit a variety of phenotypes beyond contractile that are independent of SRF-myocardin-induced transcription. To determine whether airway smooth muscle exhibits phenotypic plasticity during embryonic development, we deleted Srf from the pulmonary mesenchyme. Srf-mutant lungs branch normally, and the mesenchyme exhibits normal cytoskeletal features and patterning. scRNA-seq revealed an Srf-null smooth muscle cluster wrapping the airways of mutant lungs that lacks contractile smooth muscle markers but retains many features of control smooth muscle. Srf-null airway smooth muscle exhibits a synthetic phenotype, compared to the contractile phenotype of wildtype airway smooth muscle. Our findings reveal plasticity in mesenchymal differentiation during lung development and demonstrate that a synthetic smooth muscle layer is sufficient for airway branching morphogenesis.
Project description:Diverse functions of the homeodomain transcription factor BARX1 include Wnt-dependent, non-cell autonomous specification of the stomach epithelium, tracheo-bronchial septation, and Wnt-independent expansion of the spleen primordium. Tight spatio-temporal regulation of Barx1 levels in the mesentery and stomach mesenchyme suggests additional roles. To determine these functions, we forced constitutive BARX1 expression in the Bapx1 expression domain, which includes the mesentery and intestinal mesenchyme, and also examined Barx1-/- embryos in further detail. Transgenic embryos invariably showed intestinal truncation and malrotation, in part reflecting abnormal left-right patterning. Ectopic BARX1 expression did not affect intestinal epithelium, but intestinal smooth muscle developed with features typical of the stomach wall. BARX1, which is normally restricted to the developing stomach, drives robust smooth muscle expansion in this organ by promoting proliferation of myogenic progenitors at the expense of other sub-epithelial cells. Undifferentiated embryonic stomach and intestinal mesenchyme showed modest differences in mRNA expression and BARX1 was sufficient to induce much of the stomach profile in intestinal cells. However, limited binding at cis-regulatory sites implies that BARX1 may act principally through other transcription factors. Genes expressed ectopically in BARX1+ intestinal mesenchyme and reduced in Barx1-/- stomach mesenchyme include Isl1, Pitx1, Six2 and Pitx2, transcription factors known to control left-right patterning and influence smooth muscle development. The sum of evidence suggests that potent BARX1 functions in intestinal rotation and stomach myogenesis occur through this small group of intermediary transcription factors.
Project description:The mammalian genome contains two ERK/MAP kinase kinase genes, Mek1 and Mek2, which encode dual-specificity kinases responsible for ERK/MAP kinase activation. To define the function of ERK/MAPK signaling pathway in lung development, we performed tissue-specific deletions of Mek1 function in a Mek2 null background. Inactivation of both Mek genes in mesenchyme resulted in several phenotypes including giant omphalocele, skeletal defects, pulmonary hypoplasia, abnormal trachea patterning, and death at birth. Microarray analysis with RNA extracted from lungs of E15.5 Dermo1+/Cre, Mek1+/flox;Mek2-/-;Dermo1+/Cre and Mek1flox/flox;Mek2-/-;Dermo1+/Cre embryos was performed to evaluate the molecular impact of the loss of all Mek alleles in mesenchyme on lung development. . Total RNA was isolated from lungs of E15.5 Dermo1+/Cre embryos (control), from E15.5 Mek1+/flox;Mek2- /-;Dermo1+/Cre embryos (experimental) and from E15.5 Mek1flox/flox;Mek2-/-;Dermo1+/Cre embryos (experimental). Four specimens were analyzed per genotype.
Project description:The mammalian genome contains two ERK/MAP kinase kinase genes, Mek1 and Mek2, which encode dual-specificity kinases responsible for ERK/MAP kinase activation. To define the function of ERK/MAPK signaling pathway in lung development, we performed tissue-specific deletions of Mek1 function in a Mek2 null background. Inactivation of both Mek genes in mesenchyme resulted in several phenotypes including giant omphalocele, skeletal defects, pulmonary hypoplasia, abnormal trachea patterning, and death at birth. Microarray analysis with RNA extracted from lungs of E15.5 Dermo1+/Cre, Mek1+/flox;Mek2-/-;Dermo1+/Cre and Mek1flox/flox;Mek2-/-;Dermo1+/Cre embryos was performed to evaluate the molecular impact of the loss of all Mek alleles in mesenchyme on lung development. .
Project description:Mapping the transcriptional landscape of human embryonic skeletogenesis at single-cell resolution during limb bud and primary ossification center (POC) formation. We found significant heterogeneity of stromal cells within the limb bud mesenchyme that specified proximal-distal and anterior-posterior patterning. Embryonic skeletal stem and progenitor cells first appeared during POC formation, which were highly enriched by CADM1 expression and could differentiate into osteoblasts, chondrocytes and periosteal mesenchymal stromal cells.
Project description:Diverse functions of the homeodomain transcription factor BARX1 include Wnt-dependent, non-cell autonomous specification of the stomach epithelium, tracheo-bronchial septation, and Wnt-independent expansion of the spleen primordium. Tight spatio-temporal regulation of Barx1 levels in the mesentery and stomach mesenchyme suggests additional roles. To determine these functions, we forced constitutive BARX1 expression in the Bapx1 expression domain, which includes the mesentery and intestinal mesenchyme, and also examined Barx1-/- embryos in further detail. Transgenic embryos invariably showed intestinal truncation and malrotation, in part reflecting abnormal left-right patterning. Ectopic BARX1 expression did not affect intestinal epithelium, but intestinal smooth muscle developed with features typical of the stomach wall. BARX1, which is normally restricted to the developing stomach, drives robust smooth muscle expansion in this organ by promoting proliferation of myogenic progenitors at the expense of other sub-epithelial cells. Undifferentiated embryonic stomach and intestinal mesenchyme showed modest differences in mRNA expression and BARX1 was sufficient to induce much of the stomach profile in intestinal cells. However, limited binding at cis-regulatory sites implies that BARX1 may act principally through other transcription factors. Genes expressed ectopically in BARX1+ intestinal mesenchyme and reduced in Barx1-/- stomach mesenchyme include Isl1, Pitx1, Six2 and Pitx2, transcription factors known to control left-right patterning and influence smooth muscle development. The sum of evidence suggests that potent BARX1 functions in intestinal rotation and stomach myogenesis occur through this small group of intermediary transcription factors. To investigate how Barx1 regulates gut smooth muscle development in a cell-autonomous manner, we used Affymetrix arrays to profile genes enriched in wild-type stomach and BARX1-overexpressing intestinal mesenchyme, compared to wild-type intestinal mesenchyme.
Project description:After gut tube patterning in early embryos, the cellular and molecular changes of developing stomach and intestine remain largely unknown. Here, combining single-cell RNA-sequencing and spatial RNA-sequencing, we constructed a spatiotemporal transcriptomic landscape of the mouse stomach and intestine during embryonic day E9.5-E15.5. We observed regionalization and heterogeneity of both the epithelium and mesenchyme in the gastrointestinal (GI) tract at E9.5 and dynamic cell evolution afterwards. The spatiotemporal distributions of cell clusters and the epithelium-mesenchyme interactions indicate a coordinated development of the epithelium and mesenchyme. The cell evolution and signaling events regulate the stomach regionalization and intestine segmentation. Using the gut tube-derived organoids, we found that the cell fate of the foregut and hindgut could be switched by the regional niche factors. Together, this work demonstrates the important function of the epithelium-mesenchyme interactions in early GI tract development, laying a foundation for further dissection of the mechanisms governing this process.