title: Cell-autonomous Notch activity maintains the temporal specification potential of skeletal muscle stem cells.
abstract: During organogenesis, a continuum of founder stem cells produces temporally distinct progeny until development is complete. Similarly, in skeletal myogenesis, phenotypically and functionally distinct myoblasts and differentiated cells are generated during development. How this occurs in muscle and other tissues in vertebrates remains largely unclear. We showed previously that committed cells are required for maintaining muscle stem cells. Here we show that active Notch signalling specifies a subpopulation of myogenic cells with high Pax7 expression. By genetically modulating Notch activity, we demonstrate that activated Notch (NICD) blocks terminal differentiation in an Rbpj-dependent manner that is sufficient to sustain stem/progenitor cells throughout embryogenesis, despite the absence of committed progeny. Although arrested in lineage progression, NICD-expressing cells of embryonic origin progressively mature and adopt characteristics of foetal myogenic cells, including expression of the foetal myogenesis regulator Nfix. siRNA-mediated silencing of NICD promotes the temporally appropriate foetal myogenic fate in spite of expression of markers for multiple cell types. We uncover a differential effect of Notch, whereby high Notch activity is associated with stem/progenitor cell expansion in the mouse embryo, yet it promotes reversible cell cycle exit in the foetus and the appearance of an adult muscle stem cell state. We propose that active Notch signalling is sufficient to sustain an upstream population of muscle founder stem cells while suppressing differentiation. Significantly, Notch does not override other signals that promote temporal myogenic cell fates during ontology where spatiotemporal developmental cues produce distinct phenotypic classes of myoblasts.
authors.affiliation: Stem Cells and Development, Department of Developmental Biology, CNRS URA 2578, Institut Pasteur, 25 rue du Dr Roux, 75105 Paris, France.
authors.forename: Philippos
authors.initials: P
authors.lastname: Mourikis
authors.forename: Swetha
authors.initials: S
authors.lastname: Gopalakrishnan
authors.forename: Ramkumar
authors.initials: R
authors.lastname: Sambasivan
authors.forename: Shahragim
authors.initials: S
authors.lastname: Tajbakhsh
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000235:genetics*; D002455:Cell Division / Q000235:genetics; D002478:Cells, Cultured; D004261:DNA Replication / Q000235:genetics; D004622:Embryo, Mammalian; D047108:Embryonic Development / Q000235:genetics / Q000502:physiology; D053595:Embryonic Stem Cells / Q000378:metabolism / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D051379:Mice; D008822:Mice, Transgenic; D018482:Muscle, Skeletal / Q000196:embryology* / Q000378:metabolism; D032448:Myoblasts, Skeletal / Q000378:metabolism / Q000502:physiology*; D009928:Organ Specificity / Q000235:genetics; D051881:Receptor, Notch1 / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D013997:Time Factors
chemical_list: C497762:Notch1 protein, mouse; D051881:Receptor, Notch1