title: The Mesp2 transcription factor establishes segmental borders by suppressing Notch activity.
abstract: The serially segmented (metameric) structures of vertebrates are based on somites that are periodically formed during embryogenesis. A 'clock and wavefront' model has been proposed to explain the underlying mechanism of somite formation, in which the periodicity is generated by oscillation of Notch components (the clock) in the posterior pre-somitic mesoderm (PSM). This temporal periodicity is then translated into the segmental units in the 'wavefront'. The wavefront is thought to exist in the anterior PSM and progress backwards at a constant rate; however, there has been no direct evidence as to whether the levels of Notch activity really oscillate and how such oscillation is translated into a segmental pattern in the anterior PSM. Here, we have visualized endogenous levels of Notch1 activity in mice, showing that it oscillates in the posterior PSM but is arrested in the anterior PSM. Somite boundaries formed at the interface between Notch1-activated and -repressed domains. Genetic and biochemical studies indicate that this interface is generated by suppression of Notch activity by mesoderm posterior 2 (Mesp2) through induction of the lunatic fringe gene (Lfng). We propose that the oscillation of Notch activity is arrested and translated in the wavefront by Mesp2.
authors.affiliation: Division of Mammalian Development, National Institute of Genetics, Mishima, Japan.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Morimoto
authors.forename: Yu
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Maho
authors.initials: M
authors.lastname: Endo
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Saga
mesh_terms: D000818:Animals; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D001683:Biological Clocks / Q000502:physiology; D004622:Embryo, Mammalian; D047108:Embryonic Development / Q000235:genetics / Q000502:physiology*; D004742:Enhancer Elements, Genetic / Q000235:genetics; D017353:Gene Deletion; D018507:Gene Expression Regulation, Developmental; D016695:Glycosyltransferases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D010507:Periodicity; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051881:Receptor, Notch1; D011956:Receptors, Cell Surface / Q000378:metabolism*; D019170:Somites / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D016695:Glycosyltransferases; D012333:RNA, Messenger; D051881:Receptor, Notch1; D011956:Receptors, Cell Surface; D014157:Transcription Factors; C107407:Mesp2 protein, mouse; C497762:Notch1 protein, mouse; C498392:Lfng protein, mouse