title: Somites without a clock.
abstract: The formation of body segments (somites) in vertebrate embryos is accompanied by molecular oscillations (segmentation clock). Interaction of this oscillator with a wave traveling along the body axis (the clock-and-wavefront model) is generally believed to control somite number, size, and axial identity. Here we show that a clock-and-wavefront mechanism is unnecessary for somite formation. Non-somite mesoderm treated with Noggin generates many somites that form simultaneously, without cyclic expression of Notch-pathway genes, yet have normal size, shape, and fate. These somites have axial identity: The Hox code is fixed independently of somite fate. However, these somites are not subdivided into rostral and caudal halves, which is necessary for neural segmentation. We propose that somites are self-organizing structures whose size and shape is controlled by local cell-cell interactions.
authors.affiliation: Department of Cell and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: Ana S
authors.initials: AS
authors.lastname: Dias
authors.affiliation: Department of Cell and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: Irene
authors.initials: I
authors.lastname: de Almeida
authors.affiliation: Department of Physics, Biocomplexity Institute, University of Indiana at Bloomington, Simon Hall MSB1, 047G, 212 South Hawthorne Drive, Bloomington, IN 47405-7003, USA.
authors.forename: Julio M
authors.initials: JM
authors.lastname: Belmonte
authors.affiliation: Department of Physics, Biocomplexity Institute, University of Indiana at Bloomington, Simon Hall MSB1, 047G, 212 South Hawthorne Drive, Bloomington, IN 47405-7003, USA.
authors.forename: James A
authors.initials: JA
authors.lastname: Glazier
authors.affiliation: Department of Cell and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: Claudio D
authors.initials: CD
authors.lastname: Stern
mesh_terms: D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000037:antagonists & inhibitors; D056926:CLOCK Proteins / Q000235:genetics; D002352:Carrier Proteins / Q000494:pharmacology; D002450:Cell Communication; D057906:Circadian Clocks / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D011784:Quail; D051880:Receptors, Notch / Q000378:metabolism; D019170:Somites / Q000166:cytology / Q000187:drug effects / Q000254:growth & development*; D000099176:Noggin Protein
chemical_list: D019485:Bone Morphogenetic Proteins; D056926:CLOCK Proteins; D002352:Carrier Proteins; D018398:Homeodomain Proteins; D051880:Receptors, Notch; D000099176:Noggin Protein