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  1. Article: Somite number and vertebrate evolution.

    Richardson, M K / Allen, S P / Wright, G M / Raynaud, A / Hanken, J

    Development (Cambridge, England)

    1998  Volume 125, Issue 2, Page(s) 151–160

    Abstract: ... stable during evolution than somite number, possibly because segmentation and positional specification ... in relation to recent models of evolution and development. Surprisingly, differences in vertebral number are ... Variation in segment number is an important but neglected feature of vertebrate evolution ...

    Abstract Variation in segment number is an important but neglected feature of vertebrate evolution. Some vertebrates have as few as six trunk vertebrae, while others have hundreds. We examine this phenomenon in relation to recent models of evolution and development. Surprisingly, differences in vertebral number are foreshadowed by different somite counts at the tailbud stage, thought to be a highly conserved (phylotypic) stage. Somite number therefore violates the 'developmental hourglass' model. We argue that this is because somitogenesis shows uncoupling or dissociation from the conserved positional field encoded by genes of the zootype. Several other systems show this kind of dissociation, including limbs and feathers. Bmp-7 expression patterns demonstrate dissociation in the chick pharyngeal arches. This makes it difficult to recognise a common stage of pharyngeal development or 'pharyngula' in all species. Rhombomere number is more stable during evolution than somite number, possibly because segmentation and positional specification in the hindbrain are relatively interdependent. Although developmental mechanisms are strongly conserved, dissociation allows at least some major evolutionary changes to be generated in phylotypic stages.
    MeSH term(s) Animals ; Biological Evolution ; Genes, Homeobox ; Pharynx/embryology ; Somites ; Vertebrates/embryology
    Language English
    Publishing date 1998-01
    Publishing country England
    Document type Journal Article ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, Non-P.H.S. ; Review
    ZDB-ID 90607-4
    ISSN 1477-9129 ; 0950-1991
    ISSN (online) 1477-9129
    ISSN 0950-1991
    DOI 10.1242/dev.125.2.151
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  2. Article ; Online: A multi-cell, multi-scale model of vertebrate segmentation and somite formation.

    Hester, Susan D / Belmonte, Julio M / Gens, J Scott / Clendenon, Sherry G / Glazier, James A

    PLoS computational biology

    2011  Volume 7, Issue 10, Page(s) e1002155

    Abstract: ... in response to changes in the PSM growth rate and segmentation-clock period, and in the number and width ... spatially and temporally regular somites, realistic dynamic morphologies and spontaneous emergence ... for a complete understanding of somitogenesis and its evolutionary flexibility. So far, mechanisms ...

    Abstract Somitogenesis, the formation of the body's primary segmental structure common to all vertebrate development, requires coordination between biological mechanisms at several scales. Explaining how these mechanisms interact across scales and how events are coordinated in space and time is necessary for a complete understanding of somitogenesis and its evolutionary flexibility. So far, mechanisms of somitogenesis have been studied independently. To test the consistency, integrability and combined explanatory power of current prevailing hypotheses, we built an integrated clock-and-wavefront model including submodels of the intracellular segmentation clock, intercellular segmentation-clock coupling via Delta/Notch signaling, an FGF8 determination front, delayed differentiation, clock-wavefront readout, and differential-cell-cell-adhesion-driven cell sorting. We identify inconsistencies between existing submodels and gaps in the current understanding of somitogenesis mechanisms, and propose novel submodels and extensions of existing submodels where necessary. For reasonable initial conditions, 2D simulations of our model robustly generate spatially and temporally regular somites, realistic dynamic morphologies and spontaneous emergence of anterior-traveling stripes of Lfng. We show that these traveling stripes are pseudo-waves rather than true propagating waves. Our model is flexible enough to generate interspecies-like variation in somite size in response to changes in the PSM growth rate and segmentation-clock period, and in the number and width of Lfng stripes in response to changes in the PSM growth rate, segmentation-clock period and PSM length.
    MeSH term(s) Animals ; Biological Clocks ; Body Patterning ; Cell Adhesion ; Cell Adhesion Molecules/genetics ; Cell Adhesion Molecules/metabolism ; Cell Division ; Cell Movement ; Computational Biology ; Fibroblast Growth Factor 8/genetics ; Fibroblast Growth Factor 8/metabolism ; Gene Expression Regulation ; Intracellular Signaling Peptides and Proteins/genetics ; Intracellular Signaling Peptides and Proteins/metabolism ; Membrane Proteins/genetics ; Membrane Proteins/metabolism ; Mesoderm/cytology ; Mesoderm/embryology ; Mesoderm/metabolism ; Models, Biological ; RNA, Messenger/genetics ; RNA, Messenger/metabolism ; Receptors, Notch/genetics ; Receptors, Notch/metabolism ; Signal Transduction ; Somites/cytology ; Somites/embryology ; Somites/metabolism ; Wnt3A Protein/genetics ; Wnt3A Protein/metabolism
    Chemical Substances Cell Adhesion Molecules ; Intracellular Signaling Peptides and Proteins ; Membrane Proteins ; RNA, Messenger ; Receptors, Notch ; Wnt3A Protein ; delta protein ; Fibroblast Growth Factor 8 (148997-75-5)
    Language English
    Publishing date 2011-10-06
    Publishing country United States
    Document type Journal Article ; Research Support, N.I.H., Extramural ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, Non-P.H.S. ; Review
    ZDB-ID 2193340-6
    ISSN 1553-7358 ; 1553-734X
    ISSN (online) 1553-7358
    ISSN 1553-734X
    DOI 10.1371/journal.pcbi.1002155
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  3. Article ; Online: A multi-cell, multi-scale model of vertebrate segmentation and somite formation.

    Susan D Hester / Julio M Belmonte / J Scott Gens / Sherry G Clendenon / James A Glazier

    PLoS Computational Biology, Vol 7, Iss 10, p e

    2011  Volume 1002155

    Abstract: ... in response to changes in the PSM growth rate and segmentation-clock period, and in the number and width ... spatially and temporally regular somites, realistic dynamic morphologies and spontaneous emergence ... for a complete understanding of somitogenesis and its evolutionary flexibility. So far, mechanisms ...

    Abstract Somitogenesis, the formation of the body's primary segmental structure common to all vertebrate development, requires coordination between biological mechanisms at several scales. Explaining how these mechanisms interact across scales and how events are coordinated in space and time is necessary for a complete understanding of somitogenesis and its evolutionary flexibility. So far, mechanisms of somitogenesis have been studied independently. To test the consistency, integrability and combined explanatory power of current prevailing hypotheses, we built an integrated clock-and-wavefront model including submodels of the intracellular segmentation clock, intercellular segmentation-clock coupling via Delta/Notch signaling, an FGF8 determination front, delayed differentiation, clock-wavefront readout, and differential-cell-cell-adhesion-driven cell sorting. We identify inconsistencies between existing submodels and gaps in the current understanding of somitogenesis mechanisms, and propose novel submodels and extensions of existing submodels where necessary. For reasonable initial conditions, 2D simulations of our model robustly generate spatially and temporally regular somites, realistic dynamic morphologies and spontaneous emergence of anterior-traveling stripes of Lfng. We show that these traveling stripes are pseudo-waves rather than true propagating waves. Our model is flexible enough to generate interspecies-like variation in somite size in response to changes in the PSM growth rate and segmentation-clock period, and in the number and width of Lfng stripes in response to changes in the PSM growth rate, segmentation-clock period and PSM length.
    Keywords Biology (General) ; QH301-705.5
    Subject code 612
    Language English
    Publishing date 2011-10-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  4. Article: The origin and morphogenesis of amphibian somites.

    Keller, R

    Current topics in developmental biology

    2000  Volume 47, Page(s) 183–246

    Abstract: ... conservative and has been capable of accommodating the use of a number of quite different morphogenic processes ... The origin and development of the amphibian somitic mesoderm is summarized and reviewed ... of the gastrulation movements, the role of the somitic mesoderm in early patterning and morphogenic processes, and ...

    Abstract The origin and development of the amphibian somitic mesoderm is summarized and reviewed with the goal of identifying issues most profitably pursued in these organisms. The location of the prospective somitic mesoderm as well as the cell movements bringing this tissue into its definitive position varies among amphibians. These variations have implications for the tissue interactions patterning the embryo, the design of the gastrulation movements, the role of the somitic mesoderm in early patterning and morphogenic processes, and the nature of the developmental pathway leading to somites. The presegmentation morphogenesis, the process of segmentation, and the subsequent, postsegmentation morphogenesis of the somitic mesoderm also varies considerably among amphibians. Although segmentation in amphibians shares what may be highly conserved and general patterning mechanisms with other vertebrates, the somitic developmental pathway as a whole is not conservative and has been capable of accommodating the use of a number of quite different morphogenic processes, all leading to very similar ends. The major challenges in studying amphibian somitogenesis are to develop molecular markers for major components of the somite, to determine the derivatives of the somite with better cell tracing experiments, and learning to work with the small dermatomal and sclerotomal cell populations found in most species. A potential advantage is that the diversity of somitogenesis among the amphibians makes this group ideal for studying the evolution of developmental processes. In addition, many amphibians allow direct observation of somitogenesis with great resolution and permit biomechanical analysis of tissues participating in morphogenesis, thus making it possible to analyze cellular mechanisms of morphogenesis in ways not possible in most other systems.
    MeSH term(s) Amphibians/genetics ; Animals ; Body Patterning ; Gastrula/physiology ; Mesoderm/physiology ; Morphogenesis ; Somites/physiology
    Language English
    Publishing date 2000
    Publishing country United States
    Document type Journal Article ; Review
    ISSN 1557-8933 ; 0070-2153
    ISSN (online) 1557-8933
    ISSN 0070-2153
    DOI 10.1016/s0070-2153(08)60726-7
    Database MEDical Literature Analysis and Retrieval System OnLINE

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