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Development, Growth & Differentiation Apr 2020Vertebrate segments called somites are generated by periodic segmentation of the presomitic mesoderm (PSM). In the most accepted theoretical model for somite... (Review)
Review
Vertebrate segments called somites are generated by periodic segmentation of the presomitic mesoderm (PSM). In the most accepted theoretical model for somite segmentation, the clock and wavefront (CW) model, a clock that ticks to determine particular timings and a wavefront that moves posteriorly are presented in the PSM, and somite positions are determined when the clock meets the posteriorly moving wavefront somewhere in the PSM. Over the last two decades, it has been revealed that the molecular mechanism of the clock and wavefront in vertebrates is based on clock genes including Hes family transcription factors and Notch effectors that oscillate within the PSM to determine particular timings and fibroblast growth factor (FGF) gradients, acting as the posteriorly moving wavefront to determine the position of somite segmentation. A clock-less condition in the CW model was predicted to form no somites; however, irregularly sized somites were still formed in mice and zebrafish, suggesting that this was one of the limitations of the CW model. Recently, we performed interdisciplinary research of experimental and theoretical biological studies and revealed the mechanisms of somite boundary determination in normal and clock-less conditions by characterization of the FGF/extracellular signal-regulated kinase (ERK) activity dynamics. Since features of the molecular clock have already been described in-depth in several reviews, we summarized recent findings regarding the role of FGF/ERK signaling in somite boundary formation and described our current understanding of how FGF/ERK signaling contributes to somitogenesis in normal and clock-less conditions in this review.
Topics: Animals; Body Patterning; Extracellular Signal-Regulated MAP Kinases; Fibroblast Growth Factors; Models, Biological; Signal Transduction; Somites; Vertebrates
PubMed: 32108939
DOI: 10.1111/dgd.12655 -
Cells & Development Dec 2021Vertebrate segmentation, the process that generates a regular arrangement of somites and thereby establishes the pattern of the adult body and of the musculoskeletal and... (Review)
Review
Vertebrate segmentation, the process that generates a regular arrangement of somites and thereby establishes the pattern of the adult body and of the musculoskeletal and peripheral nervous systems, was noticed many centuries ago. In the last few decades, there has been renewed interest in the process and especially in the molecular mechanisms that might account for its regularity and other spatial-temporal properties. Several models have been proposed but surprisingly, most of these do not provide clear links between the molecular mechanisms and the cell behaviours that generate the segmental pattern. Here we present a short survey of our current knowledge about the cellular aspects of vertebrate segmentation and the similarities and differences between different vertebrate groups in how they achieve their metameric pattern. Taking these variations into account should help to assess each of the models more appropriately.
Topics: Animals; Body Patterning; Somites; Vertebrates
PubMed: 34391979
DOI: 10.1016/j.cdev.2021.203732 -
Anatomy and Embryology Dec 2006Somites are a common feature of the phylotypic stage of embryos of all higher chordates. In amniote species like mouse and chick, somite development has been the subject... (Review)
Review
Somites are a common feature of the phylotypic stage of embryos of all higher chordates. In amniote species like mouse and chick, somite development has been the subject of intense research over many decades, giving insight into the morphological and molecular processes leading to somite compartmentalization and subsequent differentiation. In anamniotes, somite development is much less understood. Except for recent data from zebrafish, and morphological studies in Xenopus, very little is known about the formation of somite compartments and the differentiation of somite derivatives in anamniotes. Here, we give a brief overview on the development of myotome, sclerotome and dermomyotome in various anamniote organisms, and point out the different mechanisms of somite development between anamniotes and the established amniote model systems.
Topics: Amphibians; Animals; Body Patterning; Cell Differentiation; Cell Lineage; Chordata, Nonvertebrate; Fishes; Models, Biological; Somites
PubMed: 17006657
DOI: 10.1007/s00429-006-0127-8 -
Developmental Dynamics : An Official... Sep 2007Somites are segments of paraxial mesoderm that give rise to a multitude of tissues in the vertebrate embryo. Many decades of intensive research have provided a wealth of... (Review)
Review
Somites are segments of paraxial mesoderm that give rise to a multitude of tissues in the vertebrate embryo. Many decades of intensive research have provided a wealth of data on the complex molecular interactions leading to the formation of various somitic derivatives. In this review, we focus on the crucial role of the somites in building the body wall and limbs of amniote embryos. We give an overview on the current knowledge on the specification and differentiation of somitic cell lineages leading to the development of the vertebral column, skeletal muscle, connective tissue, meninges, and vessel endothelium, and highlight the importance of the somites in establishing the metameric pattern of the vertebrate body.
Topics: Amnion; Animals; Cell Differentiation; Cell Lineage; Chick Embryo; Embryonic Development; Endothelium; Epithelium; Extremities; Microscopy, Electron, Scanning; Models, Anatomic; Models, Biological; Muscles; Somites; Spinal Cord
PubMed: 17557304
DOI: 10.1002/dvdy.21189 -
International Review of Cytology 2000As a consequence of their segmented arrangement and the diversity of their tissue derivatives, somites are key elements in the establishment of the metameric body plan... (Review)
Review
As a consequence of their segmented arrangement and the diversity of their tissue derivatives, somites are key elements in the establishment of the metameric body plan in vertebrates. This article aims to largely review what is known about somite development, from the initial stages of somite formation through the process of somite regionalization along the three major body axes. The role of both cell intrinsic mechanisms and environmental cues are evaluated. The periodic and bilaterally synchronous nature of somite formation is proposed to rely on the existence of a developmental clock. Molecular mechanisms underlying these events are reported. The importance of an antero-posterior somitic polarity with respect to somite formation on one hand and body segmentation on the other hand is discussed. Finally, the mechanisms leading to the regionalization of somites along the dorso-ventral and medio-lateral axes are reviewed. This somitic compartmentalization is believed to underlie the segregation of dermis, skeleton, and dorsal and appendicular musculature.
Topics: Animals; Birds; Body Patterning; Somites
PubMed: 10804460
DOI: 10.1016/s0074-7696(00)98002-1 -
Seminars in Cell & Developmental Biology Nov 2020The body axis of vertebrates is subdivided into repetitive compartments called somites, which give rise primarily to the segmented architecture of the musculoskeletal... (Review)
Review
The body axis of vertebrates is subdivided into repetitive compartments called somites, which give rise primarily to the segmented architecture of the musculoskeletal system in the adult body. Somites form in a sequential and rhythmic manner in embryos and a physical boundary separates each somite from the rest of the unsegmented tissue and adjoining somites. Precise positioning of somite boundaries and determination of boundary cell fate in a select group of cells is thought to be driven by gene expression patterns and morphogen gradients. This pre-patterning step is followed by a mechanical process involving actomyosin activation in boundary cells and formation of an extracellular matrix that results in morphological boundary formation. While genes involved in somite boundary formation have been identified, there are many open questions about the underlying pre-patterning dynamics and mechanics and how these processes are coupled to generate a morphological boundary. Here, focusing on segmentation of zebrafish embryos as a model, we review pre-patterning processes critical for boundary formation and how cytoskeletal activity drives tissue separation. Our outlook is that this system holds exciting new avenues for unearthing general principles of boundary formation in developing embryos.
Topics: Animals; Biological Evolution; Body Patterning; Embryo, Nonmammalian; Models, Biological; Somites; Zebrafish
PubMed: 32444288
DOI: 10.1016/j.semcdb.2020.04.014 -
Acta Histochemica 2015Myogenesis is controlled by an elaborate system of extrinsic and intrinsic regulatory mechanisms in all development stages. The aim of this review is to provide an... (Review)
Review
Myogenesis is controlled by an elaborate system of extrinsic and intrinsic regulatory mechanisms in all development stages. The aim of this review is to provide an overview of the different stages of myogenesis and muscle differentiation in mammals, starting from somitogenesis and analysis of the different portions that constitute the mature somite. Particular attention was paid to regulatory genes, in addition to mesodermal stem cells, which represent the earliest elements of myogenesis. Finally, the crucial role of growth factors, molecules of vital importance in contractile regulation, hormones and their function in skeletal muscle differentiation, growth and metabolism, and the role played by central nervous system, are discussed.
Topics: Animals; Cell Differentiation; Gene Expression Regulation, Developmental; Humans; Intercellular Signaling Peptides and Proteins; Muscle Development; Muscle, Skeletal; Somites; Stem Cells
PubMed: 25850375
DOI: 10.1016/j.acthis.2015.02.011 -
Development (Cambridge, England) Jun 2017Skeletal muscle is the largest tissue in the body and loss of its function or its regenerative properties results in debilitating musculoskeletal disorders.... (Review)
Review
Skeletal muscle is the largest tissue in the body and loss of its function or its regenerative properties results in debilitating musculoskeletal disorders. Understanding the mechanisms that drive skeletal muscle formation will not only help to unravel the molecular basis of skeletal muscle diseases, but also provide a roadmap for recapitulating skeletal myogenesis from pluripotent stem cells (PSCs). PSCs have become an important tool for probing developmental questions, while differentiated cell types allow the development of novel therapeutic strategies. In this Review, we provide a comprehensive overview of skeletal myogenesis from the earliest premyogenic progenitor stage to terminally differentiated myofibers, and discuss how this knowledge has been applied to differentiate PSCs into muscle fibers and their progenitors .
Topics: Animals; Cell Differentiation; Cellular Reprogramming; Humans; Mesoderm; Mice; Models, Biological; Muscle Development; Muscle Fibers, Skeletal; Muscle, Skeletal; Myoblasts, Skeletal; Pluripotent Stem Cells; Somites
PubMed: 28634270
DOI: 10.1242/dev.151035 -
Journal of Anatomy Oct 2019Somites are epithelial segments of the paraxial mesoderm. Shortly after their formation, the epithelial somites undergo extensive cellular rearrangements and form...
Somites are epithelial segments of the paraxial mesoderm. Shortly after their formation, the epithelial somites undergo extensive cellular rearrangements and form specific somite compartments, including the sclerotome and the myotome, which give rise to the axial skeleton and to striated musculature, respectively. The dynamics of somite development varies along the body axis, but most research has focused on somite development at thoracolumbar levels. The development of tail somites has not yet been thoroughly characterized, even though vertebrate tail development has been intensely studied recently with respect to the termination of segmentation and the limitation of body length in evolution. Here, we provide a detailed description of the somites in the avian tail from the beginning of tail formation at HH-stage 20 to the onset of degeneration of tail segments at HH-stage 27. We characterize the formation of somite compartment formation in the tail region with respect to morphology and the expression patterns of the sclerotomal marker gene paired-box gene 1 (Pax1) and the myotomal marker genes MyoD and myogenic factor 5 (Myf5). Our study gives insight into the development of the very last segments formed in the avian embryo, and provides a basis for further research on the development of tail somite derivatives such as tail vertebrae, pygostyle and tail musculature.
Topics: Animals; Birds; Chick Embryo; Embryonic Development; Somites; Tail
PubMed: 31225912
DOI: 10.1111/joa.13032 -
Seminars in Cell & Developmental Biology Jun 2015During development, vertebrate embryos produce serially repeated elements, the somites, on each side of the midline. These generate the vertebral column, skeletal... (Review)
Review
During development, vertebrate embryos produce serially repeated elements, the somites, on each side of the midline. These generate the vertebral column, skeletal musculature and dermis. They form sequentially, one pair at a time, from mesenchymal tissue near the tail. Somite development is a complex process. The embryo must control the number, size, and timing of somite formation, their subdivision into functional regions along three axes, regional identity such that somites develop in a region-specific way, and interactions with neighbouring tissues that coordinate them with nearby structures. Here we discuss many timing-related mechanisms that contribute to set up the spatial pattern.
Topics: Animals; Body Patterning; Gene Expression Regulation; Homeodomain Proteins; Signal Transduction; Somites; Vertebrates
PubMed: 26116228
DOI: 10.1016/j.semcdb.2015.06.002