1
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Ramesh PS, Chu LF. Species-specific roles of the Notch ligands, receptors, and targets orchestrating the signaling landscape of the segmentation clock. Front Cell Dev Biol 2024; 11:1327227. [PMID: 38348091 PMCID: PMC10859470 DOI: 10.3389/fcell.2023.1327227] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Accepted: 12/20/2023] [Indexed: 02/15/2024] Open
Abstract
Somitogenesis is a hallmark feature of all vertebrates and some invertebrate species that involves the periodic formation of block-like structures called somites. Somites are transient embryonic segments that eventually establish the entire vertebral column. A highly conserved molecular oscillator called the segmentation clock underlies this periodic event and the pace of this clock regulates the pace of somite formation. Although conserved signaling pathways govern the clock in most vertebrates, the mechanisms underlying the species-specific divergence in various clock characteristics remain elusive. For example, the segmentation clock in classical model species such as zebrafish, chick, and mouse embryos tick with a periodicity of ∼30, ∼90, and ∼120 min respectively. This enables them to form the species-specific number of vertebrae during their overall timespan of somitogenesis. Here, we perform a systematic review of the species-specific features of the segmentation clock with a keen focus on mouse embryos. We perform this review using three different perspectives: Notch-responsive clock genes, ligand-receptor dynamics, and synchronization between neighboring oscillators. We further review reports that use non-classical model organisms and in vitro model systems that complement our current understanding of the segmentation clock. Our review highlights the importance of comparative developmental biology to further our understanding of this essential developmental process.
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Affiliation(s)
- Pranav S. Ramesh
- Faculty of Veterinary Medicine, University of Calgary, Calgary, AB, Canada
- Reproductive Biology and Regenerative Medicine Research Group, University of Calgary, Calgary, AB, Canada
- Alberta Children’s Hospital Research Institute, Calgary, AB, Canada
| | - Li-Fang Chu
- Faculty of Veterinary Medicine, University of Calgary, Calgary, AB, Canada
- Reproductive Biology and Regenerative Medicine Research Group, University of Calgary, Calgary, AB, Canada
- Alberta Children’s Hospital Research Institute, Calgary, AB, Canada
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2
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Özelçi E, Mailand E, Rüegg M, Oates AC, Sakar MS. Deconstructing body axis morphogenesis in zebrafish embryos using robot-assisted tissue micromanipulation. Nat Commun 2022; 13:7934. [PMID: 36566327 PMCID: PMC9789989 DOI: 10.1038/s41467-022-35632-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Accepted: 12/14/2022] [Indexed: 12/25/2022] Open
Abstract
Classic microsurgical techniques, such as those used in the early 1900s by Mangold and Spemann, have been instrumental in advancing our understanding of embryonic development. However, these techniques are highly specialized, leading to issues of inter-operator variability. Here we introduce a user-friendly robotic microsurgery platform that allows precise mechanical manipulation of soft tissues in zebrafish embryos. Using our platform, we reproducibly targeted precise regions of tail explants, and quantified the response in real-time by following notochord and presomitic mesoderm (PSM) morphogenesis and segmentation clock dynamics during vertebrate anteroposterior axis elongation. We find an extension force generated through the posterior notochord that is strong enough to buckle the structure. Our data suggest that this force generates a unidirectional notochord extension towards the tailbud because PSM tissue around the posterior notochord does not let it slide anteriorly. These results complement existing biomechanical models of axis elongation, revealing a critical coupling between the posterior notochord, the tailbud, and the PSM, and show that somite patterning is robust against structural perturbations.
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Affiliation(s)
- Ece Özelçi
- Institute of Mechanical Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland
- Institute of Bioengineering, EPFL, 1015, Lausanne, Switzerland
| | - Erik Mailand
- Institute of Mechanical Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland
| | - Matthias Rüegg
- Institute of Mechanical Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland
| | - Andrew C Oates
- Institute of Bioengineering, EPFL, 1015, Lausanne, Switzerland.
| | - Mahmut Selman Sakar
- Institute of Mechanical Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland.
- Institute of Bioengineering, EPFL, 1015, Lausanne, Switzerland.
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3
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Gomes de Almeida P, Rifes P, Martins-Jesus AP, Pinheiro GG, Andrade RP, Thorsteinsdóttir S. Cell–Fibronectin Interactions and Actomyosin Contractility Regulate the Segmentation Clock and Spatio-Temporal Somite Cleft Formation during Chick Embryo Somitogenesis. Cells 2022; 11:cells11132003. [PMID: 35805087 PMCID: PMC9266262 DOI: 10.3390/cells11132003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2022] [Revised: 06/15/2022] [Accepted: 06/21/2022] [Indexed: 12/19/2022] Open
Abstract
Fibronectin is essential for somite formation in the vertebrate embryo. Fibronectin matrix assembly starts as cells emerge from the primitive streak and ingress in the unsegmented presomitic mesoderm (PSM). PSM cells undergo cyclic waves of segmentation clock gene expression, followed by Notch-dependent upregulation of meso1 in the rostral PSM which induces somite cleft formation. However, the relevance of the fibronectin matrix for these molecular processes remains unknown. Here, we assessed the role of the PSM fibronectin matrix in the spatio-temporal regulation of chick embryo somitogenesis by perturbing (1) extracellular fibronectin matrix assembly, (2) integrin–fibronectin binding, (3) Rho-associated protein kinase (ROCK) activity and (4) non-muscle myosin II (NM II) function. We found that integrin–fibronectin engagement and NM II activity are required for cell polarization in the nascent somite. All treatments resulted in defective somitic clefts and significantly perturbed meso1 and segmentation clock gene expression in the PSM. Importantly, inhibition of actomyosin-mediated contractility increased the period of hairy1/hes4 oscillations from 90 to 120 min. Together, our work strongly suggests that the fibronectin–integrin–ROCK–NM II axis regulates segmentation clock dynamics and dictates the spatio-temporal localization of somitic clefts.
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Affiliation(s)
- Patrícia Gomes de Almeida
- cE3c—CHANGE, Departmento de Biologia Animal, Faculdade de Ciências, Universidade de Lisboa, 1740-016 Lisboa, Portugal; (P.G.d.A.); (P.R.); (G.G.P.)
- ABC-RI, Algarve Biomedical Center Research Institute, 8005-139 Faro, Portugal; (A.P.M.-J.); (R.P.A.)
- Faculdade de Medicina e Ciências Biomédicas (FMCB), Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
| | - Pedro Rifes
- cE3c—CHANGE, Departmento de Biologia Animal, Faculdade de Ciências, Universidade de Lisboa, 1740-016 Lisboa, Portugal; (P.G.d.A.); (P.R.); (G.G.P.)
| | - Ana P. Martins-Jesus
- ABC-RI, Algarve Biomedical Center Research Institute, 8005-139 Faro, Portugal; (A.P.M.-J.); (R.P.A.)
- Faculdade de Medicina e Ciências Biomédicas (FMCB), Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
| | - Gonçalo G. Pinheiro
- cE3c—CHANGE, Departmento de Biologia Animal, Faculdade de Ciências, Universidade de Lisboa, 1740-016 Lisboa, Portugal; (P.G.d.A.); (P.R.); (G.G.P.)
- ABC-RI, Algarve Biomedical Center Research Institute, 8005-139 Faro, Portugal; (A.P.M.-J.); (R.P.A.)
- Faculdade de Medicina e Ciências Biomédicas (FMCB), Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
| | - Raquel P. Andrade
- ABC-RI, Algarve Biomedical Center Research Institute, 8005-139 Faro, Portugal; (A.P.M.-J.); (R.P.A.)
- Faculdade de Medicina e Ciências Biomédicas (FMCB), Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
- Champalimaud Research Program, Champalimaud Center for the Unknown, 1400-038 Lisboa, Portugal
| | - Sólveig Thorsteinsdóttir
- cE3c—CHANGE, Departmento de Biologia Animal, Faculdade de Ciências, Universidade de Lisboa, 1740-016 Lisboa, Portugal; (P.G.d.A.); (P.R.); (G.G.P.)
- Correspondence:
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4
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Pourquié O. A brief history of the segmentation clock. Dev Biol 2022; 485:24-36. [DOI: 10.1016/j.ydbio.2022.02.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2022] [Accepted: 02/23/2022] [Indexed: 11/16/2022]
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5
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Linde-Medina M, Smit TH. Molecular and Mechanical Cues for Somite Periodicity. Front Cell Dev Biol 2021; 9:753446. [PMID: 34901002 PMCID: PMC8663771 DOI: 10.3389/fcell.2021.753446] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Accepted: 10/14/2021] [Indexed: 11/13/2022] Open
Abstract
Somitogenesis refers to the segmentation of the paraxial mesoderm, a tissue located on the back of the embryo, into regularly spaced and sized pieces, i.e., the somites. This periodicity is important to assure, for example, the formation of a functional vertebral column. Prevailing models of somitogenesis are based on the existence of a gene regulatory network capable of generating a striped pattern of gene expression, which is subsequently translated into periodic tissue boundaries. An alternative view is that the pre-pattern that guides somitogenesis is not chemical, but of a mechanical origin. A striped pattern of mechanical strain can be formed in physically connected tissues expanding at different rates, as it occurs in the embryo. Here we argue that both molecular and mechanical cues could drive somite periodicity and suggest how they could be integrated.
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Affiliation(s)
| | - Theodoor H. Smit
- Department of Orthopaedic Surgery, Amsterdam Movement Sciences, Amsterdam University Medical Centres, Amsterdam, Netherlands
- Department of Medical Biology, Amsterdam University Medical Centres, Amsterdam, Netherlands
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6
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Abstract
Arthropod segmentation and vertebrate somitogenesis are leading fields in the experimental and theoretical interrogation of developmental patterning. However, despite the sophistication of current research, basic conceptual issues remain unresolved. These include: (i) the mechanistic origins of spatial organization within the segment addition zone (SAZ); (ii) the mechanistic origins of segment polarization; (iii) the mechanistic origins of axial variation; and (iv) the evolutionary origins of simultaneous patterning. Here, I explore these problems using coarse-grained models of cross-regulating dynamical processes. In the morphogenetic framework of a row of cells undergoing axial elongation, I simulate interactions between an 'oscillator', a 'switch' and up to three 'timers', successfully reproducing essential patterning behaviours of segmenting systems. By comparing the output of these largely cell-autonomous models to variants that incorporate positional information, I find that scaling relationships, wave patterns and patterning dynamics all depend on whether the SAZ is regulated by temporal or spatial information. I also identify three mechanisms for polarizing oscillator output, all of which functionally implicate the oscillator frequency profile. Finally, I demonstrate significant dynamical and regulatory continuity between sequential and simultaneous modes of segmentation. I discuss these results in the context of the experimental literature.
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Affiliation(s)
- Erik Clark
- Department of Systems Biology, Harvard Medical School, 210 Longwood Ave, Boston, MA 02115, USA
- Trinity College Cambridge, University of Cambridge, Trinity Street, Cambridge CB2 1TQ, UK
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7
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Mechanical Coupling Coordinates the Co-elongation of Axial and Paraxial Tissues in Avian Embryos. Dev Cell 2020; 55:354-366.e5. [PMID: 32918876 DOI: 10.1016/j.devcel.2020.08.007] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Revised: 06/03/2020] [Accepted: 08/17/2020] [Indexed: 01/20/2023]
Abstract
Tissues undergoing morphogenesis impose mechanical effects on one another. How developmental programs adapt to or take advantage of these effects remains poorly explored. Here, using a combination of live imaging, modeling, and microsurgical perturbations, we show that the axial and paraxial tissues in the forming avian embryonic body coordinate their rates of elongation through mechanical interactions. First, a cell motility gradient drives paraxial presomitic mesoderm (PSM) expansion, resulting in compression of the axial neural tube and notochord; second, elongation of axial tissues driven by PSM compression and polarized cell intercalation pushes the caudal progenitor domain posteriorly; finally, the axial push drives the lateral movement of midline PSM cells to maintain PSM growth and cell motility. These interactions form an engine-like positive feedback loop, which sustains a shared elongation rate for coupled tissues. Our results demonstrate a key role of inter-tissue forces in coordinating distinct body axis tissues during their co-elongation.
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8
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Kohsokabe T, Kaneko K. Boundary-induced pattern formation from uniform temporal oscillation. CHAOS (WOODBURY, N.Y.) 2018; 28:045110. [PMID: 31906628 DOI: 10.1063/1.5013280] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Pattern dynamics triggered by fixing a boundary is investigated. By considering a reaction-diffusion equation that has a unique spatially uniform and limit cycle attractor under a periodic or Neumann boundary condition, and then by choosing a fixed boundary condition, we found three novel phases depending on the ratio of diffusion constants of activator to inhibitor: transformation of temporally periodic oscillation into a spatially periodic fixed pattern, travelling wave emitted from the boundary, and aperiodic spatiotemporal dynamics. The transformation into a fixed, periodic pattern is analyzed by crossing of local nullclines at each spatial point, shifted by diffusion terms, as is analyzed by using recursive equations, to obtain the spatial pattern as an attractor. The generality of the boundary-induced pattern formation as well as its relevance to biological morphogenesis is discussed.
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Affiliation(s)
- Takahiro Kohsokabe
- Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
| | - Kunihiko Kaneko
- Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
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9
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Janssen R, Budd GE. Gene expression analysis reveals that Delta/Notch signalling is not involved in onychophoran segmentation. Dev Genes Evol 2016; 226:69-77. [PMID: 26935716 PMCID: PMC4819559 DOI: 10.1007/s00427-016-0529-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2015] [Accepted: 02/09/2016] [Indexed: 11/24/2022]
Abstract
Delta/Notch (Dl/N) signalling is involved in the gene regulatory network underlying the segmentation process in vertebrates and possibly also in annelids and arthropods, leading to the hypothesis that segmentation may have evolved in the last common ancestor of bilaterian animals. Because of seemingly contradicting results within the well-studied arthropods, however, the role and origin of Dl/N signalling in segmentation generally is still unclear. In this study, we investigate core components of Dl/N signalling by means of gene expression analysis in the onychophoran Euperipatoides kanangrensis, a close relative to the arthropods. We find that neither Delta or Notch nor any other investigated components of its signalling pathway are likely to be involved in segment addition in onychophorans. We instead suggest that Dl/N signalling may be involved in posterior elongation, another conserved function of these genes. We suggest further that the posterior elongation network, rather than classic Dl/N signalling, may be in the control of the highly conserved segment polarity gene network and the lower-level pair-rule gene network in onychophorans. Consequently, we believe that the pair-rule gene network and its interaction with Dl/N signalling may have evolved within the arthropod lineage and that Dl/N signalling has thus likely been recruited independently for segment addition in different phyla.
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Affiliation(s)
- Ralf Janssen
- Department of Earth Sciences, Palaeobiology, Uppsala University, Villavägen 16, 75236, Uppsala, Sweden.
| | - Graham E Budd
- Department of Earth Sciences, Palaeobiology, Uppsala University, Villavägen 16, 75236, Uppsala, Sweden
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10
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Webb AB, Lengyel IM, Jörg DJ, Valentin G, Jülicher F, Morelli LG, Oates AC. Persistence, period and precision of autonomous cellular oscillators from the zebrafish segmentation clock. eLife 2016; 5. [PMID: 26880542 PMCID: PMC4803185 DOI: 10.7554/elife.08438] [Citation(s) in RCA: 72] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Accepted: 02/11/2016] [Indexed: 12/11/2022] Open
Abstract
In vertebrate development, the sequential and rhythmic segmentation of the body axis
is regulated by a “segmentation clock”. This clock is comprised of a population of
coordinated oscillating cells that together produce rhythmic gene expression patterns
in the embryo. Whether individual cells autonomously maintain oscillations, or
whether oscillations depend on signals from neighboring cells is unknown. Using a
transgenic zebrafish reporter line for the cyclic transcription factor Her1, we
recorded single tailbud cells in vitro. We demonstrate that individual cells can
behave as autonomous cellular oscillators. We described the observed variability in
cell behavior using a theory of generic oscillators with correlated noise. Single
cells have longer periods and lower precision than the tissue, highlighting the role
of collective processes in the segmentation clock. Our work reveals a population of
cells from the zebrafish segmentation clock that behave as self-sustained, autonomous
oscillators with distinctive noisy dynamics. DOI:http://dx.doi.org/10.7554/eLife.08438.001 The timing and pattern of gene activity in cells can be very important. For example,
precise gene activity patterns in 24-hour circadian clocks help to set daily cycles
of rest and activity in organisms. In such scenarios, cells often communicate with
each other to coordinate the activity of their genes. To fully understand how the
behavior of the population emerges, scientists must first understand the gene
activity patterns in individual cells. Rhythmic gene activity is essential for the spinal column to form in fish and other
vertebrate embryos. A group of cells that switch genes on/off in a coordinated
pattern act like a clock to regulate the timing of the various steps in the process
of backbone formation. However, it is not clear if each cell is able to maintain a
rhythm of gene expression on their own, or whether they rely on messages from
neighboring cells to achieve it. Now, Webb et al. use time-lapse videos of individual cells isolated from the tail of
zebrafish embryos to show that each cell can maintain a pattern of rhythmic activity
in a gene called Her1. In the experiments, individual cells were
removed from zebrafish and placed under a microscope to record and track the activity
of Her1 over time using fluorescent proteins. These experiments show
that each cell is able to maintain a rhythmic pattern of Her1
expression on its own. Webb et al. then compared the Her1 activity patterns in individual
cells with the Her1 patterns present in a larger piece of zebrafish
tissue. The experiments showed that the rhythms in the individual cells are slower
and less precise in their timing than in the tissue. This suggests that groups of
cells must work together to create the synchronized rhythms of gene expression with
the right precision and timing needed for the spinal column to be patterned
correctly. In the future, further experiment with these cells will allow researchers to
investigate the genetic basis of the rhythms in single cells, and find out how
individual cells work together with their neighbors to allow tissues to work
properly. DOI:http://dx.doi.org/10.7554/eLife.08438.002
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Affiliation(s)
- Alexis B Webb
- MRC-National Institute for Medical Research, London, United Kingdom.,Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Iván M Lengyel
- Departamento de Física, FCEyN UBA and IFIBA, CONICET, Buenos Aires, Argentina
| | - David J Jörg
- Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
| | - Guillaume Valentin
- MRC-National Institute for Medical Research, London, United Kingdom.,Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Frank Jülicher
- Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
| | - Luis G Morelli
- Departamento de Física, FCEyN UBA and IFIBA, CONICET, Buenos Aires, Argentina
| | - Andrew C Oates
- MRC-National Institute for Medical Research, London, United Kingdom.,Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany.,Department of Cell and Developmental Biology, University College London, London, United Kingdom
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11
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Sheeba CJ, Andrade RP, Palmeirim I. Mechanisms of vertebrate embryo segmentation: Common themes in trunk and limb development. Semin Cell Dev Biol 2016; 49:125-34. [DOI: 10.1016/j.semcdb.2016.01.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Accepted: 01/07/2016] [Indexed: 01/02/2023]
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12
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Acharjee UK, Gejima R, Felemban Athary Abdulhaleem M, Riyadh MA, Tanaka H, Ohta K. Tsukushi expression is dependent on Notch signaling and oscillated in the presomitic mesoderm during chick somitogenesis. Biochem Biophys Res Commun 2015; 465:625-30. [DOI: 10.1016/j.bbrc.2015.08.074] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Accepted: 08/17/2015] [Indexed: 12/31/2022]
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13
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Timing embryo segmentation: dynamics and regulatory mechanisms of the vertebrate segmentation clock. BIOMED RESEARCH INTERNATIONAL 2014; 2014:718683. [PMID: 24895605 PMCID: PMC4033425 DOI: 10.1155/2014/718683] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/28/2014] [Accepted: 04/09/2014] [Indexed: 11/18/2022]
Abstract
All vertebrate species present a segmented body, easily observed in the vertebrate column and its associated components, which provides a high degree of motility to the adult body and efficient protection of the internal organs. The sequential formation of the segmented precursors of the vertebral column during embryonic development, the somites, is governed by an oscillating genetic network, the somitogenesis molecular clock. Herein, we provide an overview of the molecular clock operating during somite formation and its underlying molecular regulatory mechanisms. Human congenital vertebral malformations have been associated with perturbations in these oscillatory mechanisms. Thus, a better comprehension of the molecular mechanisms regulating somite formation is required in order to fully understand the origin of human skeletal malformations.
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14
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Bajard L, Morelli LG, Ares S, Pécréaux J, Jülicher F, Oates AC. Wnt-regulated dynamics of positional information in zebrafish somitogenesis. Development 2014; 141:1381-91. [PMID: 24595291 PMCID: PMC3943186 DOI: 10.1242/dev.093435] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
How signaling gradients supply positional information in a field of moving cells is an unsolved question in patterning and morphogenesis. Here, we ask how a Wnt signaling gradient regulates the dynamics of a wavefront of cellular change in a flow of cells during somitogenesis. Using time-controlled perturbations of Wnt signaling in the zebrafish embryo, we changed segment length without altering the rate of somite formation or embryonic elongation. This result implies specific Wnt regulation of the wavefront velocity. The observed Wnt signaling gradient dynamics and timing of downstream events support a model for wavefront regulation in which cell flow plays a dominant role in transporting positional information.
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Affiliation(s)
- Lola Bajard
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, D-01307 Dresden, Germany
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15
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Sasai Y. Cytosystems dynamics in self-organization of tissue architecture. Nature 2013; 493:318-26. [DOI: 10.1038/nature11859] [Citation(s) in RCA: 315] [Impact Index Per Article: 28.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Accepted: 11/08/2012] [Indexed: 02/08/2023]
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16
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Sato Y. Dorsal aorta formation: separate origins, lateral-to-medial migration, and remodeling. Dev Growth Differ 2012; 55:113-29. [PMID: 23294360 DOI: 10.1111/dgd.12010] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2012] [Revised: 09/19/2012] [Accepted: 09/19/2012] [Indexed: 01/12/2023]
Abstract
Blood vessel formation is a highly dynamic tissue-remodeling event that can be observed from early development in vertebrate embryos. Dorsal aortae, the first functional intra-embryonic blood vessels, arise as two separate bilateral vessels in the trunk and undergo lateral-to-medial translocation, eventually fusing into a single large vessel at the midline. After this dramatic remodeling, the dorsal aorta generates hematopoietic stem cells. The dorsal aorta is a good model to use to increase our understanding of the mechanisms controlling the establishment and remodeling of larger blood vessels in vivo. Because of the easy accessibility to the developing circulatory system, quail and chick embryos have been widely used for studies on blood vessel formation. In particular, the mapping of endothelial cell origins has been performed using quail-chick chimera analysis, revealing endothelial, vascular smooth muscle, and hematopoietic cell progenitors of the dorsal aorta. The avian embryo model also allows conditional gene activation/inactivation and direct observation of cell behaviors during dorsal aorta formation. This allows a better understanding of the molecular mechanisms underlying specific morphogenetic events during dynamic dorsal aorta formation from a cell behavior perspective.
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Affiliation(s)
- Yuki Sato
- Priority Organization for Innovation and Excellence, Kumamoto University, 2-2-1 Honjo, Kumamoto, Japan.
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17
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Stauber M, Laclef C, Vezzaro A, Page ME, Ish-Horowicz D. Modifying transcript lengths of cycling mouse segmentation genes. Mech Dev 2012; 129:61-72. [DOI: 10.1016/j.mod.2012.01.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Revised: 01/16/2012] [Accepted: 01/17/2012] [Indexed: 10/14/2022]
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18
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Hannibal RL, Price AL, Patel NH. The functional relationship between ectodermal and mesodermal segmentation in the crustacean, Parhyale hawaiensis. Dev Biol 2012; 361:427-38. [DOI: 10.1016/j.ydbio.2011.09.033] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2011] [Revised: 09/27/2011] [Accepted: 09/27/2011] [Indexed: 11/27/2022]
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19
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Hester SD, Belmonte JM, Gens JS, Clendenon SG, Glazier JA. A multi-cell, multi-scale model of vertebrate segmentation and somite formation. PLoS Comput Biol 2011; 7:e1002155. [PMID: 21998560 PMCID: PMC3188485 DOI: 10.1371/journal.pcbi.1002155] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2010] [Accepted: 06/27/2011] [Indexed: 12/23/2022] Open
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.
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Affiliation(s)
- Susan D Hester
- Biocomplexity Institute and Department of Physics, Indiana University Bloomington, Bloomington, Indiana, United States of America.
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Aulehla A, Pourquié O. Signaling gradients during paraxial mesoderm development. Cold Spring Harb Perspect Biol 2010; 2:a000869. [PMID: 20182616 DOI: 10.1101/cshperspect.a000869] [Citation(s) in RCA: 177] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The sequential formation of somites along the anterior-posterior axis is under control of multiple signaling gradients involving the Wnt, FGF, and retinoic acid (RA) pathways. These pathways show graded distribution of signaling activity within the paraxial mesoderm of vertebrate embryos. Although Wnt and FGF signaling show highest activity in the posterior, unsegmented paraxial mesoderm (presomitic mesoderm [PSM]), RA signaling establishes a countergradient with the highest activity in the somites. The generation of these graded activities relies both on classical source-sink mechanisms (for RA signaling) and on an RNA decay mechanism (for FGF signaling). Numerous studies reveal the tight interconnection among Wnt, FGF, and RA signaling in controlling paraxial mesoderm differentiation and in defining the somite-forming unit. In particular, the relationship to a molecular oscillator acting in somite precursors in the PSM-called the segmentation clock-has been recently addressed. These studies indicate that high levels of Wnt and FGF signaling are required for the segmentation clock activity. Furthermore, we discuss how these signaling gradients act in a dose-dependent manner in the progenitors of the paraxial mesoderm, partly by regulating cell movements during gastrulation. Finally, links between the process of axial specification of vertebral segments and Hox gene expression are discussed.
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Affiliation(s)
- Alexander Aulehla
- Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA
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Martins GG, Rifes P, Amândio R, Rodrigues G, Palmeirim I, Thorsteinsdóttir S. Dynamic 3D cell rearrangements guided by a fibronectin matrix underlie somitogenesis. PLoS One 2009; 4:e7429. [PMID: 19829711 PMCID: PMC2759537 DOI: 10.1371/journal.pone.0007429] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2009] [Accepted: 09/16/2009] [Indexed: 12/26/2022] Open
Abstract
Somites are transient segments formed in a rostro-caudal progression during vertebrate development. In chick embryos, segmentation of a new pair of somites occurs every 90 minutes and involves a mesenchyme-to-epithelium transition of cells from the presomitic mesoderm. Little is known about the cellular rearrangements involved, and, although it is known that the fibronectin extracellular matrix is required, its actual role remains elusive. Using 3D and 4D imaging of somite formation we discovered that somitogenesis consists of a complex choreography of individual cell movements. Epithelialization starts medially with the formation of a transient epithelium of cuboidal cells, followed by cell elongation and reorganization into a pseudostratified epithelium of spindle-shaped epitheloid cells. Mesenchymal cells are then recruited to this medial epithelium through accretion, a phenomenon that spreads to all sides, except the lateral side of the forming somite, which epithelializes by cell elongation and intercalation. Surprisingly, an important contribution to the somite epithelium also comes from the continuous egression of mesenchymal cells from the core into the epithelium via its apical side. Inhibition of fibronectin matrix assembly first slows down the rate, and then halts somite formation, without affecting pseudopodial activity or cell body movements. Rather, cell elongation, centripetal alignment, N-cadherin polarization and egression are impaired, showing that the fibronectin matrix plays a role in polarizing and guiding the exploratory behavior of somitic cells. To our knowledge, this is the first 4D in vivo recording of a full mesenchyme-to-epithelium transition. This approach brought new insights into this event and highlighted the importance of the extracellular matrix as a guiding cue during morphogenesis.
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Affiliation(s)
- Gabriel G. Martins
- Centro de Biologia Ambiental, Departamento de Biologia Animal Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal
- Instituto Gulbenkian de Ciência, Oeiras, Portugal
- * E-mail: (GGM); (ST)
| | - Pedro Rifes
- Centro de Biologia Ambiental, Departamento de Biologia Animal Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal
- Instituto Gulbenkian de Ciência, Oeiras, Portugal
| | - Rita Amândio
- Centro de Biologia Ambiental, Departamento de Biologia Animal Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal
- Instituto Gulbenkian de Ciência, Oeiras, Portugal
| | - Gabriela Rodrigues
- Centro de Biologia Ambiental, Departamento de Biologia Animal Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal
- Instituto Gulbenkian de Ciência, Oeiras, Portugal
| | - Isabel Palmeirim
- Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho, Braga, Portugal
| | - Sólveig Thorsteinsdóttir
- Centro de Biologia Ambiental, Departamento de Biologia Animal Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal
- Instituto Gulbenkian de Ciência, Oeiras, Portugal
- * E-mail: (GGM); (ST)
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bHLH Proteins and Their Role in Somitogenesis. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2008; 638:124-39. [DOI: 10.1007/978-0-387-09606-3_7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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Andrade RP, Palmeirim I, Bajanca F. Molecular clocks underlying vertebrate embryo segmentation: A 10-year-old hairy-go-round. ACTA ACUST UNITED AC 2007; 81:65-83. [PMID: 17600780 DOI: 10.1002/bdrc.20094] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Segmentation of the vertebrate embryo body is a fundamental developmental process that occurs with strict temporal precision. Temporal control of this process is achieved through molecular segmentation clocks, evidenced by oscillations of gene expression in the unsegmented presomitic mesoderm (PSM, precursor tissue of the axial skeleton) and in the distal limb mesenchyme (limb chondrogenic precursor cells). The first segmentation clock gene, hairy1, was identified in the chick embryo PSM in 1997. Ten years later, chick hairy2 expression unveils a molecular clock operating during limb development. This review revisits vertebrate embryo segmentation with special emphasis on the current knowledge on somitogenesis and limb molecular clocks. A compilation of human congenital disorders that may arise from deregulated embryo clock mechanisms is presented here, in an attempt to reconcile different sources of information regarding vertebrate embryo development. Challenging open questions concerning the somitogenesis clock are presented and discussed, such as When?, Where?, How?, and What for? Hopefully the next decade will be equally rich in answers.
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Affiliation(s)
- Raquel P Andrade
- Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho, Braga, Portugal.
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Rifes P, Carvalho L, Lopes C, Andrade RP, Rodrigues G, Palmeirim I, Thorsteinsdóttir S. Redefining the role of ectoderm in somitogenesis: a player in the formation of the fibronectin matrix of presomitic mesoderm. Development 2007; 134:3155-65. [PMID: 17670788 DOI: 10.1242/dev.003665] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The absence of ectoderm impairs somite formation in cultured presomitic mesoderm (PSM) explants, suggesting that an ectoderm-derived signal is essential for somitogenesis. Here we show in chick that the standard enzymatic treatments used for explant isolation destroy the fibronectin matrix surrounding the anterior PSM, which fails to form somites when cultured for 6 hours. By contrast, explants isolated with collagenase retain their fibronectin matrix and form somites under identical culture conditions. The additional presence of ectoderm enhances somite formation, whereas endoderm has no effect. Furthermore, we show that pancreatin-isolated PSM explants cultured in fibronectin-supplemented medium, form significantly more somites than control explants. Interestingly, ectoderm is the major producer of fibronectin (Fn1) transcripts, whereas all but the anterior-most region of the PSM expresses the fibronectin assembly receptor, integrin alpha5 (Itga5). We thus propose that the ectoderm-derived fibronectin is assembled by mesodermal alpha5beta1 integrin on the surface of the PSM. Finally, we demonstrate that inhibition of fibronectin fibrillogenesis in explants with ectoderm abrogates somitogenesis. We conclude that a fibronectin matrix is essential for morphological somite formation and that a major, previously unrecognised role of ectoderm in somitogenesis is the synthesis of fibronectin.
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Affiliation(s)
- Pedro Rifes
- Departamento de Biologia Animal e Centro de Biologia Ambiental, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
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Zhu H, Dhar PK. Transient block of receptor may be a mechanism controlling unidirectional propagation of signaling. IEEE Trans Nanobioscience 2006; 5:193-203. [PMID: 16999245 DOI: 10.1109/tnb.2006.880832] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In tissue development, juxtacrine signaling often propagates across cells, carrying and delivering temporal and spatial information for cells to make correct patterning. Observed complex and accurate tissue patterning indicates that signaling propagation via ligand-receptor interactions is precisely controlled. It is important and interesting to reveal the possible control mechanisms. The directionality of signaling in cells, which is a common issue for all intercellular signaling pathways, is a critical aspect. To understand the propagation of Notch signaling in presomitic mesoderm cells in the mouse, a novel method is used to build a multicellular model to simulate Notch signaling. Simulation reveals that the transient block of Notch by Notch induced Lfng and the delayed removal of the block by another Notch induced protein Hes7 may explain the observed unidirectional propagation of Notch signaling in these cells. Both mutation in and overexpression of lfng cause the same signaling profile in the tissue, due to the inappropriate timing of Notch signaling block by Lfng. The reverse Notch/Delta signaling quickly develops into reciprocating signaling among cells, causing irregular expression of cyclic genes. Irregular Notch signaling in cells would change their response to the positional information provided by the Fgf8 gradient, resulting in disordered and irregular somite segmentation. As Notch signaling is highly conserved, we hypothesize that the mechanism of controlling unidirectional propagation of signaling in cells by transient receptor block may exist in other tissues and in other vertebrates. Our simulation results also suggest that segmentation clock and unidirectional propagation may be inherently coupled in Notch signaling.
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Affiliation(s)
- Hao Zhu
- Bioinformatics Institute of Singapore, Biopolis Street, 138671, Singapore.
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Echeverri K, Oates AC. Coordination of symmetric cyclic gene expression during somitogenesis by Suppressor of Hairless involves regulation of retinoic acid catabolism. Dev Biol 2006; 301:388-403. [PMID: 17098223 DOI: 10.1016/j.ydbio.2006.10.003] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2006] [Revised: 09/29/2006] [Accepted: 10/05/2006] [Indexed: 01/25/2023]
Abstract
Vertebrate embryos faithfully produce bilaterally symmetric somites that give rise to repetitive body structures such as vertebrae and skeletal muscle. Body segmentation is regulated by a cyclic gene expression system, containing the Delta-Notch pathway and targets, which generates bilaterally symmetric oscillations across the Pre-Somitic Mesoderm (PSM). The position of the forming somite boundary is controlled by interaction of this oscillator with a determination front comprised of opposing gradients of FGF and retinoic acid (RA) signalling. Disruption of RA production leads to asymmetries in cyclic gene expression, but the link between RA and the oscillator is unknown. In somitogenesis, Notch signalling activates target genes through the transcription factor Suppressor of Hairless (Su(H)). Here, we report that two Su(H) genes coordinate bilaterally symmetric positioning of somite boundaries in the zebrafish embryo. Combined Su(H) gene knockdown caused defects in visceral left/right asymmetry, neurogenic lateral inhibition, and symmetrical failure of the segmentation oscillator. However, by selectively down-regulating Su(H)2 or Su(H)1 function using specific antisense morpholinos, we observed asymmetric defects in anterior or posterior somite boundaries, respectively. These morphological abnormalities were reflected by underlying asymmetric cyclic gene expression waves in the presomitic mesoderm, indicating a key role for Su(H) in coordinating the left-right symmetry of this process. Strikingly, expression of the RA-degrading enzyme cyp26a1 in the tailbud was controlled by Su(H) activity, and morpholino knockdown of cyp26a1 alone caused asymmetric cyclic dlc expression, suggesting that excess RA in the tailbud may contribute to the cyclic asymmetries. Indeed, exogenous RA was sufficient to generate asymmetric expression of all cyclic genes. Our observations indicate that one element of the Notch signalling pathway, Su(H), is required for control of RA metabolism in the tailbud and that this regulation is involved in bilateral symmetry of cyclic gene expression and somitogenesis.
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Affiliation(s)
- Karen Echeverri
- Max Planck Institute for Molecular Cell Biology and Genetics, Pfotenhauerstr 108, 01307 Dresden, Germany
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Aulehla A, Pourquié O. On periodicity and directionality of somitogenesis. ACTA ACUST UNITED AC 2006; 211 Suppl 1:3-8. [PMID: 17024300 DOI: 10.1007/s00429-006-0124-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/17/2006] [Indexed: 10/24/2022]
Abstract
It is currently thought that the mechanism underlying somitogenesis is linked to a molecular oscillator, the segmentation clock, and to gradients of signaling molecules within the paraxial mesoderm. Here, we review the current picture of this segmentation clock and gradients, and use this knowledge to critically ask: What is the basis for periodicity and directionality of somitogenesis?
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Affiliation(s)
- Alexander Aulehla
- Howard Hughes Medical Institute and Stowers Institute for Medical Research, Kansas City, MO 64110, USA
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Rodrigues S, Santos J, Palmeirim I. Molecular characterization of the rostral-most somites in early somitic stages of the chick embryo. Gene Expr Patterns 2006; 6:673-7. [PMID: 16488196 DOI: 10.1016/j.modgep.2006.01.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2005] [Revised: 12/28/2005] [Accepted: 01/07/2006] [Indexed: 10/25/2022]
Abstract
Segmentation consists on the progressive formation of repetitive embryonic structures, named somites, which are formed from the most rostral part of the presomitic mesoderm. Somites are subdivided into anterior and posterior compartments and several genes are differentially expressed in either compartment. This has provided evidence for the importance of establishing the anterior-posterior polarity within each somite, which is critical for the correct segmented pattern of the adult vertebrate body. Although all somites appear morphologically similar, fate map studies have shown that the first 4 somites do not give rise to segmented structures, in contrast to more posterior ones. Moreover, in several somitogenesis-related mutants the anterior somites are not affected while posterior somites present clear defects or do not form at all. Altogether these data suggest relevant differences between rostral and caudal somites. In order to check for molecular differences between anterior and posterior somites, we have performed a detailed expression pattern analysis of several Notch signalling related genes. For the first time, we show that the somitic expression pattern profile is not the same along the anterior-posterior axis and that the differences are not observed always at the same somite level.
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Affiliation(s)
- Sofia Rodrigues
- Instituto Gulbenkian de Ciência, Centro de Biologia do Desenvolvimento, Oeiras, Portugal
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Linker C, Lesbros C, Gros J, Burrus LW, Rawls A, Marcelle C. beta-Catenin-dependent Wnt signalling controls the epithelial organisation of somites through the activation of paraxis. Development 2005; 132:3895-905. [PMID: 16100089 DOI: 10.1242/dev.01961] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The regulation of cell adhesion in epithelia is a fundamental process governing morphogenesis in embryos and a key step in the progression of invasive cancers. Here, we have analysed the molecular pathways controlling the epithelial organisation of somites. Somites are mesodermal epithelial structures of vertebrate embryos that undergo several changes in cell adhesion during early embryonic life. We show that Wnt6 in the ectoderm overlaying the somites, but not Wnt1 in the neighbouring neural tube, is the most likely candidate molecule responsible for the maintenance of the epithelial structure of the dorsal compartment of the somite: the dermomyotome. We characterised the signalling pathway that mediates Wnt6 activity. Our experiments suggest that the Wnt receptor molecule Frizzled7 probably transduces the Wnt6 signal. Intracellularly, this leads to the activation of the beta-catenin/LEF1-dependent pathway. Finally, we demonstrate that the bHLH transcription factor paraxis, which was previously shown to be a major player in the epithelial organisation of somites, is a target of the beta-catenin signal. We conclude that beta-catenin activity, initiated by Wnt6 and mediated by paraxis, is required for the maintenance of the epithelial structure of somites.
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Affiliation(s)
- Claudia Linker
- Laboratoire de Génétique et de Physiologie du Développement (LGPD (IBDM), CNRS UMR 6545. Université de la Méditerranée, Campus de Luminy, case 907, 13288 Marseille, Cedex 09, France.
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Sato Y, Takahashi Y. A novel signal induces a segmentation fissure by acting in a ventral-to-dorsal direction in the presomitic mesoderm. Dev Biol 2005; 282:183-91. [PMID: 15936339 DOI: 10.1016/j.ydbio.2005.03.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2004] [Revised: 03/01/2005] [Accepted: 03/08/2005] [Indexed: 10/25/2022]
Abstract
We describe here a novel inductive action that operates during somitic segmentation in chicken embryos. We previously reported that the posterior border cells located at a next-forming boundary in the anterior end of the presomitic mesoderm (PSM) exhibit an inductive activity that acts on the anterior cells to cause the formation of a somitic fissure (Sato, Y., Yasuda, K., Takahashi, Y., 2002. Morphological boundary forms by a novel inductive event mediated by Lunatic fringe and Notch during somitic segmentation. Development 129, 3633-3644). In this study, we have found a second inductive action along the dorso-ventral (D-V) axis during fissure formation. When relocated into a non-segmenting region of PSM, the ventral-most cells taken from the presumptive boundary are sufficient to induce an ectopic fissure in host cells. The ventrally derived signal acts in a ventral-to-dorsal direction but not ventrally, regardless of where the ventral cells are placed. This directional signaling is governed, at least in part, by the signal-receiving cells of the PSM, which we found to be polarized along the D-V axis, and also by intimate cell-cell interactions. Finally, we have observed that morphological segmentation is able to rearrange the anterior and posterior regionalization of individual somites. These findings suggest that discrete unidirectional signals along both the antero-posterior and the D-V axes act coordinately to achieve the formation of the intersomitic fissure, and also that fissure formation is important for the fine-tuning of A-P regionalization in individual somites.
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Affiliation(s)
- Yuki Sato
- Center for Developmental Biology (CDB), RIKEN, 2-2-3 Minatojima-minamimachi, Chuo-ku, Kobe 650-0047, Japan
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Aulehla A, Herrmann BG. Segmentation in vertebrates: clock and gradient finally joined. Genes Dev 2004; 18:2060-7. [PMID: 15342488 DOI: 10.1101/gad.1217404] [Citation(s) in RCA: 181] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The vertebral column is derived from somites formed by segmentation of presomitic mesoderm, a fundamental process of vertebrate embryogenesis. Models on the mechanism controlling this process date back some three to four decades. Access to understanding the molecular control of somitogenesis has been gained only recently by the discovery of molecular oscillators (segmentation clock) and gradients of signaling molecules, as predicted by early models. The Notch signaling pathway is linked to the oscillator and plays a decisive role in inter- and intrasomitic boundary formation. An Fgf8 signaling gradient is involved in somite size control. And the (canonical) Wnt signaling pathway, driven by Wnt3a, appears to integrate clock and gradient in a global mechanism controlling the segmentation process. In this review, we discuss recent advances in understanding the molecular mechanism controlling somitogenesis.
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Affiliation(s)
- Alexander Aulehla
- Max-Planck-Institute for Molecular Genetics, Department of Developmental Genetics, 14195 Berlin, Germany
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Kuan CYK, Tannahill D, Cook GMW, Keynes RJ. Somite polarity and segmental patterning of the peripheral nervous system. Mech Dev 2004; 121:1055-68. [PMID: 15296971 DOI: 10.1016/j.mod.2004.05.001] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2004] [Revised: 04/29/2004] [Accepted: 05/03/2004] [Indexed: 10/26/2022]
Abstract
The analysis of the outgrowth pattern of spinal axons in the chick embryo has shown that somites are polarized into anterior and posterior halves. This polarity dictates the segmental development of the peripheral nervous system: migrating neural crest cells and outgrowing spinal axons traverse exclusively the anterior halves of the somite-derived sclerotomes, ensuring a proper register between spinal axons, their ganglia and the segmented vertebral column. Much progress has been made recently in understanding the molecular basis for somite polarization, and its linkage with Notch/Delta, Wnt and Fgf signalling. Contact-repulsive molecules expressed by posterior half-sclerotome cells provide critical guidance cues for axons and neural crest cells along the anterior-posterior axis. Diffusible repellents from surrounding tissues, particularly the dermomyotome and notochord, orient outgrowing spinal axons in the dorso-ventral axis ('surround repulsion'). Repulsive forces therefore guide axons in three dimensions. Although several molecular systems have been identified that may guide neural crest cells and axons in the sclerotome, it remains unclear whether these operate together with considerable overall redundancy, or whether any one system predominates in vivo.
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Affiliation(s)
- C-Y Kelly Kuan
- Department of Anatomy, University of Cambridge, Downing Street, Cambridge CB2 3DY, UK
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Pourquié O. The chick embryo: a leading model in somitogenesis studies. Mech Dev 2004; 121:1069-79. [PMID: 15296972 DOI: 10.1016/j.mod.2004.05.002] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2004] [Revised: 05/03/2004] [Accepted: 05/04/2004] [Indexed: 11/25/2022]
Abstract
The vertebrate body is built on a metameric organization which consists of a repetition of functionally equivalent units, each comprising a vertebra, its associated muscles, peripheral nerves and blood vessels. This periodic pattern is established during embryogenesis by the somitogenesis process. Somites are generated in a rhythmic fashion from the presomitic mesoderm and they subsequently differentiate to give rise to the vertebrae and skeletal muscles of the body. Somitogenesis has been very actively studied in the chick embryo since the 19th century and many of the landmark experiments that led to our current understanding of the vertebrate segmentation process have been performed in this organism. Somite formation involves an oscillator, the segmentation clock whose periodic signal is converted into the periodic array of somite boundaries by a spacing mechanism relying on a traveling threshold of FGF signaling regressing in concert with body axis extension.
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Affiliation(s)
- Olivier Pourquié
- Stowers Institute for Medical Research, 1000E 50th Street, Kansas City, MO 64110, USA.
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Qiu X, Xu H, Haddon C, Lewis J, Jiang YJ. Sequence and embryonic expression of three zebrafishfringe genes:lunatic fringe,radical fringe, andmanic fringe. Dev Dyn 2004; 231:621-30. [PMID: 15376327 DOI: 10.1002/dvdy.20155] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Drosophila fringe and its homologues in vertebrates code for glycosyltransferases that modify Notch, altering the sensitivity of this receptor protein to its ligands Delta and Serrate and, thereby, playing an essential part in the demarcation of tissue boundaries. We describe the isolation and characterization of three zebrafish (Danio rerio) fringe homologues: lunatic fringe (lfng), radical fringe (rfng), and manic fringe (mfng). In addition to the sites previously described (Prince et al. [2001] Mech. Dev. 105:175-180; Leve et al. [ 2001] Dev. Genes Evol. 211:493-500), lfng is also expressed in the sensory patches of the inner ear. The newly described rfng is expressed in adaxial cells, tectum, rhombomere boundaries, and formed somites, but the expression of mfng is only detectable by reverse transcription-polymerase chain reaction and not by whole-mount in situ hybridization (WISH) during early embryonic development; later, it is expressed in the sensory patches of the ear. In mib mutants, where Notch signaling is defective and rhombomere boundaries fail to form, the rfng expression in hindbrain is almost completely lost. None of the three zebrafish fringe genes is detectably expressed in the posterior presomitic mesoderm, suggesting that, in contrast with chick and mouse, the somitogenesis oscillator in this tissue in the zebrafish does not depend on Fringe activity.
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Affiliation(s)
- Xuehui Qiu
- Laboratory of Developmental Signalling and Patterning, Institute of Molecular and Cell Biology, Proteos, 61 Biopolis Drive, Singapore 138673
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Abstract
Vertebrate segmentation is manifested during embryonic development as serially repeated units termed somites that give rise to vertebrae, ribs, skeletal muscle and dermis. Many theoretical models including the "clock and wavefront" model have been proposed. There is compelling genetic evidence showing that Notch-Delta signaling is indispensable for somitogenesis. Notch receptor and its target genes, Hairy/E(spl) homologues, are known to be crucial for the ticking of the segmentation clock. Through the work done in mouse, chick, Xenopus and zebrafish, an oscillator operated by cyclical transcriptional activation and delayed negative feedback regulation is emerging as the fundamental mechanism underlying the segmentation clock. Ubiquitin-dependent protein degradation and probably other posttranslational regulations are also required. Fgf8 and Wnt3a gradients are important in positioning somite boundaries and, probably, in coordinating tail growth and segmentation. The circadian clock is another biochemical oscillator, which, similar to the segmentation clock, is operated with a negative transcription-regulated feedback mechanism. While the circadian clock uses a more complicated network of pathways to achieve homeostasis, it appears that the segmentation clock exploits the Notch pathway to achieve both signal generation and synchronization. We also discuss mathematical modeling and future directions in the end.
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Affiliation(s)
- Padmashree C G Rida
- Laboratory of Developmental Signalling and Patterning, Institute of Molecular and Cell Biology, National University of Singapore, Singapore 117604, Singapore
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Tonegawa A, Kasai T, Takahashi Y. Systematic screening for signaling molecules expressed during somitogenesis by the signal sequence trap method. Dev Biol 2003; 262:32-50. [PMID: 14512016 DOI: 10.1016/s0012-1606(03)00327-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We describe a systematic screening to search for molecules that act as an extracellular signal during somitogenesis in vertebrates. Somitogenesis, which gives rise to segmented structures of axial bones and muscles, is a consequence of cooperative morphogenetic movements caused by precisely regulated cell and tissue interactions. We employed a strategy that combined subtractive hybridization to enrich paraxial mesoderm/somite-specific cDNAs and the signal sequence trap method, which selects signal sequence-containing molecules. Ninety-two independent cDNAs found to possess a putative signal sequence or a transmembrane domain are presented with a data base accession number for each. These clones include cDNAs which were previously identified with a function characterized, cDNAs previously identified with an undetermined function, and also cDNAs with no similarity to known sequences. Among them, 16 clones exhibited peculiar patterns of expression in the presomitic mesoderm/somites revealed by whole-mount and section in situ hybridization techniques, with some clones also being expressed in the forming neural tube. This is the first report in which an elaborate strategy combining three different screening steps was employed to identify signaling molecules relevant to a particular morphogenetic process.
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Affiliation(s)
- Akane Tonegawa
- Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5, Takayama, Ikoma, Nara, 630-0101, Japan
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39
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Linker C, Lesbros C, Stark MR, Marcelle C. Intrinsic signals regulate the initial steps of myogenesis in vertebrates. Development 2003; 130:4797-807. [PMID: 12917295 DOI: 10.1242/dev.00688] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
In vertebrates, despite the evidence that extrinsic factors induce myogenesis in naive mesoderm, other experiments argue that the initiation of the myogenic program may take place independent of these factors. To resolve this discrepancy, we have re-addressed this issue, using short-term in vivo microsurgery and culture experiments in chick. Our results show that the initial expression of the muscle-specific markers Myf5 and MyoD is regulated in a mesoderm-autonomous fashion. The reception of a Wnt signal is required for MyoD, but not Myf5 expression; however, we show that the source of the Wnt signal is intrinsic to the mesoderm. Gain- and loss-of-function experiments indicate that Wnt5b, which is expressed in the presomitic mesoderm, represents the MyoD-activating cue. Despite Wnt5b expression in the presomitic mesoderm, MyoD is not expressed in this tissue: our experiments demonstrate that this is due to a Bmp inhibitory signal that prevents the premature expression of MyoD before somites form. Our results indicate that myogenesis is a multistep process which is initiated prior to somite formation in a mesoderm-autonomous fashion; as somites form, influences from adjacent tissues are likely to be required for maintenance and patterning of early muscles.
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Affiliation(s)
- Claudia Linker
- Laboratoire de Génétique et de Physiologie du Développement, Developmental Biology Institute of Marseille, CNRS UMR 6545, University Aix-Marseille II, Campus de Luminy, case 907, 13288 Marseille Cedex 09, France
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40
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Lewis J. Autoinhibition with transcriptional delay: a simple mechanism for the zebrafish somitogenesis oscillator. Curr Biol 2003; 13:1398-408. [PMID: 12932323 DOI: 10.1016/s0960-9822(03)00534-7] [Citation(s) in RCA: 494] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
BACKGROUND The pattern of somites is traced out by a mechanism involving oscillating gene expression at the tail end of the embryo. In zebrafish, two linked oscillating genes, her1 and her7, coding for inhibitory gene regulatory proteins, are especially implicated in genesis of the oscillations, while Notch signaling appears necessary for synchronization of adjacent cells. RESULTS I show by mathematical simulation that direct autorepression of her1 and her7 by their own protein products provides a mechanism for the intracellular oscillator. This mechanism operates robustly even when one allows for the fact that gene regulation is an essentially noisy (stochastic) process. The predicted period is close to the observed period (30 min) and is dictated primarily by the transcriptional delay, the time taken to make an mRNA molecule. Through its coupling to her1/her7 expression, Notch signaling can keep the rapid oscillations in adjacent cells synchronized. When the coupling parameters are varied, however, the model system can switch to oscillations of a much longer period, resembling that of the mouse or chick somitogenesis oscillator and governed by the delays in the Notch pathway. Such Notch-mediated synchronous oscillations are predicted even in the absence of direct her1/her7 autoregulation, through operation of the standard Notch signaling pathway that is usually assumed simply to give lateral inhibition. CONCLUSIONS Direct autorepression of a gene by its own product can generate oscillations, with a period determined by the transcriptional and translational delays. Simple as they are, such systems show surprising behaviors. To understand them, unaided intuition is not enough: we need mathematics.
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Affiliation(s)
- Julian Lewis
- Vertebrate Development Laboratory, Cancer Research UK London Research Institute, 44 Lincoln's Inn Fields, London WC2A 3PX, United Kingdom.
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41
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Rhee J, Takahashi Y, Saga Y, Wilson-Rawls J, Rawls A. The protocadherin papc is involved in the organization of the epithelium along the segmental border during mouse somitogenesis. Dev Biol 2003; 254:248-61. [PMID: 12591245 DOI: 10.1016/s0012-1606(02)00085-4] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The anterior and posterior halves of individual somites adopt distinct fates during somitogenesis, which is crucial for establishing the metameric pattern of axial tissues such as the vertebral column and peripheral nerves. Genetic analyses have demonstrated that the specification of cells to an anterior or posterior fate is intimately related to the process of segmentation. Inactivation of the transcription factor Mesp2, or components of the Notch signaling pathway, led to defects in segmentation and a loss of anterior/posterior polarity. Target genes in mice that could mediate the morphological events associated with segmentation or polarity have not been identified. Studies in Xenopus and zebrafish have demonstrated that the protocadherin, papc, is expressed in an anterior-specific manner in the presumptive somites of the presomitic mesoderm and is required for normal somitogenesis. Here, we examine the role of papc in directing segmentation in the mouse. We demonstrate that papc is expressed in a dynamic pattern within the first two presumptive somites (0 and -1) at the anterior end of the presomitic mesoderm. The domain of papc transcription in somite 0 starts broad and becomes progressively restricted to the anterior edge. Transcription in somite -1 over the same time remains broad. Analysis of targeted null mutations revealed that transcription of papc is dependent on Mesp2. The dynamic nature of papc transcription in somite 0 requires the expression of lunatic fringe, which modifies the activation of the Notch signaling pathway and is required for proper segmentation of somites. Treatment of embryonic mouse tails in a hanging drop culture with a putative dominant-negative mutation of papc disrupted the epithelial organization of cells at the segmental borders between somites. Together, these data indicate that papc is an important regulator of somite epithelialization associated with segmentation.
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Affiliation(s)
- Jerry Rhee
- Department of Biology, Arizona State University, Tempe, AZ 85287-1501, USA
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42
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Freitas C, Rodrigues S, Charrier JB, Teillet MA, Palmeirim I. Horloge moléculaire et segmentation des vertébrés : qui fait quoi ? Med Sci (Paris) 2002. [DOI: 10.1051/medsci/20021889883] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Sato Y, Yasuda K, Takahashi Y. Morphological boundary forms by a novel inductive event mediated by Lunatic fringe and Notch during somitic segmentation. Development 2002; 129:3633-44. [PMID: 12117813 DOI: 10.1242/dev.129.15.3633] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Boundary formation plays a central role in differentiating the flanking regions that give rise to discrete tissues and organs during early development. We have studied mechanisms by which a morphological boundary and tissue separation are regulated by examining chicken somite segmentation as a model system. By transplanting a small group of cells taken from a presumptive border into a non-segmentation site, we have found a novel inductive event where posteriorly juxtaposed cells to the next-forming border instruct the anterior cells to become separated and epithelialized. We have further studied the molecular mechanisms underlying these interactions by focusing on Lunatic fringe, a modulator of Notch signaling, which is expressed in the region of the presumptive boundary. By combining DNA in ovo electroporation and embryonic transplantation techniques we have ectopically made a sharp boundary of Lunatic fringe activity in the unsegmented paraxial mesoderm and observed a fissure formed at the interface. In addition, a constitutive active form of Notch mimics this instructive phenomenon. These suggest that the boundary-forming signals emanating from the posterior border cells are mediated by Notch, the action of which is confined to the border region by Lunatic fringe within the area where mRNAs of Notch and its ligand are broadly expressed in the presomitic mesoderm.
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Affiliation(s)
- Yuki Sato
- Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5, Takayama, Ikoma, Nara, 630-0101, Japan
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Schubert FR, Mootoosamy RC, Walters EH, Graham A, Tumiotto L, Münsterberg AE, Lumsden A, Dietrich S. Wnt6 marks sites of epithelial transformations in the chick embryo. Mech Dev 2002; 114:143-8. [PMID: 12175501 DOI: 10.1016/s0925-4773(02)00039-4] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
In a screen for Wnt genes executing the patterning function of the vertebrate surface ectoderm, we have isolated a novel chick Wnt gene, chick Wnt6. This gene encodes the first pan-epidermal Wnt signalling molecule. Further sites of expression are the boundary of the early neural plate and surface ectoderm, the roof of mesencephalon, pretectum and dorsal thalamus, the differentiating heart, and the otic vesicle. The precise sites of Wnt6 expression coincide with crucial changes in tissue architecture, namely epithelial remodelling and epithelial-mesenchymal transformation (EMT). Moreover, the expression of Wnt6 is closely associated with areas of Bmp signalling.
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Affiliation(s)
- Frank R Schubert
- MRC Centre for Developmental Neurobiology, King's College London, 4th Floor New Hunt's House, Guy's Campus, London SE1 1UL, UK
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45
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Nomura-Kitabayashi A, Takahashi Y, Kitajima S, Inoue T, Takeda H, Saga Y. Hypomorphic Mesp allele distinguishes establishment of rostrocaudal polarity and segment border formation in somitogenesis. Development 2002; 129:2473-81. [PMID: 11973278 DOI: 10.1242/dev.129.10.2473] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
A bHLH-type transcription factor, Mesp2, plays an essential role in somite segmentation in mice. Zebrafish mespb (mesp-b), a putative homologue of mouse Mesp2, is transiently expressed in the rostral presomitic mesoderm similarly to Mesp2. To determine whether zebrafish mespb is a functional homologue of mouse Mesp2, zebrafish mespb was introduced into the mouse Mesp2 locus by homologous recombination. Introduced mespb almost rescued the Mesp2 deficiency in the homozygous mespb knockin mouse, indicating that mespb is a functional homologue of mouse Mesp2. Segmented somites were clearly observed although the partial fusion of the vertebral columns still occurred. Interestingly, however, the nature and dosage of the mespb gene affected the rescue event. A mouse line, which has a hypomorphic Mesp2 allele generated by the introduction of neo-mespb, gave rise to an epithelial somite without normal rostrocaudal (RC) polarity. RC polarity was also lacking in the presomitic mesoderm. The defects in RC polarity were determined by the altered expressions of Uncx4.1 and Dll1 in the segmented somites and presomitic mesoderm, respectively. In contrast, the expression of EphA4 (Epha4), lunatic fringe or protocadherin, thought to be involved in segment border formation, was fairly normal in hypomorphic mutant embryos. These results suggest that the Mesp family of transcription factors is involved in both segment border formation and establishment of RC polarity through different genetic cascades.
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Affiliation(s)
- Aya Nomura-Kitabayashi
- Cellular and Molecular Toxicology Division, National Institute of Health Sciences, 1-18-1 Kamiyohga, Setagaya-ku, Tokyo 158-8501, Japan
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46
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Abstract
In vertebrates, the paraxial mesoderm corresponds to the bilateral strips of mesodermal tissue flanking the notochord and neural tube and which are delimited laterally by the intermediate mesoderm and the lateral plate. The paraxial mesoderm comprises the head or cephalic mesoderm anteriorly and the somitic region throughout the trunk and the tail of the vertebrates. Soon after gastrulation, the somitic region of vertebrates starts to become segmented into paired blocks of mesoderm, termed somites. This process lasts until the number of somites characteristic of the species is reached. The somites later give rise to all skeletal muscles of the body, the axial skeleton, and part of the dermis. In this review I discuss the processes involved in the formation of the paraxial mesoderm and its segmentation into somites in vertebrates.
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Affiliation(s)
- O Pourquié
- Laboratoire de génétique et de physiologie du développement, Developmental Biology Institute of Marseille (IBDM), CNRS-INSERM-Université de la méditerranée-AP de Marseille, France.
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47
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Davis RL, Turner DL. Vertebrate hairy and Enhancer of split related proteins: transcriptional repressors regulating cellular differentiation and embryonic patterning. Oncogene 2001; 20:8342-57. [PMID: 11840327 DOI: 10.1038/sj.onc.1205094] [Citation(s) in RCA: 305] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The basic-helix-loop-helix (bHLH) proteins are a superfamily of DNA-binding transcription factors that regulate numerous biological processes in both invertebrates and vertebrates. One family of bHLH transcriptional repressors is related to the Drosophila hairy and Enhancer-of-split proteins. These repressors contain a tandem arrangement of the bHLH domain and an adjacent sequence known as the Orange domain, so we refer to these proteins as bHLH-Orange or bHLH-O proteins. Phylogenetic analysis reveals the existence of four bHLH-O subfamilies, with distinct, evolutionarily conserved features. A principal function of bHLH-O proteins is to bind to specific DNA sequences and recruit transcriptional corepressors to inhibit target gene expression. However, it is likely that bHLH-O proteins repress transcription by additional mechanisms as well. Many vertebrate bHLH-O proteins are effectors of the Notch signaling pathway, and bHLH-O proteins are involved in regulating neurogenesis, vasculogenesis, mesoderm segmentation, myogenesis, and T lymphocyte development. In this review, we discuss mechanisms of action and biological roles for the vertebrate bHLH-O proteins, as well as some of the unresolved questions about the functions and regulation of these proteins during development and in human disease.
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MESH Headings
- Amino Acid Sequence
- Animals
- Basic Helix-Loop-Helix Transcription Factors
- Blood Vessels/cytology
- Blood Vessels/embryology
- Cell Differentiation/genetics
- Cell Differentiation/physiology
- Cell Lineage
- Cell Transformation, Neoplastic/genetics
- DNA-Binding Proteins/genetics
- DNA-Binding Proteins/physiology
- Dimerization
- Drosophila Proteins/genetics
- Drosophila Proteins/physiology
- Drosophila melanogaster/embryology
- Drosophila melanogaster/genetics
- Drosophila melanogaster/physiology
- Embryonic and Fetal Development/genetics
- Embryonic and Fetal Development/physiology
- Evolution, Molecular
- Gene Expression Regulation, Developmental/genetics
- Gene Expression Regulation, Developmental/physiology
- Helix-Loop-Helix Motifs
- Humans
- Leukemia-Lymphoma, Adult T-Cell/genetics
- Leukemia-Lymphoma, Adult T-Cell/pathology
- Membrane Proteins/genetics
- Membrane Proteins/physiology
- Mesoderm/cytology
- Mice
- Mice, Knockout
- Molecular Sequence Data
- Morphogenesis/genetics
- Morphogenesis/physiology
- Multigene Family
- Muscles/cytology
- Muscles/embryology
- Neovascularization, Physiologic/genetics
- Neovascularization, Physiologic/physiology
- Nerve Tissue Proteins/genetics
- Nerve Tissue Proteins/physiology
- Nervous System/embryology
- Neurons/cytology
- Phylogeny
- Protein Structure, Tertiary
- Proteins/genetics
- Proteins/physiology
- Receptors, Notch
- Repressor Proteins/genetics
- Repressor Proteins/physiology
- Sequence Alignment
- Sequence Homology, Amino Acid
- Terminology as Topic
- Transcription Factors
- Transcription, Genetic
- Vertebrates/embryology
- Vertebrates/genetics
- Vertebrates/physiology
- Xenopus Proteins
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Affiliation(s)
- R L Davis
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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48
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Freitas C, Rodrigues S, Charrier JB, Teillet MA, Palmeirim I. Evidence for medial/lateral specification and positional information within the presomitic mesoderm. Development 2001; 128:5139-47. [PMID: 11748149 DOI: 10.1242/dev.128.24.5139] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In the vertebrate embryo, segmentation is built on repetitive structures, named somites, which are formed progressively from the most rostral part of presomitic mesoderm, every 90 minutes in the avian embryo. The discovery of the cyclic expression of several genes, occurring every 90 minutes in each presomitic cell, has shown that there is a molecular clock linked to somitogenesis. We demonstrate that a dynamic expression pattern of the cycling genes is already evident at the level of the prospective presomitic territory. The analysis of this expression pattern, correlated with a quail/chick fate-map, identifies a ‘wave’ of expression travelling along the future medial/lateral presomitic axis. Further analysis also reveals the existence of a medial/lateral asynchrony of expression at the level of presomitic mesoderm. This work suggests that the molecular clock is providing cellular positional information not only along the anterior/posterior but also along the medial/lateral presomitic axis. Finally, by using an in vitro culture system, we show that the information for morphological somite formation and molecular segmentation is segregated within the medial/lateral presomitic axis. Medial presomitic cells are able to form somites and express segmentation markers in the absence of lateral presomitic cells. By contrast, and surprisingly, lateral presomitic cells that are deprived of their medial counterparts are not able to organise themselves into somites and lose the expression of genes known to be important for vertebrate segmentation, such as Delta-1, Notch-1, paraxis, hairy1, hairy2 and lunatic fringe.
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Affiliation(s)
- C Freitas
- Instituto Gulbenkian de Ciência, Rua da Quinta Grande 6, 2780-156 Oeiras, Portugal
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49
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Schubert FR, Tremblay P, Mansouri A, Faisst AM, Kammandel B, Lumsden A, Gruss P, Dietrich S. Early mesodermal phenotypes in splotch suggest a role for Pax3 in the formation of epithelial somites. Dev Dyn 2001; 222:506-21. [PMID: 11747084 DOI: 10.1002/dvdy.1211] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The paired box containing transcription factor Pax3 is a crucial regulator of dermomyotome and muscle development. However, the allelic series of Pax3/Splotch mutants also displays characteristic vertebral column malformations, which do not result from defective dorsoventral somite pattern. Rather, vertebral column and sclerotomal phenotypes are reminiscent of the phenotypes observed in the segmentation/somitogenesis mutants rachiterata and pudgy. Moreover, rostrocaudal somite pattern and somitic boundaries are disturbed in Splotch as monitored by the expression of Uncx4.1 and Lunatic fringe. Alterations in EphA4, Dll1, and Uncx4.1 expression are evident already in the condensing paraxial mesoderm, correlating with the first phase of Pax3 expression before and during somite formation. This finding suggests an early function of Pax3 during the formation of epithelial somites.
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Affiliation(s)
- F R Schubert
- King's College London, MRC Centre for Developmental Neurobiology, New Hunt's House, London, United Kingdom
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50
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Dubrulle J, McGrew MJ, Pourquié O. FGF signaling controls somite boundary position and regulates segmentation clock control of spatiotemporal Hox gene activation. Cell 2001; 106:219-32. [PMID: 11511349 DOI: 10.1016/s0092-8674(01)00437-8] [Citation(s) in RCA: 485] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Vertebrate segmentation requires a molecular oscillator, the segmentation clock, acting in presomitic mesoderm (PSM) cells to set the pace at which segmental boundaries are laid down. However, the signals that position each boundary remain unclear. Here, we report that FGF8 which is expressed in the posterior PSM, generates a moving wavefront at which level both segment boundary position and axial identity become determined. Furthermore, by manipulating boundary position in the chick embryo, we show that Hox gene expression is maintained in the appropriately numbered somite rather than at an absolute axial position. These results implicate FGF8 in ensuring tight coordination of the segmentation process and spatiotemporal Hox gene activation.
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Affiliation(s)
- J Dubrulle
- Laboratoire de génétique et de physiologie du développement (LGPD), Developmental Biology Institute of Marseille (IBDM), CNRS-INSERM-Université de la méditerranée-AP de Marseille, Campus de Luminy, Case 907, 13288 Marseille Cedex 09, France
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