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Cells Jun 2022Fibronectin is essential for somite formation in the vertebrate embryo. Fibronectin matrix assembly starts as cells emerge from the primitive streak and ingress in the...
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 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 and segmentation clock gene expression in the PSM. Importantly, inhibition of actomyosin-mediated contractility increased the period of 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.
Topics: Actomyosin; Animals; Biological Clocks; Chick Embryo; Fibronectins; Integrins; Somites
PubMed: 35805087
DOI: 10.3390/cells11132003 -
Science Advances Jun 2023Two influential concepts in tissue patterning are Wolpert's positional information and Turing's self-organized reaction-diffusion (RD). The latter establishes the...
Two influential concepts in tissue patterning are Wolpert's positional information and Turing's self-organized reaction-diffusion (RD). The latter establishes the patterning of hair and feathers. Here, our morphological, genetic, and functional-by CRISPR-Cas9-mediated gene disruption-characterization of wild-type versus "scaleless" snakes reveals that the near-perfect hexagonal pattern of snake scales is established through interactions between RD in the skin and somitic positional information. First, we show that ventral scale development is guided by hypaxial somites and, second, that ventral scales and epaxial somites guide the sequential RD patterning of the dorsolateral scales. The RD intrinsic length scale evolved to match somite periodicity, ensuring the alignment of ribs and scales, both of which play a critical role in snake locomotion.
Topics: Animals; Somites; Diffusion; Feathers; Hair; Locomotion
PubMed: 37315141
DOI: 10.1126/sciadv.adf8834 -
Developmental Biology Oct 1998In vertebrates, the segmented somites, which are the medial-most component in the paraxial mesoderm, are the entity giving rise to the axial bones and skeletal muscles....
In vertebrates, the segmented somites, which are the medial-most component in the paraxial mesoderm, are the entity giving rise to the axial bones and skeletal muscles. We previously demonstrated that the mechanism that distinguishes the somite from the more lateral mesoderm (lateral plate) involves different levels of BMP-4 activity which is highest in the lateral plate. We report that Noggin, an antagonist of BMP-4, is expressed in the presumptive somite and appears to control effective levels of BMP-4 to differentiate somitic mesoderm from the lateral plate. When Noggin-producing cells were implanted into the presumptive lateral plate, they produced ectopic somites that were respecified from the lateral plate precursors. These somites exhibited no mediolateral (M-L) polarity, but acquired it when implanted Noggin was eliminated. Thus, in normal embryogenesis no or low BMP-4 activity realized by Noggin specifies the somites in the medial-most portion of the paraxial mesoderm, and then BMP-4 emanating from the lateral plate subsequently establishes the M-L polarity in the somites.
Topics: Amino Acid Sequence; Animals; Base Sequence; Body Patterning; Bone Morphogenetic Protein 4; Bone Morphogenetic Proteins; COS Cells; Carrier Proteins; Chickens; DNA Probes; In Situ Hybridization; Mesoderm; Molecular Sequence Data; Proteins; RNA, Messenger; Sequence Homology, Amino Acid; Somites; Transfection; Xenopus; Xenopus Proteins; beta-Galactosidase
PubMed: 9769170
DOI: 10.1006/dbio.1998.8895 -
Nature Communications Oct 2023Mutations of several genes cause incomplete penetrance and variable expressivity of phenotypes, which are usually attributed to modifier genes or gene-environment...
Mutations of several genes cause incomplete penetrance and variable expressivity of phenotypes, which are usually attributed to modifier genes or gene-environment interactions. Here, we show stochastic gene expression underlies the variability of somite segmentation defects in embryos mutant for segmentation clock genes her1 or her7. Phenotypic strength is further augmented by low temperature and hypoxia. By performing live imaging of the segmentation clock reporters, we further show that groups of cells with higher oscillation amplitudes successfully form somites while those with lower amplitudes fail to do so. In unfavorable environments, the number of cycles with high amplitude oscillations and the number of successful segmentations proportionally decrease. These results suggest that individual oscillation cycles stochastically fail to pass a threshold amplitude, resulting in segmentation defects in mutants. Our quantitative methodology is adaptable to investigate variable phenotypes of mutant genes in different tissues.
Topics: Animals; Basic Helix-Loop-Helix Transcription Factors; Zebrafish; Zebrafish Proteins; Somites; Phenotype; Gene Expression; Gene Expression Regulation, Developmental; Body Patterning
PubMed: 37838784
DOI: 10.1038/s41467-023-42220-7 -
Nature Communications Dec 2022Classic microsurgical techniques, such as those used in the early 1900s by Mangold and Spemann, have been instrumental in advancing our understanding of embryonic...
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.
Topics: Animals; Zebrafish; Robotics; Morphogenesis; Somites; Mesoderm; Notochord; Micromanipulation; Body Patterning
PubMed: 36566327
DOI: 10.1038/s41467-022-35632-4 -
Mechanisms of Development Sep 2004The vertebrate body is built on a metameric organization which consists of a repetition of functionally equivalent units, each comprising a vertebra, its associated... (Review)
Review
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.
Topics: Animals; Cell Differentiation; Chick Embryo; Fibroblast Growth Factors; Models, Animal; Somites; Stem Cells; Tretinoin
PubMed: 15296972
DOI: 10.1016/j.mod.2004.05.002 -
Developmental Cell Jun 2023Oscillator systems achieve synchronization when oscillators are coupled. The presomitic mesoderm is a system of cellular oscillators, where coordinated genetic activity...
Oscillator systems achieve synchronization when oscillators are coupled. The presomitic mesoderm is a system of cellular oscillators, where coordinated genetic activity is necessary for proper periodic generation of somites. While Notch signaling is required for the synchronization of these cells, it is unclear what information the cells exchange and how they react to this information to align their oscillatory pace with that of their neighbors. Combining mathematical modeling and experimental data, we found that interaction between murine presomitic mesoderm cells is controlled by a phase-gated and unidirectional coupling mechanism and results in deceleration of their oscillation pace upon Notch signaling. This mechanism predicts that isolated populations of well-mixed cells synchronize, revealing a stereotypical synchronization in the mouse PSM and contradicting expectations from previously applied theoretical approaches. Collectively, our theoretical and experimental findings reveal the underlying coupling mechanisms of the presomitic mesoderm cells and provide a framework to quantitatively characterize their synchronization.
Topics: Mice; Animals; Biological Clocks; Somites; Mesoderm; Models, Theoretical; Signal Transduction; Gene Expression Regulation, Developmental; Receptors, Notch
PubMed: 37098349
DOI: 10.1016/j.devcel.2023.04.002 -
Developmental Biology May 1997During vertebrate embryogenesis, the paraxial mesoderm becomes segmented into somites, which form as paired epithelial spheres with a periodicity that reflects the...
During vertebrate embryogenesis, the paraxial mesoderm becomes segmented into somites, which form as paired epithelial spheres with a periodicity that reflects the segmental organization of the embryo. As a somite matures, the ventral region gives rise to a mesenchymal cell population, the sclerotome, that forms the axial skeleton. The dorsal region of the somite remains epithelial and is called dermomyotome. The dermomyotome gives rise to the trunk and limb muscle and to the dermis of the back. Epaxial and hypaxial muscle precursors can be attributed to distinct somitic compartments which are laid down prior to overt somite differentiation. Inductive signals from the neural tube, notochord, and overlying ectoderm have been shown to be required for patterning of the somites into these different compartments. Paraxis is a basic helix-loop-helix transcription factor expressed in the unsegmented paraxial mesoderm and throughout epithelial somites before becoming restricted to epithelial cells of the dermomyotome. To determine whether paraxis might be a target for inductive signals that influence somite patterning, we examined the influence of axial structures and surface ectoderm on paraxis expression by performing microsurgical operations on chick embryos. These studies revealed two distinct phases of paraxis expression, an early phase in the paraxial mesoderm that is dependent on signals from the ectoderm and independent of the neural tube, and a later phase that is supported by redundant signals from the ectoderm and neural tube. Under experimental conditions in which paraxis failed to be expressed, cells from the paraxial mesoderm failed to epithelialize and somites were not formed. We also performed an RT-PCR analysis of combined tissue explants in vitro and confirmed that surface ectoderm is sufficient to induce paraxis expression in segmental plate mesoderm. These results demonstrate that somite formation requires signals from adjacent cell types and that the paraxis gene is a target for the signal transduction pathways that regulate somitogenesis.
Topics: Amino Acid Sequence; Animals; Base Sequence; Basic Helix-Loop-Helix Transcription Factors; Central Nervous System; Chick Embryo; Cloning, Molecular; DNA Primers; DNA-Binding Proteins; Ectoderm; Gene Expression Regulation, Developmental; Helix-Loop-Helix Motifs; In Situ Hybridization; In Vitro Techniques; Mice; Molecular Sequence Data; Notochord; Sequence Homology, Amino Acid; Signal Transduction; Somites
PubMed: 9187085
DOI: 10.1006/dbio.1997.8561 -
Developmental Cell Jan 2021Somite formation is foundational to creating the vertebrate segmental body plan. Here, we describe three transcriptional trajectories toward somite formation in the...
Somite formation is foundational to creating the vertebrate segmental body plan. Here, we describe three transcriptional trajectories toward somite formation in the early mouse embryo. Precursors of the anterior-most somites ingress through the primitive streak before E7 and migrate anteriorly by E7.5, while a second wave of more posterior somites develops in the vicinity of the streak. Finally, neuromesodermal progenitors (NMPs) are set aside for subsequent trunk somitogenesis. Single-cell profiling of T chimeric embryos shows that the anterior somites develop in the absence of T and suggests a cell-autonomous function of T as a gatekeeper between paraxial mesoderm production and the building of the NMP pool. Moreover, we identify putative regulators of early T-independent somites and challenge the T-Sox2 cross-antagonism model in early NMPs. Our study highlights the concept of molecular flexibility during early cell-type specification, with broad relevance for pluripotent stem cell differentiation and disease modeling.
Topics: Animals; Body Patterning; Cell Differentiation; Cell Line; Chimera; Embryo, Mammalian; Female; Fetal Proteins; Gene Expression Profiling; Gene Expression Regulation, Developmental; Germ Cells; Heterozygote; Male; Mesoderm; Mice; Mice, Inbred C57BL; SOXB1 Transcription Factors; Single-Cell Analysis; Somites; T-Box Domain Proteins; Transcriptome
PubMed: 33308481
DOI: 10.1016/j.devcel.2020.11.013 -
Developmental Dynamics : An Official... Jun 2007One of the most visually striking patterns in the early developing embryo is somite segmentation. Somites form as repeated, periodic structures in pairs along nearly the... (Review)
Review
One of the most visually striking patterns in the early developing embryo is somite segmentation. Somites form as repeated, periodic structures in pairs along nearly the entire caudal vertebrate axis. The morphological process involves short- and long-range signals that drive cell rearrangements and cell shaping to create discrete, epithelialized segments. Key to developing novel strategies to prevent somite birth defects that involve axial bone and skeletal muscle development is understanding how the molecular choreography is coordinated across multiple spatial scales and in a repeating temporal manner. Mathematical models have emerged as useful tools to integrate spatiotemporal data and simulate model mechanisms to provide unique insights into somite pattern formation. In this short review, we present two quantitative frameworks that address the morphogenesis from segment to somite and discuss recent data of segmentation and epithelialization.
Topics: Animals; Body Patterning; Cell Differentiation; Epithelium; Gene Expression Regulation, Developmental; Somites
PubMed: 17497694
DOI: 10.1002/dvdy.21199