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Peraldi R, Kmita M. 40 years of the homeobox: mechanisms of Hox spatial-temporal collinearity in vertebrates. Development 2024; 151:dev202508. [PMID: 39167089 DOI: 10.1242/dev.202508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/23/2024]
Abstract
Animal body plans are established during embryonic development by the Hox genes. This patterning process relies on the differential expression of Hox genes along the head-to-tail axis. Hox spatial collinearity refers to the relationship between the organization of Hox genes in clusters and the differential Hox expression, whereby the relative order of the Hox genes within a cluster mirrors the spatial sequence of expression in the developing embryo. In vertebrates, the cluster organization is also associated with the timing of Hox activation, which harmonizes Hox expression with the progressive emergence of axial tissues. Thereby, in vertebrates, Hox temporal collinearity is intimately linked to Hox spatial collinearity. Understanding the mechanisms contributing to Hox temporal and spatial collinearity is thus key to the comprehension of vertebrate patterning. Here, we provide an overview of the main discoveries pertaining to the mechanisms of Hox spatial-temporal collinearity.
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Affiliation(s)
- Rodrigue Peraldi
- Genetics and Development Research Unit, Institut de Recherches Cliniques de Montréal, Montréal, Québec H2W 1R7, Canada
- Programme de Biologie Moléculaire, Université de Montréal, Montréal, Québec H3C 3J7, Canada
| | - Marie Kmita
- Genetics and Development Research Unit, Institut de Recherches Cliniques de Montréal, Montréal, Québec H2W 1R7, Canada
- Programme de Biologie Moléculaire, Université de Montréal, Montréal, Québec H3C 3J7, Canada
- Département de Médecine, Université de Montréal, Montréal, Québec H3C 3J7, Canada
- Department of Experimental Medicine, McGill University, Montreal, Quebec H4A 3J1, Canada
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2
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May-Davis S, Eckelbarger PB, Dzingle D, Saber E. Characterization and Association of the Missing Ventral Tubercle(s) from the Sixth Cervical Vertebra and Transpositions on the Ventral Surface of the Seventh Cervical Vertebra in Modern Equus ferus caballus. Animals (Basel) 2024; 14:1830. [PMID: 38929448 PMCID: PMC11200614 DOI: 10.3390/ani14121830] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2024] [Revised: 06/11/2024] [Accepted: 06/18/2024] [Indexed: 06/28/2024] Open
Abstract
In recent years, equine complex vertebral malformation (ECVM) has been of concern in the equine community, with studies identifying numerous associative morphological variations. Here, we examine the morphological association between C6 and C7 for dependency in ECVM cases, where the partially absent ventral process of C6 transposes on the ventral surface of C7. A C6 ventral process presents two tubercles, one cranial (CrVT) and one caudal (CVT). In this study, the C6 osseous specimens (n = 85) demonstrated a partial or completely absent CVT (aCVT) graded 1-4 that often extended cranially creating a partially absent cranial ventral tubercle (aCrVT) graded 1-3. In the 85 C6 osseous specimens examined, the corresponding C7s demonstrated either a complete or incomplete transposition of the ventral process from C6 in 44/85, with 30/44 replicating a transverse foramen. A strong statistical dependency existed between C6 grade 4 aCVTs and grades 1-3 aCrVTs and C7 transpositions with replicated transverse foramen. Sidedness was also demonstrated, where a left sided absent C6 associated with transposition on the left ventral surface of C7. This likewise applied to right sidedness and most bilateral cases. These findings might benefit practitioners when radiographing the extent of the ECVM configuration in patients presenting caudal cervical pain.
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Affiliation(s)
- Sharon May-Davis
- Canine and Equine Research Group, University of New England, Armidale, NSW 2351, Australia
| | | | - Diane Dzingle
- Equus Soma—Equine Osteology and Anatomy Learning Center, Aiken, SC 29805, USA; (P.B.E.); (D.D.)
| | - Elle Saber
- Biological Data Science Institute, Australian National University, Canberra, ACT 2601, Australia;
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3
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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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4
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May-Davis S, Dzingle D, Saber E, Blades Eckelbarger P. Characterization of the Caudal Ventral Tubercle in the Sixth Cervical Vertebra in Modern Equus ferus caballus. Animals (Basel) 2023; 13:2384. [PMID: 37508161 PMCID: PMC10376820 DOI: 10.3390/ani13142384] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Revised: 07/10/2023] [Accepted: 07/20/2023] [Indexed: 07/30/2023] Open
Abstract
This study examined the anomalous variations of the ventral process of C6 in modern E. ferus caballus. The aim was to provide an incremental grading protocol measuring the absence of the caudal ventral tubercle (CVT) in this ventral process. The findings revealed the most prevalent absent CVT (aCVT) was left unilateral (n = 35), with bilateral (n = 29) and right unilateral (n = 12). Grading was determined in equal increments of absence 1/4, 2/4, 3/4, with 4/4 representing a complete aCVT in 56/76, with a significance of p = 0.0013. This also applied to bilateral specimens. In those C6 osseous specimens displaying a 4/4 grade aCVT, 41/56 had a partial absence of the caudal aspect of the cranial ventral tubercle (CrVT). Here, grading absent CrVTs (aCrVT) followed similarly to aCVTs, though 4/4 was not observed. The significance between 4/4 grade aCVTs and the presentation of an aCrVT was left p = 0.00001 and right p = 0.00018. In bilateral specimens, C6 morphologically resembled C5, implying a homeotic transformation that limited the attachment sites for the cranial and thoracal longus colli muscle. This potentially diminishes function and caudal cervical stability. Therefore, it is recommended that further studies examine the morphological extent of this equine complex vertebral malformation (ECVM) as well as its interrelationships and genetic code/blueprint.
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Affiliation(s)
- Sharon May-Davis
- Canine and Equine Research Group, University of New England, Armidale, NSW 2351, Australia
| | - Diane Dzingle
- Equus Soma-Equine Osteology and Anatomy Learning Center, Aiken, SC 29805, USA
| | - Elle Saber
- Biological Data Science Institute, Australian National University, Canberra, ACT 2601, Australia
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5
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Lv X, Xu J, Jiang J, Wu P, Tan R, Wang B. Genetic animal models of scoliosis: A systematical review. Bone 2021; 152:116075. [PMID: 34174503 DOI: 10.1016/j.bone.2021.116075] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Revised: 06/16/2021] [Accepted: 06/17/2021] [Indexed: 02/07/2023]
Abstract
Scoliosis is a complex disease with undetermined pathogenesis and has a strong relationship with genetics. Models of scoliosis in animals have been established for better comprehending its pathogenesis and treatment. In this review, we searched all the genetic animal models with body curvature in databases, and reviewed the related genes and scoliosis types. Meanwhile, we also summarized the pathogenesis of scoliosis reported so far. Summarizing the positive phenotypic animal models contributes to a better understanding on the pathogenesis of scoliosis and facilitates the selection of experimental models when a possible pathogenic factor is concerned.
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Affiliation(s)
- Xin Lv
- Department of Spine Surgery, The Second Xiangya Hospital, Central South University, Changsha 410011, Hunan, China
| | - Jinghong Xu
- Department of Spine Surgery, The Second Xiangya Hospital, Central South University, Changsha 410011, Hunan, China
| | - Jiajiong Jiang
- Department of Spine Surgery, The Second Xiangya Hospital, Central South University, Changsha 410011, Hunan, China
| | - Pengfei Wu
- Department of Spine Surgery, The Second Xiangya Hospital, Central South University, Changsha 410011, Hunan, China
| | - Renchun Tan
- Department of Spine Surgery, The Second Xiangya Hospital, Central South University, Changsha 410011, Hunan, China
| | - Bing Wang
- Department of Spine Surgery, The Second Xiangya Hospital, Central South University, Changsha 410011, Hunan, China.
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Pandey A, Harvey BM, Lopez MF, Ito A, Haltiwanger RS, Jafar-Nejad H. Glycosylation of Specific Notch EGF Repeats by O-Fut1 and Fringe Regulates Notch Signaling in Drosophila. Cell Rep 2020; 29:2054-2066.e6. [PMID: 31722217 PMCID: PMC6866671 DOI: 10.1016/j.celrep.2019.10.027] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Revised: 09/13/2019] [Accepted: 10/07/2019] [Indexed: 12/27/2022] Open
Abstract
Fringe glycosyltransferases differentially modulate the binding of Notch receptors to Delta/DLL versus Serrate/Jagged ligands by adding GlcNAc to O-linked fucose on Notch epidermal growth factor-like (EGF) repeats. Although Notch has 22 O-fucosylation sites, the biologically relevant sites affecting Notch activity during animal development in vivo in the presence or absence of Fringe are not known. Using a variety of assays, we find important roles in Drosophila Notch signaling for GlcNAc-fucose-O glycans on three sites: EGF8, EGF9, and EGF12. O-Fucose monosaccharide on EGF12 (in the absence of Fringe) is essential for Delta-mediated lateral inhibition in embryos. However, wing vein development depends on the addition of GlcNAc to EGF8 and EGF12 by Fringe, with a minor contribution from EGF9. Fringe modifications of EGF8 and EGF12 together prevent Notch from cis-inhibiting Serrate, thereby promoting normal wing margin formation. Our work shows the combinatorial and context-dependent roles of GlcNAc-fucose-O glycans on these sites in Drosophila Notch-ligand interactions. POFUT1/O-Fut1 and Fringe glycosyltransferases regulate Notch signaling by adding fucose and GlcNAc, respectively, to Notch EGF repeats. Using in vitro and in vivo experiments, Pandey et al. define the critical target sites of these enzymes on Drosophila Notch and determine the distinct roles of each sugar in Notch-dependent processes.
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Affiliation(s)
- Ashutosh Pandey
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Beth M Harvey
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794, USA
| | - Mario F Lopez
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Atsuko Ito
- Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602, USA
| | - Robert S Haltiwanger
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794, USA; Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602, USA.
| | - Hamed Jafar-Nejad
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA; Program in Developmental Biology, Baylor College of Medicine, Houston, TX 77030, USA.
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7
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Haploinsufficiency of the Notch Ligand DLL1 Causes Variable Neurodevelopmental Disorders. Am J Hum Genet 2019; 105:631-639. [PMID: 31353024 DOI: 10.1016/j.ajhg.2019.07.002] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Accepted: 07/03/2019] [Indexed: 02/07/2023] Open
Abstract
Notch signaling is an established developmental pathway for brain morphogenesis. Given that Delta-like 1 (DLL1) is a ligand for the Notch receptor and that a few individuals with developmental delay, intellectual disability, and brain malformations have microdeletions encompassing DLL1, we hypothesized that insufficiency of DLL1 causes a human neurodevelopmental disorder. We performed exome sequencing in individuals with neurodevelopmental disorders. The cohort was identified using known Matchmaker Exchange nodes such as GeneMatcher. This method identified 15 individuals from 12 unrelated families with heterozygous pathogenic DLL1 variants (nonsense, missense, splice site, and one whole gene deletion). The most common features in our cohort were intellectual disability, autism spectrum disorder, seizures, variable brain malformations, muscular hypotonia, and scoliosis. We did not identify an obvious genotype-phenotype correlation. Analysis of one splice site variant showed an in-frame insertion of 12 bp. In conclusion, heterozygous DLL1 pathogenic variants cause a variable neurodevelopmental phenotype and multi-systemic features. The clinical and molecular data support haploinsufficiency as a mechanism for the pathogenesis of this DLL1-related disorder and affirm the importance of DLL1 in human brain development.
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8
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Galis F, Metz JA, van Alphen JJ. Development and Evolutionary Constraints in Animals. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2018. [DOI: 10.1146/annurev-ecolsys-110617-062339] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We review the evolutionary importance of developmental mechanisms in constraining evolutionary changes in animals—in other words, developmental constraints. We focus on hard constraints that can act on macroevolutionary timescales. In particular, we discuss the causes and evolutionary consequences of the ancient metazoan constraint that differentiated cells cannot divide and constraints against changes of phylotypic stages in vertebrates and other higher taxa. We conclude that in all cases these constraints are caused by complex and highly controlled global interactivity of development, the disturbance of which has grave consequences. Mutations that affect such global interactivity almost unavoidably have many deleterious pleiotropic effects, which will be strongly selected against and will lead to long-term evolutionary stasis. The discussed developmental constraints have pervasive consequences for evolution and critically restrict regeneration capacity and body plan evolution.
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Affiliation(s)
- Frietson Galis
- Naturalis Biodiversity Center, 2333 CR Leiden, The Netherlands
| | - Johan A.J. Metz
- Naturalis Biodiversity Center, 2333 CR Leiden, The Netherlands
- International Institute for Applied Systems Analysis, A-2361 Laxenburg, Austria
- Mathematical Institute, University of Leiden; 2333 CA Leiden, The Netherlands
| | - Jacques J.M. van Alphen
- Naturalis Biodiversity Center, 2333 CR Leiden, The Netherlands
- Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, 1090 GE Amsterdam, The Netherlands
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9
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Tveriakhina L, Schuster-Gossler K, Jarrett SM, Andrawes MB, Rohrbach M, Blacklow SC, Gossler A. The ectodomains determine ligand function in vivo and selectivity of DLL1 and DLL4 toward NOTCH1 and NOTCH2 in vitro. eLife 2018; 7:40045. [PMID: 30289388 PMCID: PMC6202052 DOI: 10.7554/elife.40045] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2018] [Accepted: 10/01/2018] [Indexed: 12/31/2022] Open
Abstract
DLL1 and DLL4 are Notch ligands with high structural similarity but context-dependent functional differences. Here, we analyze their functional divergence using cellular co-culture assays, biochemical studies, and in vivo experiments. DLL1 and DLL4 activate NOTCH1 and NOTCH2 differently in cell-based assays and this discriminating potential lies in the region between the N-terminus and EGF repeat three. Mice expressing chimeric ligands indicate that the ectodomains dictate ligand function during somitogenesis, and that during myogenesis even regions C-terminal to EGF3 are interchangeable. Substitution of NOTCH1-interface residues in the MNNL and DSL domains of DLL1 with the corresponding amino acids of DLL4, however, does not disrupt DLL1 function in vivo. Collectively, our data show that DLL4 preferentially activates NOTCH1 over NOTCH2, whereas DLL1 is equally effective in activating NOTCH1 and NOTCH2, establishing that the ectodomains dictate selective ligand function in vivo, and that features outside the known binding interface contribute to their differences. A small number of signaling systems control how an animal develops from a single cell into a complex organism made up of many different cell types. Signals pass back and forth between cells, switching genes on and off to direct the development of tissues and organs. One of these signaling systems, called Notch, is so ancient that it appears in nearly all multicellular organisms. A cell sends a Notch signal using proteins called Delta or Jagged ligands that span membrane of the cell, so that part of the protein sits inside the cell and part remains outside. To change the behavior of another cell, the ligands bind to proteins called Notch receptors that span the membrane of the receiving cell. Mammals have two types of Delta ligand, two types of Jagged ligand and four types of Notch receptor. Cells in different tissues display different combinations of these eight proteins. Two Delta ligands called DLL1 and DLL4 often appear together in developing organisms. Some tissues need both and some only the one or the other. In some cases one ligand can compensate if the other is missing, but in others not. It was not clear why this is, or which parts of the proteins are responsible. Tveriakhina et al. used mouse cells to investigate how DLL1 and DLL4 interact with two Notch receptors, called NOTCH1 and NOTCH2. The results of these experiments show that while DLL1 can bind and activate both Notch receptors equally, DLL4 prefers to partner with NOTCH1. To find out which parts of the ligands are responsible for this selectivity, Tveriakhina et al. created hybrid ligands that contained a mixture of regions from DLL1 and DLL4. These suggest that the different binding preferences depend on parts of the ligands that sit outside cells and that lie outside the known sites of binding contact with the Notch receptors. Further experiments studied mice that had been engineered to produce hybrid ligands as replacements for DLL1. A hybrid ligand consisting of the part of DLL1 that sits outside cells and the part of DLL4 found inside cells generated Notch signals in the tissue that depended on the activity of DLL1. However, a hybrid consisting of the part of DLL4 that sits outside cells and the part of DLL1 found inside cells did not, showing that in developing mice the parts that sit outside the cells contribute to the different functions of DLL1 and DLL4. Overall, the results presented by Tveriakhina et al. show that interactions between specific ligands and receptors play important roles in how mammals develop. Further efforts to understand which parts of the ligands affect selectivity could ultimately allow researchers to develop ways to modify how ligands and receptors interact. Such “molecular engineering” strategies could enable cell responses to be precisely controlled by pairing designer ligand-receptor pairs to develop cell-based therapies.
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Affiliation(s)
- Lena Tveriakhina
- Institute for Molecular Biology, Medizinische Hochschule Hannover, Hannover, Germany
| | | | - Sanchez M Jarrett
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts
| | - Marie B Andrawes
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts
| | - Meike Rohrbach
- Institute for Molecular Biology, Medizinische Hochschule Hannover, Hannover, Germany
| | - Stephen C Blacklow
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts.,Department of Cancer Biology, Dana Farber Cancer Institute, Boston, Massachusetts
| | - Achim Gossler
- Institute for Molecular Biology, Medizinische Hochschule Hannover, Hannover, Germany
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10
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Ten Broek CMA, Bots J, Bugiani M, Galis F, Van Dongen S. No relationship between vertebral column shifts and limb fluctuating asymmetry in human foetuses. PeerJ 2017. [PMID: 28626605 PMCID: PMC5470575 DOI: 10.7717/peerj.3359] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Disturbance from the normal developmental trajectory of a trait during growth—the so-called developmental instability—can be observed morphologically through phenodeviants and subtle deviations from perfect symmetry (fluctuating asymmetry). This study investigates the relationship between phenodeviance in the human vertebral column (as a result of axial patterning defects) and limb fluctuating asymmetry. Since both types of markers of developmental instability have been found associated with congenital abnormalities in humans, we anticipate a relationship between them if the concept of developmental instability, measured through either phenodeviants or asymmetry, would reflect an organism-wide process. Yet we did not find any support for this hypothesis. We argue that the vast differences in the developmental processes involved in both systems renders these two markers of developmental instability unrelated, in spite of their associations with other congenital abnormalities. Our results thus contribute to the growing awareness that developmental instability is not an organism-wide property.
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Affiliation(s)
- Clara M A Ten Broek
- Naturalis Biodiversity Center, Leiden, Netherlands.,Evolutionary Ecology Group, Department of Biology, Universiteit Antwerpen, Wilrijk, Antwerp, Belgium
| | - Jessica Bots
- Evolutionary Ecology Group, Department of Biology, Universiteit Antwerpen, Wilrijk, Antwerp, Belgium
| | - Marianna Bugiani
- Department of Pathology, VU Medical Center, Amsterdam, Netherlands
| | | | - Stefan Van Dongen
- Evolutionary Ecology Group, Department of Biology, Universiteit Antwerpen, Wilrijk, Antwerp, Belgium
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11
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Warrier S, Nuwayhid S, Sabatino JA, Sugrue KF, Zohn IE. Supt20 is required for development of the axial skeleton. Dev Biol 2016; 421:245-257. [PMID: 27894818 DOI: 10.1016/j.ydbio.2016.11.009] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Revised: 09/08/2016] [Accepted: 11/11/2016] [Indexed: 10/20/2022]
Abstract
Somitogenesis and subsequent axial skeletal development is regulated by the interaction of pathways that determine the periodicity of somite formation, rostrocaudal somite polarity and segment identity. Here we use a hypomorphic mutant mouse line to demonstrate that Supt20 (Suppressor of Ty20) is required for development of the axial skeleton. Supt20 hypomorphs display fusions of the ribs and vertebrae at lower thoracic levels along with anterior homeotic transformation of L1 to T14. These defects are preceded by reduction of the rostral somite and posterior shifts in Hox gene expression. While cycling of Notch target genes in the posterior presomitic mesoderm (PSM) appeared normal, expression of Lfng was reduced. In the anterior PSM, Mesp2 expression levels and cycling were unaffected; yet, expression of downstream targets such as Lfng, Ripply2, Mesp1 and Dll3 in the prospective rostral somite was reduced accompanied by expansion of caudal somite markers such as EphrinB2 and Hes7. Supt20 interacts with the Gcn5-containing SAGA histone acetylation complex. Gcn5 hypomorphic mutant embryos show similar defects in axial skeletal development preceded by posterior shift of Hoxc8 and Hoxc9 gene expression. We demonstrate that Gcn5 and Supt20 hypomorphs show similar defects in rostral-caudal somite patterning potentially suggesting shared mechanisms.
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Affiliation(s)
- Sunita Warrier
- Center for Neuroscience Research, Children's Research Institute, Children's National Medical Center, Washington, DC 20010, USA
| | - Samer Nuwayhid
- Center for Neuroscience Research, Children's Research Institute, Children's National Medical Center, Washington, DC 20010, USA
| | - Julia A Sabatino
- Center for Neuroscience Research, Children's Research Institute, Children's National Medical Center, Washington, DC 20010, USA
| | - Kelsey F Sugrue
- Center for Neuroscience Research, Children's Research Institute, Children's National Medical Center, Washington, DC 20010, USA; Institute for Biomedical Sciences, The George Washington University, Washington, DC 20052, USA
| | - Irene E Zohn
- Center for Neuroscience Research, Children's Research Institute, Children's National Medical Center, Washington, DC 20010, USA.
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12
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Context-Dependent Sensitivity to Mutations Disrupting the Structural Integrity of Individual EGF Repeats in the Mouse Notch Ligand DLL1. Genetics 2016; 202:1119-33. [PMID: 26801181 DOI: 10.1534/genetics.115.184515] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Accepted: 01/16/2016] [Indexed: 01/05/2023] Open
Abstract
The highly conserved Notch-signaling pathway mediates cell-to-cell communication and is pivotal for multiple developmental processes and tissue homeostasis in adult organisms. Notch receptors and their ligands are transmembrane proteins with multiple epidermal-growth-factor-like (EGF) repeats in their extracellular domains. In vitro the EGF repeats of mammalian ligands that are essential for Notch activation have been defined. However, in vivo the significance of the structural integrity of each EGF repeat in the ligand ectodomain for ligand function is still unclear. Here, we analyzed the mouse Notch ligand DLL1. We expressed DLL1 proteins with mutations disrupting disulfide bridges in each individual EGF repeat from single-copy transgenes in the HPRT locus of embryonic stem cells. In Notch transactivation assays all mutations impinged on DLL1 function and affected both NOTCH1 and NOTCH2 receptors similarly. An allelic series in mice that carried the same point mutations in endogenous Dll1, generated using a mini-gene strategy, showed that early developmental processes depending on DLL1-mediated NOTCH activation were differently sensitive to mutation of individual EGF repeats in DLL1. Notably, some mutations affected only somite patterning and resulted in vertebral column defects resembling spondylocostal dysostosis. In conclusion, the structural integrity of each individual EGF repeat in the extracellular domain of DLL1 is necessary for full DLL1 activity, and certain mutations in Dll1 might contribute to spondylocostal dysostosis in humans.
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13
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Gouveia A, Marcelino HM, Gonçalves L, Palmeirim I, Andrade RP. Patterning in time and space: HoxB cluster gene expression in the developing chick embryo. Cell Cycle 2015; 14:135-45. [PMID: 25602523 DOI: 10.4161/15384101.2014.972868] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The developing embryo is a paradigmatic model to study molecular mechanisms of time control in Biology. Hox genes are key players in the specification of tissue identity during embryo development and their expression is under strict temporal regulation. However, the molecular mechanisms underlying timely Hox activation in the early embryo remain unknown. This is hindered by the lack of a rigorous temporal framework of sequential Hox expression within a single cluster. Herein, a thorough characterization of HoxB cluster gene expression was performed over time and space in the early chick embryo. Clear temporal collinearity of HoxB cluster gene expression activation was observed. Spatial collinearity of HoxB expression was evidenced in different stages of development and in multiple tissues. Using embryo explant cultures we showed that HoxB2 is cyclically expressed in the rostral presomitic mesoderm with the same periodicity as somite formation, suggesting a link between timely tissue specification and somite formation. We foresee that the molecular framework herein provided will facilitate experimental approaches aimed at identifying the regulatory mechanisms underlying Hox expression in Time and Space.
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Affiliation(s)
- Analuce Gouveia
- a Life and Health Sciences Research Institute (ICVS); School of Health Sciences , University of Minho ; Braga , Portugal
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14
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Fournier M, Lebert-Ghali CÉ, Bijl JJ. HOXA4 provides stronger engraftment potential to short-term repopulating cells than HOXB4. Stem Cells Dev 2015; 24:2413-22. [PMID: 26166023 DOI: 10.1089/scd.2015.0063] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Genes of the HOX4 paralog group have been shown to expand hematopoietic stem cells (HSCs). Endogenous expression of HOXA4 is 10-fold higher than HOXB4 in embryonic primitive hematopoietic cells undergoing self-renewal suggesting a more potent capacity of HOXA4 to expand HSC. In this study, we provide evidence by direct competitive bone marrow cultures that HOXA4 and HOXB4 induce self-renewal of primitive hematopoietic cells with identical kinetics. Transplantation assays show that short-term repopulation by HOXA4-overexpressing multilineage progenitors was significantly greater than HOXB4-overexpressing progenitors in vivo, indicating differences in the sensitivity of the cells to external signals. Small array gene expression analysis showed an increase in multiple Notch and Wnt signaling -associated genes, including receptors and ligands, as well as pluripotency genes, for both HOXA4- and HOXB4-overexpressing cells, which was more pronounced for HOXA4, suggesting that both HOX proteins may assert their affects through intrinsic and extrinsic pathways to induce self-renewal of primitive hematopoietic cells. Thus, HOXA4 increases short-term repopulation to higher levels than HOXB4, which may involve Notch signaling.
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Affiliation(s)
- Marilaine Fournier
- 1 Centre de Recherche de l'Hôpital Maisonneuve-Rosemont , Montréal, Québec, Canada .,2 Départment de Microbiologie et Immunologie et, Université de Montréal , Montréal, Québec, Canada
| | - Charles-Étienne Lebert-Ghali
- 1 Centre de Recherche de l'Hôpital Maisonneuve-Rosemont , Montréal, Québec, Canada .,2 Départment de Microbiologie et Immunologie et, Université de Montréal , Montréal, Québec, Canada
| | - Janetta J Bijl
- 1 Centre de Recherche de l'Hôpital Maisonneuve-Rosemont , Montréal, Québec, Canada .,3 Départment de Médecine, Université de Montréal , Montréal, Québec, Canada
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15
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Preuße K, Tveriakhina L, Schuster-Gossler K, Gaspar C, Rosa AI, Henrique D, Gossler A, Stauber M. Context-Dependent Functional Divergence of the Notch Ligands DLL1 and DLL4 In Vivo. PLoS Genet 2015; 11:e1005328. [PMID: 26114479 PMCID: PMC4482573 DOI: 10.1371/journal.pgen.1005328] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Accepted: 06/01/2015] [Indexed: 11/18/2022] Open
Abstract
Notch signalling is a fundamental pathway that shapes the developing embryo and sustains adult tissues by direct communication between ligand and receptor molecules on adjacent cells. Among the ligands are two Delta paralogues, DLL1 and DLL4, that are conserved in mammals and share a similar structure and sequence. They activate the Notch receptor partly in overlapping expression domains where they fulfil redundant functions in some processes (e.g. maintenance of the crypt cell progenitor pool). In other processes, however, they appear to act differently (e.g. maintenance of foetal arterial identity) raising the questions of how similar DLL1 and DLL4 really are and which mechanism causes the apparent context-dependent divergence. By analysing mice that conditionally overexpress DLL1 or DLL4 from the same genomic locus (Hprt) and mice that express DLL4 instead of DLL1 from the endogenous Dll1 locus (Dll1Dll4ki), we found functional differences that are tissue-specific: while DLL1 and DLL4 act redundantly during the maintenance of retinal progenitors, their function varies in the presomitic mesoderm (PSM) where somites form in a Notch-dependent process. In the anterior PSM, every cell expresses both Notch receptors and ligands, and DLL1 is the only activator of Notch while DLL4 is not endogenously expressed. Transgenic DLL4 cannot replace DLL1 during somitogenesis and in heterozygous Dll1Dll4ki/+ mice, the Dll1Dll4ki allele causes a dominant segmentation phenotype. Testing several aspects of the complex Notch signalling system in vitro, we found that both ligands have a similar trans-activation potential but that only DLL4 is an efficient cis-inhibitor of Notch signalling, causing a reduced net activation of Notch. These differential cis-inhibitory properties are likely to contribute to the functional divergence of DLL1 and DLL4.
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Affiliation(s)
- Kristina Preuße
- Institut für Molekularbiologie OE5250, Medizinische Hochschule Hannover, Hannover, Germany
| | - Lena Tveriakhina
- Institut für Molekularbiologie OE5250, Medizinische Hochschule Hannover, Hannover, Germany
| | - Karin Schuster-Gossler
- Institut für Molekularbiologie OE5250, Medizinische Hochschule Hannover, Hannover, Germany
| | - Cláudia Gaspar
- Instituto de Medicina Molecular, Faculdade de Medicina da Universidade de Lisboa, Lisboa, Portugal
| | - Alexandra Isabel Rosa
- Instituto de Medicina Molecular, Faculdade de Medicina da Universidade de Lisboa, Lisboa, Portugal
| | - Domingos Henrique
- Instituto de Medicina Molecular, Faculdade de Medicina da Universidade de Lisboa, Lisboa, Portugal
| | - Achim Gossler
- Institut für Molekularbiologie OE5250, Medizinische Hochschule Hannover, Hannover, Germany
| | - Michael Stauber
- Institut für Molekularbiologie OE5250, Medizinische Hochschule Hannover, Hannover, Germany
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16
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Arya R, Sarkissian T, Tan Y, White K. Neural stem cell progeny regulate stem cell death in a Notch and Hox dependent manner. Cell Death Differ 2015; 22:1378-87. [PMID: 25633198 DOI: 10.1038/cdd.2014.235] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Revised: 12/02/2014] [Accepted: 12/12/2014] [Indexed: 01/05/2023] Open
Abstract
Cell death is a prevalent, well-controlled and fundamental aspect of development, particularly in the nervous system. In Drosophila, specific neural stem cells are eliminated by apoptosis during embryogenesis. In the absence of apoptosis, these stem cells continue to divide, resulting in a dramatically hyperplastic central nervous system and adult lethality. Although core cell death pathways have been well described, the spatial, temporal and cell identity cues that activate the cell death machinery in specific cells are largely unknown. We identified a cis-regulatory region that controls the transcription of the cell death activators reaper, grim and sickle exclusively in neural stem cells. Using a reporter generated from this regulatory region, we found that Notch activity is required for neural stem cell death. Notch regulates the expression of the abdominalA homeobox protein, which provides important spatial cues for death. Importantly, we show that pro-apoptotic Notch signaling is activated by the Delta ligand expressed on the neighboring progeny of the stem cell. Thus we identify a previously undescribed role for progeny in regulating the proper developmental death of their parental stem cells.
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Affiliation(s)
- R Arya
- CBRC, Massachusetts General Hospital/Harvard Medical School, Boston, MA 02129, USA
| | - T Sarkissian
- CBRC, Massachusetts General Hospital/Harvard Medical School, Boston, MA 02129, USA
| | - Y Tan
- CBRC, Massachusetts General Hospital/Harvard Medical School, Boston, MA 02129, USA
| | - K White
- CBRC, Massachusetts General Hospital/Harvard Medical School, Boston, MA 02129, USA
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17
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Hox gene regulation and timing in embryogenesis. Semin Cell Dev Biol 2014; 34:76-84. [PMID: 24930771 DOI: 10.1016/j.semcdb.2014.06.005] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2014] [Revised: 05/15/2014] [Accepted: 06/05/2014] [Indexed: 11/22/2022]
Abstract
Hox genes are critical regulators of embryonic development in bilaterian animals. They exhibit a unique mode of transcriptional regulation where the position of the genes along the chromosome corresponds to the time and place of their expression during development. The sequential temporal activation of these genes in the primitive streak helps determining their subsequent pattern of expression along the anterior-posterior axis of the embryo, yet the precise correspondence between these two collinear processes is not fully understood. In addition, vertebrate Hox genes evolved similar modes of regulation along secondary body axes, such as the developing limbs. We review the current understanding of the mechanisms operating during activation, maintenance and silencing of Hox gene expression in these various contexts, and discuss the evolutionary significance of their genomic organization.
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18
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Williams DR, Shifley ET, Lather JD, Cole SE. Posterior skeletal development and the segmentation clock period are sensitive to Lfng dosage during somitogenesis. Dev Biol 2014; 388:159-69. [PMID: 24560643 DOI: 10.1016/j.ydbio.2014.02.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2013] [Revised: 01/08/2014] [Accepted: 02/10/2014] [Indexed: 01/25/2023]
Abstract
The segmental structure of the axial skeleton is formed during somitogenesis. During this process, paired somites bud from the presomitic mesoderm (PSM), in a process regulated by a genetic clock called the segmentation clock. The Notch pathway and the Notch modulator Lunatic fringe (Lfng) play multiple roles during segmentation. Lfng oscillates in the posterior PSM as part of the segmentation clock, but is stably expressed in the anterior PSM during presomite patterning. We previously found that mice lacking overt oscillatory Lfng expression in the posterior PSM (Lfng(∆FCE)) exhibit abnormal anterior development but relatively normal posterior development. This suggests distinct requirements for segmentation clock activity during the formation of the anterior skeleton (primary body formation), compared to the posterior skeleton and tail (secondary body formation). To build on these findings, we created an allelic series that progressively lowers Lfng levels in the PSM. Interestingly, we find that further reduction of Lfng expression levels in the PSM does not increase disruption of anterior development. However tail development is increasingly compromised as Lfng levels are reduced, suggesting that primary body formation is more sensitive to Lfng dosage than is secondary body formation. Further, we find that while low levels of oscillatory Lfng in the posterior PSM are sufficient to support relatively normal posterior development, the period of the segmentation clock is increased when the amplitude of Lfng oscillations is low. These data support the hypothesis that there are differential requirements for oscillatory Lfng during primary and secondary body formation and that posterior development is less sensitive to overall Lfng levels. Further, they suggest that modulation of the Notch signaling by Lfng affects the clock period during development.
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Affiliation(s)
- Dustin R Williams
- The Department of Molecular Genetics, The Ohio State University, 105 Biological Sciences Building, 484 West 12th Avenue, Columbus, OH 43210, USA
| | - Emily T Shifley
- The Department of Molecular Genetics, The Ohio State University, 105 Biological Sciences Building, 484 West 12th Avenue, Columbus, OH 43210, USA
| | - Jason D Lather
- The Department of Molecular Genetics, The Ohio State University, 105 Biological Sciences Building, 484 West 12th Avenue, Columbus, OH 43210, USA
| | - Susan E Cole
- The Department of Molecular Genetics, The Ohio State University, 105 Biological Sciences Building, 484 West 12th Avenue, Columbus, OH 43210, USA.
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19
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Franzosa JA, Bugel SM, Tal TL, La Du JK, Tilton SC, Waters KM, Tanguay RL. Retinoic acid-dependent regulation of miR-19 expression elicits vertebrate axis defects. FASEB J 2013; 27:4866-76. [PMID: 23975936 DOI: 10.1096/fj.12-225524] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Retinoic acid (RA) is involved in multifarious and complex functions necessary for vertebrate development. RA signaling is reliant on strict enzymatic regulation of RA synthesis and metabolism. Improper spatiotemporal expression of RA during development can result in vertebrate axis defects. microRNAs (miRNAs) are also pivotal in orchestrating developmental processes. While mechanistic links between miRNAs and axial development are established, the role of miRNAs in regulating metabolic enzymes responsible for RA abundance during axis formation has yet to be elucidated. Our results uncovered a role of miR-19 family members in controlling RA metabolism through the regulation of CYP26A1 during vertebrate axis formation. Global miRNA expression profiling showed that developmental RA exposure suppressed the expression of miR-19 family members during zebrafish somitogenesis. A reporter assay confirmed that cyp26a1 is a bona fide target of miR-19 in vivo. Transient knockdown of miR-19 phenocopied axis defects caused by RA exposure. Exogenous miR-19 rescued the axis defects induced by RA exposure. Taken together, these results indicate that the teratogenic effects of RA exposure result, in part, from repression of miR-19 expression and subsequent misregulation of cyp26a1. This highlights a previously unidentified role of miR-19 in facilitating vertebrate axis development via regulation of RA signaling.
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Affiliation(s)
- Jill A Franzosa
- 3Department of Environmental and Molecular Toxicology, Oregon State University, 28645 East HWY 34. Corvallis, OR 97333, USA.
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20
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Ten Tusscher KHWJ. Mechanisms and constraints shaping the evolution of body plan segmentation. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2013; 36:54. [PMID: 23708840 DOI: 10.1140/epje/i2013-13054-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2012] [Accepted: 05/07/2013] [Indexed: 06/02/2023]
Abstract
Segmentation of the major body axis into repeating units is arguably one of the major inventions in the evolution of animal body plan pattering. It is found in current day vertebrates, annelids and arthropods. Most segmented animals seem to use a clock-and-wavefront type mechanism in which oscillations emanating from a posterior growth zone become transformed into an anterior posterior sequence of segments. In contrast, few animals such as Drosophila use a complex gene regulatory hierarchy to simultaneously subdivide their entire body axis into segments. Here I discuss how in silico models simulating the evolution of developmental patterning can be used to investigate the forces and constraints that helped shape these two developmental modes. I perform an analysis of a series of previous simulation studies, exploiting the similarities and differences in their outcomes in relation to model characteristics to elucidate the circumstances and constraints likely to have been important for the evolution of sequential and simultaneous segmentation modes. The analysis suggests that constraints arising from the involved growth process and spatial patterning signal--posterior elongation producing a propagating wavefront versus a tissue wide morphogen gradient--and the evolutionary history--ancestral versus derived segmentation mode--strongly shaped both segmentation mechanisms. Furthermore, this implies that these patterning types are to be expected rather than random evolutionary outcomes and supports the likelihood of multiple parallel evolutionary origins.
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Affiliation(s)
- K H W J Ten Tusscher
- Theoretical Biology and Bioinformactics Group, Utrecht University, Padualaan 8, 3584, CH Utrecht, The Netherlands.
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21
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Makino Y, Takahashi Y, Tanabe R, Tamamura Y, Watanabe T, Haraikawa M, Hamagaki M, Hata K, Kanno J, Yoneda T, Saga Y, Goseki-Sone M, Kaneko K, Yamaguchi A, Iimura T. Spatiotemporal disorder in the axial skeleton development of the Mesp2-null mouse: a model of spondylocostal dysostosis and spondylothoracic dysostosis. Bone 2013; 53:248-58. [PMID: 23238123 DOI: 10.1016/j.bone.2012.11.033] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Revised: 11/01/2012] [Accepted: 11/19/2012] [Indexed: 12/18/2022]
Abstract
Spondylocostal dysostosis (SCDO) is a genetic disorder characterized by severe malformation of the axial skeleton. Mesp2 encodes a basic helix-loop-helix type transcription factor that is required for somite formation. Its human homologue, Mesp2, is a gene affected in patients with SCDO and a related vertebral disorder, spondylothoracic dysostosis (STDO). This work investigated how the loss of Mesp2 affects axial skeleton development and causes the clinical features of SCDO and STDO. We first confirmed, by three-dimensional computed tomography scanning, that Mesp2-null mice exhibited mineralized tissue patterning resembling the radiological features of SCDO and STDO. Histological observations and in situ hybridization probing for extracellular matrix molecules demonstrated that the developing vertebral bodies in Mesp2-null mice were extensively fused with rare insertions of intervertebral tissue. Unexpectedly, the intervertebral tissues were mostly fused longitudinally in the vertebral column, instead of exhibiting extended formation, as was expected based on the caudalized properties of Mesp2-null somite derivatives. Furthermore, the differentiation of vertebral body chondrocytes in Mesp2-null mice was spatially disordered and largely delayed, with an increased cell proliferation rate. The quantitative three-dimensional immunofluorescence image analyses of phospho-Smad2 and -Smad1/5/8 revealed that these chondrogenic phenotypes were associated with spatially disordered inputs of TGF-β and BMP signaling in the Mesp2-null chondrocytes, and also demonstrated an amorphous arrangement of cells with distinct properties. Furthermore, a significant delay in ossification in Mesp2-null vertebrae was observed by peripheral quantitative computed tomography. The current observations of the spatiotemporal disorder of vertebral organogenesis in the Mesp2-null mice provide further insight into the pathogenesis of SCDO and STDO, and the physiological development of the axial skeleton.
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Affiliation(s)
- Yuji Makino
- Section of Oral Pathology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Japan
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22
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Williams T, Blachuta B, Hegna TA, Nagy LM. Decoupling elongation and segmentation: notch involvement in anostracan crustacean segmentation. Evol Dev 2012; 14:372-82. [PMID: 22765208 DOI: 10.1111/j.1525-142x.2012.00555.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Repeated body segments are a key feature of arthropods. The formation of body segments occurs via distinct developmental pathways within different arthropod clades. Although some species form their segments simultaneously without any accompanying measurable growth, most arthropods add segments sequentially from the posterior of the growing embryo or larva. The use of Notch signaling is increasingly emerging as a common feature of sequential segmentation throughout the Bilateria, as inferred from both the expression of proteins required for Notch signaling and the genetic or pharmacological disruption of Notch signaling. In this study, we demonstrate that blocking Notch signaling by blocking γ-secretase activity causes a specific, repeatable effect on segmentation in two different anostracan crustaceans, Artemia franciscana and Thamnocephalus platyurus. We observe that segmentation posterior to the third or fourth trunk segment is arrested. Despite this marked effect on segment addition, other aspects of segmentation are unaffected. In the segments that develop, segment size and boundaries between segments appear normal, engrailed stripes are normal in size and alignment, and overall growth is unaffected. By demonstrating Notch involvement in crustacean segmentation, our findings expand the evidence that Notch plays a crucial role in sequential segmentation in arthropods. At the same time, our observations contribute to an emerging picture that loss-of-function Notch phenotypes differ significantly between arthropods suggesting variability in the role of Notch in the regulation of sequential segmentation. This variability in the function of Notch in arthropod segmentation confounds inferences of homology with vertebrates and lophotrochozoans.
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Affiliation(s)
- Terri Williams
- Department of Biology, Trinity College, Hartford, CT 06106, USA.
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23
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Ten Broek CMA, Bakker AJ, Varela-Lasheras I, Bugiani M, Van Dongen S, Galis F. Evo-Devo of the Human Vertebral Column: On Homeotic Transformations, Pathologies and Prenatal Selection. Evol Biol 2012; 39:456-471. [PMID: 23226903 PMCID: PMC3514701 DOI: 10.1007/s11692-012-9196-1] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2012] [Accepted: 07/11/2012] [Indexed: 12/21/2022]
Abstract
Homeotic transformations of vertebrae are particularly common in humans and tend to come associated with malformations in a wide variety of organ systems. In a dataset of 1,389 deceased human foetuses and infants a majority had cervical ribs and approximately half of these individuals also had missing twelfth ribs or lumbar ribs. In ~10 % of all cases there was an additional shift of the lumbo-sacral boundary and, hence, homeotic transformations resulted in shifts of at least three vertebral boundaries. We found a strong coupling between the abnormality of the vertebral patterns and the amount and strength of associated malformations, i.e., the longer the disturbance of the vertebral patterning has lasted, the more associated malformations have developed and the more organ systems are affected. The germ layer of origin of the malformations was not significantly associated with the frequency of vertebral patterns. In contrast, we find significant associations with the different developmental mechanisms that are involved in the causation of the malformations, that is, segmentation, neural crest development, left-right patterning, etc. Our results, thus, suggest that locally perceived developmental signals are more important for the developmental outcome than the origin of the cells. The low robustness of vertebral A-P patterning apparent from the large number of homeotic transformations is probably caused by the strong interactivity of developmental processes and the low redundancy of involved morphogens during early organogenesis. Additionally, the early irreversibility of the specification of the A-P identity of vertebrae probably adds to the vulnerability of the process by limiting the possibility for recovery from developmental disturbances. The low developmental robustness of vertebral A-P patterning contrasts with a high robustness of the A-P patterning of the vertebral regions. Not only the order is invariable, also the variation in the number of vertebrae per region is small. This robustness is in agreement with the evolutionary stability of vertebral regions in tetrapods. Finally, we propose a new hypothesis regarding the constancy of the presacral number of vertebrae in mammals.
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Affiliation(s)
- Clara M A Ten Broek
- Group of Evolutionary Ecology, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium ; Naturalis Biodiversity Center, Darwinweg 2, 2333 CR Leiden, The Netherlands
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24
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Sparrow DB, Chapman G, Smith AJ, Mattar MZ, Major JA, O'Reilly VC, Saga Y, Zackai EH, Dormans JP, Alman BA, McGregor L, Kageyama R, Kusumi K, Dunwoodie SL. A mechanism for gene-environment interaction in the etiology of congenital scoliosis. Cell 2012; 149:295-306. [PMID: 22484060 DOI: 10.1016/j.cell.2012.02.054] [Citation(s) in RCA: 154] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2011] [Revised: 12/15/2011] [Accepted: 02/15/2012] [Indexed: 12/16/2022]
Abstract
Congenital scoliosis, a lateral curvature of the spine caused by vertebral defects, occurs in approximately 1 in 1,000 live births. Here we demonstrate that haploinsufficiency of Notch signaling pathway genes in humans can cause this congenital abnormality. We also show that in a mouse model, the combination of this genetic risk factor with an environmental condition (short-term gestational hypoxia) significantly increases the penetrance and severity of vertebral defects. We demonstrate that hypoxia disrupts FGF signaling, leading to a temporary failure of embryonic somitogenesis. Our results potentially provide a mechanism for the genesis of a host of common sporadic congenital abnormalities through gene-environment interaction.
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Affiliation(s)
- Duncan B Sparrow
- Developmental and Stem Cell Biology Division, Victor Chang Cardiac Research Institute, Sydney, NSW 2010, Australia.
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25
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Fisher RE, Smith HF, Kusumi K, Tassone EE, Rawls A, Wilson-Rawls J. Mutations in the Notch pathway alter the patterning of multifidus. Anat Rec (Hoboken) 2011; 295:32-9. [PMID: 22095884 DOI: 10.1002/ar.21488] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2011] [Accepted: 08/09/2011] [Indexed: 01/06/2023]
Abstract
Clinical studies have suggested that defects in the epaxial muscles, particularly multifidus, may contribute to the etiology of idiopathic scoliosis. While the epaxial muscles and the vertebrae derive from the same embryonic segmentation process, the mechanisms that pattern the multisegmental back muscles are still unclear. The process of segmentation is regulated by the Notch signaling pathway, and mutations in the modulators delta-like 3 (Dll3) and lunatic fringe (Lfng) are genetic models for spinal disorders such as scoliosis. Osteological defects have been characterized in these genetic models, but myological phenotypes have not previously been studied. We analyzed the multifidus muscle in the mouse (Mus musculus) and observed intriguing changes in the cranio-caudal borders of multifidus in Dll3 and Lfng models. Statistical analysis did not find a significant association between the majority of the multifidus anomalies and the vertebral defects, suggesting a previously unappreciated role for Notch signaling in patterning epaxial muscle groups. These findings indicate an additional mechanism by which DLL3 and LFNG may play a role in the etiology of human idiopathic scoliosis.
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Affiliation(s)
- Rebecca E Fisher
- Department of Basic Medical Sciences, The University of Arizona College of Medicine-Phoenix, USA.
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26
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Ten Tusscher KH, Hogeweg P. Evolution of networks for body plan patterning; interplay of modularity, robustness and evolvability. PLoS Comput Biol 2011; 7:e1002208. [PMID: 21998573 PMCID: PMC3188509 DOI: 10.1371/journal.pcbi.1002208] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2010] [Accepted: 08/08/2011] [Indexed: 11/30/2022] Open
Abstract
A major goal of evolutionary developmental biology (evo-devo) is to understand how multicellular body plans of increasing complexity have evolved, and how the corresponding developmental programs are genetically encoded. It has been repeatedly argued that key to the evolution of increased body plan complexity is the modularity of the underlying developmental gene regulatory networks (GRNs). This modularity is considered essential for network robustness and evolvability. In our opinion, these ideas, appealing as they may sound, have not been sufficiently tested. Here we use computer simulations to study the evolution of GRNs' underlying body plan patterning. We select for body plan segmentation and differentiation, as these are considered to be major innovations in metazoan evolution. To allow modular networks to evolve, we independently select for segmentation and differentiation. We study both the occurrence and relation of robustness, evolvability and modularity of evolved networks. Interestingly, we observed two distinct evolutionary strategies to evolve a segmented, differentiated body plan. In the first strategy, first segments and then differentiation domains evolve (SF strategy). In the second scenario segments and domains evolve simultaneously (SS strategy). We demonstrate that under indirect selection for robustness the SF strategy becomes dominant. In addition, as a byproduct of this larger robustness, the SF strategy is also more evolvable. Finally, using a combined functional and architectural approach, we determine network modularity. We find that while SS networks generate segments and domains in an integrated manner, SF networks use largely independent modules to produce segments and domains. Surprisingly, we find that widely used, purely architectural methods for determining network modularity completely fail to establish this higher modularity of SF networks. Finally, we observe that, as a free side effect of evolving segmentation and differentiation in combination, we obtained in-silico developmental mechanisms resembling mechanisms used in vertebrate development.
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Affiliation(s)
- Kirsten H Ten Tusscher
- Theoretical Biology and Bioinformatics Group, Department of Biology, Utrecht University, Utrecht, The Netherlands.
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27
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del Álamo D, Rouault H, Schweisguth F. Mechanism and significance of cis-inhibition in Notch signalling. Curr Biol 2011; 21:R40-7. [PMID: 21215938 DOI: 10.1016/j.cub.2010.10.034] [Citation(s) in RCA: 194] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Notch receptors in a given cell are activated by cell surface ligands in neighbouring cells but can also be inhibited by the ligands present within the same cell. This process is known as cis-inhibition of Notch. Additionally, reciprocal cis-inhibition of the ligands by Notch has also been observed, albeit to a limited extent. Here, we review the mechanisms, functional relevance and potential implications of these cis-inhibitory interactions for Notch-mediated fate decisions.
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Affiliation(s)
- David del Álamo
- Institut Pasteur, Dépt. Biologie du Développement, F-75015 Paris, France
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28
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Breaking evolutionary and pleiotropic constraints in mammals: On sloths, manatees and homeotic mutations. EvoDevo 2011; 2:11. [PMID: 21548920 PMCID: PMC3120709 DOI: 10.1186/2041-9139-2-11] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2010] [Accepted: 05/06/2011] [Indexed: 01/25/2023] Open
Abstract
Background Mammals as a rule have seven cervical vertebrae, except for sloths and manatees. Bateson proposed that the change in the number of cervical vertebrae in sloths is due to homeotic transformations. A recent hypothesis proposes that the number of cervical vertebrae in sloths is unchanged and that instead the derived pattern is due to abnormal primaxial/abaxial patterning. Results We test the detailed predictions derived from both hypotheses for the skeletal patterns in sloths and manatees for both hypotheses. We find strong support for Bateson's homeosis hypothesis. The observed vertebral and rib patterns cannot be explained by changes in primaxial/abaxial patterning. Vertebral patterns in sloths and manatees are similar to those in mice and humans with abnormal numbers of cervical vertebrae: incomplete and asymmetric homeotic transformations are common and associated with skeletal abnormalities. In sloths the homeotic vertebral shift involves a large part of the vertebral column. As such, similarity is greatest with mice mutant for genes upstream of Hox. Conclusions We found no skeletal abnormalities in specimens of sister taxa with a normal number of cervical vertebrae. However, we always found such abnormalities in conspecifics with an abnormal number, as in many of the investigated dugongs. These findings strongly support the hypothesis that the evolutionary constraints on changes of the number of cervical vertebrae in mammals is due to deleterious pleitropic effects. We hypothesize that in sloths and manatees low metabolic and activity rates severely reduce the usual stabilizing selection, allowing the breaking of the pleiotropic constraints. This probably also applies to dugongs, although to a lesser extent.
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Guinard G, Marchand D. Modularity and Complete Natural Homeoses in Cervical Vertebrae of Extant and Extinct Penguins (Aves: Sphenisciformes). Evol Biol 2010. [DOI: 10.1007/s11692-010-9097-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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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: 178] [Impact Index Per Article: 12.7] [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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Stauber M, Sachidanandan C, Morgenstern C, Ish-Horowicz D. Differential axial requirements for lunatic fringe and Hes7 transcription during mouse somitogenesis. PLoS One 2009; 4:e7996. [PMID: 19956724 PMCID: PMC2776510 DOI: 10.1371/journal.pone.0007996] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2009] [Accepted: 10/28/2009] [Indexed: 12/19/2022] Open
Abstract
Vertebrate segmentation is regulated by the “segmentation clock”, which drives cyclic expression of several genes in the caudal presomitic mesoderm (PSM). One such gene is Lunatic fringe (Lfng), which encodes a modifier of Notch signalling, and which is also expressed in a stripe at the cranial end of the PSM, adjacent to the newly forming somite border. We have investigated the functional requirements for these modes of Lfng expression during somitogenesis by generating mice in which Lfng is expressed in the cranial stripe but strongly reduced in the caudal PSM, and find that requirements for Lfng activity alter during axial growth. Formation of cervical, thoracic and lumbar somites/vertebrae, but not sacral and adjacent tail somites/vertebrae, depends on caudal, cyclic Lfng expression. Indeed, the sacral region segments normally in the complete absence of Lfng and shows a reduced requirement for another oscillating gene, Hes7, indicating that the architecture of the clock alters as segmentation progresses. We present evidence that Lfng controls dorsal-ventral axis specification in the tail, and also suggest that Lfng controls the expression or activity of a long-range signal that regulates axial extension.
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Affiliation(s)
- Michael Stauber
- Developmental Genetics Laboratory, Cancer Research UK, London Research Institute, London, United Kingdom
| | - Chetana Sachidanandan
- Developmental Genetics Laboratory, Cancer Research UK, London Research Institute, London, United Kingdom
| | - Christina Morgenstern
- Developmental Genetics Laboratory, Cancer Research UK, London Research Institute, London, United Kingdom
| | - David Ish-Horowicz
- Developmental Genetics Laboratory, Cancer Research UK, London Research Institute, London, United Kingdom
- * E-mail:
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Rubio-Aliaga I, Przemeck GKH, Fuchs H, Gailus-Durner V, Adler T, Hans W, Horsch M, Rathkolb B, Rozman J, Schrewe A, Wagner S, Hoelter SM, Becker L, Klopstock T, Wurst W, Wolf E, Klingenspor M, Ivandic BT, Busch DH, Beckers J, Hrabé de Angelis M. Dll1 haploinsufficiency in adult mice leads to a complex phenotype affecting metabolic and immunological processes. PLoS One 2009; 4:e6054. [PMID: 19562077 PMCID: PMC2699037 DOI: 10.1371/journal.pone.0006054] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2009] [Accepted: 05/26/2009] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The Notch signaling pathway is an evolutionary conserved signal transduction pathway involved in embryonic patterning and regulation of cell fates during development and self-renewal. Recent studies have demonstrated that this pathway is integral to a complex system of interactions, involving as well other signal transduction pathways, and implicated in distinct human diseases. Delta-like 1 (Dll1) is one of the known ligands of the Notch receptors. The role of the Notch ligands is less well understood. Loss-of-function of Dll1 leads to embryonic lethality, but reduction of Delta-like 1 protein levels has not been studied in adult stage. METHODOLOGY/PRINCIPAL FINDINGS Here we present the haploinsufficient phenotype of Dll1 and a missense mutant Dll1 allele (Dll1(C413Y)). Haploinsufficiency leads to a complex phenotype with several biological processes altered. These alterations reveal the importance of Dll1 mainly in metabolism, energy balance and in immunology. The animals are smaller, lighter, with altered fat to lean ratio and have increased blood pressure and a slight bradycardia. The animals have reduced cholesterol and triglyceride levels in blood. At the immunological level a subtle phenotype is observed due to the effect and fine-tuning of the signaling network at the different levels of differentiation, proliferation and function of lymphocytes. Moreover, the importance of the proteolytic regulation of the Notch signaling network emphasized. CONCLUSIONS/SIGNIFICANCE In conclusion, slight alterations in one player of Notch signaling alter the entire organism, emphasizing the fine-tuning character of this pathway in a high number of processes.
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Affiliation(s)
- Isabel Rubio-Aliaga
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
| | - Gerhard K. H. Przemeck
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
| | - Helmut Fuchs
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
| | - Valérie Gailus-Durner
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
| | - Thure Adler
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
- Institute for Medical Microbiology, Immunology and Hygiene, Technische Universitaet Muenchen, Munich, Germany
| | - Wolfgang Hans
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
| | - Marion Horsch
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
| | - Birgit Rathkolb
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
- Chair for Molecular Animal Breeding and Biotechnology/LAFUGA, Gene Center, Ludwig-Maximilians-Universitaet Muenchen, Munich, Germany
| | - Jan Rozman
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
- Molecular Nutritional Medicine, Technische Universitaet Muenchen, Else Kroener-Fresenius Center, Freising-Weihenstephan, Germany
| | - Anja Schrewe
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
- Department of Medicine III, Division of Cardiology, University of Heidelberg, Heidelberg, Germany
| | - Sibylle Wagner
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
| | - Sabine M. Hoelter
- Institute of Developmental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
| | - Lore Becker
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
- Friedrich-Baur-Institute, Department of Neurology, Ludwig-Maximilians-Universitaet, Munich, Germany
| | - Thomas Klopstock
- Friedrich-Baur-Institute, Department of Neurology, Ludwig-Maximilians-Universitaet, Munich, Germany
| | - Wolfgang Wurst
- Institute of Developmental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
- Lehrstuhl fuer Entwicklungsgenetik, Technische Universitaet Muenchen, Freising-Weihenstephan, Germany
| | - Eckhard Wolf
- Chair for Molecular Animal Breeding and Biotechnology/LAFUGA, Gene Center, Ludwig-Maximilians-Universitaet Muenchen, Munich, Germany
| | - Martin Klingenspor
- Molecular Nutritional Medicine, Technische Universitaet Muenchen, Else Kroener-Fresenius Center, Freising-Weihenstephan, Germany
| | - Boris T. Ivandic
- Department of Medicine III, Division of Cardiology, University of Heidelberg, Heidelberg, Germany
| | - Dirk H. Busch
- Institute for Medical Microbiology, Immunology and Hygiene, Technische Universitaet Muenchen, Munich, Germany
| | - Johannes Beckers
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
- Lehrstuhl fuer Experimentelle Genetik, Technische Universitaet Muenchen, Freising-Weihenstephan, Germany
| | - Martin Hrabé de Angelis
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
- Lehrstuhl fuer Experimentelle Genetik, Technische Universitaet Muenchen, Freising-Weihenstephan, Germany
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Iimura T, Denans N, Pourquié O. Establishment of Hox vertebral identities in the embryonic spine precursors. Curr Top Dev Biol 2009; 88:201-34. [PMID: 19651306 DOI: 10.1016/s0070-2153(09)88007-1] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The vertebrate spine exhibits two striking characteristics. The first one is the periodic arrangement of its elements-the vertebrae-along the anteroposterior axis. This segmented organization is the result of somitogenesis, which takes place during organogenesis. The segmentation machinery involves a molecular oscillator-the segmentation clock-which delivers a periodic signal controlling somite production. During embryonic axis elongation, this signal is displaced posteriorly by a system of traveling signaling gradients-the wavefront-which depends on the Wnt, FGF, and retinoic acid pathways. The other characteristic feature of the spine is the subdivision of groups of vertebrae into anatomical domains, such as the cervical, thoracic, lumbar, sacral, and caudal regions. This axial regionalization is controlled by a set of transcription factors called Hox genes. Hox genes exhibit nested expression domains in the somites which reflect their linear arrangement along the chromosomes-a property termed colinearity. The colinear disposition of Hox genes expression domains provides a blueprint for the regionalization of the future vertebral territories of the spine. In amniotes, Hox genes are activated in the somite precursors of the epiblast in a temporal colinear sequence and they were proposed to control their progressive ingression into the nascent paraxial mesoderm. Consequently, the positioning of the expression domains of Hox genes along the anteroposterior axis is largely controlled by the timing of Hox activation during gastrulation. Positioning of the somitic Hox domains is subsequently refined through a crosstalk with the segmentation machinery in the presomitic mesoderm. In this review, we focus on our current understanding of the embryonic mechanisms that establish vertebral identities during vertebrate development.
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McCollum MA, Rosenman BA, Suwa G, Meindl RS, Lovejoy CO. The vertebral formula of the last common ancestor of African apes and humans. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2009; 314:123-34. [DOI: 10.1002/jez.b.21316] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Geffers I, Serth K, Chapman G, Jaekel R, Schuster-Gossler K, Cordes R, Sparrow DB, Kremmer E, Dunwoodie SL, Klein T, Gossler A. Divergent functions and distinct localization of the Notch ligands DLL1 and DLL3 in vivo. ACTA ACUST UNITED AC 2007; 178:465-76. [PMID: 17664336 PMCID: PMC2064846 DOI: 10.1083/jcb.200702009] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The Notch ligands Dll1 and Dll3 are coexpressed in the presomitic mesoderm of mouse embryos. Despite their coexpression, mutations in Dll1 and Dll3 cause strikingly different defects. To determine if there is any functional equivalence, we replaced Dll1 with Dll3 in mice. Dll3 does not compensate for Dll1; DLL1 activates Notch in Drosophila wing discs, but DLL3 does not. We do not observe evidence for antagonism between DLL1 and DLL3, or repression of Notch activity in mice or Drosophila. In vitro analyses show that differences in various domains of DLL1 and DLL3 individually contribute to their biochemical nonequivalence. In contrast to endogenous DLL1 located on the surface of presomitic mesoderm cells, we find endogenous DLL3 predominantly in the Golgi apparatus. Our data demonstrate distinct in vivo functions for DLL1 and DLL3. They suggest that DLL3 does not antagonize DLL1 in the presomitic mesoderm and warrant further analyses of potential physiological functions of DLL3 in the Golgi network.
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Affiliation(s)
- Insa Geffers
- Institut für Molekularbiologie, Medizinische Hochschule Hannover, Hannover, Germany
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White JD, Vuocolo T, McDonagh M, Grounds MD, Harper GS, Cockett NE, Tellam R. Analysis of the callipyge phenotype through skeletal muscle development; association of Dlk1 with muscle precursor cells. Differentiation 2007; 76:283-98. [PMID: 17697128 DOI: 10.1111/j.1432-0436.2007.00208.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The callipyge mutation in sheep in the form of the paternal heterozygote results in skeletal muscle hypertrophy, which is most pronounced in the hindquarters. Overexpression of one of the genes in the region of the causative single-nucleotide polymorphism, Dlk1, is postulated to be a primary cause of the muscle hypertrophy although the mechanism is not clear. This study examined the expression of Dlk1 mRNA and its encoded protein in skeletal muscles of callipyge and wild-type sheep. The muscles examined included those that demonstrate hypertrophy in callipyge sheep as well as an unaffected muscle. The expression pattern of Dlk1 protein in these muscles was also measured over a developmental time course ranging from 80 days of gestation to 12 weeks after birth. Quantitative reverse transcription-polymerase chain reaction demonstrated that Dlk1 mRNA was significantly increased in affected, but not unaffected, muscles from callipyge sheep at 120 days of gestation through to 12 weeks of age. Immuno-localization of Dlk1 was pronounced in the interstitial connective tissue of fetal muscle but was less intense at later ages. No clear difference in Dlk1 immuno-localization was noted between genotypes in the fetal samples. Strong myofiber-specific Dlk1 immuno-localization was observed in hypertrophied callipyge muscles at 12 weeks of age. This staining was exclusively associated with fast type II myofibers and these had a significantly larger mean cross-sectional area, compared with fast type II myofibers in control sheep that did not overexpress Dlk1. In addition, Dlk1 immuno-localization was associated with a sub-population of Pax7-positive mononucleated cells in all skeletal muscles examined during fetal development and at birth, but this was not apparent at 12 weeks. There were no genotype-dependent alterations in the mRNA expression patterns of a number of promyogenic transcription factors indicating that the callipyge mutation was not affecting muscle cell differentiation per se. We postulate that Dlk1 is implicated in the commitment and/or proliferation of fetal myoblasts as well as in the maintenance of hypertrophy in fully differentiated myofibers.
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Affiliation(s)
- Jason D White
- School of Veterinary Science, The University of Melbourne, Parkville, Vic. 3010, Australia.
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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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Compartmentalised expression of Delta-like 1 in epithelial somites is required for the formation of intervertebral joints. BMC DEVELOPMENTAL BIOLOGY 2007; 7:68. [PMID: 17572911 PMCID: PMC1924847 DOI: 10.1186/1471-213x-7-68] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/13/2007] [Accepted: 06/17/2007] [Indexed: 01/23/2023]
Abstract
Background Expression of the mouse Delta-like 1 (Dll1) gene in the presomitic mesoderm and in the caudal halves of somites of the developing embryo is required for the formation of epithelial somites and for the maintenance of caudal somite identity, respectively. The rostro-caudal polarity of somites is initiated early on within the presomitic mesoderm in nascent somites. Here we have investigated the requirement of restricted Dll1 expression in caudal somite compartments for the maintenance of rostro-caudal somite polarity and the morphogenesis of the axial skeleton. We did this by overexpressing a functional copy of the Dll1 gene throughout the paraxial mesoderm, in particular in anterior somite compartments, during somitogenesis in transgenic mice. Results Epithelial somites were generated normally and appeared histologically normal in embryos of two independent Dll1 over-expressing transgenic lines. Gene expression analyses of rostro-caudal marker genes suggested that over-expression of Dll1 without restriction to caudal compartments was not sufficient to confer caudal identity to rostral somite halves in transgenic embryos. Nevertheless, Dll1 over-expression caused dysmorphologies of the axial skeleton, in particular, in morphological structures that derive from the articular joint forming compartment of vertebrae. Accordingly, transgenic animals exhibited missing or reduced intervertebral discs, rostral and caudal articular processes as well as costal heads of ribs. In addition, the midline of the vertebral column did not develop normally. Transgenic mice had open neural arches and split vertebral bodies with ectopic pseudo-growth plates. Endochondral bone formation and ossification in the developing vertebrae were delayed. Conclusion The mice overexpressing Dll1 exhibit skeletal dysmorphologies that are also evident in several mutant mice with defects in somite compartmentalisation. The Dll1 transgenic mice demonstrate that vertebral dysmorphologies such as bony fusions of vertebrae and midline vertebral defects can occur without apparent changes in somitic rostro-caudal marker gene expression. Also, we demonstrate that the over-expression of the Dll1 gene in rostral epithelial somites is not sufficient to confer caudal identity to rostral compartments. Our data suggest that the restricted Dll1 expression in caudal epithelial somites may be particularly required for the proper development of the intervertebral joint forming compartment.
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Pilon N, Oh K, Sylvestre JR, Savory JGA, Lohnes D. Wnt signaling is a key mediator of Cdx1 expression in vivo. Development 2007; 134:2315-23. [PMID: 17537796 DOI: 10.1242/dev.001206] [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: 12/23/2022]
Abstract
In the mouse, Cdx1 is essential for normal anteroposterior vertebral patterning through regulation of a subset of Hox genes. Retinoic acid (RA) and certain Wnts have also been implicated in vertebral patterning, although the relationship between these signaling pathways and the regulation of mesodermal Hox gene expression is not fully understood. Prior work has shown that Cdx1 is a direct target of both Wnt and retinoid signaling pathways,and might therefore act to relay these signals to the Hox genes. Wnt and RA are believed to impact on Cdx1 through an atypical RA-response element (RARE) and Lef/Tcf-response elements (LRE), respectively, in the proximal promoter. To address the roles of these regulatory motifs and pathways, we derived mice mutated for the LRE or the LRE plus the RARE. In contrast to RARE-null mutants, which exhibit limited vertebral defects,LRE-null and LRE+RARE-null mutants exhibited vertebral malformations affecting the entire cervical region that closely phenocopied the malformations seen in Cdx1-null mutants. Mutation of the LRE also greatly reduced induction of Cdx1 by RA, demonstrating a requirement for Wnt signaling in the regulation of this gene by retinoids. LRE and LRE+RARE mutants also exhibited vertebral fusions, suggesting a defect in somitogenesis. As Wnt signaling is implicated in somitogenesis upstream of the Notch pathway, it is conceivable that Cdx1 might play a role in this process. However, none of the Notch pathway genes assessed was overtly affected.
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Affiliation(s)
- Nicolas Pilon
- Clinical Research Institute of Montreal, Montreal, Quebec, Canada
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Abstract
Vertebrae display distinct morphological features at different levels of the body axis. Links between collinear Hox gene activation and the progressive mode of body axis elongation have provided a fascinating blueprint of the mechanisms for establishing these morphological identities. In this review, we first discuss the regulation and possible role of collinear Hox gene activation during body formation and then highlight the direct role of Hox genes in controlling cellular movements during gastrulation, therefore contributing to body formation. Additional related research aspects, such as imaging of chromatin regulation, roles of micro RNAs and evolutional findings are also discussed.
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Affiliation(s)
- Tadahiro Iimura
- Howard Hughes Medical Institute, Kansas City, Missouri 64110, USA
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Mikawa S, Morozumi T, Shimanuki SI, Hayashi T, Uenishi H, Domukai M, Okumura N, Awata T. Fine mapping of a swine quantitative trait locus for number of vertebrae and analysis of an orphan nuclear receptor, germ cell nuclear factor (NR6A1). Genome Res 2007; 17:586-93. [PMID: 17416745 PMCID: PMC1855175 DOI: 10.1101/gr.6085507] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The number of vertebrae in pigs varies and is associated with meat productivity. Wild boars, which are ancestors of domestic pigs, have 19 vertebrae. In comparison, European commercial breeds have 21-23 vertebrae, probably owing to selective breeding for enlargement of body size. We previously identified two quantitative trait loci (QTL) for the number of vertebrae on Sus scrofa chromosomes (SSC) 1 and 7. These QTL explained an increase of more than two vertebrae. Here, we performed a map-based study to define the QTL region on SSC1. By using three F2 experimental families, we performed interval mapping and recombination analyses and defined the QTL within a 1.9-cM interval. Then we analyzed the linkage disequilibrium of microsatellite markers in this interval and found that 10 adjacent markers in a 300-kb region were almost fixed in European commercial breeds. Genetic variation of the markers was observed in Asian local breeds or wild boars. This region encoded an orphan nuclear receptor, germ cell nuclear factor (NR6A1, formerly known as GCNF), which contained an amino acid substitution (Pro192Leu) coincident with the QTL. This substitution altered the binding activity of NR6A1 to its corepressors, nuclear receptor-associated protein 80 (RAP80) and nuclear receptor corepressor 1 (NCOR1). In addition, somites of mouse embryos demonstrated expression of NR6A1 protein. Together, these results suggest that NR6A1 is a strong candidate for one of the QTL that influence number of vertebrae in pigs.
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Affiliation(s)
- Satoshi Mikawa
- Division of Animal Sciences, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan.
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Rubio-Aliaga I, Soewarto D, Wagner S, Klaften M, Fuchs H, Kalaydjiev S, Busch DH, Klempt M, Rathkolb B, Wolf E, Abe K, Zeiser S, Przemeck GKH, Beckers J, de Angelis MH. A genetic screen for modifiers of the delta1-dependent notch signaling function in the mouse. Genetics 2006; 175:1451-63. [PMID: 17179084 PMCID: PMC1840053 DOI: 10.1534/genetics.106.067298] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The Notch signaling pathway is an evolutionarily conserved transduction pathway involved in embryonic patterning and regulation of cell fates during development. Recent studies have demonstrated that this pathway is integral to a complex system of interactions, which are also involved in distinct human diseases. Delta1 is one of the known ligands of the Notch receptors. Mice homozygous for a loss-of-function allele of the Delta1 gene Dll1(lacZ/lacZ) die during embryonic development. Here, we present the results of two phenotype-driven modifier screens. Heterozygous Dll1(lacZ) knockout animals were crossed with ENU-mutagenized mice and screened for dysmorphological, clinical chemical, and immunological variants that are dependent on the Delta1 loss-of-function allele. First, we show that mutagenized heterozygous Dll1(lacZ) offspring have reduced body weight and altered specific clinical chemical parameters, including changes in metabolites and electrolytes relevant for kidney function. In our mutagenesis screen we have successfully generated 35 new mutant lines. Of major interest are 7 mutant lines that exhibit a Dll1(lacZ/+)-dependent phenotype. These mutant mouse lines provide excellent in vivo tools for studying the role of Notch signaling in kidney and liver function, cholesterol and iron metabolism, cell-fate decisions, and during maturation of T cells in the immune system.
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Affiliation(s)
- Isabel Rubio-Aliaga
- Institute of Experimental Genetics, GSF Research Center for Environment and Health, 85764 Neuherberg, Germany
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Galis F, Dooren TJMV, Feuth JD, Metz JAJ, Witkam A, Ruinard S, Steigenga MJ, Wunaendts LCD. EXTREME SELECTION IN HUMANS AGAINST HOMEOTIC TRANSFORMATIONS OF CERVICAL VERTEBRAE. Evolution 2006. [DOI: 10.1111/j.0014-3820.2006.tb01896.x] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Abstract
A fundamental characteristic of the vertebrate body plan is its segmentation along the anterior-posterior axis. This segmental pattern is established during embryogenesis by the formation of somites, the transient epithelial blocks of cells that derive from the unsegmented presomitic mesoderm. Somite formation involves a molecular oscillator, termed the segmentation clock, in combination with gradients of signaling molecules such as fibroblast growth factor 8, WNT3A, and retinoic acid. Disruption of somitogenesis in humans can result in disorders such as spondylocostal dysostosis, which is characterized by vertebral malformations. This review summarizes recent findings concerning the role of Notch signaling in the segmentation clock, the complex regulatory network that governs somitogenesis, the genes that cause inherited spondylocostal dysostosis, and the mechanisms that regulate bilaterally symmetric somite formation.
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Peres JN, McNulty CL, Durston AJ. Interaction between X-Delta-2 and Hox genes regulates segmentation and patterning of the anteroposterior axis. Mech Dev 2006; 123:321-33. [PMID: 16644189 DOI: 10.1016/j.mod.2006.03.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2005] [Revised: 02/28/2006] [Accepted: 03/01/2006] [Indexed: 10/24/2022]
Abstract
In vertebrates, the paraxial mesoderm already exhibits a complex Hox gene pattern by the time that segmentation occurs and somites are formed. The anterior boundaries of the Hox genes are always maintained at the same somite number, suggesting coordination between somite formation and Hox expression. To study this interaction, we used morpholinos to knockdown either the somitogenesis gene X-Delta-2 or the complete Hox paralogous group 1 (PG1) in Xenopus laevis. When X-Delta-2 is knocked down, Hox genes from different paralogous groups are downregulated from the beginning of their expression at gastrula stages. This effect is not via the canonical Notch pathway, as it is independent of the Notch effector Su(H). We also reveal for the first time a clear role for Hox genes in somitogenesis, as loss of PG1 gene function results in the perturbation of somite formation and downregulation of the X-Delta-2 expression in the PSM. This effect on X-Delta-2 expression is also observed during neurula stages, before the somites are formed. These results show that somitogenesis and patterning of the anteroposterior axis are closely linked via a feedback loop involving Hox genes and X-Delta-2, suggesting the existence of a coordination mechanism between somite formation and anteroposterior patterning. Such a mechanism is likely to be functional during gastrulation, before the formation of the first pair of somites, as suggested by the early X-Delta-2 regulation of the Hox genes.
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Affiliation(s)
- João N Peres
- Hubrecht Laboratory, Netherlands Institute for Developmental Biology, Utrecht, The Netherlands.
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Bergmann PJ, Melin AD, Russell AP. Differential segmental growth of the vertebral column of the rat (Rattus norvegicus). ZOOLOGY 2006; 109:54-65. [PMID: 16377162 DOI: 10.1016/j.zool.2005.09.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2005] [Revised: 08/11/2005] [Accepted: 09/21/2005] [Indexed: 10/25/2022]
Abstract
Despite the pervasive occurrence of segmental morphologies in the animal kingdom, the study of segmental growth is almost entirely lacking, but may have significant implications for understanding the development of these organisms. We investigate the segmental and regional growth of the entire vertebral column of the rat (Rattus norvegicus) by fitting a Gompertz curve to length and age data for each vertebra and each vertebral region. Regional lengths are calculated by summing constituent vertebral lengths and intervertebral space lengths for cervical, thoracic, lumbar, sacral, and caudal regions. Gompertz curves allow for the estimation of parameters representing neonatal and adult vertebral and regional lengths, as well as initial growth rate and the rate of exponential growth decay. Findings demonstrate differences between neonatal and adult rats in terms of relative vertebral lengths, and differential growth rates between sequential vertebrae and vertebral regions. Specifically, relative differences in the length of vertebrae indicate increasing differences caudad. Vertebral length in neonates increases from the atlas to the middle of the thoracic series and decreases in length caudad, while adult vertebral lengths tend to increase caudad. There is also a general trend of increasing vertebral and regional initial growth and rate of growth decay caudad. Anteroposterior patterns of growth are sexually dimorphic, with males having longer vertebrae than females at any given age. Differences are more pronounced (a) increasingly caudad along the body axis, and (b) in adulthood than in neonates. Elucidated patterns of growth are influenced by a combination of developmental, functional, and genetic factors.
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Affiliation(s)
- Philip J Bergmann
- Vertebrate Morphology Research Group, Department of Biological Sciences, University of Calgary, Alta., Canada.
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Chen J, Lu L, Shi S, Stanley P. Expression of Notch signaling pathway genes in mouse embryos lacking beta4galactosyltransferase-1. Gene Expr Patterns 2006; 6:376-82. [PMID: 16412699 DOI: 10.1016/j.modgep.2005.09.009] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2005] [Accepted: 09/20/2005] [Indexed: 01/26/2023]
Abstract
A requirement for beta4galactosyltransferase-1 (beta4GalT-1) activity in the modulation of Notch signaling by the glycosyltransferase Fringe was previously identified in a mammalian co-culture assay. Notch signaling is necessary for the formation of somites in mammals. We therefore investigated the expression of eleven Notch pathway and somitogenic genes in E9.5 mouse embryos lacking beta4GalT-1. Four of these genes were altered in expression pattern or expression level. The Notch target genes Hes5 and Mesp2 were affected to some degree in all mutant embryos. The Notch ligand genes Dll1 and Dll3 were reduced or altered in expression in a significant proportion of mutants. While there were no differences in the number or morphology of somites in E9.5 B4galt1 null embryos, the number of lumbar vertebrae in mutant embryos differed from control littermates (P < or = 0.01). The subtlety of the in vivo phenotype may be due to redundancy since several B4galt genes related to B4galt1 are expressed during embryogenesis.
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Affiliation(s)
- Jihua Chen
- Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, New York, NY 10461, USA
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Abstract
Unraveling the complex tissue interactions necessary to generate the structural and functional diversity present among craniofacial muscles is challenging. These muscles initiate their development within a mesenchymal population bounded by the brain, pharyngeal endoderm, surface ectoderm, and neural crest cells. This set of spatial relations, and in particular the segmental properties of these adjacent tissues, are unique to the head. Additionally, the lack of early epithelialization in head mesoderm necessitates strategies for generating discrete myogenic foci that may differ from those operating in the trunk. Molecular data indeed indicate dissimilar methods of regulation, yet transplantation studies suggest that some head and trunk myogenic populations are interchangeable. The first goal of this review is to present key features of these diversities, identifying and comparing tissue and molecular interactions regulating myogenesis in the head and trunk. Our second focus is on the diverse morphogenetic movements exhibited by craniofacial muscles. Precursors of tongue muscles partly mimic migrations of appendicular myoblasts, whereas myoblasts destined to form extraocular muscles condense within paraxial mesoderm, then as large cohorts they cross the mesoderm:neural crest interface en route to periocular regions. Branchial muscle precursors exhibit yet another strategy, establishing contacts with neural crest populations before branchial arch formation and maintaining these relations through subsequent stages of morphogenesis. With many of the prerequisite stepping-stones in our knowledge of craniofacial myogenesis now in place, discovering the cellular and molecular interactions necessary to initiate and sustain the differentiation and morphogenesis of these neglected craniofacial muscles is now an attainable goal.
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Affiliation(s)
- Drew M Noden
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
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