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Petr Valasek,
Susanne Theis,
April DeLaurier,
Yaniv Hinits,
Graham N Luke,
Anthony M Otto,
James Minchin,
Liwen He,
Bodo Christ,
Gavin Brooks,
Helen Sang,
Darrell J Evans, Malcolm Logan,
Ruijin Huang,
Ketan Patel
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ABSTRACT: The forelimbs of higher vertebrates are composed of two portions: the appendicular region (stylopod, zeugopod and autopod) and the less prominent proximal girdle elements (scapula and clavicle) that brace the limb to the main trunk axis. We show that the formation of the muscles of the proximal limb occurs through two distinct mechanisms. The more superficial girdle muscles (pectoral and latissimus dorsi) develop by the "In-Out" mechanism whereby migration of myogenic cells from the somites into the limb bud is followed by their extension from the proximal limb bud out onto the thorax. In contrast, the deeper girdle muscles (e.g. rhomboideus profundus and serratus anterior) are induced by the forelimb field which promotes myotomal extension directly from the somites. Tbx5 inactivation demonstrated its requirement for the development of all forelimb elements which include the skeletal elements, proximal and distal muscles as well as the sternum in mammals and the cleithrum of fish. Intriguingly, the formation of the diaphragm musculature is also dependent on the Tbx5 programme. These observations challenge our classical views of the boundary between limb and trunk tissues. We suggest that significant structures located in the body should be considered as components of the forelimb.
Developmental Biology 09/2011; 357(1):108-16. · 4.07 Impact Factor
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ABSTRACT: The developing mouse limb is widely used as a model system for studying tissue patterning. Despite this, few references are available that can be used for the correct identification of developing limb structures, such as muscles and tendons. Existing textual references consist of two-dimensional (2D) illustrations of the adult rat or mouse limb that can be difficult to apply when attempting to describe the complex three-dimensional (3D) relationship between tissues.
To improve the resources available in the mouse model, we have generated a free, web-based, interactive reference of limb muscle, tendon, and skeletal structures at embryonic day (E) 14.5 http://www.nimr.mrc.ac.uk/3dlimb/. The Atlas was generated using mouse forelimb and hindlimb specimens stained using immunohistochemistry to detect muscle and tendon. Limbs were scanned using Optical Projection Tomography (OPT), reconstructed to make 3D models and annotated using computer-assisted segmentation tools in Amira 3D Visualisation software. The annotated dataset is visualised using Java, JAtlasView software. Users click on the names of structures and view their shape, position and relationship with other structures within the 3D model and also in 2D virtual sections.
The Mouse Limb Anatomy Atlas provides a novel and valuable tool for researchers studying limb development and can be applied to a range of research areas, including the identification of abnormal limb patterning in transgenic lines and studies of models of congenital limb abnormalities. By using the Atlas for "virtual" dissection, this resource offers an alternative to animal dissection. The techniques we have developed and employed are also applicable to many other model systems and anatomical structures.
BMC Developmental Biology 10/2008; 8:83. · 2.79 Impact Factor
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ABSTRACT: T-box genes encode a family of DNA-binding transcription factors implicated in numerous developmental processes in all metazoans. The Tbx2/3/4/5 subfamily genes are especially interesting because of their key roles in the evolution of vertebrate appendages, eyes, and the heart, and, like the Hox genes, the longevity of their chromosomal linkage. A BAC library derived from the single male amphioxus (Branchiostoma floridae) used to sequence the amphioxus genome was screened for AmphiTbx2/3 and AmphiTbx4/5, yielding two independent clones containing both genes. Using comparative expression, genomic linkage, and phylogenetic analyses, we have reconstructed the evolutionary histories of these members of the T-box gene family. We find that the Tbx2-Tbx4 and Tbx3-Tbx5 gene pairs have maintained tight linkage in most animal lineages since their birth by tandem duplication, long before the divergence of protostomes and deuterostomes (e.g., arthropods and vertebrates) at least 600 million years ago, and possibly before the divergence of poriferans and cnidarians (e.g., sponges and jellyfish). Interestingly, we find that the gene linkage detected in all vertebrate genomes has been maintained in the primitively appendage-lacking, basal chordate, amphioxus. Although all four genes have been involved in the evolution of developmental programs regulating paired fin and (later) limb outgrowth and patterning, and most are also implicated in eye and heart development, linkage maintenance--often considered due to regulatory constraints imposed by limb, eye, and/or heart associated gene expression--is undoubtedly a consequence of other, much more ancient functional constraints.
Archiv für Entwickelungsmechanik der Organismen 10/2008; 218(11-12):613-28. · 1.77 Impact Factor
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ABSTRACT: The vertebrate forelimb and hindlimb are serially homologous structures; however, their distinctive morphologies suggest that different mechanisms are associated with each limb type to give rise to limb-type identity. Three genes have been implicated in this process; T-box transcription factors Tbx5 and Tbx4, which are expressed in the forelimb and hindlimb, respectively, and a paired-type homeodomain transcription factor Pitx1, expressed in the hindlimb. To explore the roles of Pitx1 and Tbx4 in patterning the hindlimb, we have ectopically misexpressed these genes in the mouse forelimb using transgenic methods. We have developed a novel technique for visualising the structure and organisation of tissues in limbs in 3D using optical projection tomography (OPT). This approach provides unparalleled access to understanding the relationships between connective tissues during development of the limb. Misexpression of Pitx1 in the forelimb results in the transformation and translocation of specific muscles, tendons, and bones of the forelimb so that they acquire a hindlimb-like morphology. Pitx1 also upregulates hindlimb-specific factors in the forelimb, including Hoxc10 and Tbx4. In contrast, misexpression of Tbx4 in the forelimb does not result in a transformation of limb-type morphology. These results demonstrate that Pitx1, but not Tbx4, determines the morphological identity of hindlimb tissues.
Developmental Biology 12/2006; 299(1):22-34. · 4.07 Impact Factor
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Genome biology 02/2004; 5(7):333. · 6.63 Impact Factor
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Malcolm Logan
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ABSTRACT: Despite their obvious similarities, the forelimbs and hindlimbs of tetrapod vertebrates have evolved distinct structural elements to carry out their discrete functions. Many genes required for limb initiation and patterning are involved in regulatory networks common to both limb-types. Other genes are differentially expressed between forelimb and hindlimb, and have been implicated in the initiation of limb bud outgrowth and the specification of limb-type identity. In this review, I will discuss the current understanding of how genes that control limb identity interact with regulatory networks common to both appendages to produce the fingers of the hand and toes of the foot.
Development 01/2004; 130(26):6401-10. · 6.60 Impact Factor
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ABSTRACT: T-box genes are defined by the presence of a conserved sequence, the so-called T-box; this codes for the T-domain, which is involved in DNA-binding and protein dimerisation. Members of this gene family have been found in all metazoans, from diploblasts to humans, and mutations in T-box gene family members in humans have been linked to several congenital disorders. Sequencing of the complete genomes of a range of invertebrate and vertebrate species has allowed the classification of individual T-box genes into five subfamilies: Brachyury, T-brain1, Tbx1, Tbx2 and Tbx6. This review will largely focus on T-box genes identified in organisms whose genomes have been fully sequenced, emphasising how comparative studies of the T-box gene family will help to reveal the roles of these genes during development and in the adult.
Briefings in Functional Genomics and Proteomics 11/2003; 2(3):224-33.
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Malcolm Logan
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ABSTRACT: A recent study has used serial analysis of gene expression to compare mouse forelimb and hindlimb gene-expression profiles. The method successfully identified known regulators of limb identity and has generated a candidate set of differentially expressed genes that may regulate limb identity.
Genome biology 02/2002; 3(3):REVIEWS1007. · 6.63 Impact Factor
