Gene targeting the myf-5 locus with nlacZ reveals expression of this myogenic factor in mature skeletal muscle fibres as well as early embryonic muscle

Authors

  • S. Tajbakhsh,

    Corresponding author
    1. Molecular Genetics of Development, Department of Molecular Biology, CNRS URA1947 and Mammalian Genetics Unit, Department of Immunology, CNRS URA361 Pasteur Institute, 75724 Paris, France
    • Molecular Genetics of Development, Department of Molecular Biology, CNRS URA1947, Pasteur Institute, 25 rue du Dr. Roux, 75724 Paris Cedex 15, France
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  • E. Bober,

    1. Department of Cell and Molecular Biology, University of Braunschweig, Braunschweig, Germany
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  • C. Babinet,

    1. Molecular Genetics of Development, Department of Molecular Biology, CNRS URA1947 and Mammalian Genetics Unit, Department of Immunology, CNRS URA361 Pasteur Institute, 75724 Paris, France
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  • S. Pournin,

    1. Molecular Genetics of Development, Department of Molecular Biology, CNRS URA1947 and Mammalian Genetics Unit, Department of Immunology, CNRS URA361 Pasteur Institute, 75724 Paris, France
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  • H. Arnold,

    1. Department of Cell and Molecular Biology, University of Braunschweig, Braunschweig, Germany
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  • M. Buckingham

    1. Molecular Genetics of Development, Department of Molecular Biology, CNRS URA1947 and Mammalian Genetics Unit, Department of Immunology, CNRS URA361 Pasteur Institute, 75724 Paris, France
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Abstract

We have introduced the nlacZ reporter gene into the locus of the myogenic factor gene myf-5 by homologous recombination in embryonic stem (ES) cells. Targeted ES clones were injected into precompaction morula, and the β-galactosidase expression pattern was monitored. These mice permit the sensitive visualization of myf-5 expression throughout the embryo, and provide a standard for comparing it with that seen with different myf-5/nlacZ transgenes. Thus, in a comparison using ES cells in chiameric embryos containing the targeted or randomly integrated myf-5/nlacZ construct, we demonstrate that 5.5 kbp of myf-5 upstream flanking sequence including exon1 and most of intron1 directs some skeletal muscle expression, but this is neither qualitatively nor quantitatively equivalent to that of the endogenous gene. Myf-5 is expressed early, before terminal myogenesis takes place in the medial half of the somite, and subsequently it is a major myogenic factor as skeletal muscle forms. All skeletal muscle shows β-galactosidase activity, even after birth, indicating that myf-5 expression is not confined to primary myotubes, which are derived from embryonic myoblasts, but is also present in muscles containing different adult fibre types. The presence of myf-5 transcripts from the endogenous gene in older muscle was confirmed by in situ hybridization. These results suggest that the myf-5 gene is not activated in only a subset of muscle cells and are consistent with the results on the MyoD knockout mice. © 1996 Wiley-Liss, Inc.

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