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First published online 22 March 2006
doi: 10.1242/dev.02336

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Integrin 6ß1-laminin interactions regulate early myotome formation in the mouse embryo

Fernanda Bajanca^1,2, Marta Luz^1,2,*, Karine Raymond³, Gabriel G. Martins^1,2, Arnoud Sonnenberg³, Shahragim Tajbakhsh⁴, Margaret Buckingham⁵ and Sólveig Thorsteinsdóttir^1,2,

¹ Department of Animal Biology and Centre for Environmental Biology, Faculty of Sciences, University of Lisbon, 1749-016 Lisbon, Portugal.
² Gulbenkian Institute of Science, 2781-901 Oeiras, Portugal.
³ Department of Cell Biology, Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands.
⁴ Stem Cells and Development, Department of Developmental Biology, CNRS URA 2578, Pasteur Institute, 25 rue du Dr Roux, 75724 Paris Cedex 15, France.
⁵ Molecular Genetics of Development, Department of Developmental Biology, CNRS URA 2578, Pasteur Institute, 25 rue du Dr Roux, 75724 Paris Cedex 15, France.

Author for correspondence (e-mail: solveig{at}fc.ul.pt)

Accepted 22 February 2006

We addressed the potential role of cell-laminin interactions during epaxial myotome formation in the mouse embryo. Assembly of the myotomal laminin matrix occurs as epaxial myogenic precursor cells enter the myotome. Most Myf5-positive and myogenin-negative myogenic precursor cells localise near assembled laminin, while myogenin-expressing cells are located either away from this matrix or in areas where it is being assembled. In Myf5^nlacZ/nlacZ (Myf5-null) embryos, laminin, collagen type IV and perlecan are present extracellularly near myogenic precursor cells, but do not form a basement membrane and cells are not contained in the myotomal compartment. Unlike wild-type myogenic precursor cells, Myf5-null cells do not express the 6ß1 integrin, a laminin receptor, suggesting that integrin 6ß1-laminin interactions are required for myotomal laminin matrix assembly. Blocking 6ß1-laminin binding in cultured wild-type mouse embryo explants resulted in dispersion of Myf5-positive cells, a phenotype also seen in Myf5^nlacZ/nlacZ embryos. Furthermore, inhibition of 6ß1 resulted in an increase in Myf5 protein and ectopic myogenin expression in dermomyotomal cells, suggesting that 6ß1-laminin interactions normally repress myogenesis in the dermomyotome. We conclude that Myf5 is required for maintaining 6ß1 expression on myogenic precursor cells, and that 6ß1 is necessary for myotomal laminin matrix assembly and cell guidance into the myotome. Engagement of laminin by 6ß1 also plays a role in maintaining the undifferentiated state of cells in the dermomyotome prior to their entry into the myotome.

Key words: Integrin, Laminin, Mouse embryo, Myotome, Dermomyotome, Extracellular matrix, Myf5

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