Margaret Buckingham margaret.buckingham@pasteur.fr

We are interested in the regulatory genes which direct a cell into the myogenic programme of skeletal or cardiac muscle and in the cell lineages which contribute to these two striated muscle tissues. The model studied is the mouse, with genetic manipulation as an essential tool in our experimental approach.

Skeletal Myogenesis

The myogenic regulatory factors of the MyoD family play a key role in the determination and differentiation of skeletal muscle cells. Myf5 is the first to be expressed in the mouse embryo and also in satellite cells, the progenitor cells of adult muscle. We are examining regulatory sequences which we have identified 5’ to the Mrf4-Myf5 locus, with the aim of understanding how they integrate signals and positional information leading to myogenesis (1). Pax3 and its orthologue, Pax7, also affect key aspects of myogenic progenitor cells function (2). We are studying their respective roles in this context, both in the embryo and the adult, with a particular emphasis on the co-factors and targets of Pax3.
Pax3 is also a marker of mesoangioblasts, mesodermal stem cells, present in the walls of blood vessels. The role of Pax3 in these cells, together with their potential lineage relationship to the Pax3 expressing precursors of skeletal muscle is under investigation.

Cardiogenesis

Our analyses of myosin transgenic lines which mark different regions of the heart have led to the identification of a novel population of myocardial progenitor cells present in pharyngeal mesoderm (3). Explant experiments demonstrate their contribution to the formation of the outflow tract and right ventricle. Fgfs and regulatory factors such as Nkx2.5 mark this second heart field and their role is under investigation. A parallel approach, based on a retrospective clonal analysis, using mice in which the cardiac actin gene is targeted with an nlaacZ reporter, has demonstrated the presence of two myocardial cell lineages and provides new insight into the morphogenesis of the cardiac chambers (4). Further clonal analyses address lineage relationships between specific subregions of the heart.

Selected recent publications

(1) Hadchouel, J., Carvajal, J.J., Daubas, P., Bajard, L., Chang, T., Rocancourt, D., Cox, D., Summerbell, D., Tajbakhsh, S., Rigby, P.W.J., & Buckingham, M. (2003) Analysis of a key regulatory region upstream of the Myf5 gene reveals multiple phases of myogenesis, orchestrated at each site by a combination of elements dispersed throughout the locus. Development, 130, 3415-3426.
(2) Relaix, F., Rocancourt, D.,, Mansouri, M., & Buckingham, M. (2004) Divergent functions of murine Pax3 and Pax7 in limb muscle development. Genes and Dev., 18, 1088-1105.
(3) Kelly, R., Brown, N., & Buckingham, M. (2001) The arterial pole of the mouse heart forms from Fgf10 expressing precursor cells in pharyngeal mesoderm. Dev. Cell. 1, 435-440.
(4) Meilhac, S.M., Esner, M., Kelly, R.G., Nicolas, J-F., & Buckingham, M.E. (2004). The clonal origin of myocardial cells in different regions of the embryonic mouse heart. Dev. Cell, 6, 1-20.

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