Résumé
The myogenic program is controlled by different groups of transcription factors acting during muscle development, including bHLH muscle regulatory factors (MRFs), the
paired factors Pax3 and Pax7 and the homeobox factors Six1 and Six4. This program is critically dependent on MRFs that target downstream muscle-specific genes. We now report the expression of Pitx2 and Pitx3 transcription factors throughout muscle development.
Pitx2 is first expressed in muscle progenitor cells of the dermomyotome and myotome. The onset of myoblast differentiation is concomitant with expression of
Pitx3; its expression is maintained in all skeletal muscles while
Pitx2 expression decreases thereafter. We have generated
Pitx3 mutant mice and this deficiency does not significantly perturb muscle development but it is completely compensated by the maintenance of
Pitx2 expression in all skeletal muscles. These experiments suggest that
Pitx genes are important for myogenesis and that
Pitx2 and
Pitx3 may have partly redundant roles.