Paraxis is expressed in myoblasts during their migration and proliferation in the chick limb bud

The Paraxis gene encodes a basic helix-loop-helix (bHLH) transcription factor expressed in paraxial mesoderm and whose mutant displays an inability to form epithelial somites. We analyzed the later expression pattern of Paraxis transcripts in the chick limb. Paraxis transcripts are located in the Pax3-expressing myoblasts migrating from the somites and persist in proliferating myoblasts in the limb bud. Moreover, the QH1 antibody, which recognizes quail endothelial cells, reacts with a subset of the Paraxis/Pax3 expressing cells in the quail limb. Paraxis is then down-regulated during muscle differentiation.