Figure 1.

Barx2 is expressed in embryonic and adult muscle. (A–C): E13.5 limb muscle. (A): Barx2 (red) is expressed in primary myofibers marked with the MF20 antibody (green) as well as between fibers. DAPI, blue. (B, C): Barx2 (red) and MyoD (green) coexpression is shown in a subset of muscle nuclei in the distal hind limb of E13.5 embryo. The image in (B) shows two adjacent digits, and Barx2 expression is also seen in skin and presumptive joint region (arrows). (C):Higher magnification of the muscle shown in (B). (D–H): E18 limb muscle; Barx2 expression overlaps extensively with Pax7 (Barx2, red; Pax7, green; DAPI, blue). Red arrowheads indicate Pax7-positive nuclei with low level of Barx2 expression. (I–P): Adult muscle; (I–L): Yellow arrows indicate nuclei in which Barx2 and Pax7 are coexpressed; White arrows indicate nuclei with weaker expression of Barx2 and no apparent expression of Pax7. (M–P): Barx2 is coexpressed with Pax7 in nuclei situated under the basal lamina. (M, O): Overlap of Barx2 (red) and Pax7 (green) staining is seen as yellow; the basal lamina is labeled with antibody to HS, blue. (N): The same section shown in (M) but labeled with Barx2 (red), Pax7 (green) and DAPI (blue), and without HS staining; nuclei that colocalize DAPI, Barx2, and Pax7 are white. (P): The same section shown in (O) but labeled with DAPI only (blue). Yellow arrows in (O) and (P) show nuclei expressing both Barx2 and Pax7 in (O). Abbreviations: DAPI, 4′,6-diamidino-2-phenylindole; HS, heparan sulfate.