Differences of reporter activities between wild type and Sox6-null primary myotubes. A. Schematic representations of the firefly luciferase vectors constructed to test the function of Sox6 binding sequences. Black boxes indicate the firefly luciferase gene and shaded boxes indicate the chicken β-actin promoter (Actb-p). Open boxes indicate the upstream sequences of the wild type MyHC-β gene (MHCβ3500) or its mutated version (MHCβ3500 m; cross indicates mutation), Myh7b, Tnni1, and Hdac11, or the first intron sequence of Tnnc1. Approximate positions of Sox6 binding sites are indicated by gray lines. B. The reporter constructs shown in A were cotransfected with a Renilla luciferase vector into wild type (WT) and Sox6-null (p100H) primary myoblasts. After differentiation into myotubes, both luciferase activities were measured and normalized with Renilla luciferase activity. Data were further normalized to WT MHCβ3500 value (i.e. MHCβ3500 in WT = 1.0), and represented as mean ± SD (n = 3). (*) P < 0.05; (**) P < 0.005.