Fig. 7. Histone H1 induces myoblast proliferation via a heparan-sulfate-dependent mechanism. (A) Culture dishes were coated with nitrocellulose, and 10 µl droplets containing 2 µg of affinity-purified histone H1 obtained from myotubes (H1), laminin (LN), fibronectin (FN) or BSA were applied to the surface of the dishes and dried. C₂C₁₂ myoblasts were then incubated for 2 hours and examined by phase contrast microscopy. Photographs were taken at the border of protein-coated areas (upper panel, dashed lines) and 21 hours later, at the center of the protein-coated regions (lower panel). Bar, 10 µm. (B) The time course of the [³H]thymidine incorporation in myoblasts induced by the addition of the indicated concentrations of exogenous histone H1. (C) C₂C₁₂ cultures were incubated with increasing concentrations of histone H1 for 24 hours. [³H]thymidine incorporation was determined in the last 3 hours of incubation and expressed as fold increase over controls (without histone H1). (D) Myoblast cultures incubated for 24 hours with increasing concentrations of histone H1 in the absence or presence of heparin (20 ng/ml). Results correspond to the average and s.d. of two independent experiments. (E) Myoblasts were seeded on myotube ECM preincubated with anti-histone H1 (-H1) or anti-ß galactosidase (-ßgal) antibodies. After 24 hours, [³H]thymidine incorporation was determined and expressed as a percentage of maximum effect (control ECM=1521±250 cpm). The results correspond to the average and s.d. of two independent experiments (^*P0.01).