NORMAL TRANSITIONS IN SYNTHESIS OF REPLACEMENT HISTONES H2A.Z AND H3.3 DURING DIFFERENTIATION OF DYSTROPHIC MYOTUBE CELLS - A BRIEF NOTE

We previously reported that differentiating G0 myotube cells cultured from normal chicken embryos exhibit a histone synthesis pattern that is highlighted by transitions in the expression of the minor replacement variants H3.3 and perhaps H2A.Z (Wunsch and Lough, Dev. Biol. 119 (1987) 94-99). Because these proteins may be synthesized to maintain chromatin structure during the differentiation and maturation of the skeletal muscle fiber, it was of interest to determine whether they are made at normal levels during the differentiation of dystrophic muscle. To this end, the synthesis of histone proteins in cultured myoblasts and myotubes from normal and dystrophic avian embroys has been characterized by two-dimensional polyacrylamide gel electrophoresis and fluorography. Proliferating myoblasts (day 1) as well as two stages of differentiating myotubes (days 3, 4) exhibited histone synthesis patterns that were indistinguishable when comparing normal and dystrophic cells. It is noteworthy that this study also revealed that, in both cell types, the change in H2A.Z synthesis during the myoblast/myotube transition was remarkable, increasing from approximately 20% of the non-ubiquitinated H2As in myoblasts to 80% in myotubes. Also, gel staining patterns and immunoblotting detected no differences in the degree of histone uniquitination between normal and dystrophic cells. These findings indicate that, up to this point in dystrophic differentiation, neither the synthesis nor ubiquitination of histones are perturbed.