Modulation of histone H3 variant synthesis during the myoblast-myotube transition of chicken myogenesis.

We have previously reported that nucleosomal histones are synthesized by cultured, postmitotic myotube cells at 9-29% of the rate in their dividing myoblast precursors (A. M. Wunsch, A. L. Haas, and J. Lough, 1987, Dev. Biol. 119, 85-93). In that study, histones were separated by two-dimensional polyacrylamide gels containing 8 M urea in the first-dimension to optimally separate variants of the H2A class. To separate and compare synthesis of variants in the H2B and H3 classes during myogenesis, 5.75 M urea has been used in the first dimension. Although no changes in the H2B variant pattern were discerned, a dramatic change in H3 variant synthesis was detected, in which a predominance of H3.2 synthesis in dividing myoblasts was almost completely replaced by a lower level of H3.3 synthesis after myotube formation. With increasing differentiation, H3.2 synthesis became undetectable, while H3.3 synthesis continued. Control experiments indicated that these results were not mediated by replicating cells in the myotube cultures, the effects of cytosine arabinoside, or contaminating non-histone proteins. These results suggest that histone H3.2 is replaced by histone H3.3 in nucleosomes during skeletal muscle maturation.