Independent control during myogenesis of histone and high-mobility-group (HMGs) chromosomal protein heterogeneity

Abstract

The ontogeny of high-mobility-group chromosomal protein and histone heterogeneity was followed in differentiating chicken skeletal muscle. The high-molecular-weight, high-mobility-group chromosomal proteins (HMGs 1, 2A, and 2B) showed a substantial change in their relative amounts during the period from 8 to 18 days. During this period HMG 2A decreases relative to HMG 1. There is also a decrease in the high-molecular-weight HMGs relative to the low-molecular-weight HMGs (HMGs 14 and 17). The microheterogeneity of the histones extracted from purified nuclei isolated from 8-, 11-, and 18-day embryonic myogenic tissue was analyzed by: (1) NaDodSO 4, (2) acid-urea, and (3) Triton acid-urea polyacrylamide gel electrophoresis. In contrast to the HMGs, the pattern of histone microheterogeneity for both H1 and H2A remained remarkably constant, despite the dramatic changes occurring in the rates of proliferation and the quality of gene expression in muscle cells during this developmental period. As would be expected from the decrease in cell proliferation occurring between days 8 and 18, increased amounts of phosphorylated H1 subspecies could be identified at the earlier stage. There was no change, however, in the proportion of the 4 major H1 parental variants. Thus, since the tissue-specific distribution of the H1s and HMGs are established at different times during myogenesis, it is likely that the two groups of chromatin proteins are involved in different events required for the establishment of the tissue-specific pattern of gene expression.