Structural alterations in chromatin during myogenesis in the chicken.

Differentiation of mononucleated myoblasts to multinucleated myotubes is accompanied by hypertrophy achieved by co-ordinated synthesis of muscle proteins. This process may be achieved by co-ordinated synthesis and translation of new mRNA or gradual accumulation of constitutively synthesized mRNA, followed by coordinated translational activation. If the former process occurs, many structural alterations should occur in chromatin, whereas in the latter scenario, no chromatin changes will be necessary. The results of our investigation into chromatin structure of myoblast and myotube nuclei show that according to techniques used, viz. chromatin solubilization by nucleases, thermal denaturation, in vitro transcription, nucleosome sizing, there are major structural changes in chromatin during muscle cell differentiation. Since these alterations were detectable at a fairly gross level, many genes must be affected which could account for the increase in RNA and proteins observed in myotubes. This evidence argus in favour of new mRNA synthesis for rapid translation, rather than a gradual accumulation of mRNA followed by co-ordinated translation.