Thesis title: Study of the alterations of DNA replication in terminally differentiated muscle cells.
Terminal differentiation is characterized by the acquisition of specialized functions and by a permanent withdrawal from proliferation, a condition known as the postmitotic state. The molecular mechanisms that induce and maintain this state remain poorly understood. Skeletal muscle myotubes (MTs), a classical model of terminal differentiation, can be experimentally induced to re-enter the cell cycle; however, they generally fail to complete DNA replication and undergo cell death. In this work, we investigate the causes of MT replicative failure. Nuclei from proliferating myoblasts (MBs) and differentiated MTs were incubated in Xenopus laevis egg extract, which provides the complete biochemical machinery for DNA replication Even in this permissive context, MT nuclei duplicated less than half their genome, suggesting the presence of structural hindrances within chromatin. Disrupting chromatin architecture by strong salt treatment did not rescue DNA synthesis, indicating that the replicative block is embedded within the core structural organization of differentiated chromatin.