Study of cell cycle in non-proliferating cells

Non-proliferating cells can be found in three conditions: reversible quiescence, replicative senescence and terminal differentiation(TD). Cells in any of these non-proliferative states can be made to re-enter the cell cycle through the removal of appropriate CKIs. Through a CRISPR/Cas9 strategy, we have generated conditional p21 KO mice. These animals were crossed with mice expressing a tamoxifen-activatable Cre recombinase under the control of the Pax7 promoter to knockout p21 exclusively in Pax7+ satellite cells. The first purpose of my thesis was to study the consequences of the absence of p21 in satellite cells. We show that the deletion of p21 in satellite cells only does not lead to fiber neogenesis and, after injury, does not have impact on muscle regeneration. Skeletal muscle myotubes (Mt), a model system of TD, can be forced to reenter the cell cycle but they are not able to fully duplicate their DNA. Understanding the molecular bases that prevent Mt to a regular and complete replication is the aim of the second part of this work. We used Xenopus laevis egg extracts (XEE) to study DNA replication of different genetic material from myoblasts or myotubes to identify an eventual structure obstacle, that do not permit a complete replication of myotube. The results obtained suggest that the no-histones proteins are the possible candidates responsible for the inability of these cells to proliferate.