ABSTRACT
Adult stem cells (SCs) are at high risk of accumulating deleterious mutations because they reside and self-renew in adult tissues for extended periods. Little is known about how adult SCs sense and respond to DNA damage within their natural niche. Here, using mouse epidermis as a model, we define the functional consequences and the molecular mechanisms by which adult SCs respond to DNA damage. We show that multipotent hair-follicle-bulge SCs have two important mechanisms for increasing their resistance to DNA-damage-induced cell death: higher expression of the anti-apoptotic gene Bcl-2 and transient stabilization of p53 after DNA damage in bulge SCs. The attenuated p53 activation is the consequence of a faster DNA repair activity, mediated by a higher non-homologous end joining (NHEJ) activity, induced by the key protein DNA-PK. Because NHEJ is an error-prone mechanism, this novel characteristic of adult SCs may have important implications in cancer development and ageing.
Subject(s)
DNA Repair , Hair Follicle/cytology , Multipotent Stem Cells/cytology , Multipotent Stem Cells/physiology , Stem Cells/metabolism , Adult , Aging , Animals , Biochemical Phenomena , Cell Death , DNA/metabolism , DNA Damage , Epidermis/metabolism , Hair Follicle/metabolism , Hair Follicle/physiology , Humans , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Mice, Inbred Strains , Mice, Knockout , Mice, SCID , Multipotent Stem Cells/metabolism , Tumor Suppressor Protein p53/metabolismABSTRACT
During embryonic development, multipotent cardiovascular progenitor cells are specified from early mesoderm. Using mouse ESCs in which gene expression can be temporally regulated, we have found that transient expression of Mesp1 dramatically accelerates and enhances multipotent cardiovascular progenitor specification through an intrinsic and cell autonomous mechanism. Genome-wide transcriptional analysis indicates that Mesp1 rapidly activates and represses a discrete set of genes, and chromatin immunoprecipitation shows that Mesp1 directly binds to regulatory DNA sequences located in the promoter of many key genes in the core cardiac transcriptional machinery, resulting in their rapid upregulation. Mesp1 also directly represses the expression of key genes regulating other early mesoderm and endoderm cell fates. Our results demonstrate that Mesp1 acts as a key regulatory switch during cardiovascular specification, residing at the top of the hierarchy of the gene network responsible for cardiovascular cell-fate determination.
