Research Summary
Throughout life, DNA damage constantly arises from DNA replication, spontaneous chemical reactions and assaults by external or metabolism-derived agents. Of all types of DNA damage DNA double-strand breaks (DSBs) represent the greatest threat to the integrity of the genome. Cells have evolved complex DNA damage response mechanisms to ensure genomic integrity that use signaling networks to sense DSBs, arrest the cell cycle, activate DNA repair processes, and finally, restore the original chromatin structure. In contrast to postmitotic or short-lived somatic cells, tissue-specific stem cells (SC) must persist and function throughout life to ensure tissue homeostasis and repair. These adult tissue-specific SC are functionally defined by their ability to both self-perpetuate, through a process known as self-renewal, and give rise to effector cell types, through differentiation. Long-term maintenance of these essential SC properties relies, to a large extent, on interaction with supporting cells that compromise the SC niche. The enormous functional demands and longevity of stem cells raises the possibility that SC might be uniquely equipped to maintain genomic integrity, in ways different than somatic cells.
Using an in-vivo model with repair-proficient and repair-deficient mice our lab applies a combination of various molecular approaches to analyze DSB repair mechanisms in different tissue-specific SC embedded in their physiological microenvironment. Given that the higher order chromatin structure has a decisive impact on the DNA damage response, particularly in SC employing unique chromatin compositions to regulate the balance between pluripotency and differentiation, we established a high-resolution transmission electron microscopy (TEM) approach to visualize gold-labeled DNA repair proteins in the different chromatin environments. The ultra-high resolution of TEM offers the intriguing possibility to detect the different components of the DNA repair machinery at the single-molecule level and to visualize their molecular interactions within the intact nuclear structure. We argue that DNA damage accumulation during physiological ageing and after exposure to ionizing irradiation (even after very low doses) may compromise stem cell functions and thus may have deleterious consequences to the long-term homeostasis of tissues.
