Grant: Operating Grant

Genetic diversity is provided by de novo transmittable mutations and it is now known that most new mutations are male- driven. During the formation of spermatozoa, the final steps involves a major change in the way DNA is packaged and we demonstrated that this is accompanied by the formation of transient DNA breaks in spermatids of both human and mouse pointing to an evolutionary-conserved mechanism. Interestingly, we have shown that a significant fraction of these breaks affect both DNA strands (double-stranded). These breaks occur in haploid cells where there is a single set of chromosome. The repair process cannot therefore proceed using the homologous chromosome as template as in normal somatic cells and must rather rely on a end-joining process. These end-joining repair processes are less reliable and known to induce DNA deletions and insertions. Our hypothesis is that mutations can therefore be induced when the double-stranded breaks are repaired in the subsequent steps of the spermatid's differentiation process. Our goal is therefore to confirm whether this process is indeed genetically unstable and if specific regions are involved in the ethiology of some genetic diseases. We have will therefore establish the distribution of break sites in the whole genome, the possible mutations induced by the chromatin remodeling at these sites and the DNA repair machinery involved. The effect of aging on these parameters will also be investigated. Provided with key preliminary evidence and using a candidate gene approach, we will also determine whether pathological elongation CAG repeats may origin from the chromatin remodelling in spermatids. Once this concept and the tools used are established with the mouse model, we will proceed for validation in human. These investigations may confirm the discovery of a novel mechanism contributing to genetic diversity and evolution.