Friday, May 9, 2025
5/9/2025
Germline Mutagenesis at Recombination Hotspots - Abstract Germline de novo mutations impact human health and drive genome evolution. Among variants, little is known about de novo structural variants (SVs) that are rare and difficult to identify, but can affect genome integrity more than point mutations due to their larger size (≥50 bp). Furthermore, how de novo SVs originate in the germline is not fully understood. Meiosis is a potential source, because of the abundance of DNA double-strand breaks (DSBs) that are deliberately formed by the SPO11 protein to initiate meiotic recombination. While recombination ensures the reductional division of diploid cells and thus is essential for the formation of haploid gametes, DSBs are intrinsically mutagenic. My research program will address the mechanisms and factors that promote aberrant repair at meiotic DSBs, resulting in genome alterations. We recently discovered in mice that closely spaced DSBs (double cuts) can undergo end joining, leading to de novo SVs, including deletions and tandem duplications. These events are rare in normal meiosis, but arise more frequently in the absence of the ATM kinase, which has a conserved role in regulating DSBs. Many genomic locations are at risk for end joining, as meiotic DSBs are formed at hotspots, many of which are separated by short genomic distances (<10 kb). In addition, double cuts within a single hotspot can initiate smaller deletions, and released DNA fragments can insert at other genomic sites undergoing DSBs. Thus, we uncovered new types of meiosis-specific mutational events, which are also predicted to arise at human recombination hotspots. However, the underlying molecular mechanisms remain unclear. Next generation sequencing technologies, innovative molecular assays, computational tools, and mouse mutants will be utilized to define which end joining pathway(s) is employed, how it operates in the context of SPO11-induced DSBs, and what factors promote its use. We focus on the classical and alternative nonhomologous end-joining pathways, known to repair mitotic breaks in mammalian cells, but we also hypothesize that single strand annealing may be used at hotspots flanked by repeats. Furthermore, we will expand our findings in mouse models to investigate de novo SVs at nearby DSBs in human meiosis. Here, in addition, we will ask whether age or specific genetic factors enhance illegitimate repair at meiotic DSBs. This research will advance our understanding of the mutagenic potential of the meiotic genome and the origin of de novo mutations in humans.
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