DNA of all living organisms is prone to damage. DNA breaks represent one of the most toxic forms of DNA damage. Cell can employ either of two main DNA double-strand break repair pathways, non-homologous end-joining or homologous recombination. In end joining, the two broken pieces of DNA are joined without a template, which may lead to point mutations or joining of wrong DNA fragments, leading to translocations. The other process, termed homologous recombination is more accurate, but also a more complex system that necessitates multifaceted regulatory mechanisms.
The overall aim of the project was to understand the mechanism of function of nucleases that function in the homologous recombination pathway. Nucleases act both early and late during recombination. The early function involves a process termed DNA end resection. Here, nucleolytic processing of the DNA ends commits the repair to the recombination pathway, as resected DNA end are no longer ligatable by end-joining. The first aim of the project was to understand how nucleases function in DNA end resection, and how this contributes to the pathway choice in DNA double-strand break repair.
Understanding the regulation of the pathway choice is very relevant with regard to gene editing, as only a recombination-based mechanism can introduce a specific mutation. Understanding processes that affect the balance between the two main DNA double-strand break repair pathways can thus improve the efficacy of genome editing. The resection nuclease complexes have also a poorly-defined function at challenged DNA replication forks, and were linked to chemoresistance of certain types of cancer.
The second aim of the project is to define the function of a specific nuclease complex that functions late in recombination to separate recombining DNA molecules. In meiosis, homologous recombination has a specialized function to exchange genetic information between maternal and paternal DNA molecules, which helps proper chromosome segregation and promotes genetic diversity. Our aim was to define the function of a key meiotic nuclease complex that functions in this step. We helped explain how cells manage to undergo meiotic division, generate diversity and avoid aneuploidy.
