R-loops’ effect on chromosome stability and temporal regulation of DNA double-strand break processing in the C. elegans germline

Double strand breaks are serious forms of DNA damage that can result in mutations, chromosome rearrangements, and even cell death when not properly repaired. The germline, a body tissue in which meiosis occurs and which is responsible for the formation of gametes (i.e. eggs and sperm), systematically programs for DNA double strand breaks however in order to allow for necessary exchanges between chromosomes called crossovers. The work in this thesis serves to further our understanding of how repair of these programmed breaks is regulated to ensure that chromosomes are properly distributed in eggs and sperm and that fertility is maintained. We show that the processing of programmed double strand breaks in the germline is dependent on the time during meiosis at which the break occurs and that this is related to the chromosome’s ability to form the crossover. Additionally, this work identifies a requirement for the resolution of structures called R-loops which can cause double strand breaks in cell divisions before meiosis that challenge the cell’s ability to complete meiosis faithfully, leading to broken chromosomes in the gametes. This requirement extends to programmed double strand breaks in meiosis; when R-loop-type structures arise on meiotic chromosomes, excessive crossovers are formed along the chromosomes. In totality, this thesis contributes novel insights into the intricate landscape of double strand break repair mechanisms in the germline, spanning both pre-meiotic and meiotic events. The discoveries made in this body of evidence shed light on the cellular mechanisms underlying genome maintenance and emphasize the importance of safeguarding genetic integrity during the generation of eggs and sperm.