Kinetic analysis of strand invasion during C. elegans meiosis reveals similar rates of sister- and homolog-directed repair

AbstractMeiotic chromosome segregation requires reciprocal exchanges between the parental chromosomes (homologs). Exchanges are formed via tightly-regulated repair of double-strand DNA breaks (DSBs). However, since repair intermediates are mostly quantified in fixed images, our understanding of the mechanisms that control the progression of repair remains limited. Here, we study meiotic repair kinetics in Caenorhabditis elegans by extinguishing new DSBs and following the disappearance of a crucial intermediate - strand invasion mediated by the conserved RecA-family recombinase RAD-51. We find that RAD-51 foci have a half-life of 42-132 minutes for both endogenous and exogenous DSBs. Surprisingly, we find that repair templated by the sister chromatid is not slower than repair templated by the homolog. This suggests that differential kinetics are unlikely to underlie homolog bias: the preferential use of the homolog as a repair template. We also use our kinetic information to revisit the total number of DSBs per nucleus - the substrate for the formation of exchanges - and find an average of 40 DSBs in wild-type meiosis and >50 DSBs when homolog pairing is perturbed. Our work opens the door for analysis of the interplay between meiotic repair kinetics and the fidelity of genome inheritance. Key pointsO_LIBy extinguishing new meiotic DSBs, we define the lifetime of a key repair intermediate. C_LIO_LIWe find similar rates of meiotic DNA repair templated by the sister and the homolog. C_LIO_LIKinetic information allows calculation of the total number of meiotic DSBs in C. elegans. C_LI