Completion of DNA break repair and crossover formation in mammalian meiosis; the critical functions of a previously uncharacterised meiotic protein, MES19

• Applicant: Professor Dr. Attila Tóth
• Subject Area: Cell Biology ; General Genetics and Functional Genome Biology
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 400013308

In meiosis, two consecutive cell divisions lead to generation of haploid gametes from diploid cells. During the first meiotic division, homologous chromosomes (homologues) originating from the father and mother must segregate. The mechanisms preventing segregation errors require that homologues establish physical linkages via crossovers that form by recombination during the first meiotic prophase. Meiotic recombination initiates with the programmed formation of DNA breaks (appr. 200-400 breaks/cell in mice). Single-stranded DNA ends generated by these breaks invade homologous DNA, which leads to the pairing of homologues. Most DNA breaks are repaired by non-crossover recombination, which generates only local gene-conversions but not crossovers, and only few (typically one or two in mice) breaks are turned into crossovers on each homologue pair. It is essential that at least one crossover forms from the multiple DNA strand-invasion events on each chromosome but it is poorly understood how choices between crossover or non-crossover repair are made, and how distinct recombination pathways are controlled to ensure timely DNA repair. We identified MES19 in a screen as a meiosis-specific protein that accumulates at crossover sites. We found that MES19 is crucial for both crossover formation and timely repair of non-crossover recombination intermediates. Our analysis suggests that MES19 is a key player in designating recombination intermediates as crossovers. We will test this hypothesis and position the functions of MES19 and known pro-crossover proteins relative to each other in meiotic crossover formation and DNA break repair. Our approaches will include full phenotypic and genetic analyses of Mes19-deficient mice and various meiotic recombination mutant models (e.g. Hei10, Cntd1, Mlh3) to establish functional and epistatic relationships of MES19. In particular, meiotic recombination will be assayed by both cytological analysis of recombination markers and tetrad analysis in our mouse models. The latter is a very powerful cutting edge method that directly assays recombination outcomes at DNA sequence level, and thus allows making accurate conclusions about the characteristics of recombination. Complementing these, we will address protein interactions of MES19 using biochemistry and yeast two hybrid assays. These combined efforts promise crucial new insights into mechanisms of crossover formation and DNA break repair in mammalian meiosis by revealing MES19 functions in recombination. Given that correct execution of meiotic recombination is crucial for human fertility, genome health and prevention of aneuploidies, the proposed work has important reproduction-related medical implications.

• DFG Programme: Research Grants