Meiotic recombination regulation - in functional meiosis and in hybrid sterility

• Applicant: Linda Odenthal-Hesse, Ph.D.
• Subject Area: General Genetics and Functional Genome Biology ; Evolution, Anthropology ; Evolutionary Cell and Developmental Biology (Zoology)
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 393810578

Genetic information is reshuffled from one generation to the next through meiotic recombination. Meiotic recombination events cluster into recombination hotspots, regions of the genome typically spanning 1-2 kilobases (kb) of DNA. The DNA binding domain of PR-domain containing 9 (PRDM9) determines hotspot locations in trans, at least in most mammals. The DNA binding domain consists of a variable number of C2H2 zinc fingers that confer specificity to DNA binding motifs. The SET-domain of PRDM9 then places trimethylation marks on histone-3 residues in proximity to its binding motif, specifically at lysine-4 (H3K4) and lysine-36 (H3K36). These signals then trigger downstream double-stranded DNA breaks (DSBs), which initiate repair and recombination. Recombination resolution in either reciprocal crossover or nonreciprocal gene conversion signifies successful meiotic recombination. Novel hotspot initiation sites can arise as a consequence of the rapid evolution of the minisatellite coding for the zinc-finger DNA binding domain. Mice have hundreds of functional variants, and recombination landscapes overlap only poorly in individuals with differing zinc-finger domains. Crosses of subspecies of mice with distinct PRDM9 variants can result in hybrid sterility in male offspring. As motif specificities, and thus initiation patterns, differ between progenitor genomes, asymmetry in the placement of initiating breaks ensues. Further initiation sites are formed at PRDM9 independent H3K4 trimethylation marks, mainly at actively transcribed promoters. In PRDM9 knockout mice, recombination is wholly directed to functional elements, these mice show severe chromosome asynapsis, meiotic arrest and infertility. However to date it is unknown whether initiation at these apparent default initiation sites is the underlying cause of the sterility or instead intended as a rescue mechanism. With the current focus on initiation we do not understand the proportion of asymmetric sites that are utilized for recombination resolution, or whether default initiation sites can even be successfully resolved in mice. Instead of focusing solely on initiation sites, we plan to disentangle the proportion of symmetric, asymmetric and default initiation patterns that can be successfully resolved. We do so using wild mice with diverse naturally occurring PRDM9 variants outside of the limited model of laboratory mouse hybrid sterility. Our approach allows us to measure initiation sites and then follow up measuring the genome-wide resolution of recombination events at the broad-scale and the fine-scale distribution of de-novo recombination events within punctate recombination hotspots. This comprehensive approach should allow detailed insights into the dynamics and regulating factors of meiotic recombination at PRDM9 regulated hotspots, either with symmetric or asymmetric initiation, and PRDM9-independent default hotspots.

• DFG Programme: Research Grants