Reactivation of ancestral recombination mechanisms in vertebrates

• Applicant: Linda Odenthal-Hesse, Ph.D.
• Subject Area: Cell Biology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 539767500

Meiosis is responsible for the formation of haploid germ cells in diploid eukaryotes. This specialized cell division consists of two successive rounds of cell division, with recombination giving rise to distinct haploid genomes after only one round of DNA replication. The initiation of recombination depends on the timing of germline replication, dynamic reorganization of chromatin and a number of proteins and is highly regulated. PRDM9-mediated recombination initiation regulates the placement of recombination events in many vertebrates by targeting specific motifs in the genome, which it binds using its zinc finger array. However, PRDM9 function has been lost several times in vertebrates - all dogs, foxes and wolves, as well as birds, crocodiles and some fish species. These organisms appear to recombine at existing sites with H3K4 trimethylation, such as gene promoters. In contrast to some PRDM9 knockout mouse strains that initiate recombination in gene promoters but cannot successfully repair them, these organisms can therefore successfully repair double-stranded DNA breaks in functional elements. A rare case of a fertile woman with PRDM9 null alleles suggests that this may also be possible in humans. However, it is unknown what properties such recombination events in gene promoters possess. Furthermore, it is unclear whether this is a conserved default recombination mechanism or whether each species has evolved new strategies to compensate for the secondary loss of PRDM9. Fine-scale meiotic recombination results have never been analyzed in PRDM9-deficient vertebrates, and the distribution of crossover resolution points, the frequency of crossover-associated conversion intercepts, and whether the transmission ratio is skewed in the absence of PRDM9-are unknown. Finally, it is unknown whether PRDM9-independent recombination induces mutational signatures or potential transmission ratio biases, which would be detrimental to organisms that recombine at functional gene promoters. We aim to understand how dogs and birds can successfully perform meiotic recombination in functional elements. By comparing fine recombination patterns of dogs (mammals with recent loss of PRDM9) and birds (vertebrates with a primordial loss of PRDM9), we can gain basic information on the extent to which shared features occur in their recombination hotspots. We will find out whether a common ancestral recombination pathway could be reactivated or whether organisms with such high evolutionary divergence have instead evolved different strategies to compensate for the loss of PRDM9.

• DFG Programme: Research Grants