Novel mechanistic insights into the role of Mer2 as the keystone of meiotic DNA break formation

Abstract

In meiosis, DNA double strand break (DSB) formation by Spo11 initiates recombination and enables chromosome segregation. Numerous factors are required for Spo11 activity, and couple the DSB machinery to the development of a meiosis-specific “axis-tethered loop” chromosome organization. Through in vitro reconstitution and budding yeast genetics we here provide architectural insight into the DSB machinery by focussing on a foundational DSB factor, Mer2. We characterise the interaction of Mer2 with the histone reader Spp1, and show that Mer2 directly associates to nucleosomes, likely highlighting a contribution of Mer2 to tethering DSB factors to chromatin. We reveal the biochemical basis of Mer2 association with Hop1, a HORMA domain-containing chromosomal axis factor. Finally, we identify a conserved region within Mer2 crucial for DSB activity, and show that this region of Mer2 interacts with the DSB factor Mre11. In combination with previous work, we establish Mer2 as a keystone of the DSB machinery by bridging key protein complexes involved in the initiation of meiotic recombination.

Seeding the meiotic DNA break machinery and initiating recombination on chromosome axes

“…Consistent with their conservation, the C-termini of Mer2/IHO1-family proteins are important for interactions with HORMAD1 orthologs in several taxa, including budding 29 and fission 30 yeasts in addition to mammals (Table S2). IHO1 and HORMAD1 orthologs also interact in plants 31, 36, 43, 44 .…”

“…Axial accumulation of the DSB-machinery was proposed to partially depend on interactions between Mer2/IHO1-family proteins and conserved axis-associated HORMA domain proteins in diverse taxa including fungi 20, 29, 30 , plants 31 and mammals 22 . In mammals, the HORMA domain protein HORMAD1 is hypothesized to enhance DSB activity 32, 33 by enabling the formation of extended axial IHO1 platforms, which serve as substructures for focal clusters of SPO11 auxiliary proteins 22 .…”

Construction of a DDR-related signature for predicting of prognosis in metastatic colorectal carcinoma

“…Variants in MLH3 can increase CRC risk (48). SPO11 protein formatted DNA double-strand break (DSB), which initiates recombination and allows chromosome segregation during meiosis (49). Hisham Eldai.…”

Chromosome architecture and homologous recombination in meiosis

“…Although Spp1-mediated TLACs contribute to DSB formation, meiotic cells are equipped with another layer of regulation for meiotic DSB formation, since spp1 mutants still form relatively high levels of DSBs (Acquaviva et al, 2013;Sommermeyer et al, 2013;Zhang et al, 2020). Given that Mer2 itself has an ability to directly bind to nucleosomes and the association of Mer2 to chromosome axes is regulated by its interacting axis-associated protein Hop1, the Hop1-Mer2 may contribute to TLAC formation both via and independently of Spp1 (Panizza et al, 2011;Rousova et al, 2021). In fission yeast, where most DSB hotspots are in long intergenic regions (Fowler et al, 2014), DSB hotspots are marked by another epigenetic mark, H3K9 acetylation, and the H3K4 trimethylation mark is dispensable for meiotic DSB formation (Yamada et al, 2013).…”

“…Frontiers in Cell and Developmental Biology frontiersin.org proteins and associated proteins, and SC components is providing mechanistic insights into their functions (West et al, 2018;Boekhout et al, 2019;West et al, 2019;Sanchez-Saez et al, 2020;Claeys Bouuaert et al, 2021;Dunce et al, 2021;Rousova et al, 2021;Nore et al, 2022). Further mutant analysis based on protein structure will be a key to answer these unaddressed questions.…”