Project description:To study recombination at the fine-scale, we used high-throughput sequencing of 300 to 1,000 crossovers within the RAC1 R gene hotspot. This revealed focused intragenic crossovers, overlapping exons encoding the TIR, NBS and LRR domains. To examine the role of recombination pathways, we repeated this experiment in recq4a recq4b, fancm and recq4a recq4b fancm mutants. Finally, in order to investigate how varying patterns of interhomolog divergence influence local patterns of crossover frequency, we repeated RAC1 pollen typing sequencing in different F1 hybrids.
Project description:To study recombination at the fine-scale we used high-throughput sequencing to analyse >1,000 crossovers within the RAC1 R gene hotspot. This revealed focused intragenic crossovers, overlapping exons encoding the TIR, NBS and LRR domains (RAC1 pollen typing sequencing). To analyse chromatin structure we performed micrococcal nuclease digestion of wild type (Col-0) chromatin and gel purified the resulting ~150 bp mononucleosomal DNA band. This DNA was used to generate a library and paired-end sequencing performed (MNase-seq)
Project description:Meiotic crossover formation requires the stabilization of early recombination intermediates by a set of proteins and occurs within the environment of the chromosome axis, a structure important for the regulation of meiotic recombination events. The molecular mechanisms underlying and connecting crossover recombination and axis localization are elusive. Here, we identified the ZZS (Zip2–Zip4–Spo16) complex, required for crossover formation, which carries two distinct activities: one provided by Zip4, which acts as hub through physical interactions with components of the chromosome axis and the crossover machinery, and the other carried by Zip2 and Spo16, which preferentially bind branched DNA molecules in vitro. We found that Zip2 and Spo16 share structural similarities to the structure-specific XPF–ERCC1 nuclease, although it lacks endonuclease activity. The XPF domain of Zip2 is required for crossover formation, suggesting that, together with Spo16, it has a noncatalytic DNA recognition function. Our results suggest that the ZZS complex shepherds recombination intermediates toward crossovers as a dynamic structural module that connects recombination events to the chromosome axis. The identification of the ZZS complex improves our understanding of the various activities required for crossover implementation and is likely applicable to other organisms, including mammals.
Project description:Using microarrays to genotype the parental origin of progeny resulting from a cross between S96 and YJM789 yeast strains, we mapped the distribution of crossovers that occurred during meiosis. Knowledge of the crossover distribution allowed us to assess changes in crossover control in wild type and mutant strains. The S96 strain is a S288 derivative and thus its DNA sequence has high homology to the oligo sequences used to create the S98 Affymetrix Gene chip. The YJM789 strain is ~ 0.6% divergent from S288. Keywords: wild type and mutant analysis
Project description:Programmed DNA double-strand breaks (DSBs) initiate meiotic recombination and their subsequent repair culminates in crossover (CO) formation. COs result from the asymmetric cleavage of double-Holliday junction (dHJ) intermediates, that requires the MutLγ endonuclease and a non-catalytic function of Exo1, an activity essential for fertility but at risk of generating unwanted chromosome rearrangements. Here we show how crossover formation by MutLγ is activated at the right time and at the right place. MutLγ forms a constitutive complex with Exo1, and in meiotic cells transiently contacts the upstream MutSγ (Msh4-Msh5) heterodimer. MutLγ associates with DSB hotspots only once recombination intermediates have been stabilized and engaged in the crossover repair pathway. MutLγ-Exo1 is recruited to DSB hotspots independently of the polo-like Cdc5 kinase, but to activate dHJ resolution, Cdc5 is recruited to the recombination intermediates and interacts individually with both MutLγ and Exo1, suggesting their direct modification. in vivo, MutLγ occupancy is restrained on recombination intermediates, and MutLγ associates with the vast majority of DSB hotspots, but at a lower frequency in centromeres, consistent with a strategy to reduce at-risk crossover events in these regions, and in late replicating regions. Our data highlight the tight temporal and spatial control of the activity of this constitutive, potentially harmful, nuclease.
Project description:Programmed DNA double-strand breaks (DSBs) initiate meiotic recombination and their subsequent repair culminates in crossover (CO) formation. COs result from the asymmetric cleavage of double-Holliday junction (dHJ) intermediates, that requires the MutLγ complex together with a non-catalytic function of Exo1, an activity essential for fertility but at risk of generating unwanted chromosome rearrangements. Here we show how crossover formation by MutLγ is activated at the right time and at the right place. MutLγ forms a constitutive complex with Exo1, and in meiotic cells transiently contacts the upstream MutSγ (Msh4-Msh5) heterodimer. MutLγ associates with DSB hotspots at a late step in the recombinational repair, once recombination intermediates have been stabilized and engaged in the crossover repair pathway. MutLγ-Exo1 is recruited to DSB hotspots independently of the polo-like Cdc5 kinase, but to activate dHJ resolution, Cdc5 is recruited to the recombination intermediates and interacts individually with both MutLγ and Exo1, suggesting their direct modification. in vivo, MutLγ occupancy is restrained on recombination intermediates, and genome-wide, MutLγ associates with the vast majority of DSB hotspots, but at a lower frequency in centromeres, consistent with a strategy to reduce at-risk crossover events in these regions, and in late replicating regions. Our data highlight the highly temporally and spatially control of the activity of this constitutive, potentially harmful, nuclease
Project description:During meiosis, chromosomes undergo DNA double-strand breaks (DSBs), which can be repaired using a homologous chromosome to produce crossovers. Meiotic recombination frequency is variable along chromosomes and tends to concentrate in narrow hotspots. We mapped crossover hotspots located in the Arabidopsis thaliana RAC1 and RPP13 disease resistance genes, using varying haplotypic combinations. We observed a negative non-linear relationship between interhomolog divergence and crossover frequency within the hotspots, consistent with polymorphism locally suppressing crossover repair of DSBs. The fancm, recq4a recq4b, figl1 and msh2 mutants, or lines with increased HEI10 dosage, are known to show increased crossovers throughout the genome. Surprisingly, RAC1 crossovers were either unchanged or decreased in these genetic backgrounds, showing that chromosome location and local chromatin environment are important for regulation of crossover activity. We employed deep sequencing of crossovers to examine recombination topology within RAC1, in wild type, fancm, recq4a recq4b and fancm recq4a recq4b backgrounds. The RAC1 recombination landscape was broadly conserved in the anti-crossover mutants and showed a negative relationship with interhomolog divergence. However, crossovers at the RAC1 5'-end were relatively suppressed in recq4a recq4b backgrounds, further indicating that local context may influence recombination outcomes. Our results demonstrate the importance of interhomolog divergence in shaping recombination within plant disease resistance genes and crossover hotspots.
Project description:Meiotic crossover recombination is triggered by the formation of programmed double strand breaks (DSBs) catalyzed by the conserved Spo11 protein. Only a subset of these DSBs are repaired as crossovers, promoted by a group of eight evolutionarily conserved proteins, named ZMM. The synaptonemal complex (SC) that assembles between homologous chromosomes is composed of two axial elements, from which chromatin loops emanate, held together by a central region, composed of the central element and a transverse filament protein. In budding yeast, crossover formation is functionally linked to the formation of the SC, but the underlying mechanism is unknown. Here we found that the SC central element protein, Ecm11, mainly localizes on both DSB sites and sites that attach chromatin loops to the chromosome axis, in a way that strictly requires the ZMM protein Zip4. We further show that Zip4 directly interacts with Ecm11 and that point mutants that specifically abolish the Zip4-Ecm11 interaction loose Ecm11 binding to chromosomes and exhibit defective SC assembly. Interestingly, SC assembly can be partially rescued by artificially tethering interaction-defective Ecm11 to Zip4. This direct connection that ensures SC assembly from CO sites could be a way for the meiotic cell to shut down further DSB formation once enough recombination sites have been selected for crossovers, thereby preventing excess crossovers. Finally, we found that the mammalian ortholog of Zip4, TEX11, interacts with the SC central element TEX12, raising the possibility that this may be a general mechanism.
Project description:Interference exists ubiquitously in many biological processes. Crossover interference patterns meiotic crossovers, which are required for faithful chromosome segregation and evolutionary adaption. However, what the interference signal is and how it is generated and regulated are unknown. We show that yeast top2 alleles cannot bind or cleave DNA accumulate a higher level of negative supercoils and show weaker interference. However, top2 alleles cannot religate the cleaved DNA or release the religated DNA accumulate less negative supercoils and show stronger interference. Moreover, the level of negative supercoils is negatively correlated with crossover interference strength in various strains. Furthermore, negative supercoils preferentially enrich at crossover-associated Zip3 regions before the formation of meiotic DNA double-strand breaks, and regions with more negative supercoils tend to have more Zip3. Additionally, the strength of crossover interference and homeostasis change coordinately in mutants. These findings suggest that the accumulation and relief of negative supercoils pattern meiotic crossovers.