Project description:Meiotic homologous recombination is a critical DNA-templated event for sexually-reproducing organisms. It is initiated by a programmed formation of DNA double strand breaks (DSBs), mainly formed at recombination hotspots, and is, like all other DNA-related processes, under great influence of chromatin structure. For example, local chromatin around hotspots directly impacts DSB formation. In addition, DSB is proposed to occur in a higher-order chromatin architecture termed “axis-loop”, in which many loops protrude from proteinaceous axis. Despite many recent insightful studies, still much remains unknown about how meiotic DSBs are generated in chromatin structure. Here, we show that the highly conserved histone H2A variant H2A.Z promotes meiotic DSB formation in fission yeast. Subsequent investigation revealed that H2A.Z is neither enriched around hotspots nor axis sites, and that transcript levels of DSB-promoting factors were maintained in the absence of H2A.Z. Instead, we found that H2A.Z facilitates chromatin binding of various proteins required for DSB formation. Strikingly, artificial tethering of one of such proteins, Rec10, to chromatin partially restored DSB reduction in H2A.Z-lacking cells. Based on these, we conclude that fission yeast H2A.Z promotes initiation of meiotic recombination partly through delivering DSB-related proteins onto chromatin.
Project description:Meiotic homologous recombination is a critical DNA-templated event for sexually-reproducing organisms. It is initiated by a programmed formation of DNA double strand breaks (DSBs), mainly formed at recombination hotspots, and is, like all other DNA-related processes, under great influence of chromatin structure. For example, local chromatin around hotspots directly impacts DSB formation. In addition, DSB is proposed to occur in a higher-order chromatin architecture termed “axis-loop”, in which many loops protrude from proteinaceous axis. Despite many recent insightful studies, still much remains unknown about how meiotic DSBs are generated in chromatin structure. Here, we show that the highly conserved histone H2A variant H2A.Z promotes meiotic DSB formation in fission yeast. Subsequent investigation revealed that H2A.Z is neither enriched around hotspots nor axis sites, and that transcript levels of DSB-promoting factors were maintained in the absence of H2A.Z. Instead, we found that H2A.Z facilitates chromatin binding of various proteins required for DSB formation. Strikingly, artificial tethering of one of such proteins, Rec10, to chromatin partially restored DSB reduction in H2A.Z-lacking cells. Based on these, we conclude that fission yeast H2A.Z promotes initiation of meiotic recombination partly through delivering DSB-related proteins onto chromatin.
Project description:Among the collection of chromatin modifications that influence its function and structure, the substitution of canonical histones by the so-called histone variants is one of the most prominent actions. Since crucial meiotic transactions are modulated by chromatin, here we investigate the functional contribution of the H2A.Z histone variant during both unperturbed meiosis and upon challenging conditions where the meiotic recombination checkpoint is triggered in budding yeast by the absence of the synaptonemal complex component Zip1. We have found that H2A.Z localizes to meiotic chromosomes in an SWR1-dependent manner. Although meiotic recombination is not substantially altered, the htz1 mutant (lacking H2A.Z) shows slower meiotic progression, impaired sporulation and reduced spore viability. These phenotypes are likely accounted for by the misregulation of meiotic gene expression landscape observed in htz1. In the zip1 mutant, the absence of H2A.Z results in a tighter meiotic arrest imposed by the meiotic recombination checkpoint. We have found that Mec1-dependent Hop1-T318 phosphorylation and the ensuing Mek1 activation are not significantly altered in zip1 htz1; however, downstream checkpoint targets, such as the meiosis I-promoting factors Ndt80, Cdc5 and Clb1, are drastically down-regulated. The study of the checkpoint response in zip1 htz1 has also allowed us to reveal the existence of an additional function of the Swe1 kinase, independent of CDK inhibitory phosphorylation, which is relevant to restrain meiotic cell cycle progression. In summary, our study shows that the H2A.Z histone variant impacts various aspects of meiotic development adding further insight into the relevance of chromatin dynamics for accurate gametogenesis.
Project description:Meiotic recombination differs between males and females, however, when and how these differences are established is unknown. We identify extensive sex differences at recombination initiation by mapping hotspots of meiotic DNA double strand breaks in male and female mice. Contrary to past findings in humans, few hotspots are used uniquely in either sex. Instead, grossly different recombination landscapes result from up to 15-fold differences in hotspot use between males and females. Indeed, most recombination occurs at sex-biased hotspots. Sex biased hotspots appear to be partly determined by chromosome structure, and DNA methylation, absent in females at the onset of meiosis, plays a substantial role. Sex differences are also evident later in meiosis as the repair frequency of distal meiotic breaks as crossovers diverges in males and females. Suppression of distal crossovers may help to minimize age-related aneuploidy that arises due to cohesion loss during dictyate arrest in females.
Project description:To investigate the relationship between meiotic recombination initiation and H3K4m3 in Arabidopsis, we generated and sequenced H3K4m3 ChIP libraries from meiotic stage floral buds in wild type, arp6 and met1. To produce high-resolution of H3K4m3 mapping, we used micrococcal nuclease (MNase) to digest chromatins that were cross-linked by formaldehyde for ChIP. This experiment provides for H3K4m3 maps with the resolution of mononucleosomal DNA level (~150 bp).
Project description:To determine meiotic recombination initiation sites in Arabidopsis thaliana genome we purified and sequenced oligonucleotides (35-45 nt) bound to SPO11-1, meiosis specific transesterase that induces meiotic DSB formation. This reveals that SPO11-1-oligonucleotide hotspots occur at nucleosome depleted regions of gene promoters, introns, terminators and specific families of DNA transposons (recomposons). To investigate the influence of chromatin structure and epigenetic factors on meiotic DSB formation we performed sequencing of SPO11-1-oligonucleotides in arp6, met1 and suvh4 suvh5 suvh6.
Project description:Orderly segregation of chromosomes during meiosis requires that crossovers form between homologous chromosomes by recombination. Programmed DNA double-strand breaks (DSBs) initiate meiotic recombination. We identify ANKRD31 as a critical component of complexes of DSB-promoting proteins which assemble on meiotic chromosome axes. Genome-wide, ANKRD31 deficiency causes delayed recombination initiation. In addition, loss of ANKRD31 alters DSB distribution owing to reduced selectivity for sites that normally attract DSBs. Strikingly, ANKRD31 deficiency also abolishes uniquely high rates of recombination that normally characterize pseudoautosomal regions (PARs) of X and Y chromosomes. Consequently, sex chromosomes do not form crossovers leading to chromosome segregation failure in ANKRD31-deficient spermatocytes. These defects are accompanied by a genome-wide delay in assembling DSB-promoting proteins on axes and a loss of a pecialized PAR-axis domain that is highly enriched for DSB-promoting proteins. Thus, we propose a model for spatiotemporal patterning of recombination by ANKRD31-dependent control of axis-associated complexes of DSB-promoting proteins.
Project description:Meiotic recombination is initiated by programmed formation of DNA double strand breaks (DSBs), which are mainly formed at recombination hotspots. Meiotic DSBs require multiple proteins including the conserved protein Spo11 and its cofactors, and are influenced by chromatin structure. For example, local chromatin around hotspots directly impacts DSB formation. Moreover, DSB is proposed to occur in a higher-order chromatin architecture termed 'axis-loop', in which many loops protrude from cohesin-enriched axis. However, still much remains unknown about how meiotic DSBs are generated in chromatin. Here, we show that the conserved histone H2A variant H2A.Z promotes meiotic DSB formation in fission yeast. Detailed investigation revealed that H2A.Z is neither enriched around hotspots nor axis sites, and that transcript levels of DSB-promoting factors were maintained without H2A.Z. Moreover, H2A.Z appeared to be dispensable for chromatin binding of meiotic cohesin. Instead, in H2A.Z-lacking mutants, multiple proteins involved in DSB formation, such as the fission yeast Spo11 homolog and its regulators, were less associated with chromatin. Remarkably, nuclei were more compact in the absence of H2A.Z. Based on these, we propose that fission yeast H2A.Z promotes meiotic DSB formation partly through modulating chromosome architecture to enhance interaction between DSB-related proteins and cohesin-loaded chromatin.
Project description:The H2A.Z histone variant is deposited into chromatin by the SWR1 complex affecting multiple aspects of meiosis. Here we describe a SWR1-independent localization of H2A.Z at meiotic telomeres and the centrosome. We demonstrate that H2A.Z colocalizes and interacts with Mps3, the SUN component of the LINC complex that spans the nuclear envelope and links meiotic telomeres to the cytoskeleton promoting meiotic chromosome movement. H2A.Z also interacts with the meiosis-specific Ndj1 protein that anchors telomeres to the nuclear periphery via Mps3. Telomeric localization of H2A.Z depends on Ndj1 and the N-terminal domain of Mps3. Although telomeric attachment to the nuclear envelope is maintained in the absence of H2A.Z, the distribution of Mps3 is altered. The velocity of chromosome movement during meiotic prophase I is reduced in the htz1? mutant lacking H2A.Z, but it is unaffected in swr1? cells. We reveal that H2A.Z is an additional LINC-associated factor that contributes to promote telomere-driven chromosome motion critical for error-free gametogenesis.