Project description:In mouse and human meiosis, DNA double strand breaks (DSBs) initiate homologous recombination and occur at specific sites called hotspots. The localization of these sites is determined by the sequence specific DNA binding domain of the PRDM9 histone methyl transferase. Here we performed an extensive analysis of PRDM9 binding in mouse spermatocytes. Unexpectedly, we identified a non-canonical recruitment of PRDM9 to sites which are devoid of both, recombination activity and the PRDM9-binding consensus motif. These sites include transcription promoters, where PRDM9 is recruited in a DSB-dependent manner. Another subset of non-canonical sites also reveals DSB-independent interactions between PRDM9 and genomic sites, which include binding sites for the insulator protein CTCF. We propose that these DSB-independent sites result from interactions between hotspot bound PRDM9 and genomic sequences located on the chromosome axis.
Project description:PRDM9 is a histone methyltransferase expressed in meiotic germ cells that determines the location of genetic recombination hotspots through binding of its allele-specific DNA binding domain. Here we characterize the genome-wide chromatin modification for two human PRDM9 alleles (A and C) in human cell lines. HEK293 cells were transfected with both alleles and an empty vector control. Resulting chromatin was subjected to H3K4me3 ChIP followed by high-throughput sequencing. We find that different PRDM9 allele largely modified chromatin in entirely different genomic regions in somatic cells determined by the protein's zinc-finger DNA binding domains. Many of the allele-specific peaks overlap sites of meiotic double-strand breaks found in vivo in human germ cells suggesting that transient expression of PRDM9 in somatic cells can reflect binding in vivo. Identify PRDM9-dependent H3K4me3 sites by comparing modified chromatin after expression of different human PRDM9 alleles in HEK293 cells.
Project description:Here we characterize the genome-wide chromatin modification by PRDM9, a histone H3 lysine 4 methyltransferase. In order to detect PRDM9 binding sites we created coisogenic strains of mice differing only in the zinc finger array of PRDM9. One strain is C57BL/6J, which carries the Prdm9Dom2 allele, the other strain was created using genomic replacement and named B6.PRDM9Cst (also called KI), and contains the Prdm9Cst allele originally found in CAST/EiJ mice. Many H3K4me3 positions are common between strains and represent other methyltransferase activity (such as promoters), sites that are unique to one mouse strain likely represent the binding position of that allele of PRDM9. Identify PRDM9-dependent H3K4me3 sites by comparing modified chromatin from mice coisogenic for Prdm9.
Project description:Meiotic recombination starts with the formation of DNA double-strand breaks (DSBs) at specific genomic locations that correspond to PRDM9-binding sites. The molecular steps occurring from PRDM9 binding to DSB formation are unknown. Using proteomic approaches to find PRDM9 partners, we identified HELLS, a member of the SNF2-like family of chromatin remodelers. Upon functional analyses during mouse male meiosis, we demonstrated that HELLS is required for PRDM9 binding and DSB activity at PRDM9 sites. However, HELLS is not required for DSB activity at PRDM9-independent sites. HELLS is also essential for 5-hydroxymethylcytosine (5hmC) enrichment at PRDM9 sites. Analyses of 5hmC in mice deficient for SPO11, which catalyzes DSB formation, and in PRDM9 methyltransferase deficient mice reveal that 5hmC is triggered at DSB-prone sites upon PRDM9 binding and histone modification, but independent of DSB activity. These findings highlight the complex regulation of the chromatin and epigenetic environments at PRDM9-specified hotspots.
Project description:We report a novel technique, Affinity-seq, that for the first time identifies both the genome-wide binding sites of DNA-binding proteins and quantitates their relative affinities. We have applied this in vitro technique to PRDM9, the zinc-finger protein that activates genetic recombination, obtaining new information on the regulation of hotspots, whose locations and activities determine the recombination landscape. We identified 31,770 binding sites in the mouse genome for the PRDM9Dom2 variant. Comparing these results with hotspot usage in vivo, we find that less than half of potential PRDM9 binding sites are utilized in vivo. We show that hotspot usage is increased in actively transcribed genes and decreased in genomic regions containing H3K9me2/3 histone marks or bound to the nuclear lamina. These results show that a major factor determining whether a binding site will become an active hotspot and what its activity will be are constraints imposed by prior chromatin modifications on the ability of PRDM9 to bind to DNA in vivo. These constraints lead to the presence of long genomic regions depleted of recombination.
Project description:PRDM9 is a histone methyltransferase expressed in meiotic germ cells that determines the location of genetic recombination hotspots through binding of its allele-specific DNA binding domain. Here we characterize the genome-wide chromatin modification for two human PRDM9 alleles (A and C) in human cell lines. HEK293 cells were transfected with both alleles and an empty vector control. Resulting chromatin was subjected to H3K4me3 ChIP followed by high-throughput sequencing. We find that different PRDM9 allele largely modified chromatin in entirely different genomic regions in somatic cells determined by the protein's zinc-finger DNA binding domains. Many of the allele-specific peaks overlap sites of meiotic double-strand breaks found in vivo in human germ cells suggesting that transient expression of PRDM9 in somatic cells can reflect binding in vivo.
Project description:We report a novel technique, Affinity-seq, that for the first time identifies both the genome-wide binding sites of DNA-binding proteins and quantitates their relative affinities. We have applied this in vitro technique to PRDM9, the zinc-finger protein that activates genetic recombination, obtaining new information on the regulation of hotspots, whose locations and activities determine the recombination landscape. We identified 31,770 binding sites in the mouse genome for the PRDM9Dom2 variant. Comparing these results with hotspot usage in vivo, we find that less than half of potential PRDM9 binding sites are utilized in vivo. We show that hotspot usage is increased in actively transcribed genes and decreased in genomic regions containing H3K9me2/3 histone marks or bound to the nuclear lamina. These results show that a major factor determining whether a binding site will become an active hotspot and what its activity will be are constraints imposed by prior chromatin modifications on the ability of PRDM9 to bind to DNA in vivo. These constraints lead to the presence of long genomic regions depleted of recombination. The terminal zinc finger domain of PRDM9Dom2 (PRDM9ΔZnF1Dom2, 412–847 aa), the allele present in C57BL/6J (B6) mice was cloned and tagged with 6His-HALO and then expressed in E. coli. DNA sheared to 180–200 bp is provided in considerable excess to provide competition between DNA binding sites. Following binding, DNA–protein complexes are then isolated on streptavidin beads and the DNA extracted for deep sequencing. Two replicate Affinity-seq samples were sequenced at 100-bp reads using the Illumina HiSeq 2500. Alignments to the mm9 mouse genome were obtained utilizing BWA v1.2.3 with default parameters and reads which failed to align to unique positions in the genome were discarded. Peaks were called individually for the two replicates with MACS2 at a p value threshold of 0.01 utilizing a control dataset obtained by sequencing the input DNA and subsequently compared, leading ultimately to combining the two replicates for definitive analysis.
Project description:Here we characterize the genome-wide chromatin modification by PRDM9, a histone H3 lysine 4 methyltransferase. In order to detect PRDM9 binding sites we created coisogenic strains of mice differing only in the zinc finger array of PRDM9. One strain is C57BL/6J, which carries the Prdm9Dom2 allele, the other strain was created using genomic replacement and named B6.PRDM9Cst (also called KI), and contains the Prdm9Cst allele originally found in CAST/EiJ mice. Many H3K4me3 positions are common between strains and represent other methyltransferase activity (such as promoters), sites that are unique to one mouse strain likely represent the binding position of that allele of PRDM9.
Project description:Genetic recombination occurs during meiosis, the key developmental program of gametogenesis. Recombination in mammals has been recently linked to the activity of a histone H3 methyl-transferase, PRDM9, the product of the only known speciation gene in mammals. PRDM9 is thought to determine the preferred recombination sites - recombination hotspots - through sequence-specific binding of its highly polymorphic multi-Zn-finger domain. Nevertheless, Prdm9 knockout mice are proficient at initiating recombination. Here we map and analyze the genome-wide distribution of recombination initiation sites in Prdm9 knockout mice and in two mouse strains with different Prdm9 alleles and their F1 hybrid. We show that PRDM9 determines the positions of practically all hotspots in the mouse genome, with the remarkable exception of the pseudoautosomal region – the only area of the genome that undergoes recombination in 100% of cells. Surprisingly, hotspots are still observed in Prdm9 knockout mice and as in wild-type, these hotspots are found at H3K4 trimethylation marks. However, in the absence of PRDM9, the majority of recombination is initiated at promoters and at other sites of PRDM9-independent H3K4 trimethylation. Such sites are rarely targeted in wild-type mice indicating an unexpected role of the PRDM9 protein in sequestering the recombination machinery away from gene promoter regions and other functional genomic elements.
Project description:The programmed formation of hundreds DNA double strand breaks (DSBs) is essential for proper meiosis and fertility. In mice and humans, the location of these breaks is determined by the meiosis-specific protein PRDM9, through the DNA binding specificity of its zinc finger domain. PRDM9 also has methyltransferase activity. Here, we show that this activity is required for H3K4me3 and H3K36me3 deposition and for DSB formation at PRDM9 binding sites. By analyzing mice that express two PRDM9 variants with distinct DNA binding specificities, we reveal severalthe basic principles of PRDM9-dependent DSB site determination, in which an excess of sites are designated through PRDM9 binding and subsequent histone methylation, from which a subset are selected for DSB formation.