Project description:Centromeres are maintained epigenetically by the presence of CENP-A, an evolutionarily-conserved histone H3 variant, which directs kinetochore assembly and hence, centromere function. To identify factors that promote assembly of CENP-A chromatin, we affinity selected solubilised fission yeast CENP-ACnp1 chromatin. All subunits of the Ino80 complex were enriched, including the auxiliary subunit Hap2. In addition to a role in maintenance of CENP-ACnp1 chromatin integrity at endogenous centromeres, Hap2 is required for de novo assembly of CENP-ACnp1 chromatin on naïve centromere DNA and promotes H3 turnover on centromere regions and other loci prone to CENP-ACnp1 deposition. Prior to CENP-ACnp1 chromatin assembly, Hap2 is required for transcription from centromere DNA. These analyses suggest that Hap2-Ino80 destabilises H3 nucleosomes on centromere DNA through transcription-mediated histone H3 turnover, driving the replacement of resident H3 nucleosomes with CENP-ACnp1 nucleosomes. These inherent properties define centromere DNA by directing a program that mediates CENP-ACnp1 assembly on appropriate sequences.
Project description:Centromeres are maintained epigenetically by the presence of CENP-A, an evolutionarily conserved histone H3 variant, which directs kinetochore assembly and hence centromere function. To identify factors that promote assembly of CENP-A chromatin, we affinity-selected solubilized fission yeast CENP-ACnp1 chromatin. All subunits of the Ino80 complex were enriched, including the auxiliary subunit Hap2. Chromatin association of Hap2 is Ies4-dependent. In addition to a role in maintenance of CENP-ACnp1 chromatin integrity at endogenous centromeres, Hap2 is required for de novo assembly of CENP-ACnp1 chromatin on naïve centromere DNA and promotes H3 turnover on centromere regions and other loci prone to CENP-ACnp1 deposition. Prior to CENP-ACnp1 chromatin assembly, Hap2 facilitates transcription from centromere DNA. These analyses suggest that Hap2-Ino80 destabilizes H3 nucleosomes on centromere DNA through transcription-coupled histone H3 turnover, driving the replacement of resident H3 nucleosomes with CENP-ACnp1 nucleosomes. These inherent properties define centromere DNA by directing a program that mediates CENP-ACnp1 assembly on appropriate sequences.
Project description:Centromere is the chromosomal locus at which kinetochore is assembled to direct chromosome segregation. Histone H3 variant CENP-A epigenetically marks active centromeres; however, the mechanism by which CENP-A propagates at the centromere, replacing histone H3, remains poorly understood. Using fission yeast, we find that CENP-ACnp1 chromatin assembly at the centromere requires the Ino80 ATP-dependent chromatin remodeling complex which removes histone H3-containing nucleosomes from associated chromatin. CENP-ACnp1 chromatin actively recruits the Ino80 complex to centromeres to elicit eviction of histone H3-containing nucleosomes. Artificial targeting of Ino80 subunits to a non-centromeric DNA placed in a native centromere enhances the spreading of CENP-ACnp1 chromatin into the non-centromeric DNA. Based on these results, we propose that CENP-ACnp1 chromatin employs the Ino80 complex to mediate replacement of histone H3 with CENP-ACnp1, and thereby reinforces itself.
Project description:The centromere is the location on each chromosome that directs the assembly of the kinetochore. The underlying hallmark of centromeres in most eukaryotes is the presence of specialised nucleosomes in which canonical histone H3 is replaced by the histone H3 variant CENP-A. The molecular events that mediate a programme to install CENP-A in place of histone H3, at centromeres and how the centromeric chromatin is reorganised for CENP-A assembly during cell cycle remain poorly characterised. Histone H2A variant, H2A.Z is linked to transcriptional competence, in maintaining heterochromatin silencing and enriched in CENP-A chromatin. Our analyses demonstrate that H2A.ZPht1 and the Swr1 complex are associated with CENP-ACnp1 chromatin in fission yeast. Swr1 and Msc1 regulate H2A.ZPht1 deposition at centromeres and along with H2A.ZPht1 maintain CENP-ACnp1 chromatin integrity. Additionally, they coordinate the deposition of CENP-ACnp1 through the cell cycle, coupled with eviction of histone H3 from centromeres. Based on our results, we propose that the centromere is programmed to the widespread incorporation of H2A.ZPht1 via Swr1, and that H2A.ZPht1 dynamics likely play a role in regulating centromeric chromatin by influencing CENP-A incorporation.
Project description:INO80 is the catalytic subunit of the multi-subunit INO80-chromatin remodeling complex that has been implicated in DNA replication, repair, and transcription regulation. Ino80-deficiency in murine spermatocytes (Ino80cKO) results in pachytene arrest of spermatocytes, due to incomplete synapsis and aberrant DNA double-strand break repair (DSBR) that leads to apoptosis. We explored the mechanism by which INO80 mediates meiotic progression. RNA-seq on Ino80cKO spermatocytes revealed major changes in transcription, indicating that an aberrant transcription program arises upon INO80 depletion. In Ino80WTspermatocytes, genome-wide analysis showed that INO80-binding sites were mostly promoter proximal and necessary for the regulation of spermatogenic gene expression, primarily of premeiotic and meiotic genes. Further, most of the genes poised for activity, as well as those genes that are active, shared INO80 binding. In Ino80cKO spermatocytes, most poised genes demonstrated de-repression due to reduced H3K27me3 enrichment, and in turn showed increased expression levels. INO80 interacts with the core PRC2 complex member SUZ12 and promotes its recruitment. Further, INO80 mediates H2A.Z incorporation at the poised promoters, which was reduced in Ino80cKO spermatocytes. Taken together, INO80 is emerging as a major regulator of the meiotic transcription program by mediating poised chromatin establishment through SUZ12 binding.
Project description:INO80 is the catalytic subunit of the multi-subunit INO80-chromatin remodeling complex that has been implicated in DNA replication, repair, and transcription regulation. Ino80-deficiency in murine spermatocytes (Ino80cKO) results in pachytene arrest of spermatocytes, due to incomplete synapsis and aberrant DNA double-strand break repair (DSBR) that leads to apoptosis. We explored the mechanism by which INO80 mediates meiotic progression. RNA-seq on Ino80cKO spermatocytes revealed major changes in transcription, indicating that an aberrant transcription program arises upon INO80 depletion. In Ino80WTspermatocytes, genome-wide analysis showed that INO80-binding sites were mostly promoter proximal and necessary for the regulation of spermatogenic gene expression, primarily of premeiotic and meiotic genes. Further, most of the genes poised for activity, as well as those genes that are active, shared INO80 binding. In Ino80cKO spermatocytes, most poised genes demonstrated de-repression due to reduced H3K27me3 enrichment, and in turn showed increased expression levels. INO80 interacts with the core PRC2 complex member SUZ12 and promotes its recruitment. Further, INO80 mediates H2A.Z incorporation at the poised promoters, which was reduced in Ino80cKO spermatocytes. Taken together, INO80 is emerging as a major regulator of the meiotic transcription program by mediating poised chromatin establishment through SUZ12 binding.
Project description:INO80 is the catalytic subunit of the multi-subunit INO80-chromatin remodeling complex that has been implicated in DNA replication, repair, and transcription regulation. Ino80-deficiency in murine spermatocytes (Ino80cKO) results in pachytene arrest of spermatocytes, due to incomplete synapsis and aberrant DNA double-strand break repair (DSBR) that leads to apoptosis. We explored the mechanism by which INO80 mediates meiotic progression. RNA-seq on Ino80cKO spermatocytes revealed major changes in transcription, indicating that an aberrant transcription program arises upon INO80 depletion. In Ino80WTspermatocytes, genome-wide analysis showed that INO80-binding sites were mostly promoter proximal and necessary for the regulation of spermatogenic gene expression, primarily of premeiotic and meiotic genes. Further, most of the genes poised for activity, as well as those genes that are active, shared INO80 binding. In Ino80cKO spermatocytes, most poised genes demonstrated de-repression due to reduced H3K27me3 enrichment, and in turn showed increased expression levels. INO80 interacts with the core PRC2 complex member SUZ12 and promotes its recruitment. Further, INO80 mediates H2A.Z incorporation at the poised promoters, which was reduced in Ino80cKO spermatocytes. Taken together, INO80 is emerging as a major regulator of the meiotic transcription program by mediating poised chromatin establishment through SUZ12 binding.
Project description:INO80 is the catalytic subunit of the multi-subunit INO80-chromatin remodeling complex that has been implicated in DNA replication, repair, and transcription regulation. Ino80-deficiency in murine spermatocytes (Ino80cKO) results in pachytene arrest of spermatocytes, due to incomplete synapsis and aberrant DNA double-strand break repair (DSBR) that leads to apoptosis. We explored the mechanism by which INO80 mediates meiotic progression. RNA-seq on Ino80cKO spermatocytes revealed major changes in transcription, indicating that an aberrant transcription program arises upon INO80 depletion. In Ino80WTspermatocytes, genome-wide analysis showed that INO80-binding sites were mostly promoter proximal and necessary for the regulation of spermatogenic gene expression, primarily of premeiotic and meiotic genes. Further, most of the genes poised for activity, as well as those genes that are active, shared INO80 binding. In Ino80cKO spermatocytes, most poised genes demonstrated de-repression due to reduced H3K27me3 enrichment, and in turn showed increased expression levels. INO80 interacts with the core PRC2 complex member SUZ12 and promotes its recruitment. Further, INO80 mediates H2A.Z incorporation at the poised promoters, which was reduced in Ino80cKO spermatocytes. Taken together, INO80 is emerging as a major regulator of the meiotic transcription program by mediating poised chromatin establishment through SUZ12 binding.