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: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:Global warming imposes a major threat to plant growth and crop production. In some plants including Arabidopsis thaliana, elevated temperatures induce a series of morphological and developmental adjustments, termed thermomorphogenesis to facilitate plant cooling under high-temperature conditions. Plant thermal response is suppressed by histone variant H2A.Z. At warm temperatures, H2A.Z is evicted from nucleosomes at thermo-responsive genes, resulting in their activation. However, the mechanisms that regulate H2A.Z eviction and subsequent transcription activation are largely unknown. Here, we show that the ino80 chromatin-remodeling complex (ino80-C) promotes thermomorphogenesis and activates the expression of thermo-responsive and auxin-related genes. ino80-C associates with PHYTOCHROME-INTERACTING FACTOR 4 (PIF4), a potent regulator in thermomorphogenesis, and mediates temperature-induced H2A.Z eviction at PIF4 targets. Moreover, ino80-C directly interacts with COMPASS-like and transcription elongation factors to promote active histone modification Histone H3 lysine 4 trimethylation (H3K4me3) and RNA Polymerase II (RNA Pol II) elongation, leading to the thermal induction of transcription. Notably, transcription elongation factors are required for the eviction of H2A.Z at PIF4 targets, suggesting the cooperation of ino80-C and transcription elongation in H2A.Z removal. Our results demonstrate that the (PIF4)-(ino80-C)-(COMPASS-like)-(transcription elongator) module controls plant thermal response, and establish a link between H2A.Z eviction and active transcription.
Project description:Global warming imposes a major threat to plant growth and crop production. In some plants including Arabidopsis thaliana, elevated temperatures induce a series of morphological and developmental adjustments, termed thermomorphogenesis to facilitate plant cooling under high-temperature conditions. Plant thermal response is suppressed by histone variant H2A.Z. At warm temperatures, H2A.Z is evicted from nucleosomes at thermo-responsive genes, resulting in their activation. However, the mechanisms that regulate H2A.Z eviction and subsequent transcription activation are largely unknown. Here, we show that the ino80 chromatin-remodeling complex (ino80-C) promotes thermomorphogenesis and activates the expression of thermo-responsive and auxin-related genes. ino80-C associates with PHYTOCHROME-INTERACTING FACTOR 4 (PIF4), a potent regulator in thermomorphogenesis, and mediates temperature-induced H2A.Z eviction at PIF4 targets. Moreover, ino80-C directly interacts with COMPASS-like and transcription elongation factors to promote active histone modification Histone H3 lysine 4 trimethylation (H3K4me3) and RNA Polymerase II (RNA Pol II) elongation, leading to the thermal induction of transcription. Notably, transcription elongation factors are required for the eviction of H2A.Z at PIF4 targets, suggesting the cooperation of ino80-C and transcription elongation in H2A.Z removal. Our results demonstrate that the (PIF4)-(ino80-C)-(COMPASS-like)-(transcription elongator) module controls plant thermal response, and establish a link between H2A.Z eviction and active transcription.