Project description:Actin-related proteins are ubiquitous components of chromatin remodelers, and are conserved from yeast to man. We have examined the role of the budding yeast actin-related protein Arp6 in gene expression, both as a component of the SWR1 complex (SWR-C) and in its absence. We mapped Arp6-binding sites genome-wide using chromatin immunoprecipitation in mutant and wild-type cells. We find that the majority of Arp6-binding sites in euchromatin coincide with binding sites of Swr1, the catalytic subunit of SWR-C, and with the histone H2A variant Htz1. However, the remaining Arp6 binding in telomeres, centromeres, and the promoters of ribosomal protein (RP) genes are independent of Swr1 and Htz1 deposition. We show that Arp6 can position chromatin at nuclear pores, and is required for the pore association of the RP genes to which it binds. This anchoring is also independent of Swr1. Loss of Arp6, but not Htz1, leads to an up-regulation of RP genes and loss of relocalization. This is in contrast to the Htz1-mediated pore-association of GAL1, for which loss of Arp6 impairs activation. Given that Arp6 is required for SWR-C dependent deposition of Htz1, we conclude that Arp6 contributes to both H2AZ-dependent and H2AZ-independent association with nuclear pores and subsequent effects on gene expression. These data illustrate how nuclear actin-related proteins contribute to the long-range organization of chromatin domains in the interphase nucleus. Four replicates for the arp6 deletion mutant and three replicates for the swr1 deletion mutant compared to wild-type.
Project description:The SWR1 chromatin remodeling complex, which contains Arp6 and Swr1 as components, exchanges H2A in nucleosomes with its variant H2AZ. We have investigated the chromosome-wide dynamic distribution of Arp6 and Swr1 in budding yeast cells by chromatin immunoprecipitation analysis using a high-density genome tiling array. We found that the majority of Arp6 colocalizes with Swr1 on chromosomes and is enriched in the promoters of divergently promoters. This shows that Arp6 binds chromatin as a component of the SWR1 complex and is involved in transcriptional regulation in these regions. On the other hand, in some chromosomal regions, including telomere, centromere and ribosomal protein genes, the binding of Arp6 did not coincide with that of Swr1, and was remained in the absence of Swr1. This shows that a portion of Arp6 binds to chromosomes in Swr1-independent manner. These observations suggest that Arp6 has Swr1-dependent and –independent functions on chromosomes. Keywords: ChIP-chip
Project description:Chromatin structure and DNA accessibility are partly modulated by the incorporation of histone variants. H2A.Z, encoded by the non-essential HTZ1 gene in S. cerevisiae, is an evolutionarily conserved H2A histone variant that is predominantly incorporated at transcription start sites by the SWR1-complex (SWR1-C). While H2A.Z has often been implicated in transcription regulation, htz1Δ mutants exhibit minimal changes in gene expression compared to wild-type. However, given that growth defects of htz1Δ mutants are alleviated by simultaneous deletion of SWR1-C subunits, previous work examining the role of H2A.Z in gene expression regulation may be confounded by deleterious activity caused by SWR1-C when its missing its H2A.Z substrate (apo-SWR1-C). Furthermore, as H2A.Z mutants only display significant growth defects in genotoxic stress conditions, a more substantive role for H2A.Z in gene expression may only be uncovered after exposure to cellular stress. To explore this possibility, we generated mRNA transcript profiles for wild-type, htz1Δ, swr1Δ, and htz1Δswr1Δ mutants before and after exposure to hydroxyurea (HU), which induces DNA replication stress. Our data showed that H2A.Z played a more prominent role in gene activation than repression during HU exposure, and its incorporation was important for proper upregulation of several HU-induced genes. We also observed that apo-SWR1-C contributed to gene expression defects in the htz1Δ mutant, particularly for genes involved in phosphate homeostasis regulation. Furthermore, mapping H2A.Z incorporation before and after treatment with HU revealed that decreases in H2A.Z enrichment at transcription start sites was correlated with, but generally not required for, the upregulation of genes during HU exposure. Together this study characterized the regulatory effects of H2A.Z incorporation during the transcriptional response to HU.
Project description:The SWR1 chromatin remodeling complex, which deposits the histone variant H2A.Z into nucleosomes, has been characterized in yeast and animals but had not been purified from plants. We used the conserved SWR1 subunit ACTIN RELATED PROTEIN 6 (ARP6) as bait in tandem affinity purification experiments to isolate associated proteins from Arabidopsis thaliana. We identified all 11 subunits found in yeast SWR1 and the homologous mammalian SRCAP complexes, demonstrating that this complex is conserved in plants. We also identified several additional proteins not previously associated with SWR1, including Methyl-CpG-BINDING DOMAIN 9 (MBD9). Since mbd9 mutant plants were phenotypically similar to arp6 mutants, we further explored a potential role for MBD9 in H2A.Z deposition. We found that MBD9 is required for proper H2A.Z incorporation at thousands of discrete sites, which represent a subset of the regions normally enriched with H2A.Z. Genetic analyses showed that arp6;mbd9 double mutants have far more severe phenotypes than either single mutant. In conjunction with the finding that MBD9 does not appear to be a core subunit of the Arabidopsis SWR1 complex, this suggests that MBD9 also has important roles beyond H2A.Z deposition. Our data establish the SWR1 complex as being conserved across eukaryotes and also provide new insights into the mechanisms that target H2A.Z to chromatin.
Project description:Chromatin structure and DNA accessibility are partly modulated by the incorporation of histone variants. H2A.Z, encoded by the non-essential HTZ1 gene in S. cerevisiae, is an evolutionarily conserved H2A histone variant that is predominantly incorporated at transcription start sites by the SWR1-complex (SWR1-C). While H2A.Z has often been implicated in transcription regulation, htz1Δ mutants exhibit minimal changes in gene expression compared to wild-type. However, given that growth defects of htz1Δ mutants are alleviated by simultaneous deletion of SWR1-C subunits, previous work examining the role of H2A.Z in gene expression regulation may be confounded by deleterious activity caused by SWR1-C when its missing its H2A.Z substrate (apo-SWR1-C). Furthermore, as H2A.Z mutants only display significant growth defects in genotoxic stress conditions, a more substantive role for H2A.Z in gene expression may only be uncovered after exposure to cellular stress. To explore this possibility, we generated mRNA transcript profiles for wild-type, htz1Δ, swr1Δ, and htz1Δswr1Δ mutants before and after exposure to hydroxyurea (HU), which induces DNA replication stress. Our data showed that H2A.Z played a more prominent role in gene activation than repression during HU exposure, and its incorporation was important for proper upregulation of several HU-induced genes. We also observed that apo-SWR1-C contributed to gene expression defects in the htz1Δ mutant, particularly for genes involved in phosphate homeostasis regulation. Furthermore, mapping H2A.Z incorporation before and after treatment with HU revealed that decreases in H2A.Z enrichment at transcription start sites was correlated with, but generally not required for, the upregulation of genes during HU exposure. Together this study characterized the regulatory effects of H2A.Z incorporation during the transcriptional response to HU.
Project description:Deposition of histone variant H2A.Z by the SWR1 chromatin-remodeling complex is critical for the appropriate expression of many genes in eukaryotes, yet, despite its importance, the composition of the Arabidopsis SWR1 complex has not been thoroughly analyzed. Here we have identified the interacting partners of a conserved Arabidopsis SWR1 subunit, actin-related protein 6 (ARP6). We isolated 9 predicted components, identifying subunits implicated in histone acetylation and interacting partners implicated in chromatin biology. We found that the methyl-CpG-binding domain 9 (MBD9) subunit functioned synergistically with ARP6 to control flowering time. MBD9, in combination with ARP6, was involved in the SWR1-mediated incorporation of the majority of H2A.Z. MBD6 was further required for deposition of H2A.Z at a distinct subset of loci. MBD9 was preferentially bound to nucleosome-depleted regions at the 5’ of genes containing high levels of activating histone marks. Our data suggests a model for MBD9 in recruiting the SWR1 complex to open chromatin of actively transcribing genes.
Project description:Deposition of histone variant H2A.Z by the SWR1 chromatin-remodeling complex is critical for the appropriate expression of many genes in eukaryotes, yet, despite its importance, the composition of the Arabidopsis SWR1 complex has not been thoroughly analyzed. Here we have identified the interacting partners of a conserved Arabidopsis SWR1 subunit, actin-related protein 6 (ARP6). We isolated 9 predicted components, identifying subunits implicated in histone acetylation and interacting partners implicated in chromatin biology. We found that the methyl-CpG-binding domain 9 (MBD9) subunit functioned synergistically with ARP6 to control flowering time. MBD9, in combination with ARP6, was involved in the SWR1-mediated incorporation of the majority of H2A.Z. MBD6 was further required for deposition of H2A.Z at a distinct subset of loci. MBD9 was preferentially bound to nucleosome-depleted regions at the 5’ of genes containing high levels of activating histone marks. Our data suggests a model for MBD9 in recruiting the SWR1 complex to open chromatin of actively transcribing genes.
Project description:Deposition of histone variant H2A.Z by the SWR1 chromatin-remodeling complex is critical for the appropriate expression of many genes in eukaryotes, yet, despite its importance, the composition of the Arabidopsis SWR1 complex has not been thoroughly analyzed. Here we have identified the interacting partners of a conserved Arabidopsis SWR1 subunit, actin-related protein 6 (ARP6). We isolated 9 predicted components, identifying subunits implicated in histone acetylation and interacting partners implicated in chromatin biology. We found that the methyl-CpG-binding domain 9 (MBD9) subunit functioned synergistically with ARP6 to control flowering time. MBD9, in combination with ARP6, was involved in the SWR1-mediated incorporation of the majority of H2A.Z. MBD6 was further required for deposition of H2A.Z at a distinct subset of loci. MBD9 was preferentially bound to nucleosome-depleted regions at the 5’ of genes containing high levels of activating histone marks. Our data suggests a model for MBD9 in recruiting the SWR1 complex to open chromatin of actively transcribing genes.
Project description:Deposition of histone variant H2A.Z by the SWR1 chromatin-remodeling complex is critical for the appropriate expression of many genes in eukaryotes, yet, despite its importance, the composition of the Arabidopsis SWR1 complex has not been thoroughly analyzed. Here we have identified the interacting partners of a conserved Arabidopsis SWR1 subunit, actin-related protein 6 (ARP6). We isolated 9 predicted components, identifying subunits implicated in histone acetylation and interacting partners implicated in chromatin biology. We found that the methyl-CpG-binding domain 9 (MBD9) subunit functioned synergistically with ARP6 to control flowering time. MBD9, in combination with ARP6, was involved in the SWR1-mediated incorporation of the majority of H2A.Z. MBD6 was further required for deposition of H2A.Z at a distinct subset of loci. MBD9 was preferentially bound to nucleosome-depleted regions at the 5’ of genes containing high levels of activating histone marks. Our data suggests a model for MBD9 in recruiting the SWR1 complex to open chromatin of actively transcribing genes.
Project description:Actin-related proteins are ubiquitous components of chromatin remodelers, and are conserved from yeast to man. We have examined the role of the budding yeast actin-related protein Arp6 in gene expression, both as a component of the SWR1 complex (SWR-C) and in its absence. We mapped Arp6-binding sites genome-wide using chromatin immunoprecipitation in mutant and wild-type cells. We find that the majority of Arp6-binding sites in euchromatin coincide with binding sites of Swr1, the catalytic subunit of SWR-C, and with the histone H2A variant Htz1. However, the remaining Arp6 binding in telomeres, centromeres, and the promoters of ribosomal protein (RP) genes are independent of Swr1 and Htz1 deposition. We show that Arp6 can position chromatin at nuclear pores, and is required for the pore association of the RP genes to which it binds. This anchoring is also independent of Swr1. Loss of Arp6, but not Htz1, leads to an up-regulation of RP genes and loss of relocalization. This is in contrast to the Htz1-mediated pore-association of GAL1, for which loss of Arp6 impairs activation. Given that Arp6 is required for SWR-C dependent deposition of Htz1, we conclude that Arp6 contributes to both H2AZ-dependent and H2AZ-independent association with nuclear pores and subsequent effects on gene expression. These data illustrate how nuclear actin-related proteins contribute to the long-range organization of chromatin domains in the interphase nucleus.