Project description:The aim of this study was to uncover cell cycle dependent chromatin binding of H2A.Z and its histone chaperones. U2OS cells were stably transfected with Twin-Strep-tagged H2A.Z, ANP32e, or YL1 constructs, and WT cells were used as a negative/background control. U2OS cells were synchronised in G1 or G2-M phase using hydroxyurea or nocodazole, respectively, and protein-DNA complexes were isolated by affinity purification.
Project description:In eukaryotes, DNA wraps around histones to form nucleosomes, which are compacted into chromatin. DNA-templated processes, including transcription, require chromatin disassembly and reassembly mediated by histone chaperones. Additionally, distinct histone variants can replace core histones to regulate chromatin structure and function. Although replacement of H2A with the evolutionarily conserved H2A.Z via the SWR1 histone chaperone complex has been extensively studied, in plants little is known about how a reduction of H2A.Z levels can be achieved in plants. Here, we show that NRP proteins cause a decrease of H2A.Z-containing nucleosomes in Arabidopsis under standard growing conditions. nrp1-1 nrp2-2 double mutants show an over-accumulation of H2A.Z genome-wide, especially at heterochromatic regions normally H2A.Z-depleted in wild-type plants. Our work suggests that NRP proteins regulate gene expression by counteracting SWR1, thereby preventing excessive accumulation of H2A.Z.
Project description:While it has been clearly established that well positioned H2A.Z-containing nucleosomes flank the nucleosome depleted region (NDR) at the transcriptional start site (TSS) of active mammalian genes, how this chromatin-based information is transmitted through the cell cycle is unknown. We show here that in trophoblast stem (TS) cells, the level of H2A.Z at promoters decreases during S phase coinciding with homotypic (H2A.Z/H2A.Z) nucleosomes flanking the TSS becoming heterotypic (H2A.Z/H2A). Surprisingly, these nucleosomes remain heterotypic at M phase. At the TSS, we identify an unstable heterotypic H2A.Z-containing nucleosome in G1 which, strikingly, is lost following DNA replication. These dynamic changes in H2A.Z at the TSS mirror a global expansion of the NDR at S and M which, unexpectedly, is unrelated to transcriptional activity. Coincident with the loss of H2A.Z at promoters, it is targeted to the centromere when mitosis begins We performed ChIP-Seq experiments (on mouse Trophoblast Stem cells arrested at G1; S and M stages of thecell cycle) using antibodies against histone variant H2A.Z and sequentional ChIP-re-ChIP-Seq experiments using H2A.Z antibody and H2A antibody in sequence. Combining those data sets with microarray gene expression expression data allowed us to see H2A.Z distribution over promoters of mouse coding genes in cell cycle dependant manner. Interestingly, Input also showed cell-cycle dependent effects, but histone H3 could be used as a cell-cycle independent normalisation factor. We also performed ChIP-seq with a CTCF pull-down to investigate its cell-cycle dependent relationship with heterochromatin.
Project description:Affinity Purification Mass Spectrometry (AP-MS) of Drosophila ovaries expressing an H2A.Z-FlagHA transgene to identify interacting partners of H2A.Z to elucidate potential maternally supplied histone chaperones that deposit H2A.Z on the transcription start site (TSS).
Project description:While it has been clearly established that well positioned H2A.Z-containing nucleosomes flank the nucleosome depleted region (NDR) at the transcriptional start site (TSS) of active mammalian genes 1,2, how this chromatin-based information is transmitted through the cell cycle is unknown. We show here that in trophoblast stem (TS) cells, the level of H2A.Z at promoters decreases during S phase coinciding with homotypic (H2A.Z/H2A.Z) nucleosomes flanking the TSS becoming heterotypic (H2A.Z/H2A). Surprisingly, these nucleosomes remain heterotypic at M phase. At the TSS, we identify an unstable heterotypic H2A.Z-containing nucleosome in G1 which, strikingly, is lost following DNA replication. These dynamic changes in H2A.Z at the TSS mirror a global expansion of the NDR at S and M which, unexpectedly, is unrelated to transcriptional activity. Coincident with the loss of H2A.Z at promoters, it is targeted to the centromere when mitosis begins. We surveyed whole genome expression using microarrays, in combination with H2A.Z ChIP-Seq (Illumina) data, to study the H2A.Z distribution on promoters of coding genes in different stages of the cell cycle in Trophoblast Stem (TS) cells. These data are published in Nekrasov et al., H2AZ inheritance during the cell cycle and it's impact on promoter organization and dynamics, Nature Structural and Molecular Biology (in press: accepted for publication on 24 Sep 2012). Mouse Trophoblast stem (TS) cells were grown in cell culture medium. By adding specific drugs cells were arrested at particular stages of the cell cycle: G1; S and M. Total RNA was extracted from TS cells arrested at G1; S and M stages of cell cycle using TRizol (Invitrogen) extraction protocol and purified further the by RNAeasy Extraction Kit (Qiagen). RNA quality was assesed on Bioanalyzer total RNA chip. RNA samples were reverse transcribed and resulted cDNA samples were subjected to DNA microarray analysis (in triplicate) using the GeneChip Mouse Gene 1.0 ST Array (Affymetrix). Robust Multichip Average (RMA) correction and probe set summaries were obtained using Affymetrix Power Tools software annotation (Affymetrix) based on the mm9 mouse genome. Unless otherwise stated, all subsequent expression analyses (see Supplementary Methods) were performed in the R statistical computing environment (version 2.11.1).
Project description:While it has been clearly established that well positioned H2A.Z-containing nucleosomes flank the nucleosome depleted region (NDR) at the transcriptional start site (TSS) of active mammalian genes 1,2, how this chromatin-based information is transmitted through the cell cycle is unknown. We show here that in trophoblast stem (TS) cells, the level of H2A.Z at promoters decreases during S phase coinciding with homotypic (H2A.Z/H2A.Z) nucleosomes flanking the TSS becoming heterotypic (H2A.Z/H2A). Surprisingly, these nucleosomes remain heterotypic at M phase. At the TSS, we identify an unstable heterotypic H2A.Z-containing nucleosome in G1 which, strikingly, is lost following DNA replication. These dynamic changes in H2A.Z at the TSS mirror a global expansion of the NDR at S and M which, unexpectedly, is unrelated to transcriptional activity. Coincident with the loss of H2A.Z at promoters, it is targeted to the centromere when mitosis begins. We surveyed whole genome expression using microarrays, in combination with H2A.Z ChIP-Seq (Illumina) data, to study the H2A.Z distribution on promoters of coding genes in different stages of the cell cycle in Trophoblast Stem (TS) cells. These data are published in Nekrasov et al., H2AZ inheritance during the cell cycle and it's impact on promoter organization and dynamics, Nature Structural and Molecular Biology (in press: accepted for publication on 24 Sep 2012).
Project description:High levels of the histone variant H2A.Z are characteristic for melanoma progression and correlate with poor prognosis of melanoma patients. Two chaperone complexes are reported to deposit H2A.Z isoforms into chromatin: SRCAP and P400-TIP60. YL1 is a common subunit of both complexes and directly binds to the H2A.Z-H2B dimer. Here, we showed that the knockdown of SRCAP (SRCAP-specific), P400 (P400-TIP60-specific) and YL1 (shared subunit) results in loss of H2A.Z deposition into chromatin in melanoma cells, confirming them as H2A.Z chaperone subunits in this system. Further, we demonstrated that H2A.Z, YL1 and the SRCAP-specific subunit ZNHIT1 co-localize at active promoters of cell cycle-related genes, such as the transcription factor E2F1. Knockdown of YL1, SRCAP and P400 downregulates E2F1 and its targets, resulting in a loss of proliferation and cell cycle arrest in melanoma cells as seen after knockdown of H2A.Z (Vardabasso et al. 2015). Strikingly, besides H2A.Z loss, we observed a dramatic loss of H4 acetylation in melanoma chromatin upon knockdown of H2A.Z chaperone subunits. The majority of genes whose promoters showed a reduction in H4 acetylation were previously bound by H2A.Z, YL1 and ZNHIT1. This is suggestive of a direct link between H2A.Z deposition and H4 acetylation to promote the expression of underlying genes. In agreement, the genes that lost H4 acetylation were enriched for E2F1 target genes. Interestingly, we additionally found that knockdown of YL1 did not only prohibit cell cycle progression, but also induces apoptosis, which is in contrast to H2A.Z knockdown affecting cell cycle only. In addition, YL1 (but not SRCAP or P400) was found to be overexpressed in melanoma and high YL1 levels were a predictor of poor melanoma patient outcome. These findings provide a rationale for targeting the H2A.Z-YL1 interaction as novel epigenetic strategy for melanoma treatment.
Project description:High levels of the histone variant H2A.Z are characteristic for melanoma progression and correlate with poor prognosis of melanoma patients. Two chaperone complexes are reported to deposit H2A.Z isoforms into chromatin: SRCAP and P400-TIP60. YL1 is a common subunit of both complexes and directly binds to the H2A.Z-H2B dimer. Here, we showed that the knockdown of SRCAP (SRCAP-specific), P400 (P400-TIP60-specific) and YL1 (shared subunit) results in loss of H2A.Z deposition into chromatin in melanoma cells, confirming them as H2A.Z chaperone subunits in this system. Further, we demonstrated that H2A.Z, YL1 and the SRCAP-specific subunit ZNHIT1 co-localize at active promoters of cell cycle-related genes, such as the transcription factor E2F1. Knockdown of YL1, SRCAP and P400 downregulates E2F1 and its targets, resulting in a loss of proliferation and cell cycle arrest in melanoma cells as seen after knockdown of H2A.Z (Vardabasso et al. 2015). Strikingly, besides H2A.Z loss, we observed a dramatic loss of H4 acetylation in melanoma chromatin upon knockdown of H2A.Z chaperone subunits. The majority of genes whose promoters showed a reduction in H4 acetylation were previously bound by H2A.Z, YL1 and ZNHIT1. This is suggestive of a direct link between H2A.Z deposition and H4 acetylation to promote the expression of underlying genes. In agreement, the genes that lost H4 acetylation were enriched for E2F1 target genes. Interestingly, we additionally found that knockdown of YL1 did not only prohibit cell cycle progression, but also induces apoptosis, which is in contrast to H2A.Z knockdown affecting cell cycle only. In addition, YL1 (but not SRCAP or P400) was found to be overexpressed in melanoma and high YL1 levels were a predictor of poor melanoma patient outcome. These findings provide a rationale for targeting the H2A.Z-YL1 interaction as novel epigenetic strategy for melanoma treatment.
Project description:H2A.Z is a H2A-type histone variant essential for many aspects of cell biology, ranging from gene expression to genome stability. From deuterostomes, H2A.Z evolved into two paralogues, H2A.Z.1 and H2A.Z.2, that differ by only three amino acids and are encoded by different genes (H2AFZ and H2AFV, respectively). Despite the importance of this histone variant in development and cellular homeostasis, very little is known about the individual functions of each paralogue in mammals. Here, we have investigated the distinct roles of the two paralogues in cell cycle regulation and unveiled non-redundant functions for H2A.Z.1 and H2A.Z.2 in cell division. Our findings show that H2A.Z.1 regulates the expression of cell cycle genes such as Myc and Ki-67 and its depletion leads to a G1 arrest and cellular senescence. On the contrary, H2A.Z.2, in a transcription independent manner, is essential for centromere integrity and sister chromatid cohesion regulation, thus playing a key role in chromosome segregation.