Histone H3 Variant Research Articles

Hap2-Ino80-facilitated transcription promotes de novo establishment of CENP-A chromatin.

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.

Somatic Missense Mutations of Histone Variant H3.3 in Central Nervous System Cancers

Objective: Histone variants are important modulators of chromatin functions. Studies have pointed out that epigenetic factors are often dysregulated in carcinogenesis. Although some cancer-associated mutations of the histone variant H3.3 have been identified previously, a complete list of H3.3 mutations and their potential effects is yet to be uncovered. Therefore, this study aims to identify the missense mutations of the histone variant H3.3 in central nervous system (CNS) cancers and to computationally predict their functional consequences on pathogenicity, protein stability and structure. Materials and Methods: A complete set of human H3.3 mutations was acquired from the COSMIC v90 database and missense mutations were selected. The potential effects of these mutations were assessed using PredictSNP2 and FATHMMXF. Structural outcomes were predicted using MUpro and HOPE servers. Results: We identified 45 unique missense H3.3 substitutions in several tissues including CNS. PredictSNP2 and FATHMM-XF predicted 17 and 42 mutations as deleterious respectively, most of which caused decreased protein stability. Amino acid alterations in CNS cancers were predicted to cause alterations of the 3D structure. Conclusion: Histone variants play significant roles in epigenetic regulation and are often mutated in cancers. Our results showed that H3.3 mutations detected in CNS cancers could affect the genomic distribution of post-translational modifications and histone variants, hence dramatically alter the gene expression profile and contribute to carcinogenesis.

Histone H3 methylation orchestrates transcriptional program in mouse spermatogenic cell line

Changes in histone modifications always correlate with altered transcriptional activities of genes. Recent studies have shown that the mutation of certain lysine residues to methionine in the histone variant H3.3 can act as a valuable tool to reduce specific H3 methylation levels. In our study, we used the mouse spermatogenic cell line GC-2 as a model to generate cells stably expressing H3.3 K4, H3.3 K9, H3.3 K27, and H3.3 K36M. The expression of these H3.3 K-to-M mutants influenced the expression of different subsets of genes, and a total of 891 differentially expressed genes were identified through global gene expression profiling. Moreover, the H3.3 K-to-M transgenes, especially H3.3 K36M, impacted the expression of endogenous retrovirus ERVK. This study gives a global view of how different H3 modifications regulate transcriptomes in spermatogenic cell lines, and identifies potential targets of H3 modifications in male germ line.

A Different Twist on Centromeric Chromatin

Nucleosomes at the centromere contain CENP-A, a histone H3 variant that establishes a specific, yet poorly defined centromeric chromatin architecture. In this issue of Structure, Takizawa etal. (2019) describe an untwisted configuration for an H3-CENP-A-H3 tri-nucleosome that mimics centromeric chromatin. Untwisting may increase centromeric-protein accessibility to CENP-A in compacted chromatin.

NCI-CONNECT: Comprehensive Oncology Network Evaluating Rare CNS Tumors-Histone Mutated Midline Glioma Workshop Proceedings.

Histone mutations occur in approximately 4% of different cancer types. In 2012, mutations were found in the gene encoding histone variant H3.3 (H3F3A gene) in pediatric diffuse intrinsic pontine gliomas and pediatric hemispheric gliomas. Tumors with mutations in the H3F3A gene are generally characterized as histone mutated gliomas (HMGs) or diffuse midline gliomas. HMGs are a rare subtype of glial tumor that is malignant and fast growing, carrying a poor prognosis. In 2017, the Beau Biden Cancer Moonshot Program appropriated $1.7 billion toward cancer care in 10 select areas. The National Cancer Institute (NCI) was granted support to focus specifically on rare central nervous system (CNS) tumors through NCI-CONNECT. Its mission is to address the challenges and unmet needs in CNS cancer research and treatment by connecting patients, providers, researchers, and advocacy organizations to work in partnership. On September 27, 2018, NCI-CONNECT convened a workshop on histone mutated midline glioma, one of the 12 CNS cancers included in its initial portfolio. Three leaders in the field provided an overview of advances in histone mutated midline glioma research. These experts shared observations and experiences related to common scientific and clinical challenges in studying these tumors. Although the clinical focus of this workshop was on adult patients, one important objective was to start a collaborative dialogue between pediatric and adult clinicians and researchers. Meeting participants identified needs for diagnostic and treatment standards, disease biology and biological targets for this cancer, disease-specific trial designs, and developed a list of action items and future direction.

Maternal inheritance of centromeres through the germline.

The centromere directs chromosome segregation but is not itself genetically encoded. In most species, centromeres are epigenetically defined by the presence of a histone H3 variant CENP-A, independent of the underlying DNA sequence. Therefore, to maintain centromeres and ensure accurate chromosome segregation, CENP-A nucleosomes must be inherited across generations through the germline. In this chapter we discuss three aspects of maternal centromere inheritance. First, we propose mechanisms for maintaining CENP-A nucleosomes through the prolonged prophase arrest in mammalian oocytes. Second, we review mechanisms by which selfish centromeres bias their transmission through female meiosis. Third, we discuss regulation of centromere size through early embryonic development.

Genetic and epigenetic effects on centromere establishment.

Endogenous chromosomes contain centromeres to direct equal chromosomal segregation in mitosis and meiosis. The location and function of existing centromeres is usually maintained through cell cycles and generations. Recent studies have investigated how the centromere-specific histone H3 variant CENP-A is assembled and replenished after DNA replication to epigenetically propagate the centromere identity. However, existing centromeres occasionally become inactivated, with or without change in underlying DNA sequences, or lost after chromosomal rearrangements, resulting in acentric chromosomes. New centromeres, known as neocentromeres, may form on ectopic, non-centromeric chromosomal regions to rescue acentric chromosomes from being lost, or form dicentric chromosomes if the original centromere is still active. In addition, de novo centromeres can form after chromatinization of purified DNA that is exogenously introduced into cells. Here, we review the phenomena of naturally occurring and experimentally induced new centromeres and summarize the genetic (DNA sequence) and epigenetic features of these new centromeres. We compare the characteristics of new and native centromeres to understand whether there are different requirements for centromere establishment and propagation. Based on our understanding of the mechanisms of new centromere formation, we discuss the perspectives of developing more stably segregating human artificial chromosomes to facilitate gene delivery in therapeutics and research.

H3.3 impedes zygotic transcriptional program activated by Dux

During development, fertilization triggers totipotency establishment, featured by zygotic genome activation/embryonic genome activation (ZGA/EGA). Mouse embryonic stem cells (mESCs) occasionally cycle through a two-cell (2C)-like status with activated expression of Dux and its targeted ZGA genes. Here, we demonstrate that deficiency of histone variant H3.3 dramatically stimulates expression of ZGA genes in mESCs. Our analysis revealed that H3.3 directly associates with Dux locus and inhibits Dux expression, therefore it is an important upstream regulator of Dux. Our finding is further supported by transcriptome change in early mouse embryos with H3.3 knockdown. We suggest that proper H3.3 level in early embryos is important to orchestrate ZGA activity for totipotency establishment.

Polyadenylation of Histone H3.1 mRNA Promotes Cell Transformation by Displacing H3.3 from Gene Regulatory Elements

Replication-dependent canonical histone messenger RNAs (mRNAs) do not terminate with a poly(A) tail at the 3’ end. We previously demonstrated that exposure to arsenic, an environmental carcinogen, induces polyadenylation of canonical histone H3.1 mRNA. The addition of a poly(A) tail to the H3.1 mRNA caused transformation of human cells in vitro, but the underlying mechanisms are unknown. Here we report that polyadenylation of H3.1 mRNA increases H3.1 protein level, resulting in depletion of histone variant H3.3 at active promoters, enhancers, and insulator regions through its displacement. Cells underwent transcriptional deregulation, G2/M cell cycle arrest, chromosome aneuploidy and aberrations. Furthermore, knocking down the expression of H3.3 induced cell transformation, whereas ectopic expression of H3.3 attenuated arsenic-induced cell transformation, suggesting that H3.3 displacement might be central to tumorigenic effects of polyadenylated H3.1 mRNA. Our study provides novel insights into the importance of proper histone stoichiometry in maintaining genome integrity.

Biogenesis of Developmental Master Regulatory 27nt-RNAs in Stylonychia-Can Coding RNA Turn into Non-Coding?

In the ciliate Stylonychia, somatic macronuclei differentiate from germline micronuclei during sexual reproduction, accompanied by developmental sequence reduction. Concomitantly, over 95% of micronuclear sequences adopt a heterochromatin structure characterized by the histone variant H3.4 and H3K27me3. RNAi-related genes and histone variants dominate the list of developmentally expressed genes. Simultaneously, 27nt-ncRNAs that match sequences retained in new macronuclei are synthesized and bound by PIWI1. Recently, we proposed a mechanistic model for ‘RNA-induced DNA replication interference’ (RIRI): during polytene chromosome formation PIWI1/27nt-RNA-complexes target macronucleus-destined sequences (MDS) by base-pairing and temporarily cause locally stalled replication. At polytene chromosomal segments with ongoing replication, H3.4K27me3-nucleosomes become selectively deposited, thus dictating the prospective heterochromatin structure of these areas. Consequently, these micronucleus-specific sequences become degraded, whereas 27nt-RNA-covered sites remain protected. However, the biogenesis of the 27nt-RNAs remains unclear. It was proposed earlier that in stichotrichous ciliates 27nt-RNA precursors could derive from telomere-primed bidirectional transcription of nanochromosomes and subsequent Dicer-like (DCL) activity. As a minimalistic explanation, we propose here that the 27nt-RNA precursor could rather be mRNA or pre-mRNA and that the transition of coding RNA from parental macronuclei to non-coding RNAs, which act in premature developing macronuclei, could involve RNA-dependent RNA polymerase (RDRP) activity creating dsRNA intermediates prior to a DCL-dependent pathway. Interestingly, by such mechanism the partition of a parental somatic genome and possibly also the specific nanochromosome copy numbers could be vertically transmitted to the differentiating nuclei of the offspring.

Depletion of KNL2 Results in Altered Expression of Genes Involved in Regulation of the Cell Cycle, Transcription, and Development in Arabidopsis.

Centromeres contain specialized nucleosomes at which histone H3 is partially replaced by the centromeric histone H3 variant cenH3 that is required for the assembly, maintenance, and proper function of kinetochores during mitotic and meiotic divisions. Previously, we identified a KINETOCHORE NULL 2 (KNL2) of Arabidopsis thaliana that is involved in the licensing of centromeres for the cenH3 recruitment. We also demonstrated that a knockout mutant for KNL2 shows mitotic and meiotic defects, slower development, reduced growth rate, and fertility. To analyze an effect of KNL2 mutation on global gene transcription of Arabidopsis, we performed RNA-sequencing experiments using seedling and flower bud tissues of knl2 and wild-type plants. The transcriptome data analysis revealed a high number of differentially expressed genes (DEGs) in knl2 plants. The set was enriched in genes involved in the regulation of the cell cycle, transcription, development, and DNA damage repair. In addition to comprehensive information regarding the effects of KNL2 mutation on the global gene expression, physiological changes in plants are also presented, which provides an integrated understanding of the critical role played by KNL2 in plant growth and development.

Adult Hematopoietic Stem and Progenitor Cell Maintenance Requires Histone Variant H3.3 Regulation By Hira

The adult hematopoietic system is sustained by a balance of self-renewal and differentiation in a small pool of stem and progenitor cells. This balance must be maintained to ensure a continuous supply of blood cells throughout life and prevent malignancy from arising. There are many facets of epigenetic regulation that are well known to be key components of healthy and diseased hematopoiesis, such as DNA methylation and histone post-translational modifications. However, the role of histone variant incorporation in hematopoiesis remains relatively unexplored. In this study, we explore the role of histone variant H3.3 regulation in the hematopoietic system by assessing the function of the histone H3.3 chaperone, Hira. Toward this goal, we use inducible and early developmental conditional knockout (cKO) mouse models to assess the role of Hira within the hematopoietic system. Following Hira cKO early in hematopoietic development (Vav-iCre; Hirafl/fl), we find that HSPCs are unaffected in the fetal liver but deplete quickly after homing to the bone marrow. Using polyinosinic-polycytidylic (pIpC) inducible Hira cKO mice (Mx1-Cre; Hirafl/fl), we find a similarly severe depletion of HSPCs in adult mice within 1 month after Hira loss. In contrast, differentiated cells remain largely unaffected following Hira cKO, demonstrating that Hira is especially important in the hematopoietic stem and progenitor compartment. Since Hira is known to incorporate H3.3 throughout the cell cycle and not just during S-phase like H3.1/2, we hypothesized that adult HSPCs are more dependent upon Hira to regulate histone H3 dynamics since they are slowly dividing. The loss of Hira-mediated H3.3 deposition would also be particularly detrimental to the function of these cells given its association with actively transcribed and bivalent genes. To test the role of Hira in maintaining gene expression patterns, we performed bulk RNA-seq on adult HSPCs and found that hematopoietic differentiation genes are dysregulated after Hira cKO with increased erythroid lineage and decreased lymphoid lineage gene expression. We then assessed gene expression changes in Hira cKO HSPCs in a doxycycline-inducible H2B-GFP background (Mx1-Cre; Hirafl/fl; R26-M2rtTa; TetOP-H2B-GFP) to distinguish between the gene expression changes caused by Hira loss before and after cell division. In the absence of Hira-mediated H3.3 incorporation, we expect some highly expressed genes in slowly dividing adult HSPCs to be affected by Hira loss prior to cell division due to nucleosome turnover in the wake of RNA Polymerase II. At other loci, like bivalent promoters, H3.3 would be diluted after cell division by H3.1/2 during S-phase in Hira cKO HSPCs. In support of this hypothesis, we found that increased expression of the erythroid differentiation gene Klf1 in Hira cKO MPPs after cell division (H2B-GFPLow) relative to Hira cKO MPPs before division (H2B-GFPHigh) and WT MPPs that have divided (H2B-GFPLow). The findings from both of these transcriptome analyses point toward a role of Hira in regulating HSPC differentiation genes and are supported by our in vitro and in vivo data showing increased differentiation of Hira cKO HSPCs and decreased self-renewal. In order to more fully understand the H3.3-dependent gene expression changes after Hira cKO in HSPCs, we correlated H3.3 enrichment patterns from chromatin-immunoprecipitation and sequencing (ChIP-seq) with our data from assay for transposase-accessible chromatin and sequencing (ATAC-seq). Our results demonstrate that Hira cKO HSPCs have more open chromatin and fewer H3.3 peaks, suggesting that loss of Hira-mediated H3.3 deposition increases DNA accessibility. This study identifies a novel epigenetic mechanism required for adult HSPC maintenance and elucidates a previously unappreciated regulator of normal hematopoietic homeostasis. Further understanding how Hira-mediated H3.3 regulation maintains adult HSPCs will provide greater depth to our current understanding of the epigenetic regulators essential for hematopoiesis. Disclosures No relevant conflicts of interest to declare.

Localization of Drosophila CENP-A to non-centromeric sites depends on the NuRD complex

Centromere function requires the presence of the histone H3 variant CENP-A in most eukaryotes. The precise localization and protein amount of CENP-A are crucial for correct chromosome segregation, and misregulation can lead to aneuploidy. To characterize the loading of CENP-A to non-centromeric chromatin, we utilized different truncation- and localization-deficient CENP-A mutant constructs in Drosophila melanogaster cultured cells, and show that the N-terminus of Drosophila melanogaster CENP-A is required for nuclear localization and protein stability, and that CENP-A associated proteins, rather than CENP-A itself, determine its localization. Co-expression of mutant CENP-A with its loading factor CAL1 leads to exclusive centromere loading of CENP-A whereas co-expression with the histone-binding protein RbAp48 leads to exclusive non-centromeric CENP-A incorporation. Mass spectrometry analysis of non-centromeric CENP-A interacting partners identified the RbAp48-containing NuRD chromatin remodeling complex. Further analysis confirmed that NuRD is required for ectopic CENP-A incorporation, and RbAp48 and MTA1-like subunits of NuRD together with the N-terminal tail of CENP-A mediate the interaction. In summary, our data show that Drosophila CENP-A has no intrinsic specificity for centromeric chromatin and utilizes separate loading mechanisms for its incorporation into centromeric and ectopic sites. This suggests that the specific association and availability of CENP-A interacting factors are the major determinants of CENP-A loading specificity.

CenH3-Independent Kinetochore Assembly in Lepidoptera Requires CENP-T

Accurate chromosome segregation requires assembly of the multiprotein kinetochore complex at centromeres. In most eukaryotes, kinetochore assembly is primed by the histone H3 variant CenH3, which physically interacts with components of the inner kinetochore constitutive-centromere-associated-network (CCAN). Unexpected to its critical function, previous work identified that select eukaryotic lineages, including several insects, have lost CenH3, while having retained homologs of the CCAN. These findings imply alternative CCAN assembly pathways in these organisms that function in CenH3-independent manners. Here, we study the composition and assembly of CenH3-deficient kinetochores of Lepidoptera (butterflies and moths). We show that lepidopteran kinetochores consist of previously identified CCAN homologs as well as additional components including a divergent CENP-T homolog, which are required for accurate mitotic progression. Our study focuses on CENP-T that we find both necessary and sufficient to recruit the Mis12 outer kinetochore complex. In addition, CRISPR-mediated gene editing in Bombyx mori establishes an essential function of CENP-T in vivo. Finally, the retention of CENP-T homologs in other independently-derived CenH3-deficient insects indicates a conserved mechanism of kinetochore assembly between these lineages. Our study provides the first functional insights into CCAN-based kinetochore assembly pathways that function independently of CenH3, thus contributing to the emerging picture of an unexpected plasticity to build a kinetochore.

Cryo-EM Structures of Centromeric Tri-nucleosomes Containing a Central CENP-A Nucleosome

The histone H3 variant CENP-A is a crucial epigenetic marker for centromere specification. CENP-A forms a characteristic nucleosome and dictates the higher-order configuration of centromeric chromatin. However, little is known about how the CENP-A nucleosome affects the architecture of centromeric chromatin. In this study, we reconstituted tri-nucleosomes mimicking a centromeric nucleosome arrangement containing the CENP-A nucleosome, and determined their 3D structures by cryoelectron microscopy. The H3-CENP-A-H3 tri-nucleosomes adopt an untwisted architecture, with an outward-facing linker DNA path between nucleosomes. This is distinct from the H3-H3-H3 tri-nucleosome architecture, with an inward-facing DNA path. Intriguingly, the untwisted architecture may allow the CENP-A nucleosome to be exposed to the solvent in the condensed chromatin model. These results provide a structural basis for understanding the 3D configuration of CENP-A-containing chromatin, and may explain how centromeric proteins can specifically target the CENP-A nucleosomes buried in robust amounts of H3 nucleosomes in centromeres.

Unintegrated HIV-1 DNAs are loaded with core and linker histones and transcriptionally silenced

Upon delivery into the nucleus of the host cell, linear double-stranded retroviral DNAs are either integrated into the host genome to form the provirus or act as a target of the DNA damage response and become circularized. Little is known about the chromatinization status of the unintegrated retroviral DNAs of the human immunodeficiency virus type 1 (HIV-1). In this study, we used chromatin immunoprecipitation to investigate the nature of unintegrated HIV-1 DNAs and discovered that core histones, the histone variant H3.3, and H1 linker histones are all deposited onto extrachromosomal HIV-1 DNA. We performed a time-course analysis and determined that the loading of core and linker histones occurred early after virus application. H3.3 and H1 linker histones were also found to be loaded onto unintegrated DNAs of the Moloney murine leukemia virus. The unintegrated retroviral DNAs are potently silenced, and we provide evidence that the suppression of extrachromosomal HIV-1 DNA is histone-related. Unintegrated DNAs were marked by posttranslational histone modifications characteristic of transcriptionally inactive genes: high levels of H3K9 trimethylation and low levels of H3 acetylation. These findings reveal insights into the nature of unintegrated retroviral DNAs.

Using CRISPR/Cas9 to produce haploid inducers of carrot through targeted mutations of centromeric histone H3 (CENH3)

The generation of haploids is one of the most powerful means to accelerate the plant breeding process. Based on recent results published for Arabidopsis thaliana, manipulating the centromeres of the chromosomes has been proposed as a novel breeding tool for the production of haploid crop plants. By this way, haploids can be generated through cross-fertilizations after manipulating a single centromere protein, the centromere-specific histone H3 variant CENH3, in one of the parents designated as ‘haploid inducer’. In our carrot research, we are using the CRISPR/Cas9 technique in combination with an Agrobacterium rhizogenes-mediated transformation system to induce mutations in the carrot CENH3 gene. We are investigating two different approaches for CENH3-based uniparental genome elimination called as ‘1-Step’ and ‘2-Step’ strategies. In the ‘1-Step’ approach we are testing regenerated carrot plants carrying non-lethal mutations within the endogenous CENH3 gene for putative haploid inducer effects. The ‘2-Step’ strategy is based on a fully knocked-out carrot CENH3 gene which is rescued by an alien CENH3 gene isolated from a related plant species. Co-transformations of CRISPR/Cas9-based knockout constructs together with a ginseng (Panax ginseng) CENH3 gene were performed by using A. rhizogenes. We show that we could successfully target the carrot CENH3 gene and that the ginseng CENH3 protein is accumulated inside the kinetochore region. We also discuss preliminary results from crosses with putative haploid inducer genotypes developed by the ‘2-step’ approach.

Functional cross talk between the Fanconi anemia and ATRX/DAXX histone chaperone pathways promotes replication fork recovery.

Fanconi anemia (FA) is a chromosome instability syndrome characterized by increased cancer predisposition. Specifically, the FA pathway functions to protect genome stability during DNA replication. The central FA pathway protein, FANCD2, locates to stalled replication forks and recruits homologous recombination (HR) factors such as CtBP interacting protein (CtIP) to promote replication fork restart while suppressing new origin firing. Here, we identify alpha-thalassemia retardation syndrome X-linked (ATRX) as a novel physical and functional interaction partner of FANCD2. ATRX is a chromatin remodeler that forms a complex with Death domain-associated protein 6 (DAXX) to deposit the histone variant H3.3 into specific genomic regions. Intriguingly, ATRX was recently implicated in replication fork recovery; however, the underlying mechanism(s) remained incompletely understood. Our findings demonstrate that ATRX forms a constitutive protein complex with FANCD2 and protects FANCD2 from proteasomal degradation. ATRX and FANCD2 localize to stalled replication forks where they cooperate to recruit CtIP and promote MRE11 exonuclease-dependent fork restart while suppressing the firing of new replication origins. Remarkably, replication restart requires the concerted histone H3 chaperone activities of ATRX/DAXX and FANCD2, demonstrating that coordinated histone H3 variant deposition is a crucial event during the reinitiation of replicative DNA synthesis. Lastly, ATRX also cooperates with FANCD2 to promote the HR-dependent repair of directly induced DNA double-stranded breaks. We propose that ATRX is a novel functional partner of FANCD2 to promote histone deposition-dependent HR mechanisms in S-phase.

The H3 histone chaperone NASPSIM3 escorts CenH3 in Arabidopsis.

Centromeres define the chromosomal position where kinetochores form to link the chromosome to microtubules during mitosis and meiosis. Centromere identity is determined by incorporation of a specific histone H3 variant termed CenH3. As for other histones, escort and deposition of CenH3 must be ensured by histone chaperones, which handle the non-nucleosomal CenH3 pool and replenish CenH3 chromatin in dividing cells. Here, we show that the Arabidopsis orthologue of the mammalian NUCLEAR AUTOANTIGENIC SPERM PROTEIN (NASP) and Schizosaccharomyces pombe histone chaperone Sim3 is a soluble nuclear protein that binds the histone variant CenH3 and affects its abundance at the centromeres. NASPSIM3 is co-expressed with Arabidopsis CenH3 in dividing cells and binds directly to both the N-terminal tail and the histone fold domain of non-nucleosomal CenH3. Reduced NASPSIM3 expression negatively affects CenH3 deposition, identifying NASPSIM3 as a CenH3 histone chaperone.

Dynamic Histone H3 Incorporation Fuels Metastatic Progression

Treating metastatic cancers is an ongoing challenge in oncology. A recent paper by Gomes and colleagues proposes histone H3 variant dynamics as major regulator of cell fate transition during metastasis and suggests histone chaperones as therapeutic targets for invasive carcinoma.