Xenopus HDm, a maternally expressed histone deacetylase, belongs to an ancient family of acetyl-metabolizing enzymes

Epigenetic Modification in Macrophages: A Promising Target for Tumor and Inflammation-associated Disease Therapy

Macrophages are essential for supporting tissue homeostasis, regulating immune response, and promoting tumor progression. Due to its heterogeneity, macrophages have different phenotypes and functions in various tissues and diseases. It is becoming clear that epigenetic modification playing an essential role in determining the biological behavior of cells. In particular, changes of DNA methylation, histone methylation and acetylation regulated by the corresponding epigenetic enzymes, can directly control macrophages differentiation and change their functions under different conditions. In addition, epigenetic enzymes also have become anti-tumor targets, such as HDAC, LSD1, DNMT, and so on. In this review, we presented an overview of the latest progress in the study of macrophages phenotype and function regulated by epigenetic modifications, including DNA methylation and histone modifications, to better understand how epigenetic modification controls macrophages phenotype and function in inflammation-associated diseases, and the application prospect in anti-tumor.

A NuRD Complex from Xenopus laevis Eggs Is Essential for DNA Replication during Early Embryogenesis

DNA replication in the embryo of Xenopus laevis changes dramatically at the mid-blastula transition (MBT), with Y RNA-independent random initiation switching to Y RNA-dependent initiation at specific origins. Here, we identify xNuRD, an MTA2-containing assemblage of the nucleosome remodeling and histone deacetylation complex NuRD, as an essential factor in pre-MBT Xenopus embryos that overcomes a functional requirement for Y RNAs during DNA replication. Human NuRD complexes have a different subunit composition than xNuRD and do not support Y RNA-independent initiation of DNA replication. Blocking or immunodepletion of xNuRD inhibits DNA replication initiation in isolated nuclei in vitro and causes inhibition of DNA synthesis, developmental delay, and embryonic lethality in early embryos. xNuRD activity declines after the MBT, coinciding with dissociation of the complex and emergence of Y RNA-dependent initiation. Our data thus reveal an essential role for a NuRD complex as a DNA replication factor during early Xenopus development.

Subcellular Localization of Class I Histone Deacetylases in the Developing Xenopus tectum

Histone deacetylases (HDACs) are thought to localize in the nucleus to regulate gene transcription and play pivotal roles in neurogenesis, apoptosis, and plasticity. However, the subcellular distribution of class I HDACs in the developing brain remains unclear. Here, we show that HDAC1 and HDAC2 are located in both the mitochondria and the nucleus in the Xenopus laevis stage 34 tectum and are mainly restricted to the nucleus following further brain development. HDAC3 is widely present in the mitochondria, nucleus, and cytoplasm during early tectal development and is mainly distributed in the nucleus in stage 45 tectum. In contrast, HDAC8 is broadly located in the mitochondria, nucleus, and cytoplasm during tectal development. These data demonstrate that HDAC1, HDAC2, and HDAC3 are transiently localized in the mitochondria and that the subcellular distribution of class I HDACs in the Xenopus tectum is heterogeneous. Furthermore, we observed that spherical mitochondria accumulate in the cytoplasm at earlier stages, whereas elongated mitochondria are evenly distributed in the tectum at later stages. The activity of histone acetylation (H4K12) remains low in mitochondria during tectal development. Pharmacological blockades of HDACs using a broad spectrum HDAC inhibitor of Trichostatin A (TSA) or specific class I HDAC inhibitors of MS-275 and MGCD0103 decrease the number of mitochondria in the tectum at stage 34. These findings highlight a link between the subcellular distribution of class I HDACs and mitochondrial dynamics in the developing optic tectum of Xenopus laevis.

Histone deacetylase induces accelerated maturation in Xenopus laevis oocytes

In oocyte maturation in Xenopus laevis, nuclear material induces rapid maturation and is required for entry into meiosis II. Nuclear material contains a large number of RNAs and proteins, including histone deacetylase (HDAC); however, it is not known which materials induce accelerated maturation. The HDAC activity modifies transcription rate and is required for normal meiosis; however, its function in oocyte maturation is still unclear. We investigated the function of HDAC activity, which is localized in the nuclear material, in the regulation of the speed of oocyte maturation. Inhibition of HDAC activity with trichostatin A (TSA) induced hyperacetylation of histone H3 and prolonged oocyte maturation. In contrast, increase in HDAC activity with an injection of FLAG-tagged maternal histone deacetylase (HDACm-FLAG) mRNA induced deacetylation of histone H3 and reduced the duration of oocyte maturation. Cdc2 kinase, Cdc25C or mitogen-activated protein kinase (MAPK), which are key regulators of the meiosis, were activated coincidently with maturation progression. In oocytes, the mRNA level of Cdc25C, an activator of Cdc2, was increased by HDACm-FLAG mRNA-injection; in contrast, the mRNA level of Cdc2 inhibitor Wee1 was increased by TSA treatment. These results suggest that HDAC activity is involved in the control of maturation speed through the regulation of mRNA levels of cell cycle regulators. Thus, HDACm is a candidate for the nuclear material component that induces rapid maturation in Xenopus oocytes.

Histone deacetylase activity is necessary for left-right patterning during vertebrate development

Background

Consistent asymmetry of the left-right (LR) axis is a crucial aspect of vertebrate embryogenesis. Asymmetric gene expression of the TGFβ superfamily member Nodal related 1 (Nr1) in the left lateral mesoderm plate is a highly conserved step regulating the situs of the heart and viscera. In Xenopus, movement of maternal serotonin (5HT) through gap-junctional paths at cleavage stages dictates asymmetry upstream of Nr1. However, the mechanisms linking earlier biophysical asymmetries with this transcriptional control point are not known.

Results

To understand how an early physiological gradient is transduced into a late, stable pattern of Nr1 expression we investigated epigenetic regulation during LR patterning. Embryos injected with mRNA encoding a dominant-negative of Histone Deacetylase (HDAC) lacked Nr1 expression and exhibited randomized sidedness of the heart and viscera (heterotaxia) at stage 45. Timing analysis using pharmacological blockade of HDACs implicated cleavage stages as the active period. Inhibition during these early stages was correlated with an absence of Nr1 expression at stage 21, high levels of heterotaxia at stage 45, and the deposition of the epigenetic marker H3K4me2 on the Nr1 gene. To link the epigenetic machinery to the 5HT signaling pathway, we performed a high-throughput proteomic screen for novel cytoplasmic 5HT partners associated with the epigenetic machinery. The data identified the known HDAC partner protein Mad3 as a 5HT-binding regulator. While Mad3 overexpression led to an absence of Nr1 transcription and randomized the LR axis, a mutant form of Mad3 lacking 5HT binding sites was not able to induce heterotaxia, showing that Mad3's biological activity is dependent on 5HT binding.

Conclusion

HDAC activity is a new LR determinant controlling the epigenetic state of Nr1 from early developmental stages. The HDAC binding partner Mad3 may be a new serotonin-dependent regulator of asymmetry linking early physiological asymmetries to stable changes in gene expression during organogenesis.

Using oocyte nuclei for studies on chromatin structure and gene expression

The giant nucleus of amphibian oocytes is generally referred to as the germinal vesicle (GV). Its size allows relatively easy manual isolation from the rest of the oocyte and also presents a large target in situ for microinjection of macromolecules including plasmid DNA, RNA species, antibodies and other proteins and even whole organelles, including somatic cell nuclei. Thus the use of GVs is excellent for two major types of study: the function of endogenous nuclear processes such as gene transcription, RNA processing and intra-nuclear dynamics; and the use of the nuclear components to effect processes such as chromatin assembly, expression of foreign genes and nucleocytoplasmic transport of injected biomolecules. This article outlines some basic techniques appropriate for GV studies, particularly the preparation of oocytes for microinjection and the isolation of germinal vesicles into an oil phase. As an aid to the targeting of the GV within the nucleus, descriptions are given of the use of oocytes from albino animals.

Remodelling the paternal chromatin at fertilization in mammals

At fertilization, the highly condensed and transcriptionally inert chromatin of the spermatozoa becomes remodelled into the decondensed and transcriptionally competent chromatin of the male pronucleus. The chromatin initially becomes dispersed and then transiently recondenses into a small mass upon entry into the ooplasm. This morphological change is coincident with and likely dependent on the replacement of the sperm-specific protamines by oocyte-supplied histones and the organization of the chromatin into nucleosomes. The chromatin then extensively decondenses within the male pronucleus and acquires many of the proteins that are associated with the maternal chromatin. Nonetheless, the paternal chromatin manifests distinct characteristics, including transient hyperacetylation of histone H4, increased transcription of endogenous and microinjected genes, and replication-independent demethylation of DNA. Sperm chromatin remodelling is controlled by an oocyte activity that appears during meiotic maturation and disappears approximately 3 h after activation (release from metaphase II arrest), and which requires factors associated with the germinal vesicle of the oocyte. The molecular components of this activity remain largely unknown. In frogs, nucleoplasmin is required to assemble histones H2A and H2B onto the paternal chromatin. Evidence is presented that related proteins may perform similar functions in mammals. Identifying the mechanisms that underlie sperm chromatin remodelling at fertilization may be relevant for understanding reprogramming of somatic cell nuclei after transfer into oocytes.

Identification of putative interaction partners for the Xenopus Polycomb-group protein Xeed

The extra sex combs (esc) gene of Drosophila and its mammalian homologue embryonic ectoderm development (eed) play pivotal roles in establishing Polycomb-group (Pc-G) mediated transcriptional silencing of regulatory genes during early development. We have carried out a two-hybrid screen in yeast to identify maternally expressed proteins that interact directly with the product of the Xenopus eed homologue, Xeed. Xeed-interacting proteins that were recovered in this screen included a maternal Xenopus histone deacetylase (HDACm), the Xeed protein itself, and a Xenopus homologue of Enhancer of zeste (XEZ) - a second member of the Pc-G that is closely related by sequence similarity to histone methyltransferases. We have also identified a novel interaction between Xeed and a component of the Xenopus basal transcription machinery, TAF(II)32. We show for the first time that each of these proteins interacts with the Xeed polypeptide, both in the yeast two-hybrid assay and in vitro using purified recombinant proteins. XEZ, HDACm and TAF(II)32 mRNAs are all strongly co-expressed with Xeed mRNA in the fertilized egg, further suggesting that their encoded proteins could interact with Xeed during early embryonic development. Our observations support a multi-step model for the onset of transcriptional silencing in which Xeed binds to and inhibits the function of the transcription initiation complex and also recruits proteins that mediate the acquisition by associated chromatin of epigenetically heritable, post-translational modifications.

Essential role of Drosophila Hdac1 in homeotic gene silencing

Deacetylation of the N-terminal tails of core histones plays a crucial role in gene silencing. Rpd3 and Hda1 represent two major types of genes encoding trichostatin A-sensitive histone deacetylases. Although they have been widely found, their cellular and developmental roles remain to be elucidated in metazoa. We show that Drosophila Hdac1, an Rpd3-type gene, interacts cooperatively with Polycomb group repressors in silencing the homeotic genes that are essential for axial patterning of body segments. The biochemical copurification and cytological colocalization of HDAC1 and Polycomb group repressors strongly suggest that HDAC1 is a component of the silencing complex for chromatin modification on specific regulatory regions of homeotic genes.

Mammalian histone deacetylase 1 protein is posttranslationally modified by phosphorylation

HDAC1, a member of the histone deacetylase family, is involved in transcription regulation through the modification of chromatin structure. Several studies also implicated HDAC1 in tumorigenesis. Much attention has been concentrated on protein-protein interactions involving HDAC1 and the possibility that posttranslational modifications may occur in mammalian HDAC1 proteins has not been carefully and systematically investigated. In this study, we utilized in vivo labeling assays to demonstrate that both human and murine HDAC1 proteins are phosphorylated in cells. Assays using HDAC1 deletion mutants indicated that phosphorylation occurs in its C-terminal domain. cAMP-dependent kinase and casein kinase II, but not protein kinase C, cdc2, or MAP kinase, could phosphorylate HDAC1 in vitro, although HDAC1 contains several protein kinase C consensus sites. We also found that phosphorylation did not influence HDAC1 enzymatic activity using a human histone H4 N-terminal peptide as the substrate. Interestingly, HDAC1-FLAG fusion protein immunoprecipitated from transfected cells was found to be in association with a kinase activity, providing an in vitro assay for further studies of this posttranslational modification.

Homo-oligomerisation and nuclear localisation of mouse histone deacetylase 1

Reversible histone acetylation changes the chromatin structure and can modulate gene transcription. Mammalian histone deacetylase 1 (HDAC1) is a nuclear protein that belongs to a growing family of evolutionarily conserved enzymes catalysing the removal of acetyl residues from core histones and other proteins. Previously, we have identified murine HDAC1 as a growth factor-inducible protein in murine T-cells. Here, we characterise the molecular function of mouse HDAC1 in more detail. Co-immunoprecipitation experiments with epitope-tagged HDAC1 protein reveal the association with endogenous HDAC1 enzyme. We show that HDAC1 can homo-oligomerise and that this interaction is dependent on the N-terminal HDAC association domain of the protein. Furthermore, the same HDAC1 domain is also necessary for in vitro binding of HDAC2 and HDAC3, association with RbAp48 and for catalytic activity of the enzyme. A lysine-rich sequence within the carboxy terminus of HDAC1 is crucial for nuclear localisation of the enzyme. We identify a C-terminal nuclear localisation domain, which is sufficient for the transport of HDAC1 and of reporter fusion proteins into the nucleus. Alternatively, HDAC1 can be shuttled into the nucleus by association with another HDAC1 molecule via its N-terminal HDAC association domain. Our results define two domains, which are essential for the oligomerisation and nuclear localisation of mouse HDAC1.

Histone deacetylases, transcriptional control, and cancer

A key event in the regulation of eukaryotic gene expression is the posttranslational modification of nucleosomal histones, which converts regions of chromosomes into transcriptionally active or inactive chromatin. The most well studied posttranslational modification of histones is the acetylation of epsilon-amino groups on conserved lysine residues in the histones' amino-terminal tail domains. Significant advances have been made in the past few years toward the identification of histone acetyltransferases and histone deacetylases. Currently, there are over a dozen cloned histone acetyltransferases and at least eight cloned human histone deacetylases. Interestingly, many histone deacetylases can function as transcriptional corepressors and, often, they are present in multi-subunit complexes. More intriguing, at least some histone deacetylases are associated with chromatin-remodeling machines. In addition, several studies have pointed to the possible involvement of histone deacetylases in human cancer. The availability of the cloned histone deacetylase genes has provided swift progress in the understanding of the mechanisms of deacetylases, their role in transcription, and their possible role in health and disease.

Characterization of two putative histone deacetylase genes from Aspergillus nidulans

In eukaryotic organisms, acetylation of core histones plays a key role in the regulation of transcription. Multiple histone acetyltransferases (HATs) and histone deacetylases (HDACs) maintain a dynamic equilibrium of histone acetylation. The latter form a highly conserved protein family in many eukaryotic species. In this paper, we report the cloning and sequencing of two putative histone deacetylase genes (rpdA, hosA) of Aspergillus nidulans, which are the first to be analyzed from filamentous fungi. Hybridization with a chromosome-specific cosmid library of A. nidulans allowed the localization of rpdA to chromosome III and hosA to chromosome II, respectively. PCR analyses and Southern hybridization experiments revealed that no further members of the RPD3 family are present in the genome of the fungus. Although sequence alignment displays significant amino acid similarity to other eukaryotic RPD3-type deacetylases, the deduced RPDA sequence reveals an unusual 200-amino acid extension at the C-terminus. Expression of both genes was determined by RNA blot analysis. Treatment of the cells with trichostatin A (TSA), a potent inhibitor of HDACs, was found to stimulate expression of rpdA of A. nidulans.

Molecular cloning and characterization of the mouse histone deacetylase 1 gene: integration of a retrovirus in 129SV mice

Reversible histone acetylation plays an important role for chromatin structure and gene expression. The acetylation state of core histones is controlled by histone acetyltransferases and histone deacetylases. Here we report the cloning and characterization of the mouse histone deacetylase 1 (HDAC1) gene. The mouse genome contains several HDAC1-related structures representing the HDAC1 gene and at least three pseudogenes. The HDAC1 gene comprises 14 exons ranging from 49 to 539 bp. Interestingly the murine HDAC1 gene strongly resembles the previously published mouse HDAC2 gene (Zeng et al., J. Biol. Chem. 273 (1998) 28921-28930). The sizes of ten of the 14 exons are identical for both genes and the splicing sites for 11 introns align in identical positions suggesting a gene duplication event. The HDAC1 gene is located only 128 bp downstream from the MARCKS-related protein (MRP) gene in a tail-to-tail orientation. The murine MRP gene was previously mapped to a conserved gene cluster on chromosome 4 sharing linkage homology to human chromosome 1p32-36. The genes for HDAC1 and MRP are co-expressed in a variety of cell types. In the genome of 129SV mice the largest intervening sequence of the HDAC1 gene, intron 3, harbors a complete copy of the endogenous retrovirus MuERV-L. In contrast the HDAC1 gene in other mouse strains such as C57B16, C3H/An and C-RY lacks the retrovirus. Our study provides useful tools for future targeted gene disruption studies.

Chicken histone deacetylase-2 controls the amount of the IgM H-chain at the steps of both transcription of its gene and alternative processing of its pre-mRNA in the DT40 cell line

Histone deacetylases (HDACs) are involved in the deacetylation of core histones, which is an important event in transcription regulation in eukaryotes through alterations in the chromatin structure. We cloned cDNAs and genomic DNAs encoding two chicken HDACs (chHDAC-1 and -2), which are preferentially localized in nuclei. Treatment with trichostatin A reduced the HDAC activities in immunoprecipitates obtained with anti-chHDAC-1 and -2 antisera. Using gene targeting techniques, we generated homozygous DT40 mutants, DeltachHDAC-1 and -2, devoid of two alleles of the chHDAC-1 and -2 genes, respectively. The protein patterns on two-dimensional PAGE definitely changed for DeltachHDAC-2, and the amounts of the IgM H- and L-chains increased in it. Of the two IgM H-chain forms, the secreted form mu(s) increased in DeltachHDAC-2, but the membrane-bound form mu(m) decreased. The IgM H-chain gene was transcribed more in DeltachHDAC-2 than in DT40 cells. In the mutant, the alternative processing of IgM H-chain pre-mRNA preferentially occurred, resulting in an increase in the amount of mu(s) mRNA, whereas the stability of the two types of mRNA, mu(s) and mu(m), was unchanged. In DT40 cells, treatment with trichostatin A increased both the amounts of IgM H-chain mRNAs and the switch from mu(m) to mu(s) mRNAs. Based on these results, we propose a model for a role of chHDAC-2 in both the transcription and alternative processing steps, resulting in control of the amount of the mu(s) IgM H-chain in the DT40 cell line.

Human genes involved in chromatin remodeling in transcription initiation, and associated diseases: An overview using the GENATLAS database

Chromatin structure is inextricably linked to transcription regulation and differentiation. It consists of a multicomponent system, and impairments in such complex arrays may elicit dramatic biological effects and diseases. We present an overview of human genes involved in chromatin remodeling, which consist of the histone acetyltransferase/deacetylase system and the SWI/SNF-like complexes containing DNA-dependent ATPase activity. Special attention is given to the functional and physical interactions in which these components are involved, notably as transcriptional coactivators and/or corepressors of a large variety of genes. Linking seemingly distinct pathways allows integration of individual components into complex genetic and molecular processes and assessment of the underlying molecular bases of diseases. This was performed using GENATLAS (http://www.infobiogen.fr/), a gene database which compiles the information relevant to the mapping efforts from the published literature.

Maternal histone deacetylase is accumulated in the nuclei of Xenopus oocytes as protein complexes with potential enzyme activity

Reversible acetylation of core histones plays an important regulatory role in transcription and replication of chromatin. The acetylation status of chromatin is determined by the equilibrium between activities of histone acetyltransferases (HATs) and histone deacetylases (HDACs). The Xenopus protein HDACm shows sequence homology to other putative histone deacetylases, but its mRNA is expressed only during early development. Both HDACm protein and acetylated non-chromosomal histones are accumulated in developing oocytes, indicating that the key components for histone deposition into new chromatin during blastula formation are in place by the end of oogenesis. Here we show that the 57 kDa HDACm protein undergoes steady accumulation in the nucleus, where it is organized in a multiprotein complex of approx. 300 kDa. A second, major component of the nuclear complex is the retinoblastoma-associated protein p48 (RbAp48/46), which may be used as an adaptor to contact acetylated histones in newly assembled chromatin. The nuclear complex has HDAC activity that is sensitive to trichostatin A, zinc ions and phosphatase treatment. The 57 kDa protein serves as a marker for total HDAC activity throughout oogenesis and early embryogenesis. The active HDACm complex and its acetylated histone substrates appear to be kept apart until after chromatin assembly has taken place. However, recombinant HDACm, injected into the cytoplasm of oocytes, not only is translocated to the nucleus, but also is free to interact with the endogenous chromatin.

WD repeats of the p48 subunit of chicken chromatin assembly factor-1 required for in vitro interaction with chicken histone deacetylase-2

Chromatin assembly factor-1 (CAF-1) is essential for chromatin assembly in eukaryotes, and comprises three subunits of 150 kDa (p150), 60 kDa (p60), and 48 kDa (p48). We cloned and sequenced cDNA encoding the small subunit of the chicken CAF-1, chCAF-1p48. It consists of 425 amino acid residues including a putative initiation Met, possesses seven WD repeat motifs, and contains only one amino acid change relative to the human and mouse CAF-1p48s. The immunoprecipitation experiment followed by Western blotting revealed that chCAF-1p48 interacts with chicken histone deacetylases (chHDAC-1 and -2) in vivo. The glutathione S-transferase pulldown affinity assay revealed the in vitro interaction of chCAF-1p48 with chHDAC-1, -2, and -3. We showed that the p48 subunit tightly binds to two regions of chHDAC-2, located between amino acid residues 82-180 and 245-314, respectively. We also established that two N-terminal, two C-terminal, or one N-terminal and one C-terminal WD repeat motif of chCAF-1p48 are required for this interaction, using deletion mutants of the respective regions. These results suggest that chCAF-1p48 is involved in many aspects of DNA-utilizing processes, through alterations in the chromatin structure based on both the acetylation and deacetylation of core histones.

Identification of a new family of higher eukaryotic histone deacetylases. Coordinate expression of differentiation-dependent chromatin modifiers

The histone deacetylase domain of almost all members of higher eukaryotic histone deacetylases already identified (HDAC family) is highly homologous to that of yeast RPD3. In this paper we report the cloning of two cDNAs encoding members of a new family of histone deacetylase in mouse that show a better homology to yeast HDA1 histone deacetylase. These cDNAs encode relatively large proteins, presenting an in vitro trichostatin A-sensitive histone deacetylase activity. Interestingly, one, mHDA2, encodes a protein with two putative deacetylase domains, and the other, mHDA1, contains only one deacetylase homology domain, located at the C-terminal half of the protein. Our data showed that these newly identified genes could belong to a network of genes coordinately regulated and involved in the remodeling of chromatin during cell differentiation. Indeed, the expression of mHDA1 and mHDA2 is tightly linked to the state of cell differentiation, behaving therefore like the histone H1 degrees-encoding gene. Moreover, like histone H1(0) gene, mHDA1 and mHDA2 gene expression is induced upon deacetylase inhibitor treatment. We postulate the existence of a regulatory mechanism, commanding a coordinate expression of a group of genes involved in the remodeling of chromatin not only during cell differentiation but also after abnormal histone acetylation.

Molecular cloning of Drosophila melanogaster cDNAs that encode a novel histone deacetylase dHDAC3

The steady-state level of histone acetylation in eukaryotes is established and maintained by multiple histone acetyltransferases (HATs) and histone deacetylases (HDACs) and affects both the structure and the function of chromatin. Histone deacetylases play a key role in the regulation of transcription, and form a highly conserved protein family in many eukaryotic species. Here we describe the cloning, sequencing and genetic mapping of two histone deacetylase genes in Drosophila melanogaster: dHDAC1 is essentially identical to the previously cloned D. melanogaster d-Rpd3 gene and dHDAC3, a novel gene, is orthologous to the human and the chicken (Gallus gallus) HDAC3 genes. The predicted amino acid sequence (438 aa) of dHDAC3 shows 58.1% identity with dHDAC1/d-Rpd3, the only previously known member of the HDAC family in this organism. The map positions on polytene chromosomes for dHDAC1 and dHDAC3 were determined as 64C1-6 and 83A3-4 respectively. A search for other dHDAC3-like genes failed to find other potential paralogues in D. melanogaster, but identified significant homologies with bacterial and fungal genes encoding enzymes that metabolise acetyl groups, and with genes for other hydrolyases such as carboxypeptidase. In addition, histone deacetylase activity in D. melanogaster nuclear extracts can be inhibited by high concentrations of zinc and activated by low concentrations, which is identical to the properties of bovine carboxypeptidase A. On the basis of sequence and functional similarities, we suggest that histone deacetylases are metal-substituted enzymes.

Genetic characterisation of hda1+, a putative fission yeast histone deacetylase gene

hda1+ (histone deacetylase 1) is a fission yeast gene which is highly similar in sequence to known histone deacetylase genes in humans and budding yeast. We have investigated if this putative histone deacetylase contributes to transcriptional silencing in the fission yeast Schizosaccharomyces pombe. A precise deletion allele of the hda1+ open reading frame was created. Cells lacking the hda1+ gene are viable. However, genetic analysis reveals that cells without hda1 + display enhanced gene repression/silencing of marker genes, residing adjacent to telomeres, close to the silent mating-type loci and within centromere I. This phenotype is very similar to that recently reported for rpd3 mutants both in Drosophila and budding yeast. No defects in chromosome segregation or changes in telomere length were detected. Cells lacking the hda1+ gene display reduced sporulation. Growth of hda1 cells is partially inhibited by low concentrations of Trichostatin A (TSA), a known inhibitor of histone deacetylase enzymes. TSA treatment is also able to overcome the enhanced silencing found in heterochromatic regions of hda1 cells. These results indicate a genetic redundancy with respect to deacetylase genes and partially overlapping functions of these in fission yeast. The significance of these results is discussed in the light of recent discoveries from other eukaryotes.