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At least 19 recordsLinked to original sources
PubMed1986

Differential localization and androgen sensitivity of prostatic nuclear protein kinases in euchromatin and heterochromatin fractions.

We have examined the distribution and androgenic regulation of protein kinases and phosphoproteins in euchromatin and heterochromatin fractions of rat ventral prostate chromatin. Available procedures to prepare euchromatin and heterochromatin fractions were found to result in the loss of various chromatin-associated protein kinases even though there was no gross change in the gel electrophoretic profile of proteins in these fractions. This loss was prevented by the addition of 0.5 mM phenylmethylsulfonyl fluoride throughout the preparative procedures, which indicates that the protein kinases associated with the chromatin may be particularly susceptible to proteolytic degradation during further subfractionation. By utilizing an improved method for fractionation of chromatin, we have demonstrated a marked enrichment of protein kinase activity (towards phosvitin and endogenous chromosomal proteins) in the euchromatin fraction as compared with heterochromatin. Both of these fractions were also examined for the incorporation of 32P into two main classes of nonhistone proteins (namely, H2SO4-soluble and -insoluble nonhistones). The amount of 32P incorporated into heterochromatin-associated proteins of both classes was markedly less than that in the euchromatin-associated proteins. Protein kinase activities (especially those active towards phosvitin and nonhistone proteins) in the euchromatin fraction as compared with the heterochromatin were significantly reduced within 24 h after androgenic deprivation in the animal. The decreased phosphorylation of nonhistone proteins could be attributed to the loss of endogenous protein kinase activity. The results indicate that not only are chromatin-associated protein phosphokinases preferentially localized in euchromatin fractions but also that these euchromatin-associated protein kinases display the greatest sensitivity to androgenic status of the animal.

Androgens↗
PubMed1976

Interactions of mercury and copper with constitutive heterochromatin and euchromatin in vivo and in vitro.

Mouse liver nuclei were fractionated into (condensed) heterochromatin and (noncondensed) euchromatin by differential centrifugation of sonicated nuclei. The fractions were subsequently characterized as unique nuclear species by thermal denaturation derivative profile analysis, which revealed the heterochromatin fraction enriched in satellite DNA and by endogenous metal content, which displayed partitioning of mercury in euchromatin over heterochromatin by a 10:1 ratio, with a comparatively uniform distribution of copper in both fractions. Fractionation of nuclei following in vivo challenge with copper showed enrichment of copper in heterochromatin, relative to euchromatin, while in vivo exposure to mercury resulted in a 20-fold accumulation of mercury in euchromatin, relative to heterochromatin. Using gel filtration and equilibrium dialysis to measure in vitro binding under relatively physiologic conditions of pH (6.0-7.0) and ionic strength (standard saline citrate or saline), the condensed and noncondensed chromatin fractions exhibited binding specificities toward mercury and copper similar to that observed in the in vivo metal challenge experiments. The level of mercury which binds to euchromatin in vitro, when measured either in physiologic [standard saline citrate (SSC)] or in dilute (1:100 SSC) salt solutions, was comparable (approximately 3 mug of Hg/mg of DNA) to that of in vivo euchromatin-bound mercury after 1 month of challenge with dietary metal. In contrast, copper showed little or no preference for the nuclear fractions in dilute salt solutions and displayed patterns which mimic in vivo binding only at higher ionic strengths (saline). Removal of proteins from the chromatin fractions resulted in a loss of binding specificity toward both metals. Therefore, the binding selectivity of condensed and noncondensed chromatin toward both mercury and copper appears to arise from protein or from protein-DNA associations. The state of chromatin condensation is especially critical in the case of copper.

Animals↗
PubMed1998

Euchromatin megabase cleavages and conjoint apoptotic-autophagic death expression with nucleolar ball-and-socket joint dislocations in human Chang liver cells arrested in S-phase by etoposide.

Etoposide induced a megabase (Mb) fragmentation pattern identical with that from genomic digestion by NotI restriction endonuclease which specifically cleaves CpG islands in euchromatin domains. Redigestion by NotI produced no change, suggesting cleavage in the same or closely related sites in euchromatin domains. Preferential euchromatin cleavage was further suggested by harvested metaphase chromosomes showing self-inflicted resolution of light G-bandings (R-bandings), the euchromatin domains. Autodegeneration following Mb euchromatin fragmentations was shown by their degradation into 200 bp ladders, and expressions of apoptotic and "non-apoptotic" active death morphologies that were also seen conjointly in the same cell. The endstage further showed heterochromatin masses anchored to the nucleolus by novel ball-and-socket joints where dislocations occurred with nuclear leakage.

Apoptosis↗
PubMed1974

Transcription of fractionated mammalian chromatin by mammalian ribonucleic acid polymerase. Demonstration of temperature-dependent rifampicin-resistant initiation sites in euchromatin deoxyribonucleic acid.

The chromatin fractionation method of Frenster et al. (1963) as modified by Leake et al. (1972) was used to prepare fragments of euchromatin from rat liver nuclei. These remain soluble in 5mm-MgCl(2), and contain DNA of maximum mol.wt. 1x10(6)-2x10(6). The fragments were separated from condensable chromatin on a sucrose gradient. Euchromatin contains endogenous DNA-dependent RNA polymerase, and most of the nascent RNA labelled in vivo or in vitro. Euchromatin fragments allow initiation of transcription by added purified rat liver form-B RNA polymerase and contain temperature-dependent rifampicin-resistant initiation sites for the form-B enzyme. These findings indicate that transcription of the euchromatin regions of interphase chromosomes is not initiated in condensed chromatin, but is initiated within the euchromatin stretches. Condensable chromatin also contains most of these activities, but is not associated with nascent RNA.

Animals↗
PubMed1978

Fractionation and characterization of euchromatin isolated from mouse ascites sarcoma cells.

Euchromatin specimen prepared by the usual method formed large clumps and had various shapes under electron microscopy. A method of separation of the euchromatin specimen into chromatin fractions having relatively homogeneous form was examined and partial characterization of these fractions was carried out. The heavy euchromatin fraction was a large network of thin fibrils (about 100 A in diameter) and various thick fibers. The intermediate euchromatin fraction consisted of relatively homogeneous networks of thick knobby fibers (about 250 A in diameter). The light euchromatin fraction had metworks of thick fibers. These chromatin fractions were quantitatively prepared from sonicated nuclei of mouse ascites sarcoma cells. Twenty-one or twenty-two bands of non-histone proteins besides histones were detected in these chromatin fractions by SDS-polyacrylamide gel electrophoresis. There were significant differences in the electrophoretic patterns of non-histone proteins among these chromatin fractions.

Animals↗
PubMed1980

Toluidine blue binding capacity of heterochromatin and euchromatin of Triatoma infestans Klug.

The localization of the absorption peaks of toluidine blue-stained heterochromatin (Ho and Hs) and euchromatin (Eo and Es) of the Malpighian tubules of the blood-sucking hemipteran, Triatoma infestans Klug was studied cytophotometrically (Ho and Eo: hetero- and euchromatin of nuclei with one single chromocenter; Hs and Es: hetero- and euchromatin of nuclei with several chromocenters). shifts of the absorption peaks to longer wave-lengths were found for the euchromatin fractions and Hs after RNAse treatment. The differences in the localization of absorption peaks after RNAse digestion when comparing the various chromatin types with one another are assumed to be due to differences in the number and proximity of DNA phosphates unattached to proteins and hence available to dye binding. The localization of the absorption peak of Ho at a relatively short wavelength (lambda = 570 nm) as compared with those for Hs, Eo, and Es, is attributed to a special state of chromatin condensation and practically absence of RNA in Ho. Also a certain removal of histones (probably, Hl) by the acetic ethanol "fixation" is speculated to play a role in the absorption curve properties of Ho subjected to TB staining.

Animals↗
PubMed2000

HP1gamma associates with euchromatin and heterochromatin in mammalian nuclei and chromosomes.

Heterochromatin protein 1 (HP1) is a nonhistone chromosomal protein, first identified in Drosophila, that plays a dose-dependent role in gene silencing. Three orthologs, HP1alpha, HP1beta, and HP1gamma, have been characterized in mammals. While HP1alpha and HP1beta have been unambiguously localized in heterochromatin by immunocytochemical methods, HP1gamma has been found either exclusively associated with euchromatin or present in both euchromatin and heterochromatin. Here, using an antibody directed against a peptide epitope at the carboxyl-terminal end of the molecule, we localize HP1gamma in both euchromatin and heterochromatin compartments of interphase nuclei, as well as in the pericentromeric chromatin and arms of mitotic chromosomes of 3T3 cells. This dual location was also observed in nuclei expressing HP1gamma as a fusion protein with green fluorescent protein. In contrast, when the distribution of HP1gamma was analyzed with antibodies directed against an amino-terminal epitope, the protein was detectable in euchromatin and not in heterochromatin, except for transient heterochromatin staining during the late S phase, when the heterochromatin undergoes replication. These data suggest that the controversial immunolocalization of HP1gamma in chromatin is due to the use of antibodies directed against topologically distinct epitopes, those present at the amino-terminal end of the molecule being selectively masked in nonreplicative heterochromatin.

3T3 Cells↗
PubMed2006

Euchromatin and pericentromeric heterochromatin: comparative composition in the tomato genome.

Eleven sequenced BACs were annotated and localized via FISH to tomato pachytene chromosomes providing the first global insights into the compositional differences of euchromatin and pericentromeric heterochromatin in this model dicot species. The results indicate that tomato euchromatin has a gene density (6.7 kb/gene) similar to that of Arabidopsis and rice. Thus, while the euchromatin comprises only 25% of the tomato nuclear DNA, it is sufficient to account for approximately 90% of the estimated 38,000 nontransposon genes that compose the tomato genome. Moreover, euchromatic BACs were largely devoid of transposons or other repetitive elements. In contrast, BACs assigned to the pericentromeric heterochromatin had a gene density 10-100 times lower than that of the euchromatin and are heavily populated by retrotransposons preferential to the heterochromatin-the most abundant transposons belonging to the Jinling Ty3/gypsy-like retrotransposon family. Jinling elements are highly methylated and rarely transcribed. Nonetheless, they have spread throughout the pericentromeric heterochromatin in tomato and wild tomato species fairly recently-well after tomato diverged from potato and other related solanaceous species. The implications of these findings on evolution and on sequencing the genomes of tomato and other solanaceous species are discussed.

Centromere↗
PubMed2001

[Trans-effect of modifiers on position-effect variegation in a set of euchromatin-heterochromatin rearrangements in Drosophila melanogaster].

The effects of suppressors of position-effect variegation were studied in a set of euchromatin-heterochromatin rearrangements of the X chromosome accompanied by inactivation of the gene wapl. The rearrangements differed from one another in the size of the heterochromatic block adjacent to euchromatin, with the euchromatin-heterochromatin border remaining unchanged. In one rearrangement (r20), the position effect caused by a small block of adjacent heterochromatin may be determined by its interaction with the neighboring main heterochromatic region of the X chromosome. Chromosome 3 (the RT chromosome) was found to have a strong suppressing effect on all rearrangements, irrespective of the amount of heterochromatin adjacent to euchromatin. Su-var(3)9, a known suppressor of the position-effect variegation, had a considerably weaker suppressing effect. The RT chromosome had the strongest suppressing effect on the rearrangement r20.

Animals↗
PubMed1986

Preferential association of glycoproteins to the euchromatin regions of cross-fractured nuclei is revealed by fracture-label.

We used fracture-label to establish ultrastructural localization of glycoproteins in cross-fractured nuclei of duodenal columnar and exocrine pancreatic cells. Mannose residues were detected in cell nuclei by labeling freeze-fractured tissues with concanavalin A-horseradish peroxidase X colloidal gold (Con A-HRP X CG) or direct concanavalin A X colloidal gold (Con A X CG); fucose residues were detected with Ulex Europaeus I X colloidal gold (UEA I X CG) markers. Areas of the three main intranuclear compartments (euchromatin, heterochromatin, and nucleolus) exposed by freeze-fracture were determined by automated image analysis. Colloidal gold particles bound to each nuclear subcompartment were counted and the results expressed in number of colloidal gold particles per square micrometer +/- SEM. Duodenal and pancreatic tissues fractured and labeled with Con A-HRP X CG complex or direct Con A X CG conjugates showed that the vast majority of Con A binding sites was confined to euchromatin regions with only sparse labeling of the heterochromatin and nucleolus. UEA I labeling of duodenal columnar cells showed that colloidal gold particles were almost exclusively confined to cross-fractured areas where euchromatin is exposed. Trypsinization of the fractured tissues before labeling with Con A and UEA I abolished 95-100% of the original label. Our results show that, within the nucleoplasm, mannose and fucose are residues of glycoproteins preferentially located within the regions of euchromatin.

Animals↗
PubMed1992

Restriction enzyme banding and in situ nick-translation on different types of hetero- and euchromatin.

We studied the role of chromatin accessibility and methylation in the banding patterns produced by means of in situ nick-translation (NT) and restriction enzyme (RE) banding techniques. For these studies we used the X chromosomes of Microtus cabrerae because of their large segment with four different types of constitutive heterochromatin and because in these chromosomes we can also compare active and inactive euchromatin. The results demonstrate that constitutive heterochromatin in the X chromosomes of M. cabrerae is methylated at specific sequences in both active and inactive Xs. They also show that NT-based techniques are suitable for detecting weak differences in chromatin accessibility, such as differences between active and inactive euchromatin, and are able to distinguish methylation only at the accessible sites. Thus, when methylation has to be mapped in situ, additional experiments have to be performed in order to distinguish findings due to differential accessibility. RE banding seems less sensitive to slight differences in chromatin accessibility, and might thus be more suitable than in situ NT-based techniques for methylation mapping. In harmony with these results, HpaII-based RE banding is able to distinguish between active and inactive euchromatin, possibly depending on its methylation status.

Animals↗
PubMed2002

Methylation of a euchromatin-heterochromatin transition region in Arabidopsis thaliana chromosome 5 left arm.

Cytosine methylation was studied at the level of the euchromatin/heterochromatin transition genomic region of the Arabidopsis chromosome 5 left arm. It has been shown using a monoclonal antibody against 5-methylcytosines that the density of DNA methylation increases from the euchromatin towards the heterochromatin. YACs mapped along this region were characterized for their repeated sequences content. Some of them, corresponding to euchromatin, euchromatin/heterochromatin border and heterochromatin regions, were used as probes for a Southern blot analysis of methylation. This revealed that the degree of mCmCGG and GATmC methylation increases significantly from the euchromatin towards the heterochromatin. Moreover, an analysis of cytosine methylation levels (% of 5-methylcytosine) of different DNA fragments, inside the same genomic region, was performed using PCR and/or Southern blot approaches. There is a gradual increase of methylation along the genomic region analyzed: CpG methylation in the euchromatic fraction, CpG and CpNpG methylation at the euchromatin/heterochromatin transition and an additional asymmetrical methylation in the repeated-heterochromatic fraction. The most methylated repeated family at CpG, CpNpG and asymmetrical sites is the 5S ribosomal DNA, highly methylated even though it is transcribed.

5-Methylcytosine↗
PubMed1959

Differential uptake of tritiated thymidine into hetero- and euchromatin in Melanoplus and Secale.

Grasshoppers of the species Melanoplus differentialis were injected with tritium-labelled thymidine. At intervals thereafter autoradiographic stripping film was applied over Feulgen squashes and sections. In this species during early prophase of meiosis the sex chromosome forms a heterochromatic block large enough to be resolved in tritium autoradiographs. A study of the squash preparations reveals that the sex chromosome is synthesizing DNA at a different period of time from the euchromatic autosomes. Since there is a developmental sequence of spermatocyte cysts along the testicular tubes it is possible from the sections to show that the heterochromatin synthesizes DNA later than does the euchromatin. To find out whether the results obtained in Melanoplus were characteristic of heterochromatin in general, young seedlings of rye were grown in a tritiated thymidine solution and Feulgen squashes were made as for Melanoplus. In rye leaf nuclei there is a large block of heterochromatin constituted by the proximal regions of the chromosomes and a euchromatic one formed by the median and distal regions of the same chromosomes. Here also the heterochromatin synthesizes DNA at a different period of time from the euchromatin. It is concluded that in rye the asynchrony of synthesis occurs within each chromosome. Counts of silver grains over the two types of chromatin in nuclei of Melanoplus and Secale disclosed that the number of grains per unit area was two to three times higher over the heterochromatin. To check the DNA content, Feulgen photometric measurements were made of Melanoplus nuclei at the same stage. The Feulgen and grain counts agree in showing that the heterochromatin contains two to three times more DNA per unit area than the euchromatin.

Animals↗
PubMed2006

Mapping of the juxtacentromeric heterochromatin-euchromatin frontier of human chromosome 21.

Euchromatin and heterochromatin are functional compartments of the genome. However, little is known about the structure and the precise location of the heterochromatin-euchromatin boundaries in higher eukaryotes. Constitutive heterochromatin in centromeric regions is associated with (1) specific histone methylation patterns, (2) high levels of DNA methylation, (3) low recombination frequency, and (4) the repression of transcription. All of this contrasts with the permissive structure of euchromatin found along chromosome arms. On the sequence level, the transition between these two domains consists most often of patchworks of segmental duplications. We present here a comprehensive analysis of gene expression, DNA methylation in CpG islands, distribution of histone isoforms, and recombination activity for the juxtacentromeric (or pericentromeric) region of the long arm of human chromosome 21. We demonstrate that most HapMap data are reliable within this region. We show that high linkage disequilibrium between pairs of SNPs extends 719-737 kb from the centromeric alpha-satellite. In the same region we find a peak of histone isoforms H3K9Me3 and H3K27Me (715-822 kb distal to the alpha-satellite). In normal somatic cells, CpG islands proximal to this peak are highly methylated, whereas distal CpG islands are not or very little methylated. This methylation profile undergoes dramatic changes in cancer cells and during spermatogenesis. As a consequence, transcription from heterochromatic genes is activated in the testis, and aberrant gene activation can occur during neoplastic transformation. Our data indicate that the frontier between the juxtacentromeric heterochromatic domain and euchromatic domain of the long arm of chromosome 21 is marked by a heterochromatic peak located approximately 750 kb distal to the alpha-satellite.

Chromatin Immunoprecipitation↗
PubMed2004

Assembly and characterization of heterochromatin and euchromatin on human artificial chromosomes.

BACKGROUND: Human centromere regions are characterized by the presence of alpha-satellite DNA, replication late in S phase and a heterochromatic appearance. Recent models propose that the centromere is organized into conserved chromatin domains in which chromatin containing CenH3 (centromere-specific H3 variant) at the functional centromere (kinetochore) forms within regions of heterochromatin. To address these models, we assayed formation of heterochromatin and euchromatin on de novo human artificial chromosomes containing alpha-satellite DNA. We also examined the relationship between chromatin composition and replication timing of artificial chromosomes. RESULTS: Heterochromatin factors (histone H3 lysine 9 methylation and HP1alpha) were enriched on artificial chromosomes estimated to be larger than 3 Mb in size but depleted on those smaller than 3 Mb. All artificial chromosomes assembled markers of euchromatin (histone H3 lysine 4 methylation), which may partly reflect marker-gene expression. Replication timing studies revealed that the replication timing of artificial chromosomes was heterogeneous. Heterochromatin-depleted artificial chromosomes replicated in early S phase whereas heterochromatin-enriched artificial chromosomes replicated in mid to late S phase. CONCLUSIONS: Centromere regions on human artificial chromosomes and host chromosomes have similar amounts of CenH3 but exhibit highly varying degrees of heterochromatin, suggesting that only a small amount of heterochromatin may be required for centromere function. The formation of euchromatin on all artificial chromosomes demonstrates that they can provide a chromosome context suitable for gene expression. The earlier replication of the heterochromatin-depleted artificial chromosomes suggests that replication late in S phase is not a requirement for centromere function.

Chromobox Protein Homolog 5↗
PubMed1999

The putative nuclear receptor mediator TIF1alpha is tightly associated with euchromatin.

Ligand-dependent transcriptional regulation by nuclear receptors is believed to be mediated by intermediary factors (TIFs) acting on remodelling of the chromatin structure and/or the activity of the transcriptional machinery. The putative transcriptional mediator TIF1alpha is a nuclear protein kinase that has been identified via its interaction with liganded nuclear receptors, including retinoic acid (RAR), retinoid X (RXR) and estrogen (ER) receptors. Here, we demonstrate that TIF1alpha is a non-histone chromosomal protein tightly associated with highly accessible euchromatic regions of the genome. Immunofluorescence confocal microscopy reveals that TIF1alpha exhibits a finely granular distribution in euchromatin of interphase nuclei, while it is mostly excluded from condensed chromatin and metaphase chromosomes. Immunoelectron microscopy shows that, in contrast to the heterochromatin protein HP1alpha, most of TIF1alpha is associated with euchromatin, where it is preferentially localised on regions known to be sites for RNA polymerase II (perichromatin fibrils and borders between euchromatin and heterochromatin). Early mouse embryos as well as embryonal carcinoma (EC) and embryonic stem (ES) cells express high levels of TIF1alpha. These levels dramatically decrease during organogenesis and upon differentiation of P19 EC cells, indicating that TIF1alpha is preferentially expressed in undifferentiated pluripotent cells in the course of development. Therefore, TIF1alpha could belong to a novel class of chromatin-associated TIFs that facilitate the access of transregulators (e.g. liganded nuclear receptors) to their cognate sites in target genes, thereby participitating in the epigenetic control of transcription during embryonic development and cell differentiation.

Animals↗
PubMed1996

Mouse euchromatin specific "genome-painting" with a LINE probe: a rapid method for identification and mapping of human chromosomes in mouse-human microcell hybrids by two-color FISH.

We describe the use of a long interspersed repetitive sequence (mCPE1.51) for mouse euchromatin specific "genome-painting". In fluorescence in situ hybridization (FISH) experiments, this probe was suitable for identification of the mouse genome and disclosure of translocations of mouse chromosome segments to chromosomes of different species without suppression hybridization. The euchromatin specificity of the probe allowed the discrimination between euchromatin and heterochromatin of mouse chromosomes. Simultaneous hybridization of the biotinylated mouse specific genome-painting probe and a digoxigenin-labeled human chromosome 3-specific cosmid probe to metaphase spreads of mouse-human microcell hybrid carrying a single deleted human chromosome 3 on a mouse fibrosarcoma background, allowed rapid identification and mapping of human chromosome 3.

Animals↗
PubMed1982

In vivo sister chromatid exchanges in the euchromatin and constitutive heterochromatin of the Indian mole rat, Nesokia indica.

Distribution of in vivo SCEs in euchromatin and constitutive heterochromatin of Nesokia indica has been studied. The distinct partitioning of the euchromatin and constitutive heterochromatin into different arms of the large X chromosome greatly facilitates such a comparison. The constitutive heterochromatin showed a higher SCE rate per unit length than the total euchromatin. However, between the two types of chromatin in the X itself there was no significant difference. These values were also comparable to that observed for the largest autosome. This study suggests that factor(s) other than chromatin condensation, DNA base composition, and DNA replication kinetics is (are) responsible for the formation of SCEs.

Animals↗