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1.
In humans, it is thought that the X-inactivation phenomenon occurs no matter how many X chromosomes are present, and that
only one of them remains active. Nevertheless, individuals who have an abnormal number of X chromosomes show a wide spectrum
of abnormalities, which increase with the number of X chromosomes present in a given individual. It has been shown that the
inactive X chromosome in female mammals is distinguished by a lack of histone H4 acetylation, and that this could be used
as an accessible marker for distinguishing between Xi and Xa in spreads of metaphase chromosomes. We studied three X-polysomic
patients for the presence of active chromatin by analysis of histone H4 acetylation on unfixed metaphase spreads. Using antisera
to H4 acetylated at lysines 16, 8 and 5, respectively, we observed frequencies different from those expected from cells with
only one underacetylated X chromosome. In particular, when antiserum to H4 acetylated at lysine 16 was used about 90% of the
cells showed acetylation of all X chromosomes. This suggests a possible disturbance in the deacetylation process, probably
due to the presence of multiple Xs.
Received: 25 April 1997 / Accepted: 15 March 1998 相似文献
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Peter Jeppesen 《BioEssays : news and reviews in molecular, cellular and developmental biology》1997,19(1):67-74
Immunofluorescent labelling demonstrates that human metaphase chromosomes contain hyperacetylated histone H4. With the exception of the inactive X chromosome in female cells, where the bulk of histone H4 is under-acetylated, H4 hyperacetylation is non-uniformly distributed along the chromosomes and clustered in cytologically resolvable chromatin domains that correspond, in general, with the R-bands of conventional staining. The strongest immunolabelling is often found in T-bands, the subset of intense R-bands having the highest GC content. The majority of mapped genes also occurs in R-band regions, with the highest gene density in T-bands. These observations are consistent with a model in which hyperacetylation of histone H4 marks the position of potentially active gene sequences on metaphase chromosomes. Since acetylation is maintained during mitosis, progeny cells receive an imprint of the histone H4 acetylation pattern that was present on the parental chromosomes before cell division. Histone acetylation could provide a mechanism for propagating cell memory, defined as the maintenance of committed states of gene expression through cell lineages. 相似文献
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Nusinow DA Sharp JA Morris A Salas S Plath K Panning B 《Journal of molecular biology》2007,371(1):11-18
Histone variants replace the core histones in a substantial fraction of nucleosomes, affecting chromatin structure and impacting chromatin-templated processes. In many instances incorporation of histone variants results in formation of specialized regions of chromatin. Proper localization of histone variants to distinct regions of the genome is critical for their function, yet how this specific localization is achieved remains unclear. macroH2A1 is enriched on the inactive X chromosome in female mammalian cells, where it functions to maintain gene silencing. macroH2A1 consists of a histone H2A-like histone domain and a large, globular C-terminal macro domain that is not present in other histone proteins. The histone domain of macroH2A1 is alone sufficient to direct enrichment on the inactive X chromosome when expressed in female cells, indicating that sequences important for correct localization lie in this domain. Here we investigate whether divergent sequences of the H2A variant macroH2A1 contribute to its correct localization. We mapped the regions of the macroH2A1 histone domain that are sufficient for localization to the inactive X chromosome using chimeras between H2A and the histone domain of macroH2A1. Multiple short sequences dispersed along the macroH2A1 histone domain individually supported enrichment on the inactive X chromosome when introduced into H2A. These sequences map to the surface of the macroH2A1/H2B dimer, but are buried in the crystal structure of the macroH2A1 containing nucleosome, suggesting that they may contribute to recognition by macroH2A1/H2B deposition factors. 相似文献
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Cell-cycle-dependent dissociation of histone H1 from chromatin in nuclei of P. polycephalum. 总被引:1,自引:1,他引:0
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The dissociation curves of histone H1 from chromatin in interphase and metaphase nuclei from Physarum polycephalum have been determined using CaCl2 as dissociating agent. H1 is less strongly bound to metaphase chromosomes than to interphase chromatin. However, no differences could be detected in the binding of Hl to early S, late S or G2 phase chromatin. The number of CaCl2 molecules involved in binding one H1 molecule to chromatin was reduced from 5 in interphase to 4 in metaphase. The non-electrostatic contribution to the free-energy of binding was small in both cases. A comparison of the binding properties of H1 to sheared chromatin, native chromatin and metaphase chromosomes suggests that the electrostatic binding functions of H1 are completely satisfied within the nucleosome and that further electrostatic interactions are not involved in folding the nucleosomal fibre into the 300 A "solenoid" or the more tightly folded metaphase chromosome. 相似文献
6.
Histone variant macroH2A contains
two distinct macrochromatin domains capable of directing macroH2A
to the inactive X chromosome 总被引:3,自引:0,他引:3
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Brian P. Chadwick Cory
M. Valley Huntington
F. Willard 《Nucleic acids research》2001,29(13):2699-2705
Chromatin on the inactive X chromosome (Xi) of female mammals is enriched for the histone variant macroH2A that can be detected at interphase as a distinct nuclear structure referred to as a macro chromatin body (MCB). Green fluorescent protein-tagged and Myc epitope-tagged macroH2A readily form an MCB in the nuclei of transfected female, but not male, cells. Using targeted disruptions, we have identified two macrochromatin domains within macroH2A that are independently capable of MCB formation and association with the Xi. Complete removal of the non-histone C-terminal tail does not reduce the efficiency of association of the variant histone domain of macroH2A with the Xi, indicating that the histone portion alone can target the Xi. The non-histone domain by itself is incapable of MCB formation. However, when directed to the nucleosome by fusion to core histone H2A or H2B, the non-histone tail forms an MCB that appears identical to that of the endogenous protein. Mutagenesis of the non-histone portion of macroH2A localized the region required for MCB formation and targeting to the Xi to an ~190 amino acid region. 相似文献
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Reduced levels of histone H3 acetylation on the inactive X chromosome in human females 总被引:3,自引:0,他引:3
Barbara A. Boggs Bernadette Connors Richard E. Sobel A. Craig Chinault C. David Allis 《Chromosoma》1996,105(5):303-309
Novel antibodies were generated that are highly selective for either acetylated or unacetylated iso-forms of histone H3, or
the acetylated form of histone H4 in organisms as diverse asTetrahymena and humans. Using these antibodies as pair-wise sets in immunocytological analyses, we demonstrate that the inactive X chromosome
is hypoacetylated for both histone H3 and H4 in female mammalian cells, whereas the antibody that recognizes the unacetylated
form of histone H3 identifies all chromosomes uniformly. These data verify and extend previous results and suggest that hypoacetylation
of core histones may be a general feature of the chromatin along the inactive X chromosome.
Edited by: D. Bazett-Jones 相似文献
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It has previously been shown that the acetylated forms of histone H4 are depleted or absent in both constitutive, centric heterochromatin and in the facultative heterochromatin of the inactive X chromosome (Xi) in female cells. By immunostaining of metaphase chromosomes from human lymphocytes with antibodies to the acetylated isoforms of histones H2A and H3, we now show that these histones too are underacetylated in both Xi and centric heterochromatin. Xi shows two prominent regions of residual H3 acetylation, one encompassing the pseudoautosomal region at the end of the short arm and one at about Xg22. Both these regions have been shown previously to be sites of residual H4 acetylation. H2A acetylation on Xi is higher overall than that of H3 or H4 and is particularly high around the pseudoautosomal region, but not at Xg22. The results suggest that the acetylated isoforms of H3 and H4 have at least some effects on chromosomal structure and function that are not shared by acetylated H2A. 相似文献
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Skalníková M Bártová E Ulman V Matula P Svoboda D Harnicarová A Kozubek M Kozubek S 《Physiological research / Academia Scientiarum Bohemoslovaca》2007,56(6):797-806
To study 3D nuclear distributions of epigenetic histone modifications such as H3(K9) acetylation, H3(K4) dimethylation, H3(K9) dimethylation, and H3(K27) trimethylation, and of histone methyltransferase Suv39H1, we used advanced image analysis methods, combined with Nipkow disk confocal microscopy. Total fluorescence intensity and distributions of fluorescently labelled proteins were analyzed in formaldehyde-fixed interphase nuclei. Our data showed reduced fluorescent signals of H3(K9) acetylation and H3(K4) dimethylation (di-me) at the nuclear periphery, while di-meH3(K9) was also abundant in chromatin regions closely associated with the nuclear envelope. Little overlapping (intermingling) was observed for di-meH3(K4) and H3(K27) trimethylation (tri-me), and for di-meH3(K9) and Suv39H1. The histone modifications studied were absent in the nucleolar compartment with the exception of H3(K9) dimethylation that was closely associated with perinucleolar regions which are formed by centromeres of acrocentric chromosomes. Using immunocytochemistry, no di-meH3(K4) but only dense di-meH3(K9) was found for the human acrocentric chromosomes 14 and 22. The active X chromosome was observed to be partially acetylated, while the inactive X was more condensed, located in a very peripheral part of the interphase nuclei, and lacked H3(K9) acetylation. Our results confirmed specific interphase patterns of histone modifications within the interphase nuclei as well as within their chromosome territories. 相似文献
12.
Chromatin-associated protein phosphatase 1 regulates aurora-B and histone H3 phosphorylation 总被引:1,自引:0,他引:1
Murnion ME Adams RR Callister DM Allis CD Earnshaw WC Swedlow JR 《The Journal of biological chemistry》2001,276(28):26656-26665
Proper chromosome condensation requires the phosphorylation of histone and nonhistone chromatin proteins. We have used an in vitro chromosome assembly system based on Xenopus egg cytoplasmic extracts to study mitotic histone H3 phosphorylation. We identified a histone H3 Ser(10) kinase activity associated with isolated mitotic chromosomes. The histone H3 kinase was not affected by inhibitors of cyclin-dependent kinases, DNA-dependent protein kinase, p90(rsk), or cAMP-dependent protein kinase. The activity could be selectively eluted from mitotic chromosomes and immunoprecipitated by specific anti-X aurora-B/AIRK2 antibodies. This activity was regulated by phosphorylation. Treatment of X aurora-B immunoprecipitates with recombinant protein phosphatase 1 (PP1) inhibited kinase activity. The presence of PP1 on chromatin suggested that PP1 might directly regulate the X aurora-B associated kinase activity. Indeed, incubation of isolated interphase chromatin with the PP1-specific inhibitor I2 and ATP generated an H3 kinase activity that was also specifically immunoprecipitated by anti-X aurora-B antibodies. Nonetheless, we found that stimulation of histone H3 phosphorylation in interphase cytosol does not drive chromosome condensation or targeting of 13 S condensin to chromatin. In summary, the chromosome-associated mitotic histone H3 Ser(10) kinase is associated with X aurora-B and is inhibited directly in interphase chromatin by PP1. 相似文献
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Eukaryotic chromosomes are organized into two large and distinct domains, euchromatin and heterochromatin, which are cytologically
characterized by different degrees of chromatin compaction during interphase/prophase and by post-synthesis modifications
of histones and DNA methylation. Typically, heterochromatin remains condensed during the entire cell cycle whereas euchromatin
is decondensed at interphase. However, a fraction of the euchromatin can also remain condensed during interphase and appears
as early condensing prophase chromatin. 5S and 45S rDNA sites and telomere DNA were used to characterize these regions in
metaphase and interphase nuclei. We investigated the chromosomal distribution of modified histones and methylated DNA in the
early and late condensing prophase chromatin of two species with clear differentiation between these domains. Both species,
Costus spiralis and Eleutherine bulbosa, additionally have a small amount of classical heterochromatin detected by CMA/DAPI staining. The distribution of H4 acetylated
at lysine 5 (H4K5ac), H3 phosphorylated at serine 10 (H3S10ph), H3 dimethylated at lysine 4 or 9 (H3K4me2, H3K9me2), and 5-methylcytosine
was compared in metaphase, prophase, and interphase cells by immunostaining with specific antibodies. In both species, the
late condensing prophase chromatin was highly enriched in H4K5ac and H3K4me2 whereas the early condensing chromatin was very
poor in these marks. H3K9me2 was apparently uniformly distributed along the chromosomes whereas the early condensing chromatin
was slightly enriched in 5-methylcytosine. Signals of H3S10ph were restricted to the pericentromeric region of all chromosomes.
Notably, none of these marks distinguished classical heterochromatin from the early condensing euchromatin. It is suggested
that the early condensing chromatin is an intermediate type between classical heterochromatin and euchromatin. 相似文献
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Chromatin folding in the interphase nucleus is not known. We compared the pattern of chromatin condensation in Indian muntjac, Chinese hamster ovary, murine pre B, and K562 human erythroleukemia cells during the cell cycle. Fluorescent microscopy showed that chromosome condensation follows a general pathway. Synchronized cells were reversibly permeabilized and used to isolate interphase chromatin structures. Based on their structures two major categories of intermediates were distinguished: (1) decondensed chromatin and (2) condensed chromosomal forms. (1) Chromatin forms were found between the G1 and mid-S phase involving veil-like, supercoiled, fibrous, ribboned structures; (2) condensing chromosomal forms appeared in the late-S, G2, and M phase, including strings, chromatin bodies, elongated pre-chromosomes, pre-condensed chromosomes, and metaphase chromosomes. Results demonstrate that interphase chromosomes are clustered in domains; condensing interphase chromosomes are linearly arranged. Our results raise questions related to telomer sequences and to the chemical nature of chromosome connectivity. 相似文献
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Low angle x-ray diffraction studies of HeLa metaphase chromosomes: effects of histone phosphorylation and chromosome isolation procedure 总被引:4,自引:2,他引:2
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To test whether gross changes in chromatin structure occur during the cell cycle, we compared HeLa mitotic metaphase chromosomes and interphase nuclei by low angle x-ray diffraction. Interphase nuclei and metaphase chromosomes differ only in the 30-40-nm packing reflection, but not in the higher angle part of the x-ray diffraction pattern. Our interpretation of these results is that the transition to metaphase affects only the packing of chromatin fibers and not, to the resolution of our method, the internal structure of nucleosomes or the pattern of nucleosome packing within chromatin fibers. In particular, phosphorylation of histones H1 and H3 at mitosis does not affect chromatin fiber structure, since the same x-ray results are obtained whether or not histone dephosphorylation is prevented by isolating metaphase chromosomes in the presence of 5,5'-dithiobis(2- nitrobenzoate) or low concentrations of p-chloromercuriphenylsulfonate (ClHgPhSO3). We also compared metaphase chromosomes isolated by several different published procedures, and found that the isolation procedure can significantly affect the x-ray diffraction pattern. High concentrations of ClHgPhSO3 can also profoundly affect the pattern. 相似文献