Showing papers on "Heterochromatin published in 1995"
TL;DR: It is shown that the SIR3 and SIR4 proteins interact with specific silencing domains of the H3 and H4 N-termini in vitro, which proposes a model for heterochromatin-mediated transcriptional silencing in yeast, which may serve as a paradigm for other eukaryotic organisms as well.
809 citations
TL;DR: The models and experimental data that address the mechanisms of PEV in different cell types, the potential functions of modifiers ofPEV, and the relationship of PEv to other phenomena associated with variegated gene expression in Drosophila are evaluated.
Abstract: Heterochromatin is both necessary for the expression of heterochromatic genes and inhibitory for the expression of euchromatic genes These two properties of heterochromatin have been elucidated from the study of chromosome rearrange ments that induce position effect variegation (PEV) in Drosophila melanogaster Novel euchromatin-heteroc hromatin can affect the expression of euchromatic and heterochromatic genes located several megabases away, distin guishing higher order chromatin structure from most other regulatory mecha nis ms Studies of PEV promis e insights into the basis for heterochromatin formation and the role of higher order chromatin and chromosome structure in gene regulation We eva luate the models and experimental data that address the mechanisms of PEV in different cell types, the potential functions of modifiers of PEV, and the relationship of PEV to other phenomena associated with vari egated gene expression in Drosophila
568 citations
TL;DR: Ch Chromatin structure analysis revealed that the variegating inserts showed a reduction in accessibility to restriction enzyme digestion in the hsp26 regulatory region in isolated nuclei, suggesting that altered chromatin packaging plays a role in PEV.
Abstract: A euchromatic gene placed in the vicinity of heterochromatin by a chromosomal rearrangement generally exhibits position effect variegation (PEV), a clonally inherited pattern showing gene expression in some somatic cells but not in others The mechanism responsible for this loss of gene expression is investigated here using fly lines carrying a P element containing the Drosophila melanogaster white and hsp26 genes Following mobilization of the P element, a screen for variegation of white expression recovered inserts at pericentric, telomeric, and fourth chromosome regions Previously identified suppressors of PEV suppressed white variegation of pericentric and fourth chromosome inserts but not telomeric inserts on the second and third chromosomes This implies a difference in the mechanism for gene repression at telomeres Heat shock-induced hsp26 expression was reduced from pericentric and fourth chromosome inserts but not from telomeric inserts Chromatin structure analysis revealed that the variegating inserts showed a reduction in accessibility to restriction enzyme digestion in the hsp26 regulatory region in isolated nuclei Micrococcal nuclease digests showed that pericentric inserts were packaged in a more regular nucleosome array than that observed for euchromatic inserts These data suggest that altered chromatin packaging plays a role in PEV
496 citations
TL;DR: It is proposed that the products of these genes are integral in the assembly of a heterochromatin-like structure, with distinct domains, enclosing the entire centromeric region that reduces or excludes access to transcription factors.
Abstract: The ura4+ gene displays phenotypes consistent with variegated expression when inserted at 11 sites throughout fission yeast centromere 1. An abrupt transition occurs between the zone of centromeric repression and two adjacent expressed sites. Mutations in six genes alleviate repression of the silent-mating type loci and of ura4+ expressed from a site adjacent to the silent locus, mat3-M. Defects at all six loci affect repression of the ura4+ gene adjacent to telomeres and at the three centromeric sites tested. The clr4-S5 and rik1-304 mutations cause the most dramatic derepression at two out of three sites within cen1. All six mutations had only slight or intermediate effects on a third site in the center of cen1 or on telomeric repression. Strains with lesions at the clr4, rik1, and swi6 loci have highly elevated rates of chromosome loss. We propose that the products of these genes are integral in the assembly of a heterochromatin-like structure, with distinct domains, enclosing the entire centromeric region that reduces or excludes access to transcription factors. The formation of this heterochromatic structure may be an absolute requirement for the formation of a fully functional centromere.
469 citations
TL;DR: Point centromeres, found in the budding yeasts, are compact loci whose constituent proteins are now beginning to yield to biochemical analysis and have an important role in checkpoint regulation during mitosis.
Abstract: Centromeres are the structures that direct eukaryotic chromosome segregation in mitosis and meiosis. There are two major classes of centromeres. Point centromeres, found in the budding yeasts, are compact loci whose constituent proteins are now beginning to yield to biochemical analysis. Regional centromeres, best described in the fission yeast Schizosaccharomyces pombe, encompass many kilobases of DNA and are packaged into heterochromatin. Their associated proteins are as yet poorly understood. In addition to providing the site for microtubule attachment, centromeres also have an important role in checkpoint regulation during mitosis.
355 citations
TL;DR: The distribution of 11 different transposable elements on Drosophila melanogaster mitotic chromosomes is determined by using high-resolution fluorescent in situ hybridization (FISH) coupled with charge-coupled device camera analysis to change the current views on the role of transposables elements in host genome evolution.
Abstract: We determined the distribution of 11 different transposable elements on Drosophila melanogaster mitotic chromosomes by using high-resolution fluorescent in situ hybridization (FISH) coupled with charge-coupled device camera analysis. Nine of these transposable elements (copia, gypsy, mdg-1, blood, Doc, I, F, G, and Bari-1) are preferentially clustered into one or more discrete heterochromatic regions in chromosomes of the Oregon-R laboratory stock. Moreover, FISH analysis of geographically distant strains revealed that the locations of these heterochromatic transposable element clusters are highly conserved. The P and hobo elements, which are likely to have invaded the D. melanogaster genome at the beginning of this century, are absent from Oregon-R heterochromatin but clearly exhibit heterochromatic clusters in certain natural populations. Together these data indicate that transposable elements are major structural components of Drosophila heterochromatin, and they change the current views on the role of transposable elements in host genome evolution.
307 citations
TL;DR: It is shown that Swi6p localizes with these three chromosomal regions in the fission yeast Schizosaccharomyces pombe and is required for their proper function.
Abstract: Centromeres attach chromosomes to the spindle during mitosis, thereby ensuring the equal distribution of chromosomes into daughter cells. Transcriptionally silent heterochromatin of unknown function is associated with centromeres in many organisms. In the fission yeast Schizosaccharomyces pombe, the silent mating-type loci, centromeres, and telomeres are assembled into silent heterochromatin-like domains. The Swi6 chromodomain protein affects this silencing, and now it is shown that Swi6p localizes with these three chromosomal regions. In cells lacking Swi6p, centromeres lag on the spindle during anaphase and chromosomes are lost at high rates. Thus, Swi6p is located at fission yeast centromeres and is required for their proper function.
306 citations
TL;DR: It is reported here that point mutations in the HP1 chromo domain abolish the ability of HP1 to promote gene silencing, supporting the view that the chromodomain homology reflects a common mechanistic basis for homeotic and heterochromatic silencing.
Abstract: Heterochromatin protein 1 (HP1) is a non-histone chromosomal protein in Drosophila with dosage-dependent effects on heterochromatin-mediated gene silencing. An evolutionarily conserved amino acid sequence in the N-terminal half of HP1 (the 'chromo domain') shares > 60% sequence identity with a motif found in the Polycomb protein, a silencer of homeotic genes. We report here that point mutations in the HP1 chromo domain abolish the ability of HP1 to promote gene silencing. We show that the HP1 chromo domain, like the Polycomb chromo domain, has chromosome binding activity, but to distinct chromosomal sites. We constructed a chimeric HP1-Polycomb protein, consisting of the chromo domain of Polycomb in the context of HP1, and show that it binds to both heterochromatin and Polycomb binding sites in polytene chromosomes. In flies expressing chimeric HP1-Polycomb protein, endogenous HP1 is mislocalized to Polycomb binding sites, and endogenous polycomb is misdirected to the heterochromatic chromocenter, suggesting that both proteins are recruited to their distinct chromosomal binding sites through protein-protein contacts. Chimeric HP1-Polycomb protein expression in transgenic flies promotes heterochromatin-mediated gene silencing, supporting the view that the chromo domain homology reflects a common mechanistic basis for homeotic and heterochromatic silencing.
281 citations
TL;DR: It is concluded that nucleosomes containing acetylated H4 are scattered infrequently and possibly randomly through coding and adjacent regions and are essentially absent from heterochromatin.
Abstract: By immunoprecipitation of chromatin fragments from cultured human HL-60 cells with antibodies specific for H4 acetylated at specific lysine residues we have defined the level of H4 acetylation within transcriptionally active and inactive regions of the genome. H4 within or adjacent to coding regions had a similar level of overall acetylation to input (bulk) chromatin and a similar pattern of acetylation of individual lysines (i.e. 16 > 8, 12 > 5). The acetylation of H4 in coding (and adjacent) regions was not correlated with transcriptional activity and did not vary with position along the constitutively active c-myc gene. Turnover of H4 acetates was not selectively increased in transcriptionally active chromatin. H4 associated with centric heterochromatin or with the CCCTAA repeat of telomeric heterochromatin was infrequently acetylated (< 1%) at all lysines. We conclude that nucleosomes containing acetylated H4 are scattered infrequently and possibly randomly through coding and adjacent regions and are essentially absent from heterochromatin. Induction of differentiation of HL-60 cells by exposure to dimethylsulfoxide or 12-o-tetradecanoylphorbol 13-acetate (TPA) did not alter the level of H4 acetylation within either the c-myc or c-fos genes or other coding regions, but did induce a transient increase in H4 acetylation within centric heterochromatin.
252 citations
TL;DR: It is suggested that repetitive DNA sequences in the terminal heterochromatin of rye chromosomes define a basic higher order structure and DNA loop domains of regions of Rye chromosomes consisting of arrays of tandemly organized sequences.
Abstract: Repetitive DNA sequences in the terminal heterochromatin of rye (Secale cereale) chromosomes have consequences for the structural and functional organization of chromosomes. The large-scale genomic organization of these regions was studied using the telomeric repeat from Arabidopsis and clones of three nonhomologous, tandemly repeated, subtelomeric DNA families with complex but contrasting higher order structural organizations. Polymerase chain reaction analysis with a single primer showed a fraction of the repeat units of one family organized in a "head-to-head" orientation. Such structures suggest evolution of chromosomes by chromatid-type breakage-fusion-bridge cycles. In situ hybridization and pulse field gel electrophoresis showed the order of the repeats and the heterogeneity in the lengths of individual arrays. After Xbal digestion and pulse field gel electrophoresis, the telomeric and two subtelomeric clones showed strong hybridization signals from 40 to 100 kb, with a maximum at 50 to 60 kb. We suggest that these fragments define a basic higher order structure and DNA loop domains of regions of rye chromosomes consisting of arrays of tandemly organized sequences.
202 citations
TL;DR: The elongated prophase suggests that the segregation phenotype is a consequence of defects in events that occur during prophase, either in chromosome condensation or kinetochore assembly or function.
Abstract: Heterochromatin protein 1 is associated with centromeric heterochromatin in Drosophila, mice, and humans. Loss of function mutations in the gene encoding heterochromatin protein 1 in Drosophila, Suppressor of variegation2-5, decrease the mosaic repression observed for euchromatic genes that have been juxtaposed to centromeric heterochromatin. These heterochromatin protein 1 mutations not only suppress this position-effect variegation, but also cause recessive embryonic lethality. In this study, we analyze the latter phenotype in the hope of gaining insight into heterochromatin function. In our analyses of four alleles of Suppressor of variegation2-5, the lethality was found to be associated with defects in chromosome morphology and segregation. While some of these defects are seen throughout embryonic development, both the frequency and severity of the defects are greatest between cycles 10 and 14 when zygotic transcription of the Suppressor of variegation2-5 gene apparently begins. By this time in development, heterochromatin protein 1 levels are diminished by four-fold in a quarter of the embryos produced by parents that are both heterozygous for a null allele (Suppressor of variegation2-5(05)). In a live analysis of the phenotype, we find prophase to be lengthened by more than two-fold in Suppressor of variegation2-5(05) mutant embryos with subsequent defects in chromosome segregation. The elongated prophase suggests that the segregation phenotype is a consequence of defects in events that occur during prophase, either in chromosome condensation or kinetochore assembly or function. Immunostaining with an antibody against a centromerespecific antigen indicates that the kinetochores of most chromosomes are functional. The immunostaining results are more consistent with defects in chromosome condensation being responsible for the segregation phenotype.
TL;DR: It is proposed that constitutive heterochromatin serves as the nucleation point for a cell-type-specific organization of mouse sperm chromatin, and indicates that mammalian sperm nuclei have a highly defined nuclear architecture.
TL;DR: This paper investigates the localization of heterochromatin protein 1 in the diploid nuclei of Drosophila embryos, and finds an enrichment of HP1 in the intensely DAPI-staining regions near the apical surface of nuclear cycle 10 embryos.
Abstract: Heterochromatin protein 1 (HP1) was initially discovered as a protein that is associated with the heterochromatin at the chromocenter of polytene chromosomes in Drosophila larval salivary glands. In this paper we investigate the localization of heterochromatin protein 1 in the diploid nuclei of Drosophila embryos. We focus on its association with the interphase heterochromatin in fixed embryos before and during cycle 14, the developmental time at which heterochromatin becomes most conspicuous, and also follow its localization during mitosis. The GAGA transcription factor was recently shown to be localized at sequences within alpha-heterochromatin in pre-cycle 14 embryos, and an antibody against this protein serves as a convenient marker for these sequences. We find an enrichment of heterochromatin protein 1 in the intensely DAPI-staining regions near the apical surface of nuclear cycle 10 embryos. At this stage GAGA factor is localized into punctate structures in this same region. This enrichment for HP1 is markedly increased during nuclear cycle 14. Surprisingly, whereas GAGA factor retains its association with the heterochromatin throughout the cell cycle, a significant fraction of HP1 is dispersed throughout the spindle around the segregating chromosomes during mitosis. This dispersed pool of heterochromatin protein 1 was observed during mitosis in both early and late Drosophila embryos and in an analysis of a bacterially produced 6x histidine-heterochromatin protein 1 fusion protein injected into living Drosophila embryos. When Drosophila tissue culture cells were prepared by a method which removes soluble protein and avoids fixation of the mitotic chromosomes, an enrichment for heterochromatin protein 1 in the heterochromatin of the chromosomes was discovered also.
TL;DR: Pulsed-field Southern analysis demonstrated that Drosophila heterochromatin in general is composed of alternating blocks of complex DNA and simple satellite DNA and the presence of a retroposon is demonstrated.
Abstract: Heterochromatin is a ubiquitous yet poorly understood component of multicellular eukaryotic genomes. Major gaps exist in our knowledge of the nature and overall organization of DNA sequences present in heterochromatin. We have investigated the molecular structure of the 1 Mb of centric heterochromatin in the Drosophila minichromosome Dp1187. A genetic screen of irradiated minichromosomes yielded rearranged derivatives of Dp1187 whose structures were determined by pulsed-field Southern analysis and PCR. Three Dp1187 deletion derivatives and an inversion had one breakpoint in the euchromatin and one in the heterochromatin, providing direct molecular access to previously inaccessible parts of the heterochromatin. End-probed pulsed-field restriction mapping revealed the presence of at least three "islands" of complex DNA, Tahiti, Moorea, and Bora Bora, constituting approximately one half of the Dp1187 heterochromatin. Pulsed-field Southern analysis demonstrated that Drosophila heterochromatin in general is composed of alternating blocks of complex DNA and simple satellite DNA. Cloning and sequencing of a small part of one island, Tahiti, demonstrated the presence of a retroposon. The implications of these findings to heterochromatin structure and function are discussed.
TL;DR: Differential postmeiotic expression of the Y chromosomal genes Ubely and Sry is shown, with highest mRNA levels in round spermatids and cytoplasmic fragments, respectively, which may have implications for the understanding of X chromosome inactivation during sperMatogenesis and paternal genome imprinting.
TL;DR: In situ hybridisation to mitotic chromosomes shows that sequences homologous to different Drosophila melanogaster transposable elements are widely distributed not only in beta but also in alpha-heterochromatin.
Abstract: In situ hybridisation to mitotic chromosomes shows that sequences homologous to different Drosophila melanogaster transposable elements are widely distributed not only in beta but also in alpha-heterochromatin. Clusters of these sequences are detected in most proximal positions. They colocalise with known satellite sequences in several regions, but are also located in places where no known sequence has been mapped so far. The pattern of hybridisation is dinstinctive and specific for each element, and presents constant features in six different D. melanogaster strains studied. The entirely heterochromatic Y chromosome contains large amounts of these sequences. Additionally, some of these sequences appear to be present in substantial quantities in the smallest minichromosome of Drosophila, Dp(1;f)1187.
TL;DR: These recent studies have demonstrated the interspersion and rapid spread of transposable elements into Drosophila heterochromatin, and documented the requirement ofheterochromatic genes for heterochROMatin.
TL;DR: It can be inferred that the differences in distribution and amount of heterochromatin do not play a direct role in speciation in this group, and it is suggested that T. infestans and T. platensis are more closely related to each other than to T. delpontei.
Abstract: C-banded karyotypes, DNA content and the male meiiotic process ofTriatoma platensis andTriatoma delpontei are compared with those ofTriatoma infestans, the main vector of Chagas disease in South America. These three species present the same diploid chromosome number 2n=22 (20 autosomes+XX♂/XY♀). They also have several cytogenetic traits that differ from all other triatomines: large autosomes, C-heterochromatic blocks and meiotic heteropycnotic chromocenters formed by autosomes and sex chromosomes. In spite of these similarities, each species presents different chromosomal behavior during male meiosis, distinct DNA content and a specific amount and localization of the C-heterochromatin. The differences in DNA content are mainly due to the variation in C-heterochromatin amount, which may be interpreted as loss and/or gain of C-regions. This interpretation is supported by the presence of meiotic and mitotic chromocenters that facilitate the transference of C-positive material. The cytogenetic data presented in this work suggest thatT. infestans andT. platensis are more closely related to each other than toT. delpontei. It can also be inferred that the differences in distribution and amount of heterochromatin do not play a direct role in speciation in this group.
TL;DR: A novel method for mapping regions required for heterochromatic genes, and those that induce PEV of a euchromatic gene are described.
Abstract: Chromosomal rearrangements that juxtapose heterochromatin and euchromatin can result in mosaic inactivation of heterochromatic and euchromatic genes. This phenomenon, position effect variegation (PEV), suggests that heterochromatic and euchromatic genes differ in their regulatory requirements. This report describes a novel method for mapping regions required for heterochromatic genes, and those that induce PEV of a euchromatic gene. P transposase mutagenesis was used to generate derivatives of a translocation that variegated for the light+ (lt+) gene and carried the euchromatic white+ (w+) gene on a transposon near the heterochromatin-euchromatin junction. Cytogenetic and genetic analyses of the derivatives showed that P mutagenesis resulted in deletions of several megabases of heterochromatin. Genetic and molecular studies showed that the derivatives shared a euchromatic breakpoint but differed in their heterochromatic breakpoint and their effects on seven heterochromatic genes and the w+ gene. Heterochromatic genes differed in their response to deletions. The lt+ gene was sensitive to the amount of heterochromatin at the breakpoint but the heterochromatic 40Fa gene was not. The severity of variegated w+ phenotype did not depend on the amount of heterochromatin in cis, but varied with local heterochromatic environment. These data are relevant for considering mechanisms of PEV of both heterochromatic and euchromatic genes.
TL;DR: It is proposed that bwD fails to coalesce with the chromocenter when its position along the chromosome places it beyond a threshold distance from heterochromatin, and this threshold depends upon the configuration of both the chromosome carrying bWD and its paired homologue.
Abstract: We examined the behavior of the brownDominant (bwD) heterochromatic insertion moved to different locations relative to centric heterochromatin. Effects were measured as the degree of silencing of a wild-type brown eye pigment gene by bwD across a tandem duplication. A series of X-ray-induced effects were recovered at high frequency. Cis-acting enhancers were obtained by relocation of the duplication closer to autosomal heterochromatin. Enhancers were also recovered on the homologous chromosome when it was similarly rearranged, revealing a novel interhomologue effect whereby interactions occur between genetic elements near opposite ends of a chromosome arm rather than between paired alleles. Cis-acting suppressors were obtained as secondary rearrangements in which the duplication was moved farther away from heterochromatin. Suppression was correlated with loss of cytological association between bwD and the polytene chromocenter. Surprisingly, the distance from bwD to the chromocenter was not correlated with the strength of enhancement or suppression. We propose that bwD fails to coalesce with the chromocenter when its position along the chromosome places it beyond a threshold distance from heterochromatin, and this threshold depends upon the configuration of both the chromosome carrying bwD and its paired homologue.
TL;DR: It is suggested that regions containing heterochromatic genes are organized into dispersed chromatin configurations that are important for their function in vivo.
Abstract: Peri-centromeric regions of Drosophila melanogaster chromosomes appear heterochromatic in mitotic cells and become greatly underrepresented in giant polytene chromosomes, where they aggregate into a central mass called the chromocenter. We used P elements inserted at sites dispersed throughout much of the mitotic heterochromatin to analyze the fate of 31 individual sites during polytenization. Analysis of DNA sequences flanking many of these elements revealed that middle repetitive or unique sequence DNAs frequently are interspersed with satellite DNAs in mitotic heterochromatin. All nine Y chromosome sites tested were underrepresented > 20-fold on Southern blots of polytene DNA and were rarely or never detected by in situ hybridization to salivary gland chromosomes. In contrast, nine tested insertions in autosomal centromeric heterochromatin were represented fully in salivary gland DNA, despite the fact that at least six were located proximal to known blocks of satellite DNA. The inserted sequences formed diverse, site-specific morphologies in the chromocenter of salivary gland chromosomes, suggesting that domains dispersed at multiple sites in the centromeric heterochromatin of mitotic chromosomes contribute to polytene beta-heterochromatin. We suggest that regions containing heterochromatic genes are organized into dispersed chromatin configurations that are important for their function in vivo.
TL;DR: In this paper, the molecular characterization of heterochromatin in six lines of rye has been performed using fluorescence in situ hybridization (FISH), and the highly repetitive rye DNA sequences pSc 119.2, pSc74, and pSc34 were used.
Abstract: The molecular characterization of heterochromatin in six lines of rye has been performed using fluorescence in situ hybridization (FISH). The highly repetitive rye DNA sequences pSc 119.2, pSc74, and pSc34, and the probes pTa71 and pSc794 containing the 25S–5.8S–18S rDNA (NOR) and the 5S rDNA multigene families, respectively, were used. This allowed the individual identification of all seven rye chromosomes and most chromosome arms in all lines. All varieties showed similar but not identical patterns. A standard in situ hybridization map was constructed following the nomenclature system recommended for C-bands. All FISH sites observed appeared to correspond well with C-band locations, but not all C-banding sites coincided with hybridization sites of the repetitive DNA probes used. Quantitative and qualitative differences between different varieties were found for in situ hybridization response at corresponding sites. Variation between plants and even between homologous chromosomes of the same plant was fo...
TL;DR: A further patient with the ICF syndrome (immunodeficiency, centromeric heterochromatin instability of chromosomes 1, 9 and 16 and facial anomalies) is described, the second to be reported with consanguinity of the parents, lending support to the theory of autosomal recessive inheritance.
Abstract: A further patient with the ICF syndrome (immunodeficiency, centromeric heterochromatin instability of chromosomes 1, 9 and 16 and facial anomalies) is described. This case is the second to be reported with consanguinity of the parents. This lends support to the theory of autosomal recessive inheritance. The features of the 15 published cases are reviewed. The clinical and cytogenetic characteristics of the syndrome are discussed, and new evidence provided as to the role of centromeres and centric heterochromatin in the production of chromosome aberrations. Correspondence with other authors has made possible a review of the clinical outcome in this condition.
TL;DR: Both euchromatin and heterochromatin contain nucleosomal particles, however histones have been shown to regulate genes in these regions in quite different ways, and the mechanisms by which such regulation occurs are the topic of this paper.
Abstract: Yeast chromosomes may lack the linker histone H1 (normally required to compact 10 nm beads-on-a-string fiber into the 30 nm fiber) and there is no cytological evidence for higher order fiber structure but they do contain regions which correspond to euchromatin and heterochromatin of higher eukaryotes. Both euchromatin and heterochromatin contain nucleosomal particles (composed of two molecules each of H2A, H2B, H3 and H4), however histones have been shown to regulate genes in these regions in quite different ways. The mechanisms by which such regulation occurs are the topic of this paper.
TL;DR: The existence of different types of heterochromatin in the species analysed here, lead us to propose that what hedgehogs have inherited from their common ancestor is a mechanism which permits the accumulation of heterchromatin on specific chromosomes, rather than the heterochROMatin itself.
Abstract: Hedgehogs belong to one of the several mammalian taxa in which karyotype differences are based on variations in heterochromatin content. Furthermore, the number and location of nucleolar organizer regions (NORs) can also vary widely. In the present study these cytogenetic features were investigated in the Algerian hedgehog, Erinaceus (Aethechinus) algirus. The heterochromatin and NOR distribution patterns in the karyotype of this species are new among hedgehogs, whereas the euchromatic regions, including their G-band pattern, are similar to those reported by others. In addition, silver staining revealed a cytogenetic feature exclusive to the heterochromatic blocks of E. algirus: their silver staining with standard cytogenetic procedures. Because no similar phenomenon has been described previously in a mammalian species, several hypotheses about the significance and specificity of silver staining to NOR sites are discussed. Finally, the existence of different types of heterochromatin in the species analysed here, lead us to propose that what hedgehogs have inherited from their common ancestor is a mechanism which permits the accumulation of heterochromatin on specific chromosomes, rather than the heterochromatin itself.
TL;DR: The discovery of an S-element-insertion mutation and a reversion of this mutation indicates that S elements are at least occasionally mobile in the D. melanogaster genome.
Abstract: The S elements form a diverse family of long-inverted-repeat transposons within the genome of Drosophila melanogaster. These elements vary in size and sequence, the longest consisting of 1736 bp with 234-bp inverted terminal repeats. The longest open reading frame in an intact S element could encode a 345-amino acid polypeptide. This polypeptide is homologous to the transposases of the mariner-Tc1 superfamily of transposable elements. S elements are ubiquitous in D. melanogaster populations and also appear to be present in the genomes of two sibling species; however, they seem to be absent from 17 other Drosophila species that were examined. Within D. melanogaster strains, there are, on average, 37.4 cytologically detectable S elements per diploid genome. These elements are scattered throughout the chromosomes, but several sites in both the euchromatin and beta heterochromatin are consistently occupied. The discovery of an S-element-insertion mutation and a reversion of this mutation indicates that S elements are at least occasionally mobile in the D. melanogaster genome. These elements seem to insert at an AT dinucleotide within a short palindrome and apparently duplicate that dinucleotide upon insertion.
TL;DR: The interstitial and telomeric heterochromatin of lake trout, including that of the X chromosome, appears to comprise sequences belonging to the MboI/BglII family.
Abstract: The chromosomes of lake trout (Salvelinus namaycush) contain a considerable amount of heterochromatin located at the centromeres and/or telomeres of several chromosomes, including a sex-specific block located distally on the X chromosome. In order to investigate further the repetitive DNAs of lake trout, genomic DNA from a female was size fractionated (<600 bp) with the restriction endonuclease AluI and fragments were cloned into the bacteriophage M13. A total of 42 clones were isolated. Relative copy number of individual inserts within the lake trout genome was estimated by Southern analysis. Twelve clones were determined to be highly repetitive and were chosen for further investigation. Inserts of these clones contained sequences similar to the AluI/RsaI, EcoRI/DraI, DraI/BstEII, and MboI/BglII families reported from Arctic char (Salvelinus alpinus). The chromosomal location of several of these fragments was determined in lake trout by fluorescence in situ hybridization (FISH). Two related AluI/RsaI sequences (Type A, ∼ 140 bp, and Type B, ∼ 120 bp) showed differential hybridization. Type A hybridized to the centromeres of all metacentric as well as several acrocentric chromosomes. Type B hybridized to the centromeres of most acrocentric chromosomes. A sequence with homology to the EcoRI/DraI family hybridized to the centromeres of several acrocentric chromosomes. Sequences with partial similarity to the DraI/BstEII family hybridized to the major rDNA sites (nucleolar organizer regions, NORs) and several minor telomeric sites. The interstitial and telomeric heterochromatin of lake trout, including that of the X chromosome, appears to comprise sequences belonging to the MboI/BglII family.
TL;DR: The results suggest that apoptosis (programmed cell death) in ameloblasts, including DNA ligation is induced at the transitional stage, and the state of the DNA, including its ligation and degeneration, changes gradually during chromatin condensation and nuclear fragmentation of apoptosis.
Abstract: Ameloblasts responsible for tooth enamel formation are classified into two different phases: secretion and maturation. At the transition between these secretion and maturation stages, a considerable number of cells die. In this study, we examined the morphology of degenerating ameloblasts by conventional electron microscopy, and DNA cleavage in degenerating ameloblast nuclei by the in situ terminal transferase assay. The results suggest that apoptosis (programmed cell death) in ameloblasts, including DNA ligation is induced at the transitional stage. The nuclear fragments, chromatin condensation and DNA relocation in apoptotic nuclei were examined quantitatively by post-embedding anti-DNA immunogold electron microscopy and the in situ terminal transferase assay combined with electron microscopy. Numerical analysis revealed that immunogold labeling density in the condensed chromatin of apoptotic nuclei was comparable on the average to that in the perinuclear heterochromatin of normal nuclei, and that individual apoptotic nuclear fragments exhibited highly variable gold particle density, from fragments with lower density to that of normal heterochromatin, to fragments with densities twice as high as that of normal heterochromatin. The in situ terminal transferase assay combined with electron microscopy detected DNA ends exposed by ultrathin sectioning as well as DNA cleavage by a putative endonuclease. In conclusion, the state of the DNA, including its ligation and degeneration, changes gradually during chromatin condensation and nuclear fragmentation of apoptosis.
TL;DR: The results suggest that nickel may specifically produce oxidative DNA damage in heterochromatin because of the nature of its binding to histone H1 and core histones.
Abstract: 7,8-Dihydro-8-oxo-2'-deoxyguanosine (8-oxo-dG) was measured as an indicator of nickel-induced oxidative base damage in the presence of H 2 O 2 Heterochromatic proteins isolated from Chinese hamster liver cells enhanced the formation of 8-oxo-dG induced by NiCl 2 and H 2 O 2 in vitro, whereas euchromatic proteins inhibited this reaction The inhibitory effect of euchromatic proteins on dG oxidation may be due to the oxygen radical scavenging effects of low molecular weight protein-rich fractions Gel electrophoresis confirmed that histone H 1 was present at a higher concentration in heterochromatin than in euchromatin It is believed that the presence of nickel-protein complexes in cells is crucial for the formation of reactive oxygen species (ROS) We found that Ni 2+ binds to histone H 1 and core histones as determined by 63 Ni autoradiography of proteins on nitrocellulose membranes In vitro studies showed that commercially purified histone H 1 , and to a considerably lesser extent core histones, enhanced the NiCl 2 and H 2 O 2 catalyzed formation of 8-oxo-dG in a reaction containing free dG base Since histone H 1 is a lysine- and alanine-rich protein, the levels of 8-oxo-dG induced by NiCl 2 and H 2 O 2 were studied in the presence of these amino acids and found to be enhanced by them These results suggest that nickel may specifically produce oxidative DNA damage in heterochromatin because of the nature of its binding to histone H 1 and core histones This selective oxidation of genetically inactive heterochromatin may explain why nickel compounds which generate oxygen radicals and oxidize DNA bases are inactive in most gene mutation assays
TL;DR: The current hypothesis of recessive inheritance for this disorder suggests that the chromosomal aberrations are not a causative event in this syndrome; however, the chromosome aberration are clearly an important basic diagnostic criterion.
Abstract: We report on a new patient with immunodeficiency, centromeric heterochromatin instability, and facial anomalies (the ICF syndrome). Studies with traditional cytogenetic methods demonstrate that aberrations in this syndrome primarily involve the centromeric regions of chromosomes 1 and 16. We applied fluorescence in situ hybridization (FISH) using {open_quotes}painting{close_quotes} probes for chromosomes 1 and 16 to document the progression of centromeric instability from simple decondensation aberrations to the subsequent formation of complex multibranched chromosomes 1, and finally to the interphase aberrations of nuclear projections and micronuclei involving both chromosomes 1 and 16. The loss of the large multibranched chromosome 1 configurations from the cells as micronuclei suggests that the centromeric aberrations subsequently interfere with normal chromosome movement at anaphase in ICF syndrome. Circular areas of counterstained chromatin were observed by FISH in the micronuclei corresponding to the intertwined segments of centromeric heterochromatin seen involving multibranched chromosomes 1 in the patient`s G-banded chromosome study. The current hypothesis of recessive inheritance for this disorder suggests that the chromosomal aberrations are not a causative event in this syndrome; however, the chromosome aberrations are clearly an important basic diagnostic criterion. 22 refs., 3 figs.