Showing papers on "Heterochromatin published in 1990"

Distribution of non-telomeric sites of the (TTAGGG)n telomeric sequence in vertebrate chromosomes.

Abstract: The intrachromosomal distribution of non-telomeric sites of the (TTAGGG)n telomeric repeat was determined for 100 vertebrate species. The most common non-telomeric location of this sequence was in the pericentric regions of chromosomes. A variety of species showed relatively large amounts of this sequence present within regions of constitutive heterochromatin. We discuss possible relationships between the non-telomeric distribution of the (TTAGGG)n sequence and the process of karyotype evolution, during which these sites may provide potential new telomeres.

Mutation in a heterochromatin-specific chromosomal protein is associated with suppression of position-effect variegation in Drosophila melanogaster.

Abstract: We report here that a point mutation in the gene which encodes the heterochromatin-specific nonhistone chromosomal protein HP-1 in Drosophila melanogaster is associated with dominant suppression of position-effect variegation. The mutation, a G-to-A transition at the first nucleotide of the last intron, causes missplicing of the HP-1 mRNA. This suggests that heterochromatin-specific proteins play a central role in the gene suppression associated with heterochromatic position effects.

A view of interphase chromosomes.

Abstract: Metaphase chromosomes are dynamically modified in interphase. This review focuses on how these structures can be modified, and explores the functional mechanisms and significance of these changes. Current analyses of genes often focus on relatively short stretches of DNA and consider chromatin conformations that incorporate only a few kilobases of DNA. In interphase nuclei, however, orderly transcription and replication can involve highly folded chromosomal domains containing hundreds of kilobases of DNA. Specific "junk" DNA sequences within selected chromosome domains may participate in more complex levels of chromosome folding, and may index different genetic compartments for orderly transcription and replication. Three-dimensional chromosome positions within the nucleus may also contribute to phenotypic expression. Entire chromosomes are maintained as discrete, reasonably compact entities in the nucleus, and heterochromatic coiled domains of several thousand kilobases can acquire unique three-dimensional positions in differentiated cell types. Some aspects of neoplasia may relate to alterations in chromosome structure at several higher levels of organization.

CENP-B: a major human centromere protein located beneath the kinetochore.

Abstract: The family of three structurally related autoantigens CENP-A (17 kD), CENP-B (80 kD), and CENP-C (140 kD) are the best characterized components of the human centromere, and they have been widely assumed to be components of the kinetochore. Kinetochore components are currently of great interest since this structure, which has long been known to be the site of microtubule attachment to the chromosome, is now believed to be a site of force production for anaphase chromosome movement. In the present study we have mapped the distribution of CENP-B in mitotic chromosomes by immunoelectron microscopy using two monospecific polyclonal antibodies together with a newly developed series of ultra-small 1-nm colloidal gold probes. We were surprised to find that greater than 95% of CENP-B is distributed throughout the centromeric heterochromatin beneath the kinetochore. This strongly supports other emerging evidence that CENP-B is specifically associated with alpha-satellite heterochromatin. Although in certain instances CENP-B can be seen to be concentrated immediately adjacent to the lower surface of the kinetochore, the outer plate remains virtually unlabeled. Similar analysis with a human autoimmune serum that recognizes all three CENP antigens reveals an additional unsuspected feature of kinetochore structure. In addition to recognizing antigens in the centromeric heterochromatin, the autoantiserum recognizes a concentration of antigens lateral to the kinetochore. This difference in staining pattern may reflect the presence of a "collar" of chromatin rich in CENP-C and/or CENP-A encircling the kinetochore plates.

The effects of chromosome rearrangements on the expression of heterochromatic genes in chromosome 2L of Drosophila melanogaster.

Abstract: The light (lt) gene of Drosophila melanogaster is located at the base of the left arm of chromosome 2, within or very near centromeric heterochromatin (2Lh). Chromosome rearrangements that move the lt+ gene from its normal proximal position and place the gene in distal euchromatin result in mosaic or variegated expression of the gene. The cytogenetic and genetic properties of 17 lt-variegated rearrangements are described in this report. We show that five of the heterochromatic genes adjacent to lt are subject to inactivation by these rearrangements and that the euchromatic loci in proximal 2L are not detectably affected. The properties of the rearrangements suggest that proximity to heterochromatin is an important regulatory requirement for at least six 2Lh genes. We discuss how the properties of the position effects on heterochromatic genes relate to other proximity-dependent phenomena such as transvection.

Dependence of position-effect variegation in Drosophila on dose of a gene encoding an unusual zinc-finger protein.

Abstract: Position-effect variegation is the inactivation in some cells of a gene translocated next to heterochromatin, the region of the chromosome that is permanently condensed. The number of copies of the Drosophila gene Suvar(3)7 is a dose-limiting factor in this phenomenon, and seems from its sequence that it encodes a protein with five widely spaced zinc-fingers. This novel arrangement of zinc-fingers could help in packaging the chromatin fibre into heterochromatin, and also reflect a novel method of controlling the expression from DNA domains.

Simple repetitive sequences are associated with differentiation of the sex chromosomes in the guppy fish.

Abstract: Hybridization of restriction enzymedigested genomic guppy (Poecilia reticulata, Poeciliidae) DNA with the oligonucleotide probe (GACA)4 revealed a male-specific simple tandem repeat locus, which defines the Y chromosome in outbred populations The related (GATA)4 probe identifies certain males with the red color phenotype In contrast only in two out of eight laboratory guppy strains was the typical (GACA)4 band observed By specific staining of the constitutive heterochromatin one pair of chromosomes could also be identified as the sex chromosomes, confirming the XX/XY mechanism of sex determination All males exhibit Y chromosomes with a large region of telomeric heterochromatin Hybridization in situ with nonradioactively labeled oligonucleotide probes localized the (GACA)n repeats to this heterochromatic portion Together these results may be regarded as a recent paradigm for the differentiation of heteromorphic sex chromosomes from a pair of autosomes during the course of evolution According to the fish model system, this may have happened in several independent consecutive steps

Genome size variation in Zea mays ssp. mays adapted to different altitudes.

Abstract: Previous studies have indicated a positive correlation between genome size and altitude among plant species. It has been hypothesized that increasing genome size occurs due to increasing C-banded heterochromatin. In corn, increasing altitude has been correlated with decreasing knob (C-banded) heterochromatin, suggesting that DNA content may decrease with increasing altitude. In this study, nuclear DNA content of 12 southwestern United States Indian maize populations, collected at various altitudes, was determined. The significant positive correlation observed between genome size and altitude suggests that corn follows the trend of increasing DNA content with increasing altitude observed in other plant species. Whether this correlation is due to increasing knob heterochromatin or additional intra- or supernumerary chromosomal DNA sequences has yet to be determined.

Functional analysis of a centromere from fission yeast: a role for centromere-specific repeated DNA sequences.

Abstract: A circular minichromosome carrying functional centromere sequences (cen2) from Schizosaccharomyces pombe chromosome II behaves as a stable, independent genetic linkage group in S. pombe. The cen2 region was found to be organized into four large tandemly repeated sequence units which span over 80 kilobase pairs (kb) of untranscribed DNA. Two of these units occurred in a 31-kb inverted repeat that flanked a 7-kb central core of nonhomology. The inverted repeat region had centromere function, but neither the central core alone nor one arm of the inverted repeat was functional. Deletion of a portion of the repeated sequences that flank the central core had no effect on mitotic segregation functions or on meiotic segregation of a minichromosome to two of the four haploid progeny, but drastically impaired centromere-mediated maintenance of sister chromatid attachment in meiosis I. This requirement for centromere-specific repeated sequences could not be satisfied by introduction of random DNA sequences. These observations suggest a function for the heterochromatic repeated DNA sequences found in the centromere regions of higher eucaryotes.

Small marker chromosomes in man: origin from pericentric heterochromatin of chromosomes 1, 9, and 16.

Abstract: Three patients with different marker chromosomes were screened by in situ hybridisation using biotinylated probes to chromosome specific pericentric repeats to determine the chromosomal origin of the marker. Each marker had a different origin, with one from each of chromosomes 1, 9, and 16. This is the first time that autosomal marker chromosomes consisting of a small ring have been shown to be derived from the pericentric heterochromatin of metacentric and submetacentric chromosomes. Evidence suggests that such markers are not associated with any significant risk of phenotypic abnormalities, but additional cases need to be studied.

Heterochromatin condensation and evolution of unique satellite-DNA families in two parasitic wasp species: Diadromus pulchellus and Eupelmus vuilleti (Hymenoptera).

Abstract: Large quantities of satellite DNA families ( 15%25% of the genome) were found in the DNA of two species of parasitic wasps, Diadromus pulchellus and Eupelmus vuilleti. In both species the satellite DNA was found to consist wholly or largely of a single family unique to that species. Several clones of each family were obtained and sequenced. Palindromes in each consensus sequence suggest the formation in vivo of hairpin structures that may play a role in the mode of heterochromatin condensation in these insects. The ancestral repeating motifs were determined from the consensus sequences. Plausible scenarios are presented for the evolution of the two satellite DNAs. The occurrence of only one family of satellite DNAs in both species may indicate that, in male haploids, such families have shorter persistence times than necessary for the origins of new duplicated sequences.

Chromosomal structure is altered by mutations that suppress or enhance position effect variegation

Abstract: We examined the genetic, morphological, and molecular effects of position effect variegation inDrosophila, and the effects of mutations that either suppress [Su(var)] or enhance [E(var)] this phenomenon. All eightSu(var) mutations examined strongly suppress the inactivation of variegating alleles of the genes white [In(l) wm4], brown [In (2R)bwVDe2] and Stubble [T(2;3)SbV]. TheE(var) mutation enhances variegation of these loci. The chromosomal region 3C-E (26 bands) which includes the white locus is usually packaged as heterochromatin in salivary glands of the variegating strainwm4. Addition of any of theSu(var) mutations restores a more euchromatic morphology to this region. In situ hybridization to polytene chromosomes and DNA blot analyses of gene copy number demonstrate that the DNA of thew+ gene is less accessible to its probe in the variegatingwm4 strain than it is in the wildtype or variegation-suppressed strains. Blot analysis of larval salivary gland DNA indicates that the white gene copy number does not vary among the strains. Hence, the differences in binding of thew+ gene probe in the variegating and variegation-suppressed strains reflect differences in chromosomal packaging rather than alterations in gene number. The effects of variegation and theSu(var) mutations on chromatin structure were analyzed further by DNAse I digestion and DNA blot hybridization. In contrast to their dramatic effects on chromosomal morphology and gene expression, theSu(var) mutations had negligible effects on nuclease sensitivity of the white gene chromatin. We suggest that the changes in gene expression resulting from position effect variegation and the action of theSu(var) mutations involve alterations in chromosomal packaging.

Analysis of the structure and variability of nucleolar organizer regions of Salmo trutta by C-, Ag-, and restriction endonuclease banding.

Abstract: Nucleolar organizer regions (NORs) of brown trout were investigated using C-, Ag-, and restriction endonuclease banding. The presence of constitutive heterochromatin was confirmed by C-banding. Giemsa-staining, C-banding, and Ag-banding revealed great variability in the size of the short arm of the NOR-bearing chromosome. This size variation was due in some cases to NOR duplication. Restriction endonuclease digestion induced a specific banding pattern for AluI, DdeI, HaeIII, MboI, and HinfI, indicating some features about the sequence composition of the NOR-associated heterochromatin.

Intragenomic movement, sequence amplification and concerted evolution in satellite DNA in harvest mice, Reithrodontomys: evidence from in situ hybridization

Abstract: Three DNA probes isolated from three species ofReithrodontomys (R. montanus, R. megalotis, R. fulvescens) were used to examine within and among species variation in the chromosomal location of satellite DNA and constitutive heterochromatin. These probes hybridized to the centromeric regions on all chromosomes in six species of the subgenusReithrodontomys. Additionally, nearly all extra-centromeric C-band positive regions (with the exception of some heterochromatic material on the X and Y) hybridized to these probes. Within the subgenusReithrodontomys both the chromosomal distribution and organization of satellite DNA has changed throughout evolution. The evolutionary transition has been from a totally centromeric position inR. fulvescens to centromeric and non-centromeric regions in other species that have undergone extensive chromosomal rearrangements from the primitive karyotype for peromyscine rodents. In addition, the monomer repeat of the satellite sequence differs betweenR. fulvescens (monomer defined by PstI) and the remaining species in the subgenusReithrodontomys (monomer defined by EcoRI). These results suggest at least two amplification events for this satellite DNA sequence. Models and mechanisms concerned with the homogenization and spread of satellite sequences in complex genomes are evaluated in light of theReithrodontomys data. From a phlyogenetic standpoint, the satellite sequences composing heterochromatic regions were restricted to the subgenusReithrodontomys, which supports morphological differences used to recognize two subgenera,Reithrodontomys andAporodon. Probes failed to hybridize to any part of the karyotype ofR. mexicanus (subgenusAporodon) or to seven species from other closely related genera (Baiomys, Neotoma, Nyctomys, Ochrotomys, Onychomys, Peromyscus, Xenomys), some of which are considered as potential sister taxa forReithrodontomys.

Evolution of the Simiiformes and the phylogeny of human chromosomes.

Abstract: This paper is based on the results of Primate chromosome studies obtained using high resolution techniques in our and other laboratories. We discuss the origin and the evolution of the chromosomes in the human karyotype and the time in evolution of the Simiiformes when they acquired their present morphology. Our results indicate that the chromosomes that underwent a higher number of reorganizations during the evolution of the Simiiformes coincide with the chromosomes most often implicated in human chromosome pathology. We describe the main reorganizations that took place during Primate evolution. Centromere activation and inactivation and heterochromatin changes are discussed as mechanisms of chromosome evolution.

HeT DNA: a family of mosaic repeated sequences specific for heterochromatin in Drosophila melanogaster.

Abstract: HeT DNA is a complex family of repeated DNA found only in pericentric and telomeric heterochromatin. In contrast to other DNA families that have been specifically associated with heterochromatin, HeT DNA is not principally a family of tandemly repeated elements. Much of the HeT DNA family appears to be a mosaic of several different classes of large sequence elements arranged in a scrambled array; however, some elements of the family can be found in tandem repeats. In spite of the variable order of the different elements in HeT DNA, the sequence homology between different members of each class of element is extremely high, suggesting that the members are evolving in a concerted fashion. Sequence analysis suggests that some elements in the HeT family may make up a novel family of heterochromatin-specific transposable elements and that the mosaic organization of the elements may be produced by retroposition and other mechanisms involved in the transposition of mobile elements. We suggest that such mechanisms may be a general feature for the maintenance of chromosome structure.

Molecular and cytogenetic analysis of the heterochromatin-euchromatin junction region of the Drosophila melanogaster X chromosome using cloned DNA sequences.

Abstract: We have used three cloned DNA sequences consisting of (1) part of the suppressor of forked transcription unit, (2) a cloned 359-bp satellite, and (3), a type I ribosomal insertion, to examine the structure of the base of the X chromosome of Drosophila melanogaster where different chromatin types are found in juxtaposition. A DNA probe from the suppressor of forked locus hybridizes exclusively to the very proximal polytenized part of division 20, which forms part of the beta-heterochromatin of the chromocenter. The cloned 359-bp satellite sequence, which derives from the proximal mitotic heterochromatin between the centromere and the ribosomal genes, hybridizes to the under replicated alpha-heterochromatin of the chromocenter. The type I insertion sequence, which has major locations in the ribosomal genes and in the distal mitotic heterochromatin of the X chromosome, hybridizes as expected to the nucleolus but does not hybridize to the beta-heterochromatic division 20 of the polytene X chromosome. Our molecular data reveal that the suppressor of forked locus, which on cytogenetic grounds is the most proximal ordinary gene on the X chromosome, is very close to the junction of the polytenized and non-polytenized region of the X chromosome. The data have implications for the structure of beta-heterochromatin-alpha-heterochromatin junction zones in both mitotic and polytene chromosomes, and are discussed with reference to models of chromosome structure.

Mechanisms for the construction and developmental control of heterochromatin formation and imprinted chromosome domains.

Abstract: The study of variegating position effects in Drosophila provides a model system to explore the mechanism and material basis for the construction and developmental control of heterochromatin domains and the imprinted genomic structures that they may create. The results of our experiments in this regard have implications for a diverse assortment of long-range chromosome phenomena related to gene and chromosome inactivation. Specifically, as a consequence of our studies on position effect variegation, we propose a simple mechanism of X-chromosome inactivation, suggest a purpose for genomic imprinting, and postulate a general means for regulating the time in development at which certain genes become heterochromatically repressed.

Probing DNA structure and function with a multi-wavelength fluorescence confocal laser microscope.

Abstract: SUMMARY Three levels of organization in DNA structure in the interphase cell nucleus are assessed by confocal laser scanning microscopy: (i) the conformational state of the double helix; (ii) the distribution of eu- and heterochromatin; and (iii) the localization of replication complexes throughout S phase. Multi-parameter measurements were carried out in each optical section using two laser sources and combined stereoscopic reconstructions were used to assess the co-localization of nuclear components. DNA is highly polymorphic and can adopt a variety of different helical conformations as well as unusual structures (curved, cruciform, multi-stranded). We have assessed by laser scanning microscopy the presence of left-handed Z-DNA in polytene chromosomes of Diptera as well as the spatio-temporal distribution of Z-DNA binding proteins in whole-mount Drosophila embryos and ovaries. We have determined the 3-D distribution of replication sites relative to heterochromatin regions, nucleoli and nuclear membrane by using short pulses of BrdU incorporation in synchronized mouse and human fibroblasts. Replication sites were visualized with a monoclonal anti-BrdU antibody combined with DNA fluorescent staining and antibody labelling of nuclear lamin. The implications of dynamic DNA movement and structural rearrangement to the organization of the nucleus in domains are discussed.

Identifying a single-copy DNA sequence associated with the expression of a heterochromatic gene, the light locus of Drosophila melanogaster.

Abstract: Although little is known about the molecular organization of most genes within heterochromatin, the unusual properties of these chromosomal regions suggest that genes therein may be organized and expressed very differently from those in euchromatin. We report here the cloning, by P transposon tagging, of sequences associated with the expression of the light locus, an essential gene found in the heterochromatin of chromosome 2 of Drosophila melanogaster. We conclude that this DNA is either a segment of the light locus, or a closely linked, heterochromatic sequence affecting its expression. While other functional DNA sequences previously described in heterochromatin have been repetitive, light gene function may be associated, at least in part, with single-copy DNA. This conclusion is based upon analysis of DNA from mutations and reversions induced by P transposable elements. The cloned region is unusual in that this single-copy DNA is embedded within middle-repetitive sequences. The in situ hybridization experiments also show that, unlike most other sequences in heterochromatin, this light-associated DNA evidently replicates in polytene chromosomes, but its diffuse hybridization signal may suggest an unusual chromosomal organization.

B-chromosome and C-band heterochromatin variation in Arizona maize populations adapted to different altitudes

Abstract: The B-chromosome and C-band numbers were determined in 12 Arizona Indian maize populations. These populations were originally collected from altitudes ranging from 100 to 5300 ft (1 ft = 0.3048 m). In addition, the total nuclear DNA amounts of these populations have been observed to vary by as much as 20%. The number of B-chromosomes was not significantly correlated with altitude, C-band number, or nuclear DNA amount. C-band number was significantly correlated with both altitude and genome size. It does not appear that the amount of C-band variation can account for the large nuclear DNA variation observed in these accessions. Additional A-chromosomal DNA sequences may be involved in the nuclear DNA content variation that exists among these accessions.Key words: heterochromatin, DNA content, evolution, repeated DNA.

Chromosome numbers and C-banding in two wasp species of the genus Polistes (Hymenoptera, Polistinae, Polistini)

Abstract: A cytogenetic study was performed on 2 waps species of the tribe polistini, including the determination of chromosome number and the detection of thterochromatin by C-banding technique.Polistes (Epicnemius) cinerascens presents n=27, 2n=54 chromosomes of the meta- sub- and acrocentric types; heterochromatin has a varied distribution: in and around the centromere in chromosomes: sometimes on one of the majority of the arms or on almost throughout the entire chromosomes.Poliste (Aphanilopterus) versicolor versicolor presents n=31, 2n=62 meta- and submetacentric chromosomes; heterochromatin is distributed on one of the chromosome arms.

Inter- and intraspecific heterochromatin variation detected by restriction endonuclease digestion in two sibling species of the Anopheles maculipennis complex.

Abstract: The sibling species Anopheles atroparvus and Anopheles labranchiae are cytogenetically almost indistinguishable. The chromosome complement (2n = 6) consists of two pairs of autosomes and two heteromorphic sex chromosomes with largely homologous heterochromatic long arms. Treatment of chromosome preparations with the restriction endonucleases, Alu I, Hae III, Mbo I, Hpa II, revealed species-specific differences of the sex chromosome banding pattern. These differences involved both amount and location of digested heterochromatin. Heterochromatin heterogeneity and a high level of intraspecific polymorphism, undetected with standard banding techniques, were observed in both species. Quantitative heterochromatin differences between the sex chromosomes did not inhibit their pairing and chiasmata formation. The endonuclease Msp I, which cleaves the same target sequence as Hpa II, did not digest heterochromatic as well as euchromatic regions in both species: inhibition of cleavage by methylation of the target sequence or limited access of the enzyme to the target could be involved in this response.

Fluorescence banding in four species of Microtidae: an analysis of the evolutive changes of the constitutive heterochromatin

Abstract: Three different fluorochrome and specific counterstain combination (DAPI/AMD, DA/DAPI and CMA/DA) treatments were applied to the chromosomes of four Microtidae (Rodentia) species. The results complete the data obtained in our previous paper (Burgos, M., Jimenez, R., & Diaz de la Guardia, R., Genome 30:540–546, 1988) and prove that the changes in the constitutive heterochromatin in the evolution of the karyotypes of these species are not only due to gain or loss of heterochromatin, but are qualitative with respect to their nucleotide composition, repeated base pair organization or DNA-protein complex modification. These variations lead to the differential response to the fluorescence dye combinations used.

Somaclonal variation from cultured immature embryos of sister lines of rye differing in heterochromatic content

Abstract: Somaclonal variation occurred among rye plants regenerated from cultured immature embryos of five sister lines that differed in their content of telomeric heterochromatin. Variation was observed in morphology, chromosome number, and secalin seed storage proteins. Morphological variation was present in 9.7% of the regenerants and included albinism and variegation, which appeared in different frequencies among the lines. Chromosome variation occurred in 15.8% of the regenerants and included translocations, tetraploidy, and trisomy in addition to meiotic disturbances such as centromere misbehaviour and asyndesis. Some of the regenerated plants were mosaic for the structural and numerical chromosome aberrations. The nature of the chromosome variation also differed among the lines. A single variant in the 40K γ-secalins was detected. The occurrence of variation is discussed in relation to differences in morphogenetic response of the rye lines and to the genotypic component of instability in culture.Key words: somaclonal variation, immature embryo culture, rye heterochromatin, chromosome variation, secalins.