Showing papers on "Heterochromatin published in 1991"
TL;DR: The deduced sequence of the Pc protein exhibits a homology to the heterochromatin-associated protein HP1 encoded by the suppressor of position effect variegation gene Su(var) 205, suggesting that Pc could use analogous mechanisms at the level of the higher order chromatin structure for the stable transmission of a determined state.
Abstract: The Polycomb (Pc) gene of Drosophila melanogaster is a member of a large class of genes (Pc group) required for the segment-specific repression of homeotic selector genes Mutations in Pc-group genes show strong posterior transformations in homozygous embryos resulting from an ectopic expression of homeotic genes in segments where they are not supposed to be active Genetic evidence suggests that Pc is part of a cellular memory mechanism responsible for the transmission of the homeotic expression pattern through developmental time We have determined the nucleotide sequence for the genomic DNA of the Pc gene and for cDNAs corresponding to the 25-kilobase Pc mRNA The deduced sequence of the Pc protein exhibits a homology to the heterochromatin-associated protein HP1 encoded by the suppressor of position effect variegation gene Su(var) 205 The homology is confined to a 37-amino acid domain in the N-terminal part of the two proteins Our findings extend to the molecule level the genetically identified parallels between the Pc-group genes and the modifiers of position effect variegation This suggests that Pc could use analogous mechanisms at the level of the higher order chromatin structure for the stable transmission of a determined state, as has been proposed for the clonal propagation of heterochromatin domains
591 citations
TL;DR: The chromo box motif has been used to identify similar modifier genes in other species, such as Drosophila and humans as mentioned in this paper, using a known sequence homology between a suppressor of position-effect-variegation, Heterochromatin protein 1 (HP1), and a repressor of homeotic genes, Polycomb (Pc).
Abstract: Modifiers of position-effect-variegation in Drosophila encode proteins that are thought to modify chromatin, rendering it heritably changed in its expressibility. In an attempt to identify similar modifier genes in other species we have utilized a known sequence homology, termed chromo box, between a suppressor of position-effect-variegation, Heterochromatin protein 1 (HP1), and a repressor of homeotic genes, Polycomb (Pc). A PCR generated probe encompassing the HP1 chromo box was used to clone full-length murine cDNAs that contain conserved chromo box motifs. Sequence comparisons, in situ hybridization experiments, and RNA Northern blot analysis suggest that the murine and human sequences presented in this report are homologues of the Drosophila HP1 gene. Chromo box sequences can also be detected in other animal species, and in plants, predicting a strongly conserved structural role for the peptide encoded by this sequence. We propose that epigenetic (yet heritable) changes in gene expressibility, characteristic of chromosomal imprinting phenomena, can largely be explained by the action of such modifier genes. The evolutionary conservation of the chromo box motif now enables the isolation and study of putative modifier genes in those animal and plant species where chromosomal imprinting has been described.
288 citations
TL;DR: The existence of highly ordered organizational patterns of the cell nucleus appears to be beyond any doubt and it is difficult to escape the conclusion that interphase chromosome topology is important for the complex regulation of the many varied and interrelated nuclear processes.
215 citations
TL;DR: The macrostructure of the tomato telomeres has been investigated by in situ hybridization, genomic sequencing, and pulsed-field gel electrophoresis, and confirmed that the Tomato telomeric repeat represents the outermost DNA sequence of each tomato chromosome.
Abstract: The macrostructure of the tomato telomeres has been investigated by in situ hybridization, genomic sequencing, and pulsed-field gel electrophoresis. In situ hybridizations with a cloned telomeric sequence from Arabidopsis thaliana indicated that the telomeric repeat of tomato cross-hybridizes with that of Arabidopsis and is located at all telomeres. Bal31 digestion kinetics confirmed that the tomato telomeric repeat represents the outermost DNA sequence of each tomato chromosome. Genomic sequencing of enriched tomato telomeric sequences, using primers derived from the Arabidopsis sequence, revealed that the consensus sequence of the tomato telomeric repeat is TT(T/A)AGGG compared with the Arabidopsis consensus sequence of TTTAGGG. Furthermore, as shown by pulsed-field gel electrophoresis, the telomeric repeat of tomato is separated by not more than a few hundred kilobases from a previously described 162-base pair satellite DNA repeat of tomato (TGR I) at 20 of the 24 telomeres. Together, these sequences are found in the heterochromatic terminal knob observed in pachytene chromosomes. Therefore, these two repeats determine the structure of 20 of the 24 tomato chromosome ends over approximately 2% of the total chromosome length.
171 citations
TL;DR: The model appears to be viable as an explanation of certain patterns of chromosomal evolution such as karyotypic megaevolution and some types of karyotypes orthoselection.
Abstract: We describe a molecular model for rapid chromosomal evolution that proposes tandemly repeated DNA sequences as a driving force. A prediction of this model is that when extensive rearrangements of euchromatin have been facilitated by heterochromatin, genomes will be characterized by tandemly repeated sequences that have actively changed chromosomal fields by intragenomic movement. Alternatively, it is proposed that in conservative chromosomal lineage each class of tandemly repeated sequences will be restricted to a specific chromosomal field. To provide baseline data to test this model we examined four classes of tandemly repeated elements in six species of equids (Equus). Distribution of these sequences among species, as determined from slot blot analysis, and restriction site variation, shown by Southern blot hybridization, document that these sequences are in an evolutionarily dynamic state, and in situ hybridization documents extensive intragenomic movement among nonhomologous chromosomes and chromosomal fields. These data are interpreted as being compatible with the predictions of this model. Although this is clearly not the sole molecular factor driving chromosomal evolution, the model appears to be viable as an explanation of certain patterns of chromosomal evolution such as karyotypic megaevolution and some types of karyotypic orthoselection.
116 citations
TL;DR: From the current understanding of PEV, it appears that PEV provides a useful model for the study of determinative events that occur during development, including both the establishment of different lineages and the somatic memory or imprinting of the initial determinative decision.
Abstract: Publisher Summary This chapter discusses the position-effect variegation—an assay for nonhistone chromosomal proteins and chromatin assembly and modifying factors. The extensive analyses of the homeotic genes in Drosophila suggest that chromatin structure plays a fundamental role in the control of segment determination and differentiation. Hence, chromatin structure plays an important role in the regulation of gene expression. The formation of transcriptionally competent domains is an essential first step in proper gene expression. The phenomenon of position-effect variegation (PEV) resembles X-inactivation in mammals. It may serve as a suitable assay system for the recovery of mutations in nonhistone chromosomal proteins (NHCPs). PEV is the mosaic expression of a gene, associated with a chromosomal or genomic rearrangement. In most instances, PEV occurs when a gene, normally located in euchromatin, is placed adjacent to a broken segment of heterochromatin. The variegating gene is inactivated in some cells but remains transcriptionally competent in other cells, giving a mosaic phenotype. PEV has been most extensively studied in Drosophila , but it has also been described in vertebrates, lower eukaryotes, and plants to a broken segment of heterochromatin. The two most extensively characterized affecters of PEV are temperature and the number of Y chromosomes in the genome.
115 citations
TL;DR: The entirely heterochromatic Y chromosome of Drosophila melanogaster contains a series of simple sequence satellite DNAs which together account for about 80% of its length and 8 of these sequences are finely mapped by in situ hybridization on mitotic chromosome preparations.
Abstract: The entirely heterochromatic Y chromosome of Drosophila melanogaster contains a series of simple sequence satellite DNAs which together account for about 80% of its length. Molecular cloning of the three simple sequence satellite DNAs of D. melanogaster (1.672, 1.686 and 1.705 g/ml) revealed that each satellite comprises several distinct repeat sequences. Together 11 related sequences were identified and 9 of them were shown to be located on the Y chromosome. In the present study we have finely mapped 8 of these sequences along the Y by in situ hybridization on mitotic chromosome preparations. The hybridization experiments were performed on a series of cytologically determined rearrangements involving the Y chromosome. The breakpoints of these rearrangements provided an array of landmarks along the Y which have been used to localize each sequence on the various heterochromatic blocks defined by Hoechst and N-banding techniques. The results of this analysis indicate a good correlation between the N-banded regions and 1.705 repeats and between the Hoechst-bright regions and the 1.672 repeats. However, the molecular basis for banding does not appear to depend exclusively on DNA content, since heterochromatic blocks showing identical banding patterns often contain different combinations of satellite repeats. The distribution of satellite repeats has also been analyzed with respect to the male fertility factors of the Y chromosome. Both loop-forming (kl-5, kl-3 and ks-1) and non-loop-forming (kl-2 and ks-2) fertility genes contain substantial amounts of satellite DNAs. Moreover, each fertility region is characterized by a specific combination of satellite sequences rather than by an homogeneous array of a single type of repeat.(ABSTRACT TRUNCATED AT 250 WORDS)
108 citations
Journal Article•
TL;DR: Comparison of constitutional and tumor genotypes of 84 breast tumors at 7 polymorphic chromosome 1 loci indicates a frequent imbalance of alleles on both 1p and 1q, and suggests that there are several genes on chromosome 1 serving as targets for changes, some of them associated with breast cancer development through their deletion and others through an increase in copy number.
Abstract: Loss of heterozygosity at particular chromosomal loci in the tumor cell, as evidenced by restriction fragment length polymorphism analysis, has been taken as a hallmark of the presence of tumor suppressor genes Recent studies of breast carcinoma have suggested that such genes might be located on the short as well as on the long arm of chromosome 1 We report here that comparison of constitutional and tumor genotypes of 84 breast tumors at 7 polymorphic chromosome 1 loci indicates a frequent imbalance of alleles on both 1p (12 of 61 informative patients) and 1q (37 of 71 informative patients) In about one-half of these cases, however, this imbalance was consistent with a gain in copy number of one allele in tumor DNA relative to normal DNA, rather than loss of the other In 10 tumors we performed chromosome 1 enumeration in the interphase nucleus using in situ hybridization with a probe detecting the heterochromatin region at 1q12 These experiments confirmed the supernumary presence of region 1q12 in those tumors showing an allelic copy number gain of 1q We suggest that there are several genes on chromosome 1 serving as targets for these changes, some of them associated with breast cancer development through their deletion and others through an increase in copy number
106 citations
TL;DR: The results suggest that the wild-type gene products of some modifiers of position-effect variegation are required for proper expression of genes normally located within or near the heterochromatin of chromosome 2.
Abstract: Dominant modifiers of position-effect variegation of Drosophila melanogaster were tested for their effects on the variegation of genes normally located in heterochromatin. These modifiers were previously isolated as strong suppressors of the variegation of euchromatic genes and have been postulated to encode structural components of heterochromatin or other products that influence chromosome condensation. While eight of the modifiers had weak or no detectable effects, six acted as enhancers of light (lt) variegation. The two modifiers with the strongest effects on lt were shown to also enhance the variegation of neighboring heterochromatic genes. These results suggest that the wild-type gene products of some modifiers of position-effect variegation are required for proper expression of genes normally located within or near the heterochromatin of chromosome 2. We conclude that these heterochromatic genes have fundamentally different regulatory requirements compared to those typical of euchromatic genes.
95 citations
TL;DR: A quantitative analysis of the alterations of constitutive heterochromatin in eukaryotic chromosomal evolution was attempted using the accumulated C-banding data available for mammals, amphibians, fish, ants, grasshoppers, and plants.
Abstract: A quantitative analysis of the alterations of constitutive heterochromatin in eukaryotic chromosomal evolution was attempted using the accumulated C-banding data available for mammals, amphibians, fish, ants, grasshoppers, and plants. It was found that these eukaryotes could be classified into two types by their C-banding patterns: 1) Type I included mammals, fish, and ants, and 2) Type II included amphibians, grasshoppers, and plants. C-bands were rather scarce in Type I eukaryote chromosomes and were found around the pericentromeric region when present at all, whereas the predominance of interstitial or terminal C-bands was found in Type II eukaryote chromosomes. The Type I and II C-banding patterns can best be interpreted by assuming that in the former group of eukaryotes the saltatory increase in constitutive heterochromatin occurs preferentially at the pericentromeric regions of telocentric chromosomes induced by centric fission, with C-bands being eliminated almost completely by centric fusion and/or pericentric inversion. On the other hand, C-bands appear in the Type II eukaryotes both interstitially and in the telomeric regions of chromosomes, and there may be no effective mechanism to eliminate these bands once they are integrated.
92 citations
TL;DR: It is shown that copies of bw+ transposed to ectopic sites are not trans-inactivated by rearrangements affecting the endogenous gene, and position-effect variegation in Drosophila confirms that trans- inactivation is "chromosome local" and maps the responsive element to the immediate vicinity of brown.
Abstract: Position-effect variegation in Drosophila is the mosaic expression of a gene juxtaposed to heterochromatin by chromosome rearrangement. The brown (bw+) gene is unusual in that variegating mutations are dominant, causing "trans-inactivation" of the homologous allele. We show that copies of bw+ transposed to ectopic sites are not trans-inactivated by rearrangements affecting the endogenous gene. However, when position-effect variegation is induced on an ectopic copy by chromosome rearrangement, the allele on its paired homolog is trans-inactivated, whereas other copies of bw+ are not. This confirms that trans-inactivation is "chromosome local" and maps the responsive element to the immediate vicinity of brown. Subsequent P-transposase-induced deletions within the ectopic copy in cis to the rearrangement breakpoint caused partial suppression of trans-inactivation. Surprisingly, the amount of suppression was correlated with deletion size, with some degree of trans-inactivation persisting even when the P[bw+] transposon was completely excised. The chromosome-local nature of the phenomenon and its extreme sensitivity to small disruptions of somatic pairing leads to a model in which a regulator of the brown gene is inactivated by direct contact with heterochromatic proteins.
TL;DR: Nonradioactive in situ hybridization demonstrated that pMR9A hybridizes only to the centromeric region of chromosome 9 and reveals chromosome 9 aneuploidies in interphase nuclei.
TL;DR: There are highly specific integration patterns for each endogenous retrovirus that do not readily relate to their sequence or particle classification, and each host genome may utilize these elements for contrary, and possibly beneficial functions.
Abstract: Retroviruses have the ability to integrate into the genome of their host, in many cases with little apparent sequence or site specificity. However, relatively few studies have addressed more general features of chromosomal integration. In this study we directly visualized the chromosomal organization of three representative endogenous retroviruses by in situ hybridization. Because there are 50–1000 copies of each of these retroviruses in the genome, it was possible to evaluate repeated integration events. Each retroviral sequence exhibited a unique and markedly different integration pattern. In order to characterize more precisely the chromosomal domains targeted by each retrovirus, later replicating domains were differentially labeled. Additionally, prototypic SINES and LINES (short and long interspersed reiterated sequences), which are inhomogeneously distributed on chromosome arms, were simultaneously detected. Retroviral copies of ≥2 kb were found (i) exclusively in a discrete set of later replicating domains, most of which have the staining characteristics of constitutive heterochromatin, (ii) widely represented in disparate types of chromosome domains, or (iii) almost completely condined to CpG Alu-rich regions that are known to be early replicating. Retroviral elements in Alu-rich domains would be expected to be actively transcribed in all cells. Surprisingly, hybridization to blots of brain RNA showed an ∼25 fold lower level of transcripts from these Alu associated elements than from retroviral sequences restricted to later replicating, heterochromatic domains. Retroviral insertions may subvert more typical transcriptional characteristics of a domain. The present results indicate that there are highly specific integration patterns for each endogenous retrovirus that do not readily relate to their sequence or particle classification. Each host genome may utilize these elements for contrary, and possibly beneficial functions.
TL;DR: A G banding technique combining trypsin and hot saline treatments was used to analyze the chromosomes of two grasshopper species, Eyprepocnemis plorans and Locusta migratoria, both of which contain both standard and supernumerary heterochromatin.
Abstract: A G banding technique combining trypsin and hot saline treatments was used to analyze the chromosomes of two grasshopper species, Eyprepocnemis plorans and Locusta migratoria, both of which contain both standard and supernumerary heterochromatin. Although this technique does not produce G bands like those in mammalian chromosomes, it serves to characterize heterochromatic regions whose nature has been inferred from other banding techniques (C, N, CMA, and DAPI banding). The light regions revealed by G banding contain GC-rich DNA sequences, the more prominent of which coincide with nucleolus organizer regions (NORs). Furthermore, the proximal heterochromatin in E. plorans was heterogeneous, and the standard and supernumerary heterochromatin showed conspicuous differences in organization. Supernumerary heterochromatin is an exception to the regular patterns shown by the standard heterochromatin. The findings are related to the mechanism of action of these banding techniques.Key words: banding techniques, gr...
TL;DR: Heterochromatin distribution in barley chromosomes was investigated by analyzing the C- and N-banding patterns of four cultivars and a clear difference was observed between them at the centromeric sites on all chromosomes.
Abstract: Heterochromatin distribution in barley chromosomes was investigated by analyzing the C- and N-banding patterns of four cultivars. Enzymatic maceration and air drying were employed for the preparation of the chromosome slides. Although the two banding patterns were generally similar to each other, a clear difference was observed between them at the centromeric sites on all chromosomes. Every centromeric site consisted of N-banding positive and C-banding negative (N+ C−) heterochromatin in every cultivar examined. An intervarietal polymorphism of heterochromatin distribution was confirmed in each of the banding techniques. The appearance frequencies of some bands were different between the two banding techniques and among the cultivars. The heterochromatic differentiation observed is discussed with respect to cause.
TL;DR: Using C5 as a probe for in situ hybridizations to chromosome preparations of cells of both the Chinese and Indian muntjacs, it is shown that repeated sequences occur in centromeric heterochromatin of the chromosomes of both Chinese and indian muntjac species.
Abstract: A clone of highly repetitive DNA, designated C5, was isolated from DNA of female Chinese muntjac cells. The nucleotide sequence of this clone is 80%–85% homologous to that of the satellite IA clone and other highly repetitive DNA clones previously obtained from the Indian muntjac. Using C5 as a probe for in situ hybridizations to chromosome preparations of cells of both the Chinese and Indian muntjacs, we were able to show that these repeated sequences occur in centromeric heterochromatin of the chromosomes of both Chinese and indian muntjac species. More significantly, non-random clusters of hybridization signals were detected on the arms of chromosomes of the Indian muntjac. These latter hybridization sites are postulated to be regions of interstitial heterochromatin and could be the remnants of centromeric heterochromatin from ancestral Chinese muntjac chromosomes. Our observations provide new supportive evidence for the tandem chromosome fusion theory that has been proposed for the evolution of the Indian muntjac karyotype.
TL;DR: A detailed cytogenetic map of chromosome 3 heterochromatin was constructed that includes all of the known vital genes and was found to be "empty," in that it did not contain either known genes or known satellite DNAs.
Abstract: This paper reports the cytogenetic characterization of the second chromosome heterochromatin of Drosophila melanogaster. High resolution cytological analysis of a sample of translocations, inversions, deficiencies and free duplications involving the pericentric regions of the second chromosome was achieved by applying sequential Hoechst 33258 and N-chromosome banding techniques to larval neuroblast prometaphase chromosomes. Heterochromatic rearrangements were employed in a series of complementation assays and the genetic elements previously reported to be within or near the second chromosome heterochromatin were thus precisely assigned to specific heterochromatic bands. The results of this analysis reveal a nonhomogeneous distribution of loci along the second chromosome heterochromatin. The l(2)41Aa, l(2)41Ab, rolled (l(2)41Ac) and l(2)41Ad loci are located within the proximal heterochromatin of 2R, while the nine remaining loci in the left arm and two (l(2)41Ae and l(2)41Ah) in the right arm map to h35 and to h46, respectively, the most distal heterochromatic regions. In addition, a common feature of these loci revealed by the cytogenetic analysis is that they map to specific heterochromatic blocks but do not correspond to the blocks themselves, suggesting that they are not as large as the Y fertility factors or the Rsp locus. Mutations of the proximal most heterochromatic loci, l(2)41Aa and rolled, were also examined for their phenotypic effects. Extensive cell death during imaginal disc development was observed in individuals hemizygous for either the EMS 31 and rolled mutations, leading to a pattern of phenotypic defects of adult structures.
TL;DR: The formation of constitutive heterochromatin was studied during the embryonic development of Drosophila melanogaster, using the C-banding technique, and this event correlates with the establishment of position-effect variegation.
Abstract: The formation of constitutive heterochromatin was studied during the embryonic development of Drosophila melanogaster, using the C-banding technique. During embryonic cleavage, C-banded material is not seen in mitotic chromosomes; the differentiation between euchromatin and heterochromatin only occurs at blastoderm. This event correlates with the establishment of position-effect variegation.
TL;DR: Octoploid Z. perennis showed the smallest DNA content per basic genome and the smallest heterochromatic blocks, suggesting that the DNA lost by this species consisted mainly of repetitive sequences.
Abstract: The nuclear DNA amount and the heterochromatin content in species and hybrids of Zea were analyzed in telophase nuclei (2C) of the root apex of germinating seeds. The results revealed significant differences among taxa and also among lines and races of maize. The hybrids between Z. mays ssp. mays x Z. mays ssp. mexicana (2n=20), Z. diploperennis x Z. perennis (2n=30), and Z. diploperennis x Z.perennis (2n=40) showed DNA content intermediate between that of the parents. The number of chromosomal C-bands and the proportion of the genome comprising C-band heterochromatin were positively related to genome size. In the different lines and races of maize studied, there was a positive correlation between genome size and the interval from germination to flowering. Octoploid Z. perennis (2n=40) showed the smallest DNA content per basic genome and the smallest heterochromatic blocks, suggesting that the DNA lost by this species consisted mainly of repetitive sequences. Considering that the extant species of Zea are tetraploid (2n=20) and octoploid (2n=40) and that the ancestral diploids are extinct, any consideration of the direction (increase or decrease) of the DNA change would be entirely speculative. The extant species could be the product of natural and artificial selection acting on different genotypic and nucleotypical constitutions at the diploid and/or tetraploid levels.
TL;DR: This paper describes the characterization and chromosomal distribution of three different rice (Oryza sativa) repetitive DNA sequences, which gave 355, 498 and 756 bp for the length of the repeat unit in Os48, OsG3-498 and OsG5-756, respectively.
Abstract: This paper describes the characterization and chromosomal distribution of three different rice (Oryza sativa) repetitive DNA sequences. The three sequences were characterized by sequence analysis, which gave 355, 498 and 756 bp for the length of the repeat unit in Os48, OsG3-498 and OsG5-756, respectively. Copy number determination by quantitative DNA slot-blot hybridization analysis showed 4000, 1080 and 920 copies, respectively, per haploid rice genome for the three sequences. In situ DNA hybridization analysis revealed that 95% of the silver grains detected with the Os48 probe were localized to euchromatic ends of seven long arms and one short arm out of the 12 rice chromosomes. For the OsG3-498 repetitive sequence, the majority of silver grains (58%) were also clustered at the same chromosomal ends as that of Os48. The minority (28%) of silver grains were located at heterochromatic short arms and centromeric regions. For the OsG5-756 repetitive sequence, 81% of the silver grains labeled the heterochromatic short arms and regions flanking all of the 12 centromeres. Thus, each of these three repetitive sequences was distributed at specific defined chromosomal locations rather than randomly at many chromosomal locations. The approximate copy number of a given repetitive DNA sequence at any specific chromosomal location was calculated by combining the information from in situ DNA hybridization analysis and the total copy number as determined by DNA slot-blot hybridization.
TL;DR: C-banding studies in four species of Characiformes fish of the genus Leporinus (Anostomidae) identified interspecific differences despite the strict similarity in karyotype macrostructure among them, indicating the occurrence of modifications during karyotypes evolution in these fish.
Abstract: SUMMARYC-banding studies in four species of Characiformes fish of the genus Leporinus (Anostomidae) identified interspecific differences despite the strict similarity in karyotype macrostructure among them. A perceptible reduction in centromeric heterochromatin observed in L. piau seems to be a derived condition. L. amblyrhyncus and L. taeniatus exhibit a centromeric and telomeric heterochromatin pattern which is possibly basic in the group, and L. striatus shows a few exclusive intercalary blocks probably derived from inversions and/or transpositions. The nucleolar organizer regions, which were always found to be associated with heterochromatin segments, appear in different chromosomes or chromosome sites in the species studied, also indicating the occurrence of modifications during karyotype evolution in these fish.
TL;DR: Morphological changes found in rearangements of chromosomal material of the rearrangements Dp(1;f) 1337, D p(2;1)pn2b, and T (1;4)wm258-21 were characterized are interpreted as morphological manifestations of the discontinuity of the spreading effect.
Abstract: Variations in compaction of chromosomal material of the rearrangements Dp(1;f) 1337, Dp(1;f) R, Dp(1;1)pn2b, and T(1;4)wm258-21, which display an extended position effect, were characterized. Morphological changes found in these rearangements were assigned to two major types: (i) continuous compaction, in which bands and interbands located distal to the eu/heterochromatin junction fuse into one compacted block of chromatin. The extent of compaction is increased by enhancers of position effect (low temperature, removal of the Y or 2R chromosome heterochromatin). In extreme cases compaction extends over dozens of bands. (ii) Discontinuous compaction, in which at least two zones of compaction separated by morphologically normal zones can readily be identified. As a result, some regions located at a greater distance from heterochromatin may be compacted more frequently than others than map nearer to it. A few regions (1D, 2B1-12, 2D) were shown to be most frequently compacted in all rearrangements investigated. The 2B13-18, 2C1-2, 2E, and 2F regions exhibited the lowest frequencies of compaction. Compaction of the zone containing the 2B1-12 bands is always accompanied by inactivation of the ecs locus, which maps in the 2B3-5 puff. At the same time the 2C1-2 and 2E bands located nearer to the breakpoint can retain normal morphology and puffing in response to ecdysterone. The results are interpreted as morphological manifestations of the discontinuity of the spreading effect.
TL;DR: The results indicate that sister chromatids establish strong pairing along the translocated heterochromatin and play an important role for sister Chromatid pairing and might be involved in the process of separation.
TL;DR: In situ hybridization of biotin-labeled mouse major satellite DNA clone pMR196 was applied toMus domesticus andMus spretus chromosomes (Chr) and karyotypes were counterstained with distamycin A-DAPI to identify AT-rich heterochromatin, suggesting that A-T rich heterochromeatin in M. domesticus is mainly constructed by the pMR 196-related sequence.
Abstract: In situ hybridization of biotin-labeled mouse major satellite DNA clone pMR196 was applied to Mus domesticus and Mus spretus chromosomes (Chr). The same karyotypes were counterstained with distamycin A-DAPI to identify AT-rich heterochromatin. Chromosomes from the laboratory mouse, C57BL/6Ros (BL/6; M. domesticus) were uniformly labeled at the centromere except for the Y, while chromosomes from the divergent Mus species M. spretus showed little or no hybridization. Differences between Mus species in copy number of the major satellite DNA sequence were used to identify chromosomes of M. domesticus and M. spretus in their F1 hybrids and to discriminate domesticus and spretus centromeres in backcross progeny. The distribution pattern of heterochromatic regions demonstrated by distamycin A-DAPI counterstaining was comparable with that of in situ hybridization with pMR196, suggesting that A-T rich heterochromatin in M. domesticus is mainly constructed by the pMR196-related sequence. The in situ technique was used to examine segregation of domesticus centromeres in backcross progeny obtained by mating F1 hybrid females with M. domesticus or M. spretus males. The segregation of centromeres did not deviate from the expected among the backcross progeny from C57BL/6Ros males, whereas chromosomes with M. domesticus centromeres were prone to appear in the progeny from backcross matings by M. spretus males.
Journal Article•
TL;DR: In situ hybridization of probe DNA with metaphase chromosome preparations showed exclusive binding of probe molecules to the centromeric region of mouse chromosomes.
Abstract: Degenerate probe DNA, homologous to part of the 234-bp repeated mouse gamma (major) satellite DNA, was generated by primer-directed in vitro DNA amplification using the polymerase chain reaction with oligonucleotide primers that anneal in the most conserved parts of the repeat. Probe labeling with biotin was performed during DNA polymerization. In situ hybridization of probe DNA with metaphase chromosome preparations showed exclusive binding of probe molecules to the centromeric region of mouse chromosomes. We applied the probe DNA for labeling of mouse heterochromatin in metaphase chromosomes, as well as interphase cell nuclei, and compared results of probe visualization using avidin tagged with either fluorescein or alkaline phosphatase in combination with a chromogenic substrate.
TL;DR: In situ hybridization experiments using synthetic probes not only revealed the informative simple repeats suitable for DNA fingerprinting in a particular specie, but also reflected the wide range of distribution of the simple sequences among eukaryotes.
Abstract: Stretches of short, simple DNA sequences are widespread in all eukaryote genomes studied so far. Simple sequences are thought to undergo frequent expansion and deletion due to intrinsic genomic mechanisms. Some of the simple sequences were used successfully to detect hypervariable loci in various genomes. Hybridization experiments using synthetic probes not only revealed the informative simple repeats suitable for DNA fingerprinting in a particular species, but also reflected the wide range of distribution of the simple sequences among eukaryotes. The organization of these simple repetitive sequences at the chromosomal loci was investigated using in situ hybridization with chemically synthesized, pure oligonucleotide probes. Both biotin- and digoxigenin-attached probes detected specific chromosomal sites that are enriched in the respective simple-repeat blocks. Depending on the organism and probe used, accumulation of simple DNA sequences at individual or multiple sites on the chromosomes of different vertebrates could be demonstrated. The simple repetitive DNA sequences are located in different chromosomal regions (e.g., heterochromatin on the sex chromosomes, nucleolus organizer regions, and R-band sites), which are constrained considerably during evolution.
TL;DR: The aim of this study was to evaluate a transgene with sequence characteristics that might contribute to the de novo formation of heterochromatin in interphase nuclei, and in transgenic but not control mice, a substantial number of large neurons, including approximately 30% of cerebellar Purkinje cells, showed excessive invaginations of the nuclear membrane.
Abstract: Transgenic mice provide a remarkable experimental setting for the study of nuclear architecture. The three-dimensional localization and fine structure of a foreign DNA within the mouse genome can be conveniently followed by using high-resolution in situ hybridization. Foreign DNAs designed with specific characteristics, such as base bias, sequence motif(s), and size can stably integrate into finite positions on host chromosomes. Thus the relative importance of each of these characteristics in determining the three-dimensional nuclear position and the detailed morphology of the transgene can be evaluated in different cell types. The aim of this study was to evaluate a transgene with sequence characteristics that might contribute to the de novo formation of heterochromatin in interphase nuclei. The structure of a phenotypically silent 11-megabase transgene, containing tandem repeats of beta-globin-pBR sequences integrated into the peritelomeric region of both mouse chromosome 3 homologs, was determined in adult brain cells. Neurons that are largely euchromatic were especially informative in three-dimensional studies of transgene position. The two transgenic loci behaved much like centromeric or paracentromeric A + T-rich satellite DNAs of comparable length from a single chromosome; one or both transgene domains localized together with centromeric satellite DNA on the nucleolus. This is an unusual nuclear position for a telomeric or chromosome arm region that does not contain a substantial amount of constitutively heterochromatic satellite DNA. G + C richness did not prevent these regions from assembling as dense heterochromatic bodies of approximately 1 micron3 in volume. Ultrastructurally, transgenic domains were often intimately connected with constitutive heterochromatin and were highly condensed. Labeled supercoils, formed by a discrete approximately 250-nm-wide fiber, were observed in oblique thin sections through the center of the domain. The structural data were consistent with negligible transcriptional activity detected for this locus, as well as the predicted conformation of constitutive heterochromatin. Interestingly, in transgenic but not control mice, a substantial number of large neurons, including approximately 30% of cerebellar Purkinje cells, showed excessive invaginations of the nuclear membrane.
TL;DR: From the beginning of sperm head decondensation to early pronuclear stages, the hybridization signal of a probe targeted to the satellite III heterochromatin of chromosome 1 appeared as an irregularly shaped domain.
Abstract: After fusion with an egg, the haploid genome of a mammalian sperm expands from a volume of a few cubic microns to a volume of several thousand cubic microns in a fully developed zygote pronucleus. Using fluorescent in situ hybridization we studied two aspects of the chromatin organization of the sperm-derived genome during this process in a model system involving fusion of human sperm with hamster eggs. We found that (a) from the beginning of sperm head decondensation to early pronuclear stages, the hybridization signal of a probe targeted to the satellite III heterochromatin of chromosome 1 appeared as an irregularly shaped domain. In fully developed pronuclei, the signal became a fiber as much as 20-fold more extended compared with interphase somatic nuclei. The signal appeared as a string of non-uniformly distributed "beads" with interspersed gaps. A similar spatial distribution and appearance recurred after the first cleavage division. (b) Male- and female-derived genomes assembled non-randomly on the first mitotic spindle, and continued to be sequestered from each other in the nuclei of two-cell stages.
TL;DR: The karyotype variation detected in this study suggests that several chromosomal changes took place during the evolution of the Belostomatidae, involving C-positive heterochromatin as well as C-negative chromatin, and it is suggested that a telomeric pattern of heterochROMatin distribution is a common feature of heteropteran chromosomes, andIt is probably related to their holokinetic nature.
Abstract: The chromosome complement of Belostoma bifoveolatum, B. dentatum, B. elegans, and B. martini were analyzed by C-banding and DNA content. The four species share a similar karyotype with 26 + X1X2Y chromosomes (♂) and an equilocal distribution of C-bands at telomeric regions. The relative amount of C-banded material varies between 24 % in B. martini to approximately 59 % in the other three species. The DNA content differs significantly among all of them, and no clear correlation is found between DNA content and C-positive heterochromatin.
The karyotype variation detected in this study suggests that several chromosomal changes took place during the evolution of the Belostomatidae, involving C-positive heterochromatin as well as C-negative chromatin. It is also suggested that a telomeric pattern of heterochromatin distribution is a common feature of heteropteran chromosomes, and it is probably related to their holokinetic nature.
TL;DR: Pronounced differences in C-band pattern between two subspecies with identical basic karyotypes were due to different chromosomal locations of AT-rich and GC-rich heterochromatin, which had an equilocal distribution in the karyotype.
Abstract: C-banding differences within Gibasis karwinskyana (Roem & Schult.) Rohw. were reassessed using dual fluorochrome staining. Pronounced differences in C-band pattern between two subspecies with identical basic karyotypes were due to different chromosomal locations of AT-rich and GC-rich heterochromatin. The AT-rich component had an equilocal distribution in the karyotype and has evidently been accumulated at telomeres, as shown by its prevalence in supernumerary segments and B chromosomes. The GC-rich component also varied in amount, but was limited to nucleolus organizing regions (NORs) and centromeres. Centromeres and telomeres are suggested to constitute separate, although perhaps interdependent, centres of heterochromatin amplification. The possible role of nuclear architecture in determining the accumulation, distribution and spread of these sequences is discussed.