Showing papers on "Heterochromatin published in 1982"
TL;DR: The observed loss of nucleosomal organization in very actively transcribed genes, such as the hsp 70 genes in shocked cells, may be related to the recent finding that ubiquitin conjugates are substrates for the cytoplasmic ATP-dependent proteolytic system.
338 citations
TL;DR: It is suggested that the families of repeats in rye telomeric heterochromatin which are absent from wheat are selected against in the wheat genetic background.
Abstract: The relationship between the chromosomal location of heterochromatin C-bands and of four non-homologous repeated sequence families constituting 8 to 12% of total rye DNA has been investigated in chromosomes of rye (Secale cereale) by in situ hybridisation. Three rye varieties, a set of rye disomic additions to wheat and a triticale were studied. Only centromeric and nucleolar organizer region (NOR) associated C-bands failed to display hybridisation to at least one of the sequences and many telomeric blocks of heterochromatin contained all four repeated sequence families. Both between-variety differences in the chromosomal distribution of repeated sequences, and intravarietal heterozygosities were frequently noted and are probably widespread. — Previously reported deletions of heterochromatin from King II rye chromosomes added to the Holdfast wheat complement were correlated with deletions of some, but not all, of the highly repeated sequence families. A previously unreported loss of some families from King II rye chromosome 4R/7R in a Holdfast wheat genetic background was detected. This loss was not associated with complete deletion of a C-band. A deletion has also probably occurred from the short arm telomere of 4R/7R in the triticale variety Rosner. It is suggested that the families of repeats in rye telomeric heterochromatin which are absent from wheat are selected against in the wheat genetic background.
115 citations
TL;DR: Heterochromatin has also been characterized by the AT-specific fluorochromes quinacrine (Q) and DAPI and the GC-specific agent chromomycin A3 (CMA3), in combination with two counterstaining techniques.
Abstract: Satellite DNAs have been isolated from the monocotyledonous plants Scilla siberica, S. amoena, S. ingridae (all are highly GC-rich), and S. mischtschenkoana by using the Ag+ −Cs2SO4 density centrifugation technique. Hybridization in situ has been performed with 3H-cRNA to these satellite DNAs in all four species. In each species, the endogenous satellite DNA is located mainly in intercalary and major heterochromatin bands associated with terminal regions and nucleolar organizer regions (NORs) but not in centromeric regions. Patterns observed after cross-species hybridization show a high degree of satellite DNA homology between S. siberica, S. amoena, and S. ingridae. By contrast, satellite DNA of S. mischtschenkoana consists largely of different, non homologous DNA sequences, with two exceptions: (i) the NORs of all four species contain similar satellite sequences, and (ii) a strong homology exists between the satellite DNA of S. mischtschenkoana and centromeric DNA of S. siberica but not with those of S. amoena and S. ingridae. — Heterochromatin has also been characterized by the AT-specific fluorochromes quinacrine (Q) and DAPI and the GC-specific agent chromomycin A3 (CMA3), in combination with two counterstaining techniques. While CMA3-fluorescence is largely in agreement with data on base composition and location of the specific satellite DNAs, the results with Q and DAPI are conflicting. Prolonged fixation has been found to change the fluorescence character in certain instances, indicating that other factors than the base sequence of the DNA also play a role in fluorochrome staining of chromosomes. The results are discussed in relation to the taxonomy and phylogeny of the four species.
113 citations
TL;DR: It is found that D1 preferentially binds to A + T-rich double-stranded DNA in vitro, and it is apparently the only abundant nuclear protein in cultured D. melanogaster cells that possesses this property.
Abstract: Our previous work [Levinger, L. & Varshavsky, A. (1982) Cell 28, 375-385] has shown that D1, a 50-kilodalton chromosomal protein of Drosophila melanogaster, is specifically associated with isolated nucleosomes that contain a complex A + T-rich satellite DNA with buoyant density of 1.688 g/ml. We show here that D1 is also a component of nucleosomes containing a simple-sequence, pure A + T satellite DNA, buoyant density 1.672 g/ml. Furthermore, using a modification of a protein blotting technique in which proteins are not exposed to dodecyl sulfate denaturation, we have found that D1 preferentially binds to A + T-rich double-stranded DNA in vitro, and it is apparently the only abundant nuclear protein in cultured D. melanogaster cells that possesses this property. Synthetic poly[d(A-T)].poly[d(A-T)] and poly(dA).poly(dT) duplexes effectively compete in vitro with A + T-rich D. melanogaster satellite DNAs for binding to D1, whereas total Escherichia coli DNA is an extremely poor competitor. These findings strongly suggest that D1 is a specific component of A + T-rich, tandemly repeated, heterochromatic regions, which constitute up to 15-20% of the total D. melanogaster genome. Possible functions of D1 protein include compaction of A + T-rich heterochromatin and participation in microtubule-centromere interactions in mitosis. In addition, D1 may prevent nonspecific binding to A + T-rich satellite DNA of other nuclear proteins that have a preference for AT-DNA, such as RNA polymerase or regulatory proteins, and may also participate in the higher-order chromatin organization outside tandemly repetitive regions by binding to nonrandomly positioned stretches of A + T-rich DNA.
101 citations
TL;DR: The structure, copy number and chromosomal location of arrays of four families of highly repeated sequences have been investigated in representative species of the genus Secale.
Abstract: The structure, copy number and chromosomal location of arrays of four families of highly repeated sequences have been investigated in representative species of the genus Secale. The four unrelated families, previously characterised in Secale cereale, have repeating units of 480, 610, 630 and 120 base pairs respectively. The following general conclusions can be drawn in addition to detailed knowledge of the sequence content of heterochromatin in each accession studied: (1) Every species is unique in its complement or chromosomal distribution or both of the four highly repeated sequence families. S. montanum and S. cereale accessions studied here show the same complement of repeated sequences, but they differ substantially in the amounts they contain of the 610 and 630 base pair (bp) families, and in the distribution over the chromosomes of the 480 bp family. The structure of the repeating unit is also different in many members of the 480 bp family in S. montanum. — (2) The substantial differences between species in the amounts of the most highly repeated DNA sequences exist in the absence of any such conspicuous differences in most other repeated sequences which were detected as fluorescent bands after restriction enzyme digestion and gel electrophoresis. — (3) Each of the different highly repeated families can exist independently of the other families, though all the families have telomeric sites. Also, in the outbreeding species, heteromorphisms are frequent, and are particularly conspicuous in hybridisation detecting the 480 bp sequence family. — (4) The association of the highly repeated sequences with heterochromatin, discussed in the accompanying paper is generally true for other species in the genus, and the lower amounts of heterochromatin in other Secale species compared to S. cereale are associated with lower amounts of specific families of highly repeated DNA sequences. — (5) Analysis of highly repeated sequence families is likely to provide an easy method of identification of new accessions of Secale.
99 citations
TL;DR: A basic dichotomy exists in the amount and chromosomal position of constitutive heterochromatin (C-bands) in species of pocket gophers, genus Thomomys, and the implications of these data for current ideas on the function of heterochromeatin are discussed.
Abstract: A basic dichotomy exists in the amount and chromosomal position of constitutive heterochromatin (C-bands) in species of pocket gophers, genus Thomomys. Members of the "talpoides-group" of species (e.g., T. talpoides and T. monticola) have C-bands restricted to the centromeric regions. These taxa are characterized by Robertsonian patterns of karyotypic evolution. In contrast, species within the "bottae-group" are characterized by extensive amounts of heterochromatin, placed as whole-arm and apparent whole-chromosome (T. bottae) or as large interstitial blocks (T. umbrinus). These species are characterized by extensive non-Robertsonian variation in karyotype, variation which may be expressed from local population polymorphism to between population or species polytypy. Within T. bottae, the number of whole-arm heterochromatic autosomes is inversely proportional to the number of uniarmed chromosomes in the complement, which ranges from 0 to 36 across the species populations. In all-biarmed karyotypic populations, upward to 60 percent of the linear length of the genome is composed of heterochromatin. Populations with extensive heterochromatin variation and those with similar amounts meet and hybridize freely in nature. The implications of these date for current ideas on the function of heterochromatin, particularly as related to speciation models, are discussed.
76 citations
TL;DR: The analysis of the rDNA region provided evidence for rapid “fixation” of new repeated sequences at two levels, namely, among the 130 bp repeated sequences of the spacer and at the level of the repeated arrays of the 9 kb rDNA units.
Abstract: The nature of genome change during polyploid evolution was studied by analysing selected species within the tribe Triticeae. The levels of genome changes examined included structural alterations (translocations, inversions), heterochromatinization, and nucleotide sequence change in the rDNA regions. These analyses provided data for evaluating models of genome evolution in polyploids in the genus Triticum, postulated on the basis of chromosome pairing at metaphase I in interspecies hybrids. The significance of structural chromosome alterations with respect to reduced MI chromosome pairing in interspecific hybrids was assayed by determining the incidence of heterozygosity for translocations and paracentric inversions in the A and B genomes of T. timopheevii ssp. araraticum (referred to as T. araraticum) represented by two lines, 1760 and 2541, and T. aestivum cv. Chinese Spring. Line 1760 differed from Chinese Spring by translocations in chromosomes 1A, 3A, 4A, 6A, 7A, 3B, 4B, 7B and possibly 2B. Line 2541 differed from Chinese Spring by translocations in chromosomes 3A, 6A, 6B and possibly 2B. Line 1760 also differed from Chinese Spring by paracentric inversions in arms 1AL and 4AL whereas line 2541 differed by inversions in 1BL and 4AL (not all chromosomes arms were assayed). The incidence of structural changes in the A and B genomes did not coincide with the more extensive differentiation of the B genomes relative to the A genomes as reflected by chromosome pairing studies. To assay changing degrees of heterochromatinization among species of the genus Triticum, all the diploid and polyploid species were C-banded. No general agreement was observed between the amount of heterochromatin and the ability of the respective chromosomes to pair with chromosomes of the ancestral species. Marked changes in the amount of heterochromatin were found to have occurred during the evolution of some of the polyploids. The analysis of the rDNA region provided evidence for rapid “fixation” of new repeated sequences at two levels, namely, among the 130 bp repeated sequences of the spacer and at the level of the repeated arrays of the 9 kb rDNA units. These occurred both within a given rDNA region and between rDNA regions on nonhomologous chromosomes. The levels of change in the rDNA regions provided good precedent for expecting extensive nucleotide sequence changes associated with differentiation of Triticum genomes and these processes are argued to be the principal cause of genome differentiation as revealed by chromosome pairing studies.
75 citations
TL;DR: The localisation of specific repeated DNA sequences within Xh and the employment of this sequence map in constructing new chromosomes to analyse the nature of the heterochromatin surrounding the rDNA region are presented.
Abstract: In Drosophila melanogaster X chromosome heterochromatin (Xh) constitutes the proximal 40% of the X chromosome DNA and contains a number of genetic elements with homologous sites on the Y chromosome, one of which is well defined, namely, the bobbed locus, the repetitive structural locus for the 18S and 28S rRNAs. This report presents the localisation of specific repeated DNA sequences within Xh and the employment of this sequence map in constructing new chromosomes to analyse the nature of the heterochromatin surrounding the rDNA region. Repeated sequences were located relative to inversion breakpoints which differentiate Xh cytogenetically. When the rDNA region was manipulated to be in a position in the chromosome so that it was without the Xh which normally surrounds it, the following observations were made. (i) The rDNA region of Xh is intrinsically heterochromatic, remaining genetically active and yet possessing major heterochromatic properties even in the absence of the flanking heterochromatin regions. (ii) The size of the deletion removing the portion of Xh normally located distal to the rDNA region affected the dominance relationship between the X and Y nucleolar organizers (activity/endoreduplication assayed in male salivary glands). The X rDNA without any flanking heterochromatin was dominant over Y rDNA while the presence of some Xh allowed both the X and Y rDNA to be utilized. (iii) Enhancement of the position effect variegation on the white locus was demonstrated to occur as a result of the Xh deletions generated. EMS mutagenesis studies argue that the regions of Xh flanking the rDNA region contain no vital loci despite the fact that they strongly effect gene expression in some genotypes. This is consistent with early studies using X-ray mutagenesis (Lindsley et al., 1960). The pleiotropic effects of deleting specific regions of Xh is discussed in relation to the possible influence of heterochromatin on the organisation of the functional interphase nucleus.
67 citations
TL;DR: In situ hybridisation of the two sequences to chromosomes of the related species, Secale cereale and Hordeum vulgare showed a similar correlation between the location of highly repetitive sequences and heterochromatin.
Abstract: Two highly repetitive DNA sequences from Triticum aestivum were isolated and purified by molecular cloning. In situ hybridisation of these sequences to wheat chromosomes showed the sequence to be located predominantly at specific sites in the B genome and also chromosome 4A. Individual chromosomes could be identified by their patterns of labelling. Although one sequence was found to be mostly located close to centromeres and interstitially, and the other sequence mostly at telomeres, there was a good correlation between the distribution of these sequences and the distribution of heterochromatin as revealed by C-banding. In situ hybridisation of the two sequences to chromosomes of the related species, Secale cereale and Hordeum vulgare showed a similar correlation between the location of highly repetitive sequences and heterochromatin.
64 citations
TL;DR: The notion of a basic rodent genome of defined size to which various amounts of heterochromatin have been added is untenable and this relationship is not exact and does not hold true for individual genera.
Abstract: Nuclear DNA amounts are determined in 16 species and the C-banding patterns for 19 species of rodents. A list of rodent DNA amounts is compiled. The fraction of heterochromatin in the genome is determined as the length of C-banded chromosome material relative to the total karyotype length. Among all rodents, heterochromatin amounts tend to be larger in the larger genomes. However, this relationship is not exact and does not hold true for individual genera. In general the notion of a basic rodent genome of defined size to which various amounts of heterochromatin have been added is untenable.
53 citations
TL;DR: It is demonstrated that the rRNA coding region contributes to X / Y pairing, however, no single region of Xh is required for fidelity of male meiotic pairing of the sex chromosomes.
Abstract: The proximal breakpoints of the inversion chromosomes In ( 1 )ω m 4 and In ( 1 ) m 51 b were shown, by in situ hybridization, to define the boundaries of the ribosomal DNA region located within the X chromosome heterochromatin ( Xh ). We estimate that at least 95% of the rDNA is located between the In ( 1 )ω m 4 and In ( 1 )ω m 51 b proximal breakpoints. In contrast only 60–70% of the Type I intervening sequences located in Xh are located between these breakpoints. The Type I intervening sequences in the rDNA region occur as inserts in the 28S rRNA sequences while the remainder of the sequences are distal to the In ( 1 )ω m 4 breakpoint and not associated with rRNA genes. The regions of Xh which contain rDNA and Type I intervening sequences were related to regions shown by Cooper (1964) to contribute to meiotic pairing between the X and Y chromosomes in male Drosophila. We demonstrate that the rRNA coding region contributes to X / Y pairing. However, no single region of Xh is required for fidelity of male meiotic pairing of the sex chromosomes.
TL;DR: Detailed studies of the chromosomes of the three Austrian species of the genusCephalanthera showed them all to have basically similar karyotypes, and possible pathways of karyotype evolution involving polyploidy and Robertsonian events are discussed.
Abstract: Detailed studies of the chromosomes of the three Austrian species of the genusCephalanthera showed them all to have basically similar karyotypes. BothC. damasonium (2n = 36) andC. longifolia (2n = 32) have three large and several classes of smaller chromosome pairs. The karyotype ofC. rubra (2n = 44) is composed of four large and several groups of smaller pairs. The heterochromatin in these species amounts to about 10% of total karyotype length. All the chromosomes have Giemsa-positive centromeres, but only a few have intercalary or terminal bands. Using differential fluorescent staining with DAPI/actinomycin D, quinacrine/actinomycin D (both A-T specific), and chromomycin A3/distamycin A (G-C specific) three different types of major heterochromatic bands can be characterized in respect of their satellite DNA composition: highly A-T rich, slightly A-T rich, and very G-C rich. The chromosomes ofC. longifolia contain more A-T rich C-bands than those ofC. damasonium, while the latter's have more G-C rich heterochromatin. In both species several C-bands appear as secondary constrictions or gaps in the Feulgen-stained chromosomes, but most likely, in each species there is only one pair of chromosomes where the secondary constrictions function as nucleolus organizing regions. No major intraspecific variation could be observed except on one small chromosome pair ofC. longifolia which had a heteromorphic C-band in most individuals. Possible pathways of karyotype evolution involving polyploidy and Robertsonian events are discussed.
TL;DR: Observations indicate that nonproximal heterochromatin does not exert control over the sequence in which the centromeres in the genome separate and appears that qualitative differences among various types of constitutive heterochromeatin are as important as quantitative differences in controlling the separation of centromres.
Abstract: The late metaphase-early anaphase cells from various tissues of male Mus musculus, M. poschiavinus, M. spretus, M. castaneus, female and male Bos taurus (cattle) and female Myopus schisticolor (wood lemming) were analyzed for centromeres that showed separation into two daughter centromeres and those that did not show such separation. In all strains and species of mouse the Y chromosome is the first one to separate, as is the X or Y in the cattle. These sex chromosomes are devoid of constitutive heterochromatin, whereas all autosomes in these species carry detectable quantities. In cattle, the late replicating X chromosome appears to separate later than the active X. In the wood lemming the three pairs of autosomes with the least amount of centromeric constitutive heterochromatin separate first. These are followed by the separation of seven pairs of autosomes carrying medium amounts of constitutive heterochromatin. Five pairs of autosomes with the largest amounts of constitutive heterochromatin are the last in the sequence of separation. The sex chromosomes with medium amounts of constitutive heterochromatin around the centromere, and a very large amount of distal heterochromatin, separate among the very late ones but are not the last. These observations assign a specific role to centromeric constitutive heterochromatin and also indicate that nonproximal heterochromatin does not exert control over the sequence in which the centromeres in the genome separate. It appears that qualitative differences among various types of constitutive heterochromatin are as important as quantitative differences in controlling the separation of centromeres.
TL;DR: The sex chromosomes of 11 species of Gerbillidae are reported and a very complex evolution of the X chromosome and, to a lesser degree, of the Y chromosome was observed, including several inversions, translocations with autosomes, and an increase in heterochromatin.
Abstract: The sex chromosomes of 11 species of Gerbillidae (Meriones tristrami, M. crassus, M. libycus, M. persicus, M. unguiculatus, Gerbillus hesperinus, G. nigeriae, G. gerbillus, G. campestris, Gerbillurus tytonis, and Taterillus gracilis) are reported. A very complex evolution of the X chromosome and, to a lesser degree, of the Y chromosome was observed, including several inversions, translocations with autosomes, and an increase in heterochromatin. The role of constitutive heterochromatin, isolating autosome and gonosome segments in translocations (thus preventing any position effect), is discussed. The sequence of rearrangements affecting the sex chromosomes is considered with a view toward establishing the phylogenetic relationship of the species studied. The tendency to accumulate the same rate type of rearrangement, namely, gonosome-autosome translocations, is another demonstration that chromosomal evolution is not random in a given group of species.
TL;DR: The effects of eight recombination-defective meiotic mutants on crossing over within the X heterochromatin were examined and a minor component of the effects of mei-218 is the production of nonhomologous exchanges.
Abstract: The effects of eight recombination-defective meiotic mutants on crossing over within the X heterochromatin were examined. Since none permit substantial frequencies of exchange within heterochromatin although six lessen or abolish constraints on the location of exchanges within euchromatin, the systems that prohibit exchange within heterochromatin and that govern where exchanges will occur in euchromatin are under separate genetic control.—A minor component of the effects of mei-218 is the production of nonhomologous exchanges; of mei-9 is the recovery of deleted chromatids; and of mei-41 is the recovery of deleted chromatids and/or a low frequency of heterochromatic exchanges.
TL;DR: The endemic Australian grasshopper Heteropternis obscurella shows considerable variation in respect of both chromosome structure and chromosome behaviour, and structural differences depend upon different patterns of heterochromatin distribution as revealed by C-banding.
Abstract: The endemic Australian grasshopper Heteropternis obscurella shows considerable variation in respect of both chromosome structure and chromosome behaviour. The structural differences depend upon different patterns of heterochromatin distribution as revealed by C-banding. These involve differences between populations in respect of polytypic variation in the size of paracentromeric C-bands and differences within populations in respect of polymorphisms both for terminal blocks of heterochromatin in autosomes 3 to 8 and a large proximal block of heterochromatin in autosome 7. The behavioural differences stem in part from genotypically determined variation in the chiasma distribution pattern which is markedly localised in a majority of populations but more randomly distributed in populations from the south of Western Australia. Behavioural differences also arise as secondary consequences of the presence of those heterochromatic blocks which occur as polymorphisms. The distal blocks on autosomes 5, 6, 7 and 8 lead to a redistribution of chiasmata to more proximal sites while the proximal block on 7 leads to the virtual abolition of chiasma formation in that bivalent and its replacement by a non-chiasmate mechanism of segregation. This depends upon a persistent proximal heterochromatic association between the pairing partners. The presence of distal C-blocks on bivalents 3 to 8 gives rise to persistent pseudomultiples, formed as a result of heterochromatic associations between these blocks. Such pseudomultiples involve any two or three of these six bivalents, provided they carry distal blocks, and their frequency rises dramatically in the presence of the proximal heterochromatic block on chromosome 7.
TL;DR: A number of triticales were examined for the occurrence of modified rye chromosomes using the in situ hybridization technique and it was established that the rye chromosome 2R had been replaced by the wheat chromosome 2D.
Abstract: Although Giemsa C-banding techniques have been used extensively for assaying cereal heterochromatin, a more specific technique for analyzing cereal heterochromatin has been developed recently with the isolation of DNA sequences present in heterochromatin and their employment in in situ hybridization to cereal chromosomes. A number of triticales were examined for the occurrence of modified rye chromosomes using the in situ hybridization technique. With a heterogeneous sequence probe the amount of rye heterochromatin appears to be relatively constant in wheat backgrounds but when a specific sequence probe was employed variation was observed. Whether this variation reflects polymorphism in rye or whether it is a result of adaption of the rye genome to coexistence with the wheat genome in triticales is discussed. — The triticale Rosner was examined in detail and it was established that the rye chromosome 2R had been replaced by the wheat chromosome 2D.
01 Jan 1982
TL;DR: It will be shown that condensed chromatin at the quinternary level is species-specific in plants and probably insects, while it is tissue- specific in vertebrates, and the degree of condensation considerably varies during the cell cycle.
Abstract: The main point of this essay will be the question, how condensed chromatin can be interpreted in terms of its molecular determinants and its functional significance, in different taxa. I shall not discuss the lower levels of DNA packaging up to the quaternary structure (or solenoid) in details, as this was recently done by several authors (1–5). It will be shown that condensed chromatin at the quinternary level is species-specific in plants and probably insects, while it is tissue-specific in vertebrates. In all cases, the degree of condensation considerably varies during the cell cycle. The evolution of condensed chromatin including heterochromatin will be discussed. Its possible role in the control of gene activity, determination, differentiation, and morphogenesis is suggested and illustrated by hiterto unpublished quantitative data.
TL;DR: The influence of telomeric heterochromatin blocks on early embryo and endosperm development, and on various agronomic parameters seen at maturity, was investigated using triticales.
Abstract: The influence of telomeric heterochromatin blocks on early embryo and endosperm development, and on various agronomic parameters seen at maturity, was investigated using triticales (× Triticosecale Wittmack) isogenic for the presence or absence of the heterochromatin blocks on rye (Secale cereale L.) chromosomes 6R and 7R/4R. Absence of the telomeric heterochromatin blocks from the long arm of rye chromosome pair 7R/4R in DRIRA, and from the short arm of rye chromosome pair 6R in Rosner was significantly related with a lower production of aberrant endosperm nuclei and an increased kernel weight. The loss of the heterochromatin block on rye chromosome pair 7R/4R in DRIRA resulted in a significant yield increase, while there was no increase in yield when the heterochromatin block was missing from rye chromosome pair 6R in Rosner. The lack of yield increase in Rosner was apparently due to a significant decrease in fertility when the heterochromatin block on 6R was lost. The loss of the heterochromatin block ...
TL;DR: The data suggest that the causes of lethality are intolerable levels of cell death produced by high frequencies of chromosome aberrations and a synergistic interaction suggests there is a class of lesions that can be repaired by both mus-105(+) and mus-109(+).
Abstract: Two mutagen-sensitive loci of Drosophila melanogaster, mus-105 and mus-109, previously identified by viable alleles, are shown to specify essential functions. Lethal alleles at the loci produce larvae that have degenerate imaginal discs and die at the larva-pupa boundary. Our data suggest that the causes of lethality are intolerable levels of cell death produced by high frequencies of chromosome aberrations (in excess of 0.5 aberration per cell per cycle). The pattern of aberrations is a locus-specific character. In mus-105 mutants the most common aberrations are breaks and exchanges in euchromatic portions of the genome whereas in mus-109 mutants the most common aberrations are breaks at heterochromatin-euchromatin junctions. The sensitivity of these junctions to breakage in mus-109 mutants is a property of all such junctions whether natural or produced by a rearrangement that juxtaposes heterochromatin and euchromatin. Larvae carrying the combination of two viable mutants, mus-105A1 mus-109D1, die at the larva-pupa boundary and display a high frequency of aberrations (0.7 per cell vs. 0.075 for either mutant alone) clustered at euchromatin-heterochromatin junctions. This synergistic interaction suggests there is a class of lesions that can be repaired by both mus-105+ and mus-109+. Thus, the apparent euchromatic specificity of mus-105+, which was inferred from the pattern of predominantly euchromatic breakage observed in mus-105 mus-109+ flies, is in fact generated by the wild-type function of mus-109+ masking an effect of mus-105 in the heterochromatin. The fact that lethal mutants at the mus-105 and mus-109 loci have small imaginal discs coupled with the observation of a maternal effect of mus-105 suggests a paradigm for the control of cell division during the life cycle of Drosophila.
TL;DR: Heterochromatin distribution and differentiation in metaphase chromosomes of two morphologically identical Drosophila races, D. nasuta nasuta and D. n.
Abstract: Heterochromatin distribution and differentiation in metaphase chromosomes of two morphologically identical Drosophila races, D nasuta nasuta and D n albomicana, have been studied by C- and N-banding methods -- The total heterochromatin values differ only slightly between these races However, homologous chromosomes of the two Drosophila forms show striking differences in the size of heterochromatin regions and there is an alternating pattern in D n nasuta and D n albomicana of chromosomes which contain more, or respectively less heterochromatin than their counterparts in the other race -- Three different N-banding patterns could be obtained depending on the conditions of the method employed: One banding pattern occurs which corresponds to the C-banding pattern Another pattern is the reverse of the C-band pattern; the euchromatic chromosome regions and the centromeres are stained whereas the pericentric heterochromatin regions remain unstained In the Y chromosomes of both races and in chromosome 4 of D n albomicana, however, the heterochromatin is further differentiated In the third N-banding pattern only the centromeres are deeply stained Furthermore, between the races, subtle staining differences in the pericentric heterochromatin regions can be observed as verified in F1 hybrids On the basis of C- and N-banding results specific aspects of chromosomal differences between D n nasuta and D n albomicana are discussed
TL;DR: In order to elucidate some of the factors influencing the attachment of chromosomes to spindles, an analysis was made of the displacement of chromosomes from the metaphase plate in preparations that received no colchicine or hypotonic treatment.
Abstract: In order to elucidate some of the factors influencing the attachment of chromosomes to spindles, an analysis was made of the displacement of chromosomes from the metaphase plate in preparations that received no colchicine or hypotonic treatment. Displaced chromosomes were identified by Giemsa banding. Three hypotheses were tested and led to the following conclusions: (1) Chromosomal displacement is a function of size—smaller chromosomes are displaced more often than larger ones. (2) The position of the centromere does not influence chromosome displacement. (3) The amount of centromeric heterochromatin in the chromosome has a highly significant effect on displacement—chromosomes with more heterochromatin are displaced more often than those with less.
TL;DR: The Australian rodent, Uromys caudimaculatus, consists of two chromosome races, and despite the extensive differences between the races in the amount and organization of constitutive heterochromatin, hybrids show no abnormalities at meiosis and they are fully fertile.
Abstract: The Australian rodent, Uromys caudimaculatus, consists of two chromosome races, a) The Southern Race is characterized by the possession of two to twelve B-chromosomes. These vary considerably in size, morphology, and C- and G-banding characteristics, they behave as univalent at meiosis and are inherited in a random manner, b) The Northern Race lacks Bchromosomes, but possesses large blocks of distal C-positive heterochromatin on between 18 and 28 of the 46 chromosomes. The C-blocks may be entirely G-positive, entirely G-negative, or G-banded, suggesting heterogeneity within the C-blocks. There is extensive variation both between and within populations of the northern race in the number and size of the distal heterochromatic blocks. There is no apparent difference between the races in chiasma frequency. The northern race does have a much higher proportion of interstitial versus distal chiasmata, although it is probable that this is merely a reflection of lack of crossing over in the heterochromatic blocks rather than an actual shift of chiasma localisation within the euchromatin. Despite the extensive differences between the races in the amount and organization of constitutive heterochromatin, hybrids show no abnormalities at meiosis and they are fully fertile.
TL;DR: In this article, the authors examined the meiotic segregation of compound second autosomes sharing varying extents of heterochromatic and euchromatic homology during spermatogenesis.
Abstract: In this report we examine the meiotic segregation of compound second autosomes sharing varying extents of heterochromatic and euchromatic homology. The second chromosome heterochromatin does not appear to influence the random meiotic segregation of compound second autosomes during spermatogenesis; however, the proximal euchromatin is implicated in male meiotic pairing. We conclude that male autosomal meiotic pairing sites are specific euchromatic chromosomal regions.
TL;DR: The position of heterochromatic regions in interphase nuclei is correlated with their respective position in metaphase chromosomes and hence, independent of sequence recognition, and chromocentral associations of X-, Y- or autosomal-basedheterochromatin are not formed in these cells.
Abstract: Localization, as detected by in situ hybridization, of major heterochromatic blocks in interphase nuclei of larval brain and imaginal discs is reported. We conclude that the position of heterochromatic regions in interphase nuclei is correlated with their respective position in metaphase chromosomes and hence, independent of sequence recognition. Furthermore, chromocentral associations of X-, Y- or autosomal-based heterochromatin are not formed in these cells. Homologues do align in close proximity, but heterochromatin plays no role in this arrangement. Heterochromatin, and probably nucleoli, establish their membrane links in situ, and have no prefixed recognition sites. The most intimate association between homologous repetitive sequences was found in the histone locus, but no tendency for clustering was found among loci of multisite euchromatic gene families.
TL;DR: The meiotic behaviour of rye chromosomes 1R, 2R, 3R, 6R and 7R/4R of hexaploid triticale ‘Cachirulo’ is analyzed using the C-banding technique and a decreasing effect of large telomeric heterochromatin bands on pairing is deduced.
Abstract: The meiotic behaviour of rye chromosomes 1R, 2R, 3R, 6R and 7R/4R of hexaploid triticale ‘Cachirulo’ is analyzed using the C-banding technique. These chromosomes show different C-banding patterns and present different pairing levels at metaphase I. A decreasing effect of large telomeric heterochromatin bands on pairing is deduced from the following two main facts: i) The chromosome 7R/4R shows the highest pairing associated with the smallest amount of heterochromatin, ii) pairing levels of 2 R short arm and 3 R long arm which carry large telomeric bands are less than their respective long and short arms lacking telomeric heterochromatin. Possible desynaptic effects of heterochromatin are discussed although an asynaptic effect cannot be rejected.
TL;DR: Differences in the size of the constitutive heterochromatic regions were frequently found in many chromosome pairs in animals of different geographic origin, although the possibility that they are maintained as chromosome polymorphisms could not be reled out.
TL;DR: Eight populations of the grasshopper Euchorthippus pulvinatus gallicus have been analyzed by means of C-banding and the possible adaptative role of supernumerary heterochromatin as leading to a redistribution of chiasmata in the heterochROMatin carrier chromosomes is discussed.
Abstract: Eight populations of the grasshopper Euchorthippus pulvinatus gallicus have been analyzed by means of C-banding. Chromosome pairs M6, M7 and S8 show both quantitative and qualitative variation in their C-heterochromatin. There are at least four different types of M6, three of M7 and two of S8. Differences in the frequencies of these chromosome types have been found between populations. Within a given population the frequencies of the different M7 and S8 chromosomes fit a Hardy-Weinberg distribution and they remain constant within and between generations. The possible adaptative role of supernumerary heterochromatin as leading to a redistribution of chiasmata in the heterochromatin carrier chromosomes is discussed.
TL;DR: The results indicate that failure to observe an antigen in condensed regions of chromatin does not necessarily imply its absence, and binding sites for RNA polymerase B and start points for transcriptional activity of the enzyme appear always to be the interband regions.
Abstract: Polytene chromosomes of different chironomids, i.e., Chironomus tentans, C. melanotus and Glyptotendipes barbipes were isolated from salivary glands in a native state. These chromosomes were treated in vitro either mechanically or with different ionic strengths to modify them structurally as to yield different degrees of decondensation of the compact bands. Treated and untreated polytene chromosomes were lightly fixed with formaldehyde and stained by indirect immunofluorescence for RNA polymerase B. The distribution of this enzyme in bands, interbands, puffs and centromeric heterochromatin was scored and compared with that of histone H2B. The results indicate that failure to observe an antigen in condensed regions of chromatin does not necessarily imply its absence. Decondensation of bands, for example, leads to massive uncovering of histone H2B antigen, which appears to be masked in the bands of untreated polytene chromosomes. No evidence, however, of a corresponding unmasking of RNA polymerase B molecules was observed, indicating that few if any enzyme molecules are trapped in bands. Thus binding sites for RNA polymerase B and start points for transcriptional activity of the enzyme appear always to be the interband regions.