Showing papers on "Heterochromatin published in 1980"

Arrangement of chromatin in the nucleus

Abstract: The factors responsible for producing some degree of order to the arrangement of chromatin in the nucleus are reviewed. They are the following: 1. Chromosomes are attached to the nuclear membrane, nucleolus and intranuclear matrix. As a result they have a relatively fixed position in the nucleus. 2. In some species somatic pairing results in alignment of homologs. This is rare in mammals. 3. The association of ribosomal DNA and 5S DNA with the nucleolous results in the close approximation of the chromosomes carrying these DNA sequences. In man and other animals the most obvious consequence is satellite association. 4. Heterochromatin is condensed onto the inner nuclear membrane and periphery of the nucleolous while genetically active chromatin occupies the more central portion of the nucleus. The results is a peripheral location of late replicating DNA and a central location of early relicating DNA. 5. The DNA replication points tend to be associated with the nuclear matrix. Autoradiography of briefly labelled cells shows a high frequency of grains associated with nuclear matrix material. 6. Heterochromatin association results in chromocenters and ectopic pairing. 7. In addition to all these is the Rabl orientation or alignment of centromeres with centromeres and telomeres with telomeres. This polarization of the chromosomes results from the traction on the centromeres by the spindle fibers. There is no firm evidence for any higher degrees of order that might bring specific functioning genes into close proximity.

Chromosome banding in amphibia. IV. Differentiation of GC- and AT-rich chromosome regions in Anura.

Abstract: The chromosomes of 26 species of Anura from variously highly envolved groups were analysed with the fluorescent GC-specific antibiotics mithramycin and chromomycin A3 as well as with the AT-specific quinacrine. The mithramycin- and chromomycin A3-stainings generally resulted in a pattern of the constitutive heterochromatin opposite to the one obtained with quinacrine stain. The weaker a heterochromatic region fluoresces with quinacrine, the stronger is the intensity of the fluorescence achieved with mithramycin and chromomycin A3. Some of the telomeric and interstitial heterochromatic regions, however, exhibit no enhanced fluorescence with any of the fluorochromes. The nucleolar constrictions of the nucleolus organizer regions (NORs) displayed the brightest mithramycin- and chromomycin A3-fluorescence in the karyotypes and interphase nuclei of all species examined. The contrast of the brightly fluorescing GC-rich heterochromatin and of the NORs is considerably enhanced, when the non-fluorescent AT-specific oligopeptide distamycin A is employed as a counterstain. No banding patterns were observed with the fluorochromes in the euchromatic regions of the metaphase chromosomes; this attributed to the strong spiralization of the anuran chromosomes. A cytochemical classification of the various chromatin types in the anuran chromosomes is discussed on the basis of the differential labelings found on the constitutive heterochromatin by means of the fluorochromes.

Chromosomal sites necessary for normal levels of meiotic recombination in drosophila melanogaster. i. evidence for and mapping of the sites

Abstract: Meiotic exchange was measured in females heterozygous for a normal sequence X chromosome and for each of eleven T(1;4)s and each of sixteen T(1;Y)s. The results indicate that the X chromosome can be divided into five intervals, such that heterozygosity for a breakFoint in one interval strongly suppresses exchange within that interval, but has little or no effect on exchange in other intervals. The boundaries between these intervals are identified and mapped to regions 3C4-6/7, 7A-7E, 11Aand proximal to 18Con the standard salivary map; each boundary is located at (or within a small region containing) a major constriction (i.e., a block of intercalary heterochromatin) .αExchange was examined in females heterozygous for translocations broken within the constriction at IIA.The results imply that a boundary occupies only a subregion of the entire constriction and issubdivisible by translocation breakpoints. Several other properties of boundaries have been elucidated. Finally, the relationship of these data to a simple model of meiotic pairing proposed by I. SANDLER(1956)and to the role of intercalary heterochromatin in the meiotic process is discussed.

Satellite DNA is transcribed on lampbrush chromosomes

Abstract: During the lampbrush stage of oogenesis there is widespread transcription, and it has been estimated that the total amount of DNA transcribed may be an order of magnitude greater than that required to produce the necessary functional RNA for the oocyte1. We therefore considered it likely that some of the transcribed sequences have little, if any, translational significance, and may include both middle repetitive2 and highly repeated, or satellite, sequences. Satellite DNA is generally defined as rapidly reannealing DNA which has a short basic sequence that is repeated millions of times in the genome, usually in tandem arrays3,4. The short repeated length, coupled with the organisation of satellite sequences in high order molecular weight tandem arrays in heterochromatic regions, have been put forward as reasons for supposing that this type of DNA is not normally transcribed5. We report here that we have looked for and found evidence of transcription of satellite DNA on lampbrush loops in oocytes of the crested newt, Triturus cristatus carnifex.

r- and K-tactics in the evolution of protist developmental systems: cell and genome size, phenotype diversifying selection, and cell cycle patterns.

Abstract: I outline the significance for protist evolution of the r-, K-selection spectrum,, and of my earlier theory that the most fundamental way organisms adapt to this spectrum is by evolutionary variations in their cell volumes, cell growth rates and genome sizes. Then I introduce the concept of phenotype diversifying selection; this refers to those selective forces which favour an increase in the number of phenotypes produced during a single life cycle by an organism's genotype and epigenetic system. These ideas are then used to discuss the evolution of protist development, with special reference to modifications of the cell cycle whose evolutionary causes and consequences can be related to K-selection for large size and r-selection for rapid reproduction. The significance of multiple fission, syncytia, multicellularity, nuclear dimorphism plus polyploidy, and reversible polyploidy, is treated in detail. Predictions are made of the effects of these different developmental patterns on genome size and the distribution and amounts of nucleoskeletal RNA and heterochromatin. I suggest that heterochromatin exists primarily because of phenotype diversifying selection for differing nuclear volumes. The possibility of applying these ideas to other cell properties like mitotic or cytokinetic mechanisms is also briefly discussed.

Cytological evidence of transcription of highly repeated DNA sequences during the lampbrush stage in Triturus cristatus carnifex.

Abstract: Highly repeated, or satellite, DNA fractions have been isolated from total Triturus cristatus carnifex DNA by renaturation kinetics, caesium salt centrifugation and restriction endonuclease digestion. We have shown by DNA/DNA in situ hybridisation and autoradiography that all of these probes bind to C-band positive regions on mitotic or lampbrush chromosomes of T.c. carnifex. Under conditions of DNA to RNA-transcript in situ hybridisation labelled satellite DNA binds to nascent RNA transcripts that are still associated with the DNA axes of many lampbrush loops. The majority of the loops that label heavily in these experiments are located on the long arms of chromosome I, a region previously shown to be rich in highly repeated DNA and to have many of the properties of heterochromatin. These satellite DNA probes also label many loops on a comparable chromosome region in T. marmoratus, a species closely related to T. cristatus. However, in DNA/RNA-transcript hybrids to other more distantly related species of Triturus, there are no chromosome regions that have the same concentration of labelled loop pairs as the long arms of T.c.carnifex and T. marmoratus, although some loop pairs do label. We have cloned two satellite sequences in pBR322, and have obtained the same results using these pure probes as we obtained using satellite probes isolated by other techniques. These results demonstrate unequivocally that satellite DNA is transcribed on lampbrush chromosomes during oogenesis in crested newts.

Asynchronous replication of heterochromatin in maize.

Abstract: Replication patterns of four classes of heterochromatin in the chromosomes of maize were analyzed. Centromeric heterochromatin, distal heterochromatin of the B chromosomes, and knob heterochromatin all have asynchronous late replication, knob heterochromatin being the last chromosomal DNA to complete replication. Nucleolus organizer heterochromatin replicates during the period of euchromatin DNA replication. The proportion of the S period involved in asynchronous late replication is directly dependent on the amount of heterochromatin in the nucleus. Both additional knob and B-chromosome heterochromatin participate in this effect. Each additional B chromosome produces an increment in the proportion of nuclei with asynchronous replication; in nuclei with 12 B chromosomes, the proportion of the S phase showing asynchronous late replication is more than 3 times greater than that in nuclei without B chromosomes. The data are consistent with the hypothesis that delayed DNA replication of knob heterochromatin is responsible, in some genotypes, for the loss of chromosome segments and for B-chromosome nondisjunction in the second pollen grain mitosis.

Rye chromosome translocations in hexaploid wheat: a re-evaluation of the loss of heterochromatin from rye chromosomes.

Abstract: Using in situ hybridization techniques, we have been able to identify the translocated chromosomes resulting from whole arm interchanges between homoeologous chromosomes of wheat and rye. This was possible because radioactive probes are available which recognize specific sites of highly repeated sequence DNA in either rye or wheat chromosomes. The translocated chromosomes analysed in detail were found in plants from a breeding programme designed to substitute chromosome 2R of rye into commercial wheat cultivars. The distribution of rye highly repeated DNA sequences showed modified chromosomes in which (a) most of the telomeric heterochromatin of the short arm and (b) all of the telomeric heterochromatin of the long arm, had disappeared. Subsequent analyses of these chromosomes assaying for wheat highly repeated DNA sequences showed that in type (a), the entire short arm of 2R had been replaced by the short arm of wheat chromosome 2B and in (b), the long arm of 2R had been replaced by the long arm of 2B. The use of these probes has also allowed us to show that rye heterochromatin has little effect on the pairing of the translocated wheat arm to its wheat homologue during meiosis. We have also characterized the chromosomes resulting from a 1B-1R translocation event. From these results, we suggest that the observed loss of telomeric heterochromatin from rye chromosomes in wheat is commonly due to wheat-rye chromosome translocations.

Interaction between wheat chromosomes and rye telomeric heterochromatin on meiotic pairing of chromosome pair 1R of rye in wheat-rye derivatives.

Abstract: The effect of telomere heterochromatin on metaphase I association of chromosome pair 1R of rye was analyzed in normal diploid plants of rye (2n=14) and in wheat-rye derivatives with the chromosome constitution (0–7)A(0–7)BRR (2n=20, 21 and 22). The C-banding pattern of 1R was variable between plants. In diploid rye the presence or absence of telomeric heterochromatin in 1R does not influence its meiotic pairing. However, in wheat-rye derivatives the presence of telomeric heterochromatin decreases chiasma frequency in the 1R bivalent. This cannot be attributed to interference of heterochromatin with chiasma terminalization. This effect of heterochromatin is most pronounced in heterozygous condition. In plants heterozygous for telomeric C-bands the reduction of pairing is stronger in the short arm than in the long arm of the 1R bivalent.

Two phases of DNA replication in human cells

Abstract: The course of DNA synthesis in the chromosomes was studied in synchronized human lymphocyte cultures, by means of the BrdU-Hoechst-Giemsa method. In comparing replication patterns and G-banding it was found that with regard to banding the process of DNA replication can be divided into two separate phases, an “early replication period” which is characterized by DNA synthesis in R bands of the autosomes and active X chromosome, and a “late replication period” which concerns the G-positive regions of the autosomes and all the bands of the heterochromatic X and Y chromosomes. No overlapping was found between the two phases mentioned. The possible role of regulatory mechanisms was discussed.

Regional assignment of a 2.1-kb repetitive sequence to the distal part of the human Y heterochromatin.

Abstract: Variants in structure and content of the human Y chromosome were investigated by cytogenetic methods and by restriction endonuclease analysis. It is shown that most or all of the 2.1-kb male-specific reiterated sequence is located in the distal part of the brightly fluorescing heterochromatin.

Heterochromatin variation in Cryptobothrus chrysophorus: III. Synthetic hybrids

Abstract: Synthetic F1 hybrids between individuals taken from selected populations of the northern (Glenn Innés, Bolivia Hill) and southern (Forbes Creek, Mount Aggie) chromosome races of the grasshopper Cryptobothrus chrysophorus confirm that these two ‘races’ are indeed distinguished by fixed differences in heterochromatin content. These differences affect five of the six medium sized members of the complement (M 4, 5, 6, 8 and 9). Added to this there is a marked change in the character of the remaining medium pair (M 7) which functions as the megameric in this species. — Meiosis in F1 males is characterised by the presence of univalency in from 22–32% of the meiocytes. This appears to be genotypic in causation and may involve from one to three chromosome pairs in any one cell. Laggards produced from such univalents lead to a failure of anaphase separation at either first or second division or at both of them. Consequently from 17–36% of the sperm produced are giant (diploid or tetraploid) in size. Added to this the medium members commonly form end to end associations involving the heterochromatic (northern race) and euchromatic (southern race) terminii. This is a modified form of the heterochromatic end associations which occur between homologous medium pairs in northern populations. The two small pairs (S10 and 11) show comparable behaviour in both races when they carry terminal heterochromatic supernumerary segments. Such associations persist despite the fact that they are non-chiasmate in character. Moreover, despite the asynapsis found in F1 males they produce F2s when allowed to intersib mate, although many of the embryos fail to develop, presumably as a result of genotypic imbalance, or else are aneuploid in constitution. In the F2s that do survive to maturity the chromosome differences which distinguish the northern and southern forms are recombined to give a wide variety of karyotypes in which the observed pairing is much improved and from which F3s were subsequently obtained.

Cytogenetic analysis of chromosomal translocations in the tomato: preferential breakage in heterochromatin.

Abstract: A tester set of eight translocations has been selected involving all 12 chromosomes of tomato (Lycopersicon esculentum Mill.). Using the entire tester set, seven other translocations were identifie...

Intraspecific polymorphism of sex chromosome heterochromatin in two species of the Anopheles gambiae complex.

Abstract: The Hoechst 33258 banding pattern of the mitotic chromosomes of several laboratory and natural populations of the sibling species A. gambiae and A. arabiensis has been analyzed. A clear intraspecific polymorphism of sex chromosome heterochromatin has been observed. Nevertheless in each species heterochromatic variations fall within a characteristic species-specific pattern. Moreover, while laboratory polulations tend to be monomorphic for a given heterchromatic variant, natural populations exhibit a high degree of intrapopulation polymorphism. The possible role of sex chromosome heterochromatin in controlling fertility and mating behaviour of Anopheles mosquitoes is discussed.

A Study of the Heterochromatin of Asellus Aquaticus (Crust. Isop.)

Abstract: The constitutive heterochromatin of Asellus aquaticus can be differentially stained using the C-banding technique. It is present in the proximity of the NOs and, only rarely, in some of the other t...

Individual variation of centric heterochromatin in man.

Abstract: C-banded chromosome preparations were obtained from cord blood of normal newborns, from venous blood of abnormal newborns, and from both parents of all the babies studied. Heterochromatin and euchromatin length was recorded in five cells per person for chromosomes 1, 9, and 16. 1655 karyotypes from 231 subjects have been studied. Standardised heterochromatin lengths were estimated from the regression of heterochromatin on euchromatin measurements. A maximum likelihood procedure was used to estimate heterochromatin lengths in chromosomes of either maternal or paternal origin and the distributions were compared with those of average absolute differences. An error variance of difference between homologues was derived from measurements of heterochromatin length in cells from carriers of structurally altered chromosomes in which it was possible to identify parental origin.

C‐band polymorphism: Comparison between trisomy 21 cases and mentally retarded controls

Abstract: C-banding was done prospectively on 50 Down syndrome (trisomy 21) cases and 50 mentally retarded controls. Heterochromatin was quantitated by measuring the lengths of heterochromatin blocks and comparing these segments to the length of the short arm of chromosome 16 for 1, 9 and 16 heterochromatin, and to the total length of the Y chromosome for the Y heterochromatin in the distal long arm. For the first 30 individuals in each group, there was no difference in the mean lengths of C-band blocks of the 1, 9, 16 and Y chromosomes. For the total sample, there also was no difference between the trisomy 21 cases and controls in the number or size of pericentric inversions involving the heterochromatin blocks of chromosomes 1 and 9. Assuming random segregation of the parental C-band polymorphisms, this study gives no evidence for an association between such polymorphisms of the 1, 9, 16 and Y chromosomes and nondisjunction of chromosome 21.

Differential staining of late replicating DNA-rich regions in Allium cepa chromosomes.

Abstract: SUMMARYBy using BrdU-dye methodology, the location of late replicating DNA and the degree of coincidence between it and heterochromatic regions (C-bands) have been determined in Allium cepa chromosomes.In this karyotype, heterochromatin replicates late in the S period and there is a considerable amount of late replicating DNA that is not heterochromatic preferentially located in pericentromeric regions. In short, we discuss the detailed morphology and late replication pattern of the onion karyotype.

The C-banding pattern of 6 Japanese species of vespertilionine bats (Mammalia: Chiroptera)

Abstract: The C-banding patterns of 6 species of Japanese vespertilionine bats are presented. The variation in amount and distribution of heterochromatin indicates that deletions and additions of heterochromatin have contributed to the karyotypic diversity in Vespertilioninae.

Telomere and centromere association tendencies in the human male metaphase complement.

Abstract: 'Generalized distances' between centromeres and between telomeres were statistically analyzed (x2 tests) in 100 trypsin-banded metaphase figures derived from normal males. Analysis of association tendencies on the first column of obtained c-c, p-p, q-p, and p-q histograms showed significant heterochromatic attraction not only between nonacrocentrics and acrocentrics but also between 2 nonacrocentric chromosome pairs (1 and 16). However, since not all c-heterochromatin-rich chromosomes were involved in associations (pair 5), and conversely, since chromosomes without an important centrometric heterochromatin block were involved in associations (pairs 8 and 11), it is probable that centromeric heterochromatin is not the only factor responsible for chromosome association. Moreover associations occur not only at the centromeres; in the circle analysis of the binding capacity of the telomeres or centromere of one chromosome pair with the telomeres or the centromeres of all other chromosome pairs, the authors also found preferential associations for T(4,13), T(9,15), T(11,15), T(13,19), T(15,19), T(17,18), T(17,22), and T(19,20). They therefore suggest that heterochromatin is not the only reason for chromosome association and that telomeres may also play an important part in this process.

Quantitative variation of “Mus musculus-like” constitutive heterochromatin and satellite DNA-sequences in the genus Mus

Abstract: The extent of conservation of constitutive heterochromatin in three species of Mus viz. M. musculus, M. booduga and M. dunni, with shared cytological properties and homologous DNA sequences has been studied. The cytological properties were investigated by doing fluorescence staining and condensation inhibition of their chromosomes with Hoechst 33258. Both the parameters indicate the occurrence of a reduced quantum of “M. musculus like heterochromatin” at specific sites in the other two genomes. In situ hybridization of the nick translated 3H-labelled M. musculus satellite DNA with M. booduga and M. dunni chromosomes, also corroborates our Hoechst 33258 findings and comparable variation in the amount and site of occurrence of sequences homologous to M. musculus satellite DNA in these species are noticed. The study thus provides a good example of a gradual quantitative variation of a particular type of heterochromatin and in turn of the repetitive DNA constituting it in different related species. Further since the heterochromatin in M. booduga and M. dunni is expected to contain different repetitive DNA sequences in addition to those homologous to M. musculus satellite DNA, it is proposed that a change in the balance between two or more repetitive sequences in heterochromatin may be more crucial in its evolutionary consequences rather than a mere increase or decrease of a homogeneous repetitive sequence.

Kinetics of DNA replication in the Indian muntjac chromosomes as studied by quantitative autoradiography.

Abstract: DNA replication patterns of individual chromosomes and their various euchromatic and heterochromatic regions were analyzed by means of quantitative autoradiography. The cultured cells of the skin fibroblast of a male Indian muntjac were pulse labeled with 3H-thymidine and chromosome samples were prepared for the next 32 h at 1–2 h intervals. A typical late replication pattern widely observed in heterochromatin was not found in the muntjac chromosomes. The following points make the DNA replication of the muntjac chromosomes characteristics: (1) Heterochromatin replicated its DNA in a shorter period with a higher rate than euchromatin. (2) Two small euchromatic regions adjacent to centromeric heterochromatin behaved differently from other portions of euchromatin, possessing shorter Ts, higher DNA synthetic rates and starting much later and ending earlier their DNA replication. (3) Segmental replication patterns were observed in the chromosomes 2 and 3 during the entire S phase. (4) Both homologues of the chromosome 3 showed a synchronous DNA replication pattern throughout the S phase except in the distal portion of the long arms during the mid-S phase.

A study of spontaneous chromosome variations in seven cell lines derived from Drosophila melanogaster stocks marked by translocations

Abstract: The present work reports the observations on numerical and structural changes in 7 embryonic cell lines, derived from two stocks marked by reciprocal and heterozygous translocations between the Y and chromosome 3 Karyological analyses were carried out by using different techniques, such as Q-, C- banding and autoradiography, capable to define the distribution of heterochromatin and to identify individual chromosomes These procedures, considering also synaptic prophases, provided characteristics for distinguishing each line, besides some very similar features common to all cells Of particular interest was the appearance of various unusual chromosome morphological variants, characterized by centromeric and interstitial or terminal displaced heterochromatic segments, observed never before in Drosophila lines, whereas the original translocation was not found Moreover, cell lines were found which had been exclusively polyploid since their establishment, irrespective of the length of their quiescence period These observations confirm previous findings The probable origin of the marker chromosomes, as well as a possible correlation between the chromosomal constitution of the cultured cells and the original parental karyotype, are discussed

Modification of the DNA content in translocated regions of Drosophila polytene chromosomes.

Abstract: The DNA content of translocated polytene chromosome regions in Drosophila melanogaster is affected by heterochromatic position effect. Microdensitometric studies on w m258-21 translocation heterozygotes showed (Hartmann-Goldstein and Cowell, 1976; Cowell and Hartmann Goldstein, 1980) that band region 3D1-E2, adjacent to the breakpoint, contained less DNA than the homologous non-translocated region whereas the neighbouring 3C1-10 region contained more DNA than its non-translocated counterpart. In the nuclei selected for measurement the translocated X chromosome was morphologically euchromatic, but both regions undergo heterochromatisation in other nuclei within the same salivary gland. To explore the relationship between changes in DNA content and heterochromatisation, the effect on DNA content of two known modifiers of heterochromatisation has now been studied. Larvae cultured at 15° C, which exhibit more heterochromatisation than those grown at 25° C, have the same relative DNA contents as at the higher temperature. The addition of a Y chromosome markedly reduced heterochromatisation; in XXY larvae there was no difference between the DNA contents of translocated and non-translocated 3D1-E2 regions, and in region 3C1-10 the percentage excess of DNA in the translocated homologue was approximately double that found in XX larvae. The relationship between replication behaviour and compaction suggested by these results is discussed.