Amount Of Heterochromatin Research Articles

Centromeric heterochromatin and satellite DNA in the Chironomus plumosus species group

Species of the Chironomus plumosus group display significant differences in their amount of centromeric heterochromatin. A tandem-repetitive satellite-like DNA has been isolated from C. plumosus. This DNA accounts for a major part of the centromeric heterochromatin. The DNA element has a Sau3AI restriction site ("Sau elements") and a monomer length of 165 or 166 bp. It is A-T rich (73%) and reveals a moderate DNA curvature, as shown by gel migration and computer analysis. The chromosomal localization and genomic organization of Sau elements were studied in 24 Chironomus species by in situ hybridization and (or) Southern analysis. The DNA is predominantly located in the centromeric regions of nine species, six from the plumosus group and three others. In some cases, inter- and intra-specific differences in the size of the centromeric heterochromatin seem to correlate with the strength of Sau element hybridization signals. Few species contain Sau repeats outside of the centromeres (C. borokensis, C. plumosus). Additionally, Sau elements are revealed to be present in ectopic threads between centromeres, and in B chromosomes found in C. borokensis and C. annularius.

Characterization of different chromatin types in Mytilus galloprovincialis L. after C-banding, fluorochrome and restriction endonuclease treatments

In this study, we have carried out the cytogenetical characterization of Mytilus galloprovincialis L. (2n = 28) using conventional staining and banding techniques such as fluorochromes and restriction endonucleases treatment. Chromosome digestion with trypsin enzyme resulted in a G-banding pattern which allowed us to clearly identify and classify the chromosome pairs of M. galloprovincialis. C-banding and chromomycin A3 staining confirmed the existence of small amounts of constitutive heterochromatin. The treatment of samples with AluI, HaeIII, DpnI, MspI, HpaII and HinfI restriction endonucleases produced specific banding patterns which demonstrate the potential of endonucleases for chromosome banding in mussels. The results obtained allow us to describe six different types of chromatin in M. galloprovincialis. The type is determined by the response of the chromosomes to the different treatments. Differential digestion by the enzyme pair HpaII-MspI of specific C-band positive heterochromatic areas in some of the chromosomes suggests the presence of methylation.

Stallion karyotype variability and lack of association with abortion: A case reprot

Karyotype analysis was done on a stallion that impregnated 23 mares during the 1991 breeding season, of which 14 aborted between 2 and 4 mo fo gestation. Lymphocytes examined contained a 64,XY complement of normal appearing sex chromosomes and autosomes, except for slight dimorphism of the centric heterochromatin of chromosome No. 1. A skin biopsy was procured form the stallion for karyotype analysis, and the stallion was bred to 11 mares. Three mares were detected pregnant 16, 35, 45 d after breeding. The fetuses were recovered transcervically using curved intestinal forceps 47 (n=2) and 49 (n=1) d after breeding. Fetal tissue was rinsed and packed in culture media, transported overnight in a chilled container, cultured by standard tissue culture techniques, and prepared for karyotype analysis. No abnormalities were found in standard karyotypes from those cultures. One fetal karyotype revealed slight dimorphism of the heterochromatin of chromosome No. 1. Chromosome spreads obtained from the stallion's skin biopsy revealed a normal karyotype with no difference in the amount of heterochromatin present in No. 1 chromosomes. During the 1992 breeding season, the stallion impregnated 23 of 25 mares bred. Only 1 mare aborted, at 8 mo of gestation. Apparently, the amount of heterochromatin of No. 1 horse chromosomes can vary, and caution should be used in diagnosing this as a cause of pregnancy failure.

Evolutionary Changes in Genomic DNA Constituents and the Duration of Cell Cycle in Lathyrus species.

The duration of the complete mitotic cycle and its component phases were compared with the amounts of 2C nuclear DNA, heterochromatin DNA and euchromatin DNA in four Lathyrus species. The total cycle time as a whole was not correlated with the variation in 2C nuclear DNA amount which was two fold between the 4 related species. However, the duration of synthesis phase was positively correlated with the amounts of total DNA and heterochromatin DNA. The results have further shown that a disproportionate increase in the amount of heterochromatin in the genome can increase the total duration of the mitotic cycle as well as the duration of its component phases.

New chromosome arm combination of genusGlyptotendipesKieff. (Diptera, Chironomidae)

SUMMARYGlyptotendipes material was collected form the littoral zone in seven reservoirs distributed in three Spanish watersheds (Tajo, Guadiana and Guadalquivir). By the external larval and pupal morphological analysis the material studied could be referred to either as G. glaucus or as G. gripekoveni. But its cytotaxonomical analysis shows that this is a new species, with 2n = 6 and with a new chromosome arm combination: AB, CD, GEF. The main characters used to differentiate the species Glyptotendipes sp. were chromosome number, amount of heterochromatin at the centromeres, simple homozygous inversions between sections of chromosomes, length of larval antennal blade and morphology of front border of ventromental plates.

Cytotaxonomy and karyotype evolution inPhleum sect.Phleum (Poaceae) in Poland

Three taxa are distinguished in the sectionPhleumGriseb. in Poland:P. nodosum (2n = 14),P. pratense (2n = 42), and the third one unformally named hereP. “commutatum” (2n = 14). It corresponds morphologically toP. commutatumGaud. reported as a tetraploid taxon (2n = 28) from other geographic regions. Giemsa C-banded karyotypes of these three taxa help clarify the taxonomic status ofP. “commutatum” and the origin of the hexaploidP. pratense. It is suggested that changes in the amount of telomeric heterochromatin played an important role in the evolution ofPhleum karyotypes.

Comparison of the Giemsa C-banded karyotypes of the three subspecies ofPsathyrostachys fragilis, subspp.villosus (2x),secaliformis (2x, 4x), andfragilis (2x) (Poaceae), with notes on chromosome pairing

The karyotypes of diploidP. fragilis subsp.villosus (2n = 2x = 14) and tetraploid subsp.secaliformis (2n = 4x = 28) were studied by Giemsa C- and N-banding, and AgNO3 staining and compared with the karyotype of subsp.fragilis (2x). The complements of subsp.villosus and subsp.fragilis were similar, with 8 metacentric and 6 SAT-chromosomes, one metacentric and two submetacentric pairs, with small to minute, polymorphic, heterochromatic satellites. The complement of subsp.secaliformis on the whole agreed with a doubling of the complement of diploidP. fragilis, suggesting autopolyploidy. Only the presence of 12 nucleoli in interphases identified 6 SAT-chromosome pairs. In subsp.villosus one or two extra micronucleoli indicated a chromosome pair with very low nucleolusforming activity, bringing the number of SAT-chromosome pairs to 4. This number may be a characteristc ofPsathyrostachys. Besides very small, inconsistently observed bands, the C-banding pattern consisted of 0–3 small bands per chromosome at intercalary and terminal locations, and at NORs. The level of banding pattern polymorphism was low, but enough to indicate that the taxa are outbreeders. Similarities in chromosome morphology and C-banding patterns identified homology of all chromosomes of subsp.villosus, but for 12 pairs only in subsp.secaliformis. Between plants, reliable identification of homology and homoeology (subsp.secaliformis) was possible only for the SAT-chromosomes and the shortest metacentrics. Chromocentres were very small and the amount of constitutive heterochromatin was low. N-banding stained chromosomes uniformly. The basic karyotypes of theP. fragilis taxa were similar to those ofP. juncea, P. lanuginosa, andP. stoloniformis supporting a close relationship and the presence of a common genome, N. NORs had different nucleolus-forming activities. Meiotic analysis demonstrated a high level of bivalent pairing in the three taxa. A chromosomal rearrangement was suggested in subsp.villosus. The low multivalent frequency in subsp.secaliformis indicates the presence of a pairing regulation mechanism. The majority of chiasmata were interstitial. Pollen grain size discriminated between diploid and tetraploid taxa. The existence of a diploid cytotype of subsp.secaliformis is supported by pollen measurements of herbarium material.

Cytogenetics of Rutaceae. V. High chromosomal variability in Citrus species revealed by CMA/DAPI staining

The CMA/DAPI chromosome banding pattern of six Citrus species was analysed. All of them showed a large amount of heterochromatin and heterozygosity. Most of the heterochromatin was CMA+/DAPI− and was located mainly in the terminal region of the long arms. Each individual was heterozygous for at least one chromosome pair and each species presented a different banding pattern. The greatest amount of information on karyotype variation can be obtained from the four largest pairs. Pairs I and III showed the highest amount of heterochromatin and heterozygosity whereas pair II was highly stable and almost completely lacked CMA+ heterochromatin. On the other hand, some features common to all species suggest a strong chromosome homoeology conservation. The CMA staining revealed some chromosome markers for each Citrus species that may be very useful in the identification of zygotic versus nucellar embryos, as well as for further evolutionary studies.

Satellite DNA and heterochromatin of the flour beetle Tribolium confusum

The chromosomes of Tribolium confusum have conspicuous bulks of pericentromeric constitutive heterochromatin. The amount of heterochromatin measured by C-banding in metaphase chromosomes is estimated to be 40-45%. It is composed of an A + T rich DNA according to the distamycin A/diamidinophenylindol staining of chromosomes. Restriction analysis of isolated T. confusum genomic DNA shows that this species has a satellite DNA that constitutes about 40% of the genome. Cloning and sequencing experiments reveal a monomer length of 158 base pairs and a copy number of 5.77 x 10(5) per haploid genome. Its sequence is A + T rich (73%), with direct and inverted repeats, one of them with a possibility of forming stable cruciform structure. The abundance, monomer length, and the mutation rate are similar to those found in other satellite families from different species of Tenebrionidae, but no sequence homology has been found among them. No retarded mobility of satellite DNA, characteristic for molecules with sequence-induced curvature, has been detected by electrophoresis on nondenaturing polyacrylamide gels. In situ digestions with restriction enzymes and in situ hybridization show that this satellite DNA is located in pericentromeric positions of all chromosomes coinciding with C-bands.

Cytology of Vicia species II. Banding patterns and chromatin organization in Vicia atropurpurea Desf

Banding techniques on metaphase chromosomes of Vicia atropurpurea were carried out and nuclear DNA content in root meristematic cells was determined by cytophotometric analysis. Feulgen absorptions at different thresholds of optical density provided evidence of the organization of the chromatin in interphase nuclei and permitted an evaluation of the cytophotometrically determined heterochromatin amount. These results corroborated the analysis of the banding patterns.

Cytophotometric and Biochemical Analyses of DNA Variations in the Genus Aloe L.

The nuclear 4C DNA content in 10 species of Aloe L. (Liliaceae), determined by Feulgen cytophotometry, was found to vary by 35.8%. Absorption measurements of the nucleus showed that this variation is positively correlated with changes in the amount of heterochromatin, although quantitative variations in euchromatin cannot be excluded. Buoyant density analyses of extracted DNA in CsCl gradients showed differences in DNA density among species and the possible presence of satellite DNA in some species. These variations might have played a role in Aloe speciation. In general, the experimental data are in agreement with the accepted taxonomic position of the examined species.

Karyotype and C-banding in Medicago noeana Boiss., Leguminosae.

Somatic chromosomes of Medicago noeana Boiss (2n=16), a wild annual species belonging to the section Rotatae of the subgenus Spirocarpos, were analyzed to confirm the chromosome number as 2n=16 and to characterize each chromosome pair on the basis of its length and arm ratio value. The karyotype of this species was symmetric and consisted of four median chromosomes and three submedian chromosomes. The C-banded metaphases included a considerable amount of heterochromatin which is localized at the centromeric region of each chromosome. The results allow us to make some considerations on the genus Medicago and to demonstrate that cytogenetic studies can provide useful information for breeding programs.

Effect of α 1-Adrenergic Blockade on Nucleolar Growth, Chromatin Relaxation, and Histone H1° Content in Regenerating Liver

α 1-Adrenergic agonists are known to be involved in the regulation of hepatocyte proliferation after a partial hepatectomy. The blockade of α 1-adrenergic receptors with the specific antagonist prazosin inhibits DNA synthesis which peaks at 24 h after surgery. In this report we have studied the effects of prazosin administration on several events occuring during liver regeneration. The results show that the nuclear volume and nucleolar volume density of hepatocytes were increased and that the relative amount of heterochromatin decreased at 24 h. The increase in hepatocyte nucleolar volume density and the decrease in the relative amount of heterochromatin were partially abolished by prazosin administration while the increase in the nuclear volume was not affected. The relative amount of the histone H1 variant H1° was reduced in 24-h regenerating liver and prazosin treatment prevented this reduction.

High Amount of Heterochromatin in a Tropical Tree Species: Genipa americana L. (Rubiaceae).

The chromosomes and interphase nuclei of Genipa americana L. were analyzed after CMA/DAPI staining. Most of the large chromocentres was CMA+/DAPI+, except that associated with the nucleolus which was CMA + + /DAPI - -, whilst the diffuse euchromatin was CMA-/DAPI+. In addition, some small chromocentres were CMA-/DAPI+. The chromosome bands were CMA + /DAPI + or CMA + +/DAPI- -. Most of the chromosome pairs showed size heteromorphism, mainly in the CMA+/DAPI+ bands. Measurements of the heterochromatin/euchromatin ratio in metaphase chromosomes gave an estimate of about 50%, one of the highest ratio observed in angiosperms. Comparison with some other species with a high heterochromatin amount suggest that heterochromatin accumulation may be an aleatory rather than an adaptive process.

Chromosomal and cell size analysis of cold tolerant maize

C-band number, guard cell length, and chloroplast number per guard cell were determined for eight maize populations. These populations consisted of maize selected for cold tolerance at the University of Nebraska as well as the original unselected populations. The genome size of these populations had previously been determined. C-band number fluctuated concertedly with the changes in genome size indicating that deletions and additions of constitutive heterochromatin occurred during selection, resulting in altered genome sizes. Guard cell size of all the cold tolerant populations was greater than the cell size of the respective nonselected populations. Chloroplast number per guard cell was also higher in all the cold tolerant populations than in their parental populations, but the increases were not statistically significant. The results indicate that changes in genome size that occurred during selection for cold tolerance are the result of changes in amounts of C-band heterochromatin and that the selection process results in an increase in cell size in the cold tolerant populations.

Synthesis and cytological characterization of trigeneric hybrids involving durum wheat, Thinopyrum bessarabicum, and Lophopyrum elongatum

In an attempt to transfer genes for salt tolerance and other desirable traits from the diploid wheatgrasses, Thinopyrum bessarabicum (2n=2x=14; JJ genome) and Lophopyrum elongatum (2n=2x=14; EE genome), into durum wheat cv 'Langdon' (2n=4x=28; AABB genomes), trigeneric hybrids with the genomic constitution ABJE were synthesized and cytologically characterized. C-banding analysis of somatic chromosomes of the A, B, J, and E genomes in the same cellular environment revealed distinct banding patterns; each of the 28 chromosomes could be identified. They differed in the total amount of constitutive heterochromatin. Total surface area and C-banded area of each chromosome were calculated. The B genome was the largest in size, followed by the J, A, and E genomes, and its chromosomes were also the most heavily banded. Only 25.8% of the total chromosome complement in 10 ABJE hybrids showed association, with mean arm-pairing frequency (c) values from 0.123 to 0.180 and chiasma frequencies from 3.36 to 5.02 per cell. The overall mean pairing was 0.004 ring IV + 0.046 chain IV + 0.236 III + 0.21 ring II + 2.95 rod II + 20.771. This is total pairing between chromosomes of different genomes, possibly between A and B, A and J, A and E, B and J, B and E, and J and E, in the presence of apparently functional pairing regulator Ph1. Because chromosome pairing in the presence of Ph1 seldom occurs between A and B, or between J and E, it was inferred that pairing between the wheat chromosomes and alien chromosomes occurred. The trigeneric hybrids with two genomes of wheat and one each of Thinopyrum and Lophopyrum should be useful in the production of cytogenetic stocks to facilitate the transfer of alien genes into wheat.

A cytogenetic and genetic characterization of a group of closely linked second chromosome mutations that suppress position-effect variegation in Drosophila melanogaster.

Characterization of a group of dominant second chromosome suppressor of position-effect variegation (PEV) (Su(var)) mutants has revealed a variety of interesting properties, including: maternal-effect suppression of PEV, homozygous lethality or semilethality and male-specific hemizygous lethality, female infecundity, acute sensitivity to the amount of heterochromatin in the cell and sensitivity to sodium butyrate. Deficiency/duplication mapping and complementation tests have revealed that eight of the mutants define at least two genes in section 31 of the left arm of chromosome 2 and they suggest that a ninth corresponds to an additional nonessential Su(var) gene within or near this region. The effects of specific deficiencies and a duplication on PEV indicate that the expression of one or more of the Su(var) genes in this region of the chromosome is dose-dependent, i.e., capable of haplo-abnormal suppression and triplo-abnormal enhancement. Interestingly, the appearance of certain visible phenotypes among a subset of the mutants suggests that they may possess antimorphic properties. Our results are consistent with the hypothesis that two of these Su(var) genes encode structural components of heterochromatin. We also report that two previously isolated mutants located in 31E and 31F-32A act as recessive suppressors of PEV.

Variation of genome size and organization within hexaploid Festuca arundinacea

Cytophotometric, karyological, and biochemical analyses were carried out in the meristems of seedlings obtained from seeds collected from 35 natural populations of hexaploid Festuca amndinacea in Italy. Highly significant differences between populations were observed in the amount of nuclear DNA (up to 32.3%). These changes are linked to variations in the amount of heterochromatin and in the frequency of repeated DNA sequences, and particularly of a fraction of them. Differences between populations in the arm ratios and total length of the chromosomes were also observed. The genome sizes of the populations are correlated positively with the mean temperature during the year and with that of the coldest month at the stations, and correlate negatively with their latitudes. The intraspecific genome changes observed are discussed in relation to other pertinent data to be found in the literature and in relation to their possible role in environmental adaptation.

Chromosomal heterochromatin differentiation of cyprinid fishes

The chromosomes of 10 species of Chinese cyprinid fishes were analyzed by means of C-banding technique. It has been found that there is extensive variation in the constitutive heterochromatin among these fishes. Some of these species possess considerable quantities of heterochromatin, and some possess little heterochromatin. These results seem to show that constitutive heterochromatin has played an important part in the chromosomal evolution of cyprinids.

Chromosome Studies in Hypoptopomatinae (Pisces, siluriformes, Loricariidae): I. XX/XY Sex Chromosome Heteromorphism in Pseudotocinclus tietensis.

The cytogenetic analysis of 13 specimens (9 males and 4 females) of Pseudotocinclus tietensis showed that this species has 2n=54 chromosomes (26M+20SM+6ST) plus one heteromorphic pair (SM/M) in the males and one homomorphic pair (SM/SM) in the females. Ag-NORs are located interstitially on the long arm of the largest metacentric pair and a small amount of constitutive heterochromatin is present in the karyotypes. The occurrence of a heteromorphic pair in the males is demonstrable by the presence of one extra C-banded block in the Y chromosome. The presence of one heterochromatin block distinguishing the sexual chromosomes suggests that this species presents a very primitive mechanism of sex chromosome differentiation.