Heterochromatin Bands Research Articles

Characterization of heterochromatin in different species of the Scilla siberica group (Liliaceae) by in situ hybridization of satellite DNAs and fluorochrome banding

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.

Nonfluorescent Y chromosomes. Cytologic evidence of origin.

Twelve presumptive structurally altered Y chromosomes were studied with Q-, G-, G-11, C-, Cd, and lateral asymmetric banding techniques and were compared with normal X and Y chromosomes and with an abnormal [i(Yq)] Y chromosome that exhibited intact fluorescence. Significant to this work is the fact that the Y chromosome has a small block of Giemsa-11 heterochromatin adjacent to the centromere on the long arm, while the X chromosome does not, which allows a distinction between the X- and Y-derived chromosomes. Two of the twelve altered chromosomes of either X or Y origin are small nonfluorescent rings. Each ring has a G-11-positive band of heterochromatin at the centromere, confirming Y origin. Each of the normal-length nonfluorescent presumed Ys and a Y with a fluorescent band in the center have one G-11 band at the centromere and another at an equal distance from the end of the long arm, the bands also being Cd positive, indicating that these chromosomes are pseudodicentric. The likely mechanism of origin is a break at the distal bright heterochromatin/euchromatin junction (or within the bright segment in the chromosome with the bright center band), fusion of the sister chromatids at the breakpoints, and loss of the distal segment.

Human chromosomal polymorphism. IV. Chromosomal Q polymorphism in Russians living in Kirghizia.

Chromosomal Q polymorphism was studied in 200 Russian individuals (94 females and 106 males) living in Kirghizia. Of the 200 individuals, 191 had chromosomal Q polymorphic variants, while nine (4.5%) had no Q bands with fluorescence levels 4 and 5. The mean number of Q variants per individual ranged from 0 to 7, with a mean of 2.9. There were no differences in the frequency of Q variants between sexes. The observed homo- and heteromorphic frequencies completely agreed with those predicted by the law of Hardy-Weinberg. Of the 200 individuals, 12 (6.0%) had pericentric inversion of the Q band in chromosome 3, one individual (0.5%) having a homomorphic form of this inversion. The possible selective value of chromosomal Q heterochromatin material in the adaptation of human populations to extreme environmental factors, in particular to cold, and the possible taxonomic value of inverted Q heterochromatin bands in chromosome 3 in ethnic anthropology, are discussed.

HETEROCHROMATIN BANDING IN BOYKINIA, HEUCHERA, MITELLA, SULLIVANTIA, TIARELLA, AND TOLMIEA (SAXIFRAGACEAE)

Karyotypic differences were sought among species of Boykinia, Heuchera, Mitella, Sullivantia, Tiarella, and Tolmiea utilizing a modification of the Hy‐banding technique. Prominent centromeric and some telomeric heterochromatin banding was observed. Boykinia aconitifolia and species of Sullivantia possess an identical banded karyotype, while four species of Heuchera, Mitella diphylla, Tiarella cordifolia, and Tolmiea menziesii (the latter at the tetraploid level) are characterized by a second, slightly different banded karyotype. In Sullivantia, Giemsa C‐banding stains the same chromosomal regions revealed by Hy‐banding. Larger amounts of heterochromatin are present in chromosomes of species of Heuchera, Mitella, Tiarella, and Tolmiea than in chromosomes of Sullivantia species and Boykinia aconitifolia. These karyological observations confirm generic relationships and demonstrate the systematic applicability of chromosome banding techniques to plants with very small chromosomes.

Evolutionary relationships based on heterochromatin bands in six species of the Triticinae

Evolutionary relationships based on heterochromatin bands in six species of the Triticinae

Clinicopathologic Correlations in Alibert-type Mycosis Fungoides

Five cases of mycosis fungoides of the Alibert type were studied by taking multiple biopsy specimens at different stages of the disease. Large hyperchromatic, slightly irregular mononuclear cells are the most frequent cells. Ultrastructurally, the cells were only slightly convoluted, had prominent heterochromatin banding at the nuclear membrane, and unremarkable cytoplasmic organelles. Highly convoluted cerebriform nucleated cells were few. Large regular vesicular histiocytes were prominent in the early stages. Ultrastructurally, the cells showed evenly distributed euchromatin. Epidermotrophism was equally as important as Pautrier's abscess as a hallmark of the disease. Stereologic techniques comparing the infiltrate with regard to size and convolution of cells in all stages of mycosis fungoides with infiltrates seen in a variety of benign dermatoses showed no statistically significant differences.

Staining of heterochromatin bands and the determination of rye chromosomes in triticale (wheat × rye hybrid)

Fifteen lines of triticale were studied using the C-banding staining method. A typical, complete chromosomal complement was found in 11 lines, while the remaining lines demonstrated some variations. A slight modification in the technique is discussed.

Evidence of crossing-over inhibition in rye anthers cultured with colchicine

In order to investigate wheter colchicine affects crossing-over, rye anthers of an inbred line of rye forming bridges and fragments at anaphase I produced by erroneous chiasmata, and anthers of plants heterozygous for a conspicuous heterochromatin band, were cultured in a medium with colchicine. Anthers planted at zygotene did not show bridges at AI in the inbred line. In the heterozygotes no difference between associated chromatids in respect to the heterochromatin band, resulting from crossingover, were observed. In anthers planted at pachytene both bridges and chromosomes showing difference between associated chromatids were observed at a stage equivalent to AI with the same frequency as in anaphase I cells of untreated anthers. This demonstrates that crossing-over or a prerequisite to crossing-over is established at zygotene, and also that absence of chiasmate association at later stages is not due to precocious slipping off of chiasmata.

Nuclear DNA and heterochromatin contents in theScilla hohenackeri group,S. persica, andPuschkinia scilloides (Liliaceae)

DNA contents (presented as 1C-values) have been determined cytophotometrically in 7 species of theScilla hohenackeri group (10.18 to 22.71 pg), and in the systematically more isolated taxaS. persica (21.02 pg) andPuschkinia scilloides (6.80 pg). The heterochromatin amount is not correlated with the nuclear DNA content. Euchromatin, therefore, is not a particularly “conservative” part of the genome. However, high C-values and large but few terminal heterochromatin bands, and lower C-values and numerous but smaller heterochromatin bands are found to be linked in theS. hohenackeri group. Obviously, numerous chromosomal changes have accompanied speciation in this group. DNA contents, and C-banded karyotypes are consistent with systematic affinities based on morphological similarities.

THE GENOMIC ORIGIN OF THE UNPAIRED CHROMOSOMES IN TRITICALE

Differential staining of telomeric rye heterochromatin and telocentric chromosomes were used to identify chromosomes which were unpaired at first meiotic metaphase of hexaploid triticale (× Triticosecale Wittmack). Both approaches showed that it was the rye chromosomes which were seen as univalents. Differences in the rate of pairing from triticale to triticale were mostly explained by variation in the pairing of the rye genome. Within the rye genome, chromosome arms with telomeric heterochromatin showed pairing rates much lower than chromosome arms lacking heterochromatin. Wheat telocentrics and heterochromatin-free rye telocentrics which showed intermediate levels of pairing failure (65-90%), had mostly terminal chiasmata. On the other hand rye telocentrics with large heterochromatin bands on the telomeres had mostly nonterminal chiasmata and very low pairing (5-35%). It is concluded that the presence of heterochromatin on certain telomeres of rye chromosomes blocks the formation of terminal chiasmata and this results in desynapsis and univalents at MI.

Modified method of C banding using barium hydroxide.

A modified centromeric heterochromatin banding technique using barium hydroxide octahydrate is described. The relationship between slide maturity and time of denaturation by barium-hydroxide is discussed.

Giemsa banding of chromosome 1gh+ and linkage analysis.

A four-generation transmission of 1qh+ chromosome was ascertained by routine chromosome analysis of a mildly dysmorphic and retarded 61/2-year-old female. Concordance between synophrys and the 1qh+ marker was the only consistent phenotypic relationship. The variant chromosome did not appear uncoiled, and Giemsa centromeric staining (C-bands) revealed an increased width of the heterochromatin commensurate with the increased length of the long arm. Giemsa banding of the entire chromosome (G-bands) revealed two heterochromatin bands, identical in appearance, in the centromeric region with the remainder of the chromosome showing normal banding. The distribution of Duffy blood groups in the pedigree was consistent with the locus being on chromosome No. 1.

Identification of Rye Chromosomes in Wheat‐rye Addition Lines and Triticale by Heterochromatin Bands1

The rye (Secale cereale L.) chromosomes of four series of wheat (Triticum aestivum L.) ‐ rye addition line were identified according to their heterochromatic banding patterns using Leishman staining. The characteristics of chromosomes 1R, 3R, 4R/7R, 5R, and 6R were relatively consistent from series to series, while 2R and 7R/4R varied considerably and were therefore difficult to classify. In some of the six triticales (✕ Triticosecale Wittmack) analyzed, certain rye chromosomes easily identified as 2R and 4R/7R, were absent.

A possible effect of heterochromatin on chromosome pairing.

Rye chromosomes were selectively stained in the meiosis of triticale by means of heterochromatin banding techniques. Compared to wheat chromosomes, rye chromosomes showed reduced pairing at first meiotic metaphase. Within the rye genome this pairing failure was associated with the presence of large, terminal heterochromatic bands. Since these terminal bands of rye chromosomes are late replicating, the effect of heterochromatin could arise from an overlap between the processes of chromosome replication and chromosome pairing.

Structural basis of banding pattern of human chromosomes

Human chromosomes treated to demonstrate centromeric heterochromatin and trypsin-induced bands were observed under the scanning electron microscope and by Nomarski phase-contrast optics. The bulging appearance of the bands suggests that extracting the DNA with the proper agents will result in an alteration of the three-dimensional structure of the chromosome. The bands take up more Giemsa stain simply because of the higher density of the remaining chromatin in particular areas.

Distribution of constitutive heterochromatin in mamallian chromosomes.

Using a special staining technique, a survey of the chromosomes of many mammalian species showed that constitutive heterochromatin is present in all cases and that the heterochromatin pattern appears to be specific and consistent or each chromosome and each taxon. Usually heavy heterochromatin is found in the centromeric areas, but terminal heterochromatin is not uncommon. Occasionally interstitial heterochromatin bands occur. In some species, such as the Syrian hamster and Peromyscus, many chromosome arms are completely heterochromatic.