Gene for selenium-dependent glutathione peroxidase maps to human chromosomes 3, 21 and X

A human glutathione peroxidase cDNA has been used as a probe to hybridize to DNAs isolated from human - rodent somatic cell hybrids that have segregated human chromosomes. A 609 bp probe which contains the entire coding region hybridizes to human chromosomes 3, 21 and Xp. Fragments of the cDNA coding sequence and of the 3' untranslated region were also used as probes. These fragments hybridized to each of the three chromosomes with the same efficiency, suggesting similarity between the loci, whereas an intronic probe detected only the gene on chromosome 3. The general organization of each gene was determined from the hybridization data. The data suggest that the locus on chromosome 3 is a functional gene containing a single intron and a pattern of restriction sites identical to those found in the cDNA coding sequence. The data also suggest that the sequences on chromosomes X and 21 have equal conservation of the 3' untranslated and coding sequences but do not contain introns, providing evidence that the latter two sequences are processed pseudogenes. A simple two allele polymorphism in PvuII digests was detected at the locus on chromosome 21.     

DNA image-fluorimetry of individual human chromosomes

A microfluorimetric method has been developed for determination of DNA content in individual human chromosomes. The method is based on a preliminary identification of chromosomes with Hoechst 33258 followed by staining of the chromosomes with Feulgen reaction by using Schiff’s reagent type ethidium bromide-SO₂ and then by measuring the fluorescence intensity of the chromosomes by using an image analyzer. The method allows determining the DNA content of individual chromosomes with an accuracy up to 4.5 fg. The DNA content of individual human chromosomes and their p-and q-arms, as well as homologous chromosomes, were measured by using the developed method. It has been shown that the DNA content in chromosomes of the normal human karyotype is unstable and can fluctuate in some chromosomes within 35–40 fg.     

Discrimination between groups of chromosomes and individual chromosomes in the normal human karyotype

The karyotypes of 200 normal individuals are examined in a study designed to investigate the extent to which the cytologist's classification of chromosomes into the A–G autosomal groups and identification of individual chromosomes are reflected in the values of measurements made on these chromosomes. The statistical technique of discriminant function analysis is employed to obtain linear functions of the chromosomal measurements which may be used to classify and identify chromosomes. The results of the study indicate that while chromosomes can be grouped with a reasonably high probability of success using measurements alone, identification of individual chromosomes is somewhat more difficult.     

Chromatin structure of active and inactive human X chromosomes

Nuclei from a variety of human cell lines and tissues were digested with gradually increasing levels of DNase I. The DNA was then purified, treated with restriction enzymes and subjected to Southern blot hybridization using a cloned cDNA probe to 3-phosphoglycerate kinase (PGK) a housekeeping enzyme. At relatively high levels of DNase I, a specific, slightly sensitive site in chromatin sequences encoding PGK was observed in all of the cell types examined. This slightly sensitive site resides on the active X-chromosome since cell lines with increased numbers of inactive X-chromosomes do not show an increase in the region of chromatin which is sensitive. Except for this restricted region of enhanced sensitivity on the active X-chromosome, the data suggest that, for PGK encoding sequences, chromatin configurations on the active and inactive X-chromosomes are similar.     

Fusion of two apparently intact human X chromosomes

Summary Cytological studies have been presented from a 15-year-old girl with short stature and failure of puberty. Buccal mucosa preparations revealed X-chromatin mass approximately double in size of that of a normal female. Leukocyte metaphases suggested a two cell line composition of the patient. One population of cells conformed with 45,X chromosome distribution. The chromosome complement of her other cell line had a modal number of 46. In this cell line a C chromosome was replaced by an exceptionally large submetacentric chromosome. This abnormal element exhibited late DNA replicating pattern. G-banding study revealed that the abnormal chromosome was produced as a result of fusion involving telomeric ends of long arms of 2 intact X chromosomes. This translocation X was bearing 2 C-banded areas; one around the centromere and the other at the distal end of the long arm. The distal C-band area did not show any evidence for centromeric function. It appears that a centromere becomes latent in the presence of another centromere in a translocation bearing 2 total chromosomes. Such a change of state in the additional centromere is vital for the stability of the translocation chromosome.     

G-banding patterns of high-resolution human chromosomes 6–22, X,and Y

Summary A precise schematic representation of the number, height, position, and staining intensity of the Giemsa bands of late prophase, prometaphase, early metaphase, and mid-metaphase chromosomes 6–22, X, and Y is presented. Late prophase chromosomes were found to have 2–21/2 times the length and 3–31/2 times the number of bands previously observed in mid-metaphase, whereas prometaphases and early metaphases were intermediate in length and number of bands. In this work, the maximum number of bands observed per haploid set in late prophase was 1353, while more than 350 were generally found in mid-metaphase.     

Structural organization of the human genome: distribution of nucleotides, Alu-repeats and exons in chromosomes 21 and 22]

Analysis of DNA sequences of the human chromosomes 21 and 22 performed using a specially designed MegaGene software allowed us to obtain the following results. Purine and pyrimidine nucleotide residues are unevenly distributed along both chromosomes, displaying maxima and minima (Y waves phi) with a period of about 3 Mbp. Distribution of G + C along both chromosomes has no distinct maxima and minima, however, chromosome 21 contains considerably less G + C than chromosome 22. Both exons and Alu repeats are unevenly distributed along chromosome 21: they are scarce in its left part and abundant in the right part, while MIR elements are quite monotonously spread along this chromosome. The Alu repeats show a wave-like distribution pattern similar for both repeat orientations. The number of the Alu repeats of opposite orientations was equal for both studied chromosomes, and this may be considered a new property of the human genome. The positive correlation between the exon and Alu distribution patterns along the chromosome, the concurrent distribution of Alu repeats in both orientations along the chromosome, and the equal copy numbers for Alu in direct and inverted orientations within an individual chromosome point to their important role in the human genome, and do not fit the notion that Alu repeats belong to parasitic (junk) DNA.     

Relationship between group G chromosomes, especially chromosome 21, and the sensitivity of human cells to Coxsackie B viruses]

The R-method of differential chromosome staining by length was applied to comparative karyological studies on the culture of J 96 human cells susceptible to enteroviruses, and on the J 41 cell line derived from this culture and possessing high specific resistance to Coxsackie B viruses. Karyotype of the J 41 cell line was shown to be deprived of chromosome G21 (P less than 0.0001). The number of other chromosomes varied from cell to cell, but they are constantly present in the majority of cells of both the J 96 and J 41 cell lines. A conclusion is drawn that chromosome G21 incorporates gene(s) which controls the human cells susceptibility to Coxsackie B viruses.     

X-ray-induced breaks in the X chromosomes in Drosophila lines of various radiosensitivities

The frequency of X-ray induced X-chromosome breaks has been studied in females of the line rad (2) 201G1 hypersensitive to radiation and in females of the control line selected from the same population. The frequency of X-chromosome breaks was judged based on the frequency of X0 males occurrence. Synergism of the effects of X-rays (at doses 0.1, 0.5 and 1.0 kr) and of hyperthermia (+37 degrees C, 5.5 hours) applied after irradiation served as an indirect evidence for the functioning of DNA repair systems. It is demonstrated that radiosensitivity of mature oocytes of the lines compared was equal and that hyperthermia applied after irradiation increased the latter effect in both lines. Young oocytes of the control line were radioresistant, and hyperthermia applied after irradiation enhanced its effect. Opposite to them, young oocytes of the rad line females were radiosensitive. They did not differ from mature oocytes in the frequency of X-chromosome losses. Synergism of the two factors (irradiation and hyperthermia) was not registered in young oocytes. On the basis of the results obtained, it may be concluded that radiosensitivity of young oocytes in the hypersensitive line is conditioned by the failure of DNA repair systems and that the rad (2) 201G1 gene may be considered, in relation to the genes controlling DNA repair, as a suppressor functioning selectively at a certain stage of oogenesis.     

Microfluorometric analysis of DNA replication in human X chromosomes

BUdR-sensitive fluorescence of the dye 33258 Hoechst allows microfluorometric analysis of replication in human chromosomes. Comparison of the fluorescence patterns of male and female X chromosomes obtained with this technique reveals differences that may reflect regional alterations in DNA synthesis kinetics.     

Coincident maternal meiotic nondisjunction of chromosomes X and 21 without evidence of autosomal aysnapsis

Summary A family in which the proband showed phenotypic signs of both the Turner and Down syndromes was studied cytogenetically and with restriction fragment length polymorphisms. The proband's karyotype was 46,X,+21, showing double aneuploidy without any signs of mosaicism. The single X and one chromosome 21 were of paternal origin while two chromosomes 21 were of maternal origin. The nondisjunction of chromosome 21 took place in maternal meiosis II. If it is assumed that the absence of mosaicism renders postzygotic mitotic loss of the X chromosome unlikely, then the X chromosome would have been lost in maternal meiosis I or II. Recombination had occurred between the nondisjoined chromosomes 21. We conclude that double nondisjunction took place in one parent and that asynapsis was not a prerequisite for the autosomal nondisjunction.     

Selective transfer of individual human chromosomes to recipient cells.

Two hypoxanthine phosphoribosyltransferase-deficient human cell lines, D98/AH-2 and HT1080-6TG, were stably transfected with pSV2 gpt, a plasmid containing the selectable marker Escherichia coli xanthine-guanine phosphoribosyl transferase (Eco gpt). Hypoxanthine-aminopterin-thymidine-resistant transformants arose with a frequency of ca. 10(-6) and contained mostly single, but occasionally multiple, copies of the plasmid sequences. These transformants actively express the Eco gpt marker. Single chromosomes from two different HT1080 gpt transformants and one D98 gpt transformant, containing the integrated plasmid sequences, were transferred via microcell-mediated chromosome transfer to hypoxanthine phosphoribosyl transferase-deficient mouse A9 cells. The transferred human chromosomes were identified as 2, 4, and 22, by using a combination of G-11 staining, G-banding, isoenzyme analysis, and in situ hybridization. This system is being used to create a library of interspecies microcell hybrid clones, each clone containing a unique single human chromosome in a mouse background. The complete library will represent the entire human karyotype.     

Preparation and bivariate analysis of suspensions of human chromosomes

Chromosomes were isolated from a variety of human cell types using a HEPES-buffered hypotonic solution (pH 8.0) containing KCl, MgSO4, dithioerythritol, and RNase. The chromosomes isolated by this procedure could be stained with a variety of fluorescent stains including propidium iodide, chromomycin A3, and Hoechst 33258. Addition of sodium citrate to the stained chromosomes was found to improve the total fluorescence resolution. High-quality bivariate Hoechst vs. chromomycin fluorescence distributions were obtained for chromosomes isolated from a human fibroblast cell strain, a human colon carcinoma cell line, and human peripheral blood lymphocyte cultures. Good flow karyotypes were also obtained from primary amniotic cell cultures. The Hoechst vs. chromomycin flow karyotypes of a given cell line, made at different times and at dye concentrations varying over fourfold ranges, show little variation in the relative peak positions of the chromosomes. The size of the DNA in chromosomes isolated using this procedure ranges from 20 to over 50 kilobases. The described isolation procedure is simple, it yields high-quality flow karyotypes, and it can be used to prepare chromosomes from clinical samples.     

Positional clustering of differentially expressed genes on human chromosomes 20, 21 and 22

Background  

Clusters of genes co-expressed are known in prokaryotes (operons) and were recently described in several eukaryote organisms, including Human. According to some studies, these clusters consist of housekeeping genes, whereas other studies suggest that these clustered genes exhibit similar tissue specificity. Here we further explore the relationship between co-expression and chromosomal co-localization in the human genome by analyzing the expression status of the genes along the best-annotated chromosomes 20, 21 and 22.