DNA content and DNA-based centromeric index of the 24 human chromosomes.

The chromosomes of two human males were identified by fluorescent banding, restained, and measured by scanning microscopy and computer analysis. The two variables, DNA content and DNA-based centromeric index, provided almost complete discrimination of chromosome types. Some chromosomes showed significant differences in DNA content between the men, and for one man two pairs of chromosomes showed significant differences between homologs.

[Epstein-Barr virus and human chromosomes: Close association of the resident viral genome and the expression of the virus-determined nuclear antigen (EBNA) with the presence of chromosome 14 in human/mouse hybrid cells (author's transl)].

Fourteen hybrid clones derived from the fused cultures of human lymphoblastoid FV5 cells and 5-bromodeoxyuridine-resistant mouse fibroblastic MCB2 cells grown in HAT selective medium were examined for the presence of Epstein-Barr virus (EBV) DNA, the expression of the virus-determined nuclear antigen (EBNA), and the presence of human chromosomes, in the course of serial passage in vitro. Among the hybrid clones tested, three were positive for EBV DNA and EBNA, whereas the remaining 11 clones were totally negative. The chromosome investigations showed that human chromosome 14 was consistently involved in all three EBV genome-positive and EBNA-positive hybrid clones, but not in any negative clones. In 10 subclones isolated from one of the three positive clones, all of which contained chromosome 14 alone as human chromosomes, a concordant segregation of EBNA, EBV DNA and No. 14 chromosome was evident. These findings suggest that the resident EBV genome is closely associated with chromosome 14 and the presence of this particular chromosome alone is sufficient for the maintenance and the expression of EBV genetic information in human lymphoblastoid cells.

Structural organization of ribosomal cistrons in human nucleolar organizing chromosomes.

The variable morphology of nucleolar organizer regions (NORs) of human acrocentric chromosome 13 was studied in detail by the N-banding technique. It was demonstrated that NOR may become further segmented and several hypotheses have been proposed for structural variability. The polymorphic nature of NORs may have an important significance in human evolution.

Investigations on the chromosomal localizations of the human and chimpanzee interferon genes: possible role of chromosomes 9 and 13.

Analysis of a great number of independent hamster-human and mouse-chimpanzee somatic cell hybrid clones confirms the role of chromosome 9 as carrying one or more primate beta interferon genes. The presence of chromosome 13 in producing hybrids and its absence in all non producing clones must be kept in mind for future studies. The strong negative regulation of interferon production in the parental hamster cells also affects the human gene product. The UV irradiation target for these regulatory genes is significantly greater than the structural genes responsible for interferon production.

High-resolution analysis of chromosome markers in Burkitt lymphoma cell lines.

Using a high-resolution chromosome banding technique, which provided more elongated and distinctly banded chromosomes, some new evidence was obtained for localization of break points in Burkitt lymphoma marker chromosomes. As a result, the characteristic translocation between chromosomes 8 and 14 was designated as t(8;14) (q24.1;q32.5) and the deletion of chromosome 15 was designated as del(15) (q13q15).

Double in situ hybridization in combination with digital image analysis: a new approach to study interphase chromosome topography.

Double in situ hybridization with mercurated and biotinylated chromosome specific DNA probes in combination with digital image analysis provides a new approach to compare the distribution of homologous and nonhomologous chromosome targets within individual interphase nuclei. Here we have used two DNA probes representing tandemly repeated sequences specific for the constitutive heterochromatin of the human chromosomes 1 and 15, respectively, and studied the relative arrangements of these chromosome targets in interphase nuclei of human lymphocytes, amniotic fluid cells, and fibroblasts, cultivated in vitro. We have developed a 2D-image analysis approach which allows the rapid evaluation of large numbers of interphase nuclei. Models to test for a random versus nonrandom distribution of chromosome segments are discussed taking into account the three-dimensional origin of the evaluated 2D-distribution. In all three human diploid cell types the measurements of target-target and target-center distances in the 2D-nuclear image revealed that the labeled segments of the two chromosomes 15 were distributed both significantly closer to each other and closer to the center of the nuclear image than the labeled chromosome 1 segments. This result can be explained by the association of nucleolus organizer regions on the short arm of chromosome 15 with nucleoli located more centrally in these nuclei and does not provide evidence for a homologous association per se. In contrast, evaluation of the interphase positioning of the two chromosome 1 segments fits the random expectation in amniotic fluid and fibroblast cells, while in experiments using lymphocytes a slight excess of larger distances between these homologous targets was occasionally observed. 2D-distances between the labeled chromosome 1 and 15 segments showed a large variability in their relative positioning. In conclusion our data do not support the idea of a strict and permanent association of these homologous and nonhomologous targets in the cell types studied so far.

Heterogeneities in the distribution of (GACA)n simple repeats in the karyotypes of primates and mouse.

Tandemly organized simple repetitive sequences are widespread in all eukaryotes. The organization of the simple tetrameric (GACA)n sequences at chromosomal loci has been investigated using in situ hybridization with chemically pure oligonucleotide probes. Both biotin- and digoxigenin-attached (GACA)4 probes reveal specific hybridization signals over the short arms of all acrocentric autosomes in man. In the other examined primates the NOR-bearing autosomes could be detected by in situ hybridization with (GACA)4, and a major concentration of the GACA simple repeats could be observed on the Y chromosome in the gibbon and mouse: the hybridization site in the gibbon Y chromosome coincides particularly with the silver-stainable NOR. In the past, accumulations of (GACA)n sequences were demonstrated mainly on vertebrate sex chromosomes. Therefore, the organization of GACA simple sequences is discussed in the context of their evolutionary potential accumulation and the possible linkage with the primate rDNA loci.

Chromosomal constitution of nucleolus-associated chromatin in man.

Use of specific stains permits analysis of the frequency of nucleolus-associated heterochromatin in chromosomes 1 and 9 from human fibroblasts. In 81 per cent of interphase nuclei the heterochromatic segment of both No. 1 chromosomes is associated with the nucleolus, while in 19 per cent only one heterochromatic segment shows such an association with the other occupying a random position in the nucleoplasm. The nucleolar association of chromosome 9 heterochromatin is less constant: in 42.3 per cent of the nuclei both segments are associated with the nucleolus, in 39 per cent of the nuclei only one heterochromatic segment presents such an association, and in 18.7 per cent neither of the two heterochromatic segments is in nucleolar association. In 6 per cent of the cells, one or two chromosome 9 heterochromatic segments are in contact with the nuclear membrane. In situ hybridization using tritium-labeled 28S and 18S RNA shows that in the interphase nucleus the acrocentric short arms, carriers of ribosomal cistrons, are associated with the nucleolus. These observations demonstrate the complexity of the nucleolus-associated chromatin which, in addition to segments of chromosomes 1, 9, 13, 14, 15, 21, 22, may include the Y chromosome. They also confirm that the nucleolus constitutes one of the orientation points determining the relative localization of chromosomes in the interphase nucleus.

Location of ribosomal DNA in the human chromosome complement.

Hybridization of (3)H-labeled ribosomal RNA to human chromosomes on slides resulted in specific labeling of the satellite regions of chromosomes 13, 14, 15, 21, and 22, with an over-all efficiency of about 5%. Differences between D and G chromosomes, and between associated and unassociated satellites, were not significant. Labeling of all other parts of the preparations was nonspecific, and increased in the order: extrachromosomal regions < chromosome arms < centric regions.