Condensation of all human chromosomes in phase G2 and early mitosis can be drastically inhibited by 33258-Hoechst treatment

Inhibition of condensation in human chromosomes induced by the thymidine analogue 5-iododeoxyuridine

Human lymphocyte cultures were treated with iododeoxyuridine. This 5-halogenated thymidine analogue induces distinct undercondensations of the heterochromatin of human chromosome 9. The condensation of the other heterochromatic regions on chromosomes 1, 15, 16 and Y is also inhibited, but to a lesser extent. Optimum cell culture conditions required for the induction of undercondensations were determined. Up to 90% of mitotic cells reveal chromosome 9 heterochromatin decondensations when the substance is present in quantities of 1 x 10(-4) M during the last 7 h before cell fixation. In addition, examples of the usefulness of 5-IUDR in the analysis of chromosome aberrations involving chromosome 9 are presented. The interaction between 5-IUDR and chromosomal DNA, the modification of chromosomal proteins and factors inducing chromosomal decondensations are discussed.

Sequence-specific interaction of Hoechst 33258 with the minor groove of an adenine-tract DNA duplex studied in solution by 1H NMR spectroscopy

The interaction of Hoechst 33258 with the minor groove of the adenine-tract DNA duplex d(CTTTTGCAAAAG)2 has been studied in both D2O and H2O solutions by 1D and 2D 1H NMR spectroscopy. Thirty-one nuclear Overhauser effects between drug and nucleotide protons within the minor groove of the duplex, together with ring-current induced perturbations to the chemical shifts of basepair and deoxyribose protons, define the position and orientation of the bound dye molecules. Two drug molecules bind cooperatively and in symmetry related orientations at the centre of the 5'-TTTT and 5'-AAAA sequences with the binding interactions spanning only the four A-T basepairs. The positively charged N-methylpiperazine moieties point towards the centre of the duplex while the phenol groups are disposed towards the 3'-ends of the sequence. Resonance averaging is apparent for both the D2/D6 and D3/D5 phenol protons and D2"'/D6"' and D3"'/D5"' of the N-methylpiperazine ring and is consistent with these groups being involved in rapid rotation or ring-flipping motions in the bound state. Interstrand NOEs between adenine H2s and deoxyribose H1' are consistent with a high degree of propeller twisting of the A-T basepairs at the binding site of the aromatic benzimidazole and phenol rings of Hoechst. The data imply that the minor groove is particularly narrow with many contacts between the complementary curved surfaces of the drug and DNA indicating that strong van der Waals interactions, involving the floor and the walls of the minor groove, stabilize the complex. In our model the NH groups of the benzimidazole rings are positioned to make a pair of bifurcated hydrogen bonds with the adenine N3 and thymine O2 on the floor of the minor groove.

Prefixation treatment with ethidium bromide for high resolution banding analysis of chromosomes from cultured human bone marrow cells

Prefixation treatment of cultured human bone marrow cells with a DNA intercalating agent, ethidium bromide (EBr), induced a dose- and time-related elongation of chromosomes. When compared with EBr-free cultures, a 2.9-fold increase in the yield of early mitotic cells with more than 400 bands per haploid set of chromosomes was achieved by simply adding 10 micrograms/ml of EBr during the last 2 hours of culture. The proportion of early mitotic cells was equal to that obtained in methotrexate synchronized cultures. Fluorescence banding methods using base composition specific agents actinomycin D/DAPI for AT base pairs and chromomycin A3/distamycin A for GC suggested that EBr does not have base specificity, because EBr did not alter the banding patterns of chromosomes obtained with these staining procedures.

Analysis of the fragile-X chromosome: localization and detection of the fragile site in high resolution preparations

Fragile X chromosome preparations were analyzed at levels of up to 850 bands per haploid set. We were able to consistently sublocalize the Xqter fragile site to band Xq27.3 using high-resolution methods. Chromosome length versus the frequency of fragile X expression was also compared. The fragile site appeared at a higher percentage in more condensed chromosome preparations. The importance of this finding is that high-resolution chromosome preparations do not optimize fragile-X detection.

5-Azacytidine-induced undercondensations in human chromosomes

The cytosine analogue 5-azacytidine induces very distinct undercondensations in human chromosomes if applied to lymphocyte cultures. The number of induced undercondensations and their chromosomal localization can be varied by the 5-azacytidine dose and the treatment time. "Pulverized" chromosomes or undercondensations in the G-band-positive chromosome regions are produced with high doses and long treatment times. If applied in low doses during the last hours of culture, 5-azacytidine induces specific undercondensations in the heterochromatin of chromosomes 1, 9, 15, 16, and Y. Optimum conditions required for inducing the various types of undercondensation in the chromosomes were determined. Various examples of the use of 5-azacytidine in the analysis of chromosome rearrangements involving heterochromatic regions are presented.

Specific silver staining of experimentally undercondensed chromosome regions

Treatment of human and mouse cell cultures with DNA binding AT-specific compounds and with some base analogues induced distinct undercondensations in several heterochromatic chromosome regions. All those heterochromatic regions undercondensed by AT-specific DNA ligands (distamycin A, DAPI, Hoechst 33258) could be heavily labeled with the silver(Ag)-staining technique; but the heterochromatic regions undercondensed with the cytidine analogue 5-azacytidine were Ag-negative. In metaphase chromosomes from BrdU-treated human cell cultures, the bifilarly substituted chromatids, which show a slight undercondensation, were also Ag-negative. Cytochemical analyses of the Ag-stained undercondensed heterochromatic regions showed that the Ag-stainable material consisted of nonhistone proteins. The mechanism of Ag staining in the undercondensed heterochromatic regions was compared with Ag staining of the nucleolus organizer regions.

The use of distamycin A in human lymphocyte cultures

The effect of the oligopeptide antibiotic distamycin A on human lymphocyte cultures was examined. Distamycin A specifically inhibits the condensation of the Y heterochromatin and induces a fragile site in the chromosome 16 (band q22) in some individuals. The optimal culture conditions under which an undercondensation of the Y heterochromatin and an induction of the fragile site in 16q22 can be achieved by in vitro treatment of lymphocytes were determined. This also permits the use of distamycin A in routine diagnostics of human chromosomes. The use of this technique in the analysis of translocations involving the Y chromosome is presented. The distamycin A-DNA interaction and the different possible explanations for the distamycin A-induced undercondensations of the Y heterochromatin and fragile sites 16q22 are discussed.

Hoechst 33258 induced uncondensed sites in marsupial chromosomes

The fluorochrome Hoechst 33258 induces pronounced uncondensed regions at mitosis at one or more specific sites on the X chromosomes of all eighteen species of marsupials belonging to the family Macropodidae which have been examined. The Y chromosomes of nearly all of these species also show sensitive sites. Autosomal regions which respond to this chemical were observed in only five species and there is evidence of polymorphism for two of these. The regions which respond usually show C-banding, but not all C-banding regions are affected. No specific effect was found in the chromosomes of eleven other species examined which are representative of 5 different Australian marsupial families. The implications of the apparent restriction of sex chromosome sensitive sites to macropods are discussed.

Detection of G-C rich heterochromatin by 5-azacytidine in mammals

A new effect of 5-ACR (5-azacytidine), observed in fibroblast or kidney cell cultures is described in the calf (Bos taurus) and in some selected primates (Cebus capucinus, Erythrocebus patas, and Cercopithecus cephus). This cytidine analogue, used at low doses during the last late S phase, prevents the condensation of R-band positive heterochromatin (G-C rich segments). Thus, 5-ACR treatment can be used as a simple method for the detection of G-C rich heterochromatin.

Establishment in continuous culture of a T-lymphoid cell line (HD-Mar) from a patient with Hodgkin's lymphoma

A new cell line, HD-Mar, was established from a pleural effusion of a patient with Hodgkin's lymphoma. Formation of E rosettes, sensitivity to anti-T serum, elevated terminal deoxynucleotidyl transferase activity, presence of T-cell and the common ALL membrane antigens, morphology, and cytochemical staining indicate that the HD-Mar line is of thymic derivation. Absence of any immunoglobulin determinants, the lack of EBNA or any other EBV-associated antigen or function are also characteristics associated with established T-cell-derived lymphoma cell lines. Karyotype analysis indicated a tetraploid origin of the cell line.