Chromosomal alterations in cell lines derived from mouse rhabdomyosarcomas induced by crystalline nickel sulfide

Prior studies have shown a preferential decondensation (or fragmentation) of the heterochromatic long arm of the X chromosome of Chinese hamster ovary cells when treated with carcinogenic crystalline NiS particles (crNiS). In this report, we show that the heterochromatic regions of mouse chromosomes are also more frequently involved in aberrations than euchromatic regions, although the heterochromatin in mouse cells is restricted to centromeric regions. We also present the karyotypic analyses of four cell lines derived from tumors induced by leg muscle injections of crystalline nickel sulfide which have been analyzed to determine whether heterochromatic chromosomal regions are preferentially altered in the transformed genotypes. Common to all cell lines was the presence of minichromosomes, which are acrocentric chromosomes smaller than chromosome 19, normally the smallest chromosome of the mouse karyotype. The minichromosomes were present in a majority of cells of each line although the morphology of this extra chromosome varied significantly among the cell lines. C-banding revealed the presence of centromeric DNA and thus these minichromosomes may be the result of chromosome breaks at or near the centromere. In three of the four lines a marker chromosome could be identified as a rearrangement between two chromosomes. In the fourth cell line a rearranged chromosome was present in only 15% of the cells and was not studied in detail. One of the three major marker chromosomes resulted from a centromeric fusion of chromosome 4 while another appeared to be an interchange involving the centromere of chromosome 2 and possibly the telomeric region of chromosome 17.(ABSTRACT TRUNCATED AT 250 WORDS)

Curvature of mouse satellite DNA and condensation of heterochromatin

Cloned, sequenced mouse satellite DNA exhibits properties characteristic of molecules that possess a stable curvature. Circularly permuted fragments containing the region predicted to bend were used to map the curvature relative to DNA sequence. The altered mobility of these fragments in polyacrylamide gels is reversed when gels are run in the presence of distamycin A, a drug that binds preferentially to AT-rich DNA. Treatment of living mouse cells with this drug dramatically reduces the condensation of centromeric heterochromatin, the exclusive location of satellite sequences. In situ hybridization of satellite probes to extended chromosomes at the electron microscope level shows that satellite does not comprise a single block but is distributed throughout the centromere region. Based on these experiments, we hypothesize that the structure of mouse satellite DNA is an important feature of centromeric heterochromatin condensation.

Persistent and heritable structural damage induced in heterochromatic DNA from rat liver by N-nitrosodimethylamine

Analysis, by benzoylated DEAE-cellulose chromatography, has been made of structural change in eu- and heterochromatic DNA from rat liver following administration of the carcinogen N-nitrosodimethylamine (10 mg/kg body weight). Either hepatic DNA was prelabeled with [3H]thymidine administered 2-3 weeks before injection of the carcinogen or the labeled precursor was given during regenerative hyperplasia in rats treated earlier with N-nitrosodimethylamine. Following phenol extraction of either whole liver homogenate or nuclease-fractionated eu- and heterochromatin, carcinogen-modified DNA was examined by stepwise or caffeine gradient elution from benzoylated DEAE-cellulose. In whole DNA, nitrosamine-induced single-stranded character was maximal 4-24 h after treatment, declining rapidly thereafter; gradient elution of these DNA preparations also provided short-term evidence of structural change. Following incubation of purified nuclei with micrococcal nuclease, 10-12% of labeled DNA was solubilized (eu-chromatin) by 1.0 unit of micrococcal nuclease (5 mg of DNA)-1 mL-1 after 9 min. In prelabeled animals, administration of N-nitrosodimethylamine caused a marked fall in the specific radioactivity of solubilized DNA, while that of sedimenting DNA was not affected. Caffeine gradient chromatography suggested short-term nitrosamine-induced structural change in euchromatic DNA, while increased binding of heterochromatic DNA was evident for up to 3 months after carcinogen treatment. Preparations of newly synthesized heterochromatic DNA from animals subjected to hepatectomy up to 2 months after carcinogen treatment provided evidence of heritable structural damage. Carcinogen-induced binding of heterochromatic DNA to benzoylated DEAE-cellulose was indicative of specific structural lesions whose affinity equalled that of single-stranded DNA up to 1.0 kilobase in length.(ABSTRACT TRUNCATED AT 250 WORDS)

5-aza-C-induced changes in the time of replication of the X chromosomes of Microtus agrestis are followed by non-random reversion to a late pattern of replication

Treatment with 5-azacytidine (5-aza-C) causes an advance in the time of replication and enhances the DNase-I sensitivity of the inactive X chromosome in Gerbillus gerbilllus fibroblasts. We found that these changes were not stably inherited and upon removal of the drug the cells reverted to the original state of one active and one inactive X chromosome. In order to determine whether this reversion was random, we used a cell line of female Microtus agrestis fibroblasts in which the two X chromosomes are morphologically distinguishable. In this work we show that the reversion to a late pattern of replication is not random, and the originally late replicating X chromosome is preferentially "reinactivated", suggesting an imprinting-like marking of one or both X chromosomes. The changes in the replication pattern of the X chromosome were associated with changes in total DNA methylation. Double treatment of cells with 5-aza-C did not alter this pattern of euchromatin activation and reinactivation. A dramatic advance in the time of replication of the entire X linked constitutive heterochromatin (XCH) region was however, observed in the doubly treated cells. This change in the replication timing of the XCH occurred in both X chromosomes and was independent of the changes observed in the euchromatic region. These observations suggest the existence of at least two independent regulatory sites which control the timing of replication of two large chromosomal regions.

Sequence of centromere separation: kinetochore formation in induced laggards and micronuclei

Mouse L-cells were treated with bis-benzimidazole derivative (Hoechst 33258), caffeine and bleomycin in order to study genesis of laggards and micronuclei and formation of kinetochores as revealed by antikinetochore antibody staining. Apparently, the Hoechst 33258-induced decondensation experienced by the A:T-rich pericentric heterochromatin does not extend into the centromeric region and does not affect formation, physical appearance or function of kinetochores. The laggards induced by Hoechst 33258 are generally whole chromosome laggards which have antikinetochore antibody binding sites. These kinetochore-carrying laggards were seen to lie outside the spindle region in cells untreated with spindle inhibitors or hypotonic and stained differentially for spindle and chromosomes. Some micronuclei did not show kinetochore dots indicating their origin in acentric chromosome fragments. When cells were treated with caffeine or bleomycin, both types of micronuclei, namely those carrying kinetochores and those generated by acentric fragments, were seen. These results are interesting in that caffeine prevents the rejoining of chromosome breaks and one would expect only kinetochore-less micronuclei in caffeine-treated cells. It may mean that caffeine also induces aneuploidy. The L-cells carry minichromosomes which are no more than a pair of kinetochore dots. Such chromosomes, though detectable by antikinetochore antibody staining, may be missed in routine, acid-fixed, Giemsa-stained preparations.

Pathway of nickel uptake influences its interaction with heterochromatic DNA

Exposure of intact Chinese hamster ovary cells to water-soluble NiCl2 and to particulate crystalline NiS induced a concentration-dependent incidence of chromosomal aberrations which included gaps, breaks, and exchanges. Exposure of cells to crystalline NiS particles caused a high incidence of chromatid exchanges and dicentrics and produced what appears to be an effect on the condensation state of the heterochromatic long arm of the X chromosome. Treatment of cells with NiCl2 did not cause any significant effect on the long arm of the X chromosome, and there was a much lower incidence of the dicentric type of chromosomal aberrations compared to NiS. To examine whether the fragmentation/decondensation of the long arm of the X chromosome produced by crystalline NiS particles was due to a phagocytic pathway of uptake of NiS particles, cells were treated with NiCl2-albumin complexes that had been encapsulated in liposomes. Although treatment of cells with NiCl2-albumin complexes yielded higher intracellular nickel levels than were obtained by treatment of cells with NiCl2, at comparable intracellular levels fragmentation/decondensation of the heterochromatic long arm of the X chromosome was observed when nickel (II) was delivered by way of a liposome but not when cells were treated with unencapsulated NiCl2. Ionic nickel alone irrespective of its delivery mechanism exhibited some preference for heterochromatin, since there was a higher incidence of aberrations observed in the heterochromatic centromeric region of chromosomes. These observations suggest that the pathway of delivery of Ni2+ from NiS particles may be responsible for a preferential interaction of this metal with heterochromatin leading to an effect on the condensation state/fragmentation of the heterochromatic long arm of the X chromosome.

[Statistical patterns of the anomalous staining of 5-bromodeoxyuridine-substituted chromosomes]

Five large chromosome segments showing sometimes an abnormal staining were found in the genome of Chinese hamster (clone 237). Three types of abnormal staining were recorded. After one round of replication in the presence of BrdUrd these segments showed a hetero-staining, whereas after two rounds of replication the same segments showed iso-dark or iso-light staining. Pulse labeling with 3H-thymidine showed that all these segments were the late-replicating ones. The labeling proceeded according to all-or-none principle; in a given cell all five segments showed either presence or absence of the label. On the contrary, the abnormal staining was statistically distributed among these segments. These results are in disagreement with the current view that the abnormal staining is associated with asymmetrical distribution of thymine among two strands of DNA duplex. The above regularities are considered as an argument for the two-stranded model of chromosome.

Theoretical mechanisms for synthesis of carcinogen-induced embryonic proteins: XV. Preliminary generalizations

The term embryonic gene is discussed in which an operational definition is given, namely that it be restricted for those genes which are active during the embryonic state but repressed during differentiation. After generalizing a large variety of different types of carcinogenic agents and their action, which in principle are capable of activating embryonic genes, a preliminary notion of the carcinogenic process was derived. It appears that the bioalkylation pattern can be perturbed by a variety of agents from electromagnetic radiation to ethionine. Specific genes or their corresponding repressors such as an embryonic type phospho-protein kinase would become derepressed because of their methylation status (or by some other analogous alteration, e.g., via a specific mutation of a proto-oncogene that would create an embryonic type kinase, DNA intercalation by planar molecules, or, a hereditary process such as V-type position effect). This would cause competent stem type precursor cells containing easily derepressed or partially repressed arrays of embryonic genes to become activated, producing many features characteristic of a neoplastic cell.

A quantitative electron microscopic study of the effect of glucocorticoids in vivo on the early postnatal differentiation of paraneuronal cells in the carotid body and the adrenal medulla of the rat

The postnatal differentiation of carotid body chief cells and endocrine adrenal medullary cells was comparatively examined during ontogenesis and in rats which were treated with dexamethasone for 7 days after birth. Ultrastructure and innervation of carotid body chief cells are mature in neonates according to the functional requirements of chemoreception. By the end of the first postnatal week, only an increase in number of dense core vesicles can be noticed, the concentration of which then will reach the adult level. Under the effect of dexamethasone most of the heterochromatin is transformed into finely dispersed euchromatin within the nuclei of carotid body chief cells. In the cytoplasm, the Golgi apparatus becomes larger and the granular endoplasmic reticulum hypertrophic. The number of catecholamines storing dense core vesicles increases considerably. The innervation density remains constant. In contrast to the carotid body chief cells, the adrenal medullary cells have not reached their definitive maturity at the time of birth. Besides phenotypes of adrenaline-cells, noradrenaline-cells and small granules containing cells, pheochromoblasts and intermediary cells can be seen as well. Their cytoplasm is sparse, the concentration of dense core vesicles and the innervation density very low. After 8 days of postnatal ontogenesis, pheochromoblasts and intermediary cells are no longer present in the adrenal medulla. In adrenaline-cells and noradrenaline-cells, important processes of growth can be noticed, the cytoplasm has grown in extent, the number of dense core vesicles doubled and the innervation density of single cells triplicated. Only the few small granules containing cells remain small. Under the effect of dexamethasone also in the nuclei of chromaffin cells a transformation of heterochromatin into euchromatin occurs. The increase in number of dense core vesicles is relatively lower than in carotid body chief cells. The significant growth of innervation density during the first postnatal week was inhibited. Our observations suggest that dexamethasone stimulates the synthesis of catecholamines in adrenal medullary cells of newborn rats less pronouncedly than in carotid body chief cells. This could be attributed to the inhibited formation of synapses of growing chromaffin cells and to the in vivo active endocrine counter-regulation.

Heterochromatin in the chromosomes of the gorilla: characterization with distamycin A/DAPI, D287/170, chromomycin A3, quinacrine, and 5-azacytidine

The chromosomes of the gorilla were extensively studied with various staining techniques labeling the different classes of heterochromatin. The chromosomal distribution of distamycin A/DAPI-, D287/170-, quinacrine-, and chromomycin A3-positive heterochromatic regions, as well as the nucleolus organizer regions, is described and compared with the karyotypes of other hominoid species. Lymphocyte cultures were treated with low doses of 5-azacytidine during the last hours of culture. This cytidine analog induces distinct undercondensation in 37 heterochromatic regions in the 24 gorilla chromosomes. The 5-azacytidine-induced undercondensations are localized not only in most of the distamycin A/DAPI-bright heterochromatic regions but also in many telomeric C-bands of the chromosomes. Furthermore, 5-azacytidine preserves the somatic pairing between heterochromatic regions from the interphase nuclei into the metaphase stage. The homeologies and differences in the chromosomal localization of the various classes of heterochromatin, 5-azacytidine-sensitive regions, 5-methylcytosine-rich DNA sequences, and satellite DNAs in the gorilla, chimpanzee, orangutan, and man are discussed.

Mitomycin C-induced mosaicism in C-band regions of human chromosomes 1, 9, 16, and Y

In order to test the hypothesis that somatic mosaicism involving C-band polymorphism of human chromosomes 1, 9, 16 may arise from mitotic crossing over, peripheral blood lymphocytes from normal males were treated with mitomycin C, which is known to induce somatic crossing over in lower eukaryotes. Evidence is presented which shows that mitomycin C is able to alter the heterochromatic pattern in human lymphocytes.

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.

Distamycin A/DAPI bands and the effects of 5-azacytidine on the chromosomes of the chimpanzee, Pan troglodytes

The chromosomes of the chimpanzee were stained with distamycin A/DAPI, which labels specific C-bands. Bright distamycin A/DAPI fluorescence was found in the heterochromatic regions of chromosomes 6, 11, 14 to 16, 18 to 20, and 23 and the Y. Lymphocyte cultures from chimpanzees were treated with low doses of 5-azacytidine during the last hours of culture. This cytosine analog induces highly distinct undercondensations in 28 heterochromatic regions of 19 chromosomes. These 5-azacytidine-sensitive regions are predominantly located in the terminal C-bands of the chromosomes. In vitro treatment with 5-azacytidine also preserves into the metaphase stage somatic pairings between the 5-azacytidine-sensitive heterochromatic regions in interphase nuclei. The homologies and differences regarding the chromosomal localization of distamycin A/DAPI-bright C-bands, 5-azacytidine-sensitive heterochromatin, 5-methylcytosine-rich DNA sequences, and satellite DNAs in the chimpanzee and man are discussed.

High resolution of heterochromatin of Drosophila melanogaster by distamycin A

A DNA-binding AT-specific antibiotic, distamycin A, was used as inhibitor of the condensation process of the heterochromatic regions in Drosophila melanogaster embryonic cells. By this treatment the structural organization of heterochromatin at interphase is preserved until metaphase. The different patterns observed are interpreted as chronological steps in the condensation process.

Satellite DNA and heterochromatin variants: the case for unequal mitotic crossing over

Variations of constitutive heterochromatin (heteromorphisms) appear to be a general feature of eucaryotes. A variety of molecular and cytogenetic evidence supports the hypothesis that heteromorphisms result from unequal double-strand exchanges during mitotic DNA replication. Constitutive heterochromatin consists of highly repeated DNA sequences that are not transcribed. Thus, heteromorphisms are tolerated without overt phenotypic effect. Several of the highly repeated DNAs that comprise constitutive heterochromatin have been shown to contain site-specific endonuclease recognition sequences interspersed at regular intervals dependent upon nucleosome structure. These interspersed short repeated sequences could mediate unequal crossovers, resulting in quantitative variability of constitutive heterochromatin and satellite DNA. De novo variations of constitutive heterochromatin may be useful as markers of exposure to mutagens and/or carcinogens.

[Early effect of estradiol on ultrastructure of chromatin in the endometrium and hormone-dependent mammary tumors]

After in vivo and in vitro administration of aestradiol, the chromatin of lamb endometrium and of hormone-dependent 7,12-dimethylbenzanthracene Rat mammary tumors is rapidly transformed from a condensed into a diffuse chromatin. A stimulation of 3H leucine incorporation into protein was also observed. These modifications were specific for estrogen receptor ligands and for estrogen responsive tissues. In vitro tamoxifen induced pycnosis. These changes could be used to improve the prediction of hormone dependency of human breast and uterine cancers.

Asymmetric decondensation of the L cell heterochromatin by Hoechst 33258

A benzimidazole derivative, Hoechst 33258 can induce decondensation of constitutive heterochromatin in the mouse derived L cell chromosomes when the compound is given in sufficiently high concentration (40 micrograms/ml) to the L cell culture. Hoechst 33258 at low concentration (1 micrograms/ml, 16 h) cannot produce this effect on L cell chromosomes. Bromodeoxyuridine (BUdR) incorporation for one cell cycle simultaneous with the Hoechst 33258 treatment at low concentration could decondense heterochromatin segments in metaphase chromosomes. The heterochromatin decondensation, however, was asymmetric; it was observed only on one chromatid and the other of a chromosome remained in condensed state. The observation of asymmetric decondensation of heterochromatin by Hoechst 33258 after BUdR incorporation for one cell cycle, the association of A-T rich satellite DNA to mouse heterochromatin, and available data on the specific binding of Hoechst 33258 to A-T base pairs of DNA and on the higher affinity of the compound to BUdR substituted DNA than to ordinary DNA implied that the binding of Hoechst 33258 molecules to A-T rich satellite DNA is the cause of heterochromatin decondensation.

The effects of busulphan on the chromosomes of normal human lymphocytes

In vitro exposure of human lymphocytes to busulphan (BUS) produced an increase in chromosome aberrations and in sister-chromatid exchange (SCE) frequency. The distribution of chromosome breaks throughout the karyotype was non-random and they occurred mainly in the G-negative bands. Certain bands had a marked susceptibility to BUS and comparisons with the human chromosome-break distributions reported for a number of drugs revealed that some of these bands were equally susceptible to other alkylating agents. Both the number of chromosome gaps and breaks and the SCE frequency increased with BUS concentration, but only the SCE dose--response was a clearly defined linear relationship. Therefore a standard SCE dose--response curve was constructed for future comparison with the results of similar investigations of patients on BUS therapy.