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The processes taking place during routine chromosome preparation are not well understood. In this study, the morphological changes in amniotic fluid cells, blood lymphocytes, and bone marrow cells in the metaphase stage were examined under an inverted microscope during chromosome preparation. The putative processes that occur during chromosome preparation were simulated in suspension, and the cells were treated with different mixtures of hypotonic solution, fixative, methanol, acetic acid, and water. Evaporation of the fixative was performed under normal atmospheric conditions and under vacuum at different levels of humidity. Freeze fracture electron microscopy was used to analyze the effects of fixative on the cell membrane. Confocal microscopic analysis was used to investigate three-dimensionally the effects of hypotonic treatment on the positions of chromosomes in fixed mitotic lymphocytes. Chromosome preparation-induced changes in the lengths of single chromosomes were also investigated. The results show that chromosome spreading involves significant water-induced swelling of mitotic cells during evaporation of the fixative from the slide, which is a prerequisite for chromosomal elongation, the production of metaphase spreads for chromosome analysis, and the appearance of Giemsa banding patterns. Hypotonic treatment is essential for well-spread metaphase chromosomes because it moves the chromosomes from a central to a more peripheral position in the cell, where they can be stretched more effectively during mitotic swelling. Like mitotic cells, isolated single chromosomes also have their own potential to swell and lengthen during chromosome preparation. We hypothesize that chromosome preparation leads to a genome-wide chromosomal region-specific opening of chromatin structures as GTG-light bands and sub-bands. Living cells may possess a similar mechanism, which is used only to open single chromatin structures to facilitate transcription. We propose the concept of chromosomal region-specific protein swelling.
Our previous studies demonstrated that human chromosome 8 contains metastasis suppressor gene(s) for rat prostate cancer. However, it is still unknown which portion of human chromosome 8 is associated with suppression of metastatic ability, because all of the clones in which metastatic ability is suppressed contain at least one copy of intact human chromosome 8. In the present study, we used the irradiated microcell-mediated chromosome transfer technique to enrich for specific chromosomal arm deletions of selected chromosomes. The resultant series of human chromosomes 8 with a variety of chromosomal deletions was introduced into highly metastatic Dunning rat prostate cancer cells. All of the resultant microcell hybrids showed reduced metastatic ability. To obtain a smaller size of human chromosome 8 and to locate further the region of metastasis suppressor gene(s), the most reduced size of human chromosome 8 that was generated with the initial irradiated chromosome transfer was retransferred into the Dunning cancer cells without irradiation. The resultant microcell hybrids were analyzed to determine which portion of human chromosome 8 suppressed the metastatic ability of the recipient cells. This analysis demonstrates that the portion of human chromosome 8 containing metastasis suppressor gene(s) for rat prostate cancer cells lies on human chromosome segment 8p21-p12, where frequent allelic losses have been detected in allelotype analyses of human prostate cancer. This suggests that one of the metastasis suppressor genes for rat prostate cancer on human chromosome 8 may also play an important role in the progression of human prostate cancer.
Chromosomal lagging and non-disjunction are the main mechanisms of chromosomal malsegregation at mitosis. To date, the relative importance of these two events in the genesis of spontaneous or induced aneuploidy has not been fully elucidated. A methodology based on in situ hybridization with centromeric probes in binucleated lymphocytes was previously developed to provide some insight into this matter. With this method, both chromosomal loss and non-disjunction can be simultaneously detected by following the distribution of specific chromosomes in the nuclei and micronuclei of binucleated cells. In this study, this approach was used for studying the role of chromosomal loss and non-disjunction in the age-related malsegregation of sex chromosomes in females. For this purpose, cultures of cytokinesis-blocked lymphocytes were established from 12 healthy women ranging in age from 25 to 56. The occurrence of malsegregation of X chromosomes in vitro was estimated in binucleated cells that contained four signals, which originates from the division of normal disomic cells. In this cell population, the frequencies of X chromosome loss and non-disjunction ranged from 0% to 1.69% (mean 0.75%), and from 0.20% to 1.33% (mean 0.57%), respectively. This indicates that both events contribute to malsegregation of X chromosomes in vitro. Moreover, a small but not negligible fraction of binucleated cells with two or six copies of the X chromosome was noticed in all donors. These cells, which are thought to arise from parental monosomic and trisomic types, may indicate the malsegregation of X chromosomes in vivo. The frequency of X chromosome aneuploidy both in vivo and in vitro significantly correlated with the age of donors. Analysis of chromosomal distribution in unbalanced cells demonstrated that both X homologues were frequently involved. The frequency of such multiple events (0.17%) was far greater than that expected by mere chance, indicating a tendency to multiple malsegregation events in the cell population investigated. Finally, parallel analysis of the segregation of chromosomes X and 1 in five of the donors confirmed the greater (about tenfold) susceptibility of X chromosomes to malsegregate compared with autosomes.
Chromosome-specific DNA libraries can be very useful in molecular and cytogenetic genome mapping studies. We have developed a rapid and simple method for the generation of chromosome-specific DNA sequences that relies on polymerase chain reaction (PCR) amplification of a single flow-sorted chromosome or chromosome fragment. Previously reported methods for the development of chromosome libraries require larger numbers of chromosomes, with preparation of pure chromosomes sorted by flow cytometry, generation of somatic cell hybrids containing targeted chromosomes, or a combination of both procedures. These procedures are labor intensive, especially when hybrid cell lines are not already available, and this has limited the generation of chromosome-specific DNA libraries from nonhuman species. In contrast, a single sorted chromosome is a pure source of DNA for library production even when flow cytometric resolution of chromosome populations is poor. Furthermore, any sorting cytometer may be used with this technique. Using this approach, we demonstrate the generation of PCR libraries suitable for both molecular and fluorescence in situ hybridization studies from individual baboon and canine chromosomes, separate human homologues, and a rearranged marker chromosome from a transformed cell line. PCR libraries specific to subchromosomal regions have also been produced by sorting a small chromosome fragment. This simple and rapid technique will allow generation of nonhuman linkage maps and probes for fluorescence in situ hybridization and the characterization of marker chromosomes from solid tumors. In addition, allele-specific libraries generated by this strategy may also be useful for mapping genetic diseases.
Chromosome homology between chicken (Gallus gallus) and guinea fowl (Numida meleagris) was investigated by comparative chromosome painting with chicken whole chromosome paints for chromosomes 1-9 and Z and by comparative mapping of 38 macrochromosome-specific (chromosomes 1-8 and Z) and 30 microchromosome-specific chicken cosmid DNA clones. The comparative chromosome analysis revealed that the homology of macrochromosomes is highly conserved between the two species except for two inter-chromosomal rearrangements. Guinea fowl chromosome 4 represented the centric fusion of chicken chromosome 9 with the q arm of chicken chromosome 4. Guinea fowl chromosome 5 resulted from the fusion of chicken chromosomes 6 and 7. A pericentric inversion was found in guinea fowl chromosome 7, which corresponded to chicken chromosome 8. All the chicken microchromosome-specific DNA clones were also localized to microchromosomes of guinea fowl except for several clones localized to the short arm of chromosome 4. These results suggest that the cytogenetic genome organization is highly conserved between chicken and guinea fowl.
Putative tumor suppressor genes can be mapped to specific chromosomes by the introduction of individual chromosomes derived from normal cells via microcell fusion. We have examined whether a highly malignant human uterine endometrial carcinoma cell line, HHUA, can be suppressed by only one normal chromosome or by multiple chromosomes. A library of mouse A9 clones containing different human chromosomes tagged with the pSV2-neo plasmid DNA were constructed. Transfer by microcell fusion of either chromosome 1, 6, 9, 11, or 19 into the HHUA tumor cell line was performed, and the abilities of the microcell hybrids to form tumors in nude mice were examined. The introduction of a chromosome 19 had no effect on the tumorigenicity of the cells, whereas microcell-hybrid clones with an introduced chromosome 1, 6 or 9 were completely suppressed for tumorigenicity. A decrease in tumor-take incidence in some but not all clones was observed following the introduction of a chromosome 11. The nontumorigenic microcell hybrids with an introduced chromosome 1 differed from the nontumorigenic microcell hybrids with an introduced chromosome 6, 9, or 11. A large percentage of hybrids with chromosome 1 senesced and/or showed alterations in cellular morphology and transformed growth properties in vitro. No growth or morphology alterations were observed following transfer of the other chromosomes. These results may indicate that more than one chromosome carries a tumor suppressor gene(s) for this human uterine endometrial carcinoma cell line and support the hypothesis that multiple tumor suppressor genes control the tumorigenic phenotype in the multistep process of neoplastic development.
We have investigated chromosomal segregation during meiosis in a cross between two polymorphic haploid laboratory strains of Saccharomyces cerevisiae, FL100 and GRF18. These two strains have large chromosome-length polymorphisms for chromosomes I and III allowing for easy scoring of parental chromosomes after meiotic segregation. Chromosome III in the FL100 strain was 35 kb shorter than chromosome III in GRF18, while FL100 chromosome I was 40 kb larger than chromosome I in GRF18. Segregation analysis of chromosomes I and III in 50 tetrads showed an apparent association between chromosomes I and III, whereas only the original parental association of chromosomes I and III was found in the spores. By hybridization with chromosome-specific probes we have shown that the polymorphisms are due to a large translocation from chromosome III onto chromosome I in FL100. The translocated fragment is larger than 80 kb and was mapped between Ty and HML. In nine tetrads analyzed, chromosome-length polymorphisms which did not segregate according to Mendelian law were observed.
The phytopathogenic bacterium Agrobacterium tumefaciens is unique in that it possesses both linear and circular DNA chromosomes in addition to a plant-tumor-inducing (Ti) plasmid. We analyzed the two chromosomal DNA molecules in strain MAFF301001, whose Ti plasmid has already been sequenced completely. Physical maps of the chromosomal DNAs were constructed by Southern hybridization experiments using Pme I and Swa I fragments and short fragments bridging the Swa I fragments with special care to avoid any missing fragment. Hybridization with 16S rDNA probe showed one rDNA locus on the linear chromosome and two loci on the circular chromosome. For this bacterium to be pathogenic, not only Ti plasmid but also chromosomal genes are required. The chromosomal virulence (chv) genes (chvA, chvB, chvD, chvE, chvG, chvH, and chvI) and the chromosomal genes affecting the virulence [acvB, pgm(exoC), glgP, miaA, and ros] were successfully mapped onto 5 different regions in the chromosomal physical maps. These chv genes and the chromosomal genes affecting the virulence other than pgm and glgP were found on the circular chromosome, whereas the pgm and glgP genes were located on the linear chromosome. In contrast to the large terminal inverted repeats of Streptomyces linear chromosomal DNA, no hybridization signal was detected between left and right terminal fragments of the linear A. tumefaciens chromosome. Quantitative analysis of DNA fragments indicated that the copy numbers of the two chromosomal DNAs and the Ti plasmid are identical.
Fluorescence in situ hybridization procedures were used to examine the influence of chromosome locus on the frequency and type of chromosome aberrations induced by 60Co gamma rays in the human lymphoblastoid cell line TK6. Aberrations involving the X chromosome were compared to those involving the similarly sized autosome chromosome 7. When corrected for DNA content, acentric fragments were induced with equal frequency in the X and 7 chromosomes. Dose-dependent increases in chromosomal interchanges involving chromosome 7 were noted and the frequencies of balanced translocations and dicentrics produced were approximately equal. Chromosome interchanges involving the X chromosome were rare and showed no apparent dose dependence. Thus, while chromosomes 7 and X are equally sensitive to the induction of chromosome breaks, the X chromosome is much less likely to interact with autosomes than chromosome 7. The noninvolvement of the X chromosome in translocations with autosomes may reflect a more peripheral and separate location for the X chromosome in the mammalian nucleus.
BACKGROUND: The analysis of complex cytogenetic databases of distinct leukaemia entities may help to detect rare recurring chromosome aberrations, minimal common regions of gains and losses, and also hot spots of genomic rearrangements. The patterns of the karyotype alterations may provide insights into the genetic pathways of disease progression. RESULTS: We developed a simplified computer readable cytogenetic notation (SCCN) by which chromosome findings are normalised at a resolution of 400 bands. Lost or gained chromosomes or chromosome segments are specified in detail, and ranges of chromosome breakpoint assignments are recorded. Software modules were written to summarise the recorded chromosome changes with regard to the respective chromosome involvement. To assess the degree of karyotype alterations the ploidy levels and numbers of numerical and structural changes were recorded separately, and summarised in a complex karyotype aberration score (CKAS). The SCCN and CKAS were used to analyse the extend and the spectrum of additional chromosome aberrations in 94 patients with Philadelphia chromosome positive (Ph-positive) acute lymphoblastic leukemia (ALL) and secondary chromosome anomalies. Dosage changes of chromosomal material represented 92.1% of all additional events. Recurring regions of chromosome losses were identified. Structural rearrangements affecting (peri)centromeric chromosome regions were recorded in 24.6% of the cases. CONCLUSIONS: SCCN and CKAS provide unifying elements between karyotypes and computer processable data formats. They proved to be useful in the investigation of additional chromosome aberrations in Ph-positive ALL, and may represent a step towards full automation of the analysis of large and complex karyotype databases.
Using 14 Chinese hamster stocks with various reciprocal translocations, chromosomally unbalanced gametes were produced and used to investigate the participation of the unbalanced gametes in fertilization and the development of unbalanced embryos. The selection of chromosomally abnormal gametes during fertilization was investigated by the chromosomal analysis of meiotic cells in heterozygotes for the 14 reciprocal translocations and pronuclei of fertilized ova obtained from crossing these heterozygotes. Compared with the expected frequencies from meiotic metaphase II (MII) scoring, the frequencies of male pronuclei having commonly a deficiency of chromosome 1 (q14-->q42) or chromosome 3 (p23-->q31) in one-cell embryos decreased significantly. However, the frequencies of male pronuclei with other abnormalities were all consistent with those expected from MII scoring. In contrast, the frequencies of female pronuclei with any karyotype including the same ones, as those decreased in male pronuclei from the translocation heterozygotes were all consistent with those estimated from MII scoring. These results suggest that gametes with nullisomies as well as disomies for any chromosomal segments may mostly participate in fertilization, whereas some sperm nullisomic for the specific segments of chromosomes 1 and 3 may fail to fertilize. On the other hand, the zygotic selection of chromosomal imbalance was investigated by direct analyses of pre-implantation embryos from crosses between chromosomally normal females and male heterozygotes from the 14 stocks with various reciprocal translocations. The chromosomal and morphological analysis revealed that some embryos were arrested in development at the two-cell stage and their common abnormality was partial monosomy for chromosome 1 or 2. Embryos with partial monosomy including chromosomes 1, 3 and 4 showed arrested development at four-eight-cell stages. Among day 4 embryos, some chromosomally unbalanced embryos, mainly with a deficiency of other segments, such as chromosomes 1p, 2q, 5q and 8, had fewer blastomeres than karyotypically normal and balanced embryos. The homology between the mouse and the Chinese hamster chromosomes relating to the developmental abnormalities at early stages was partially confirmed.
The chromosomal localization of the gene which complements radiation hypersensitivity of AT cells was studied by microcell-mediated chromosome transfer. A 6-thioguanine-resistant derivative of an immortalized AT cell line, AT2KYSVTG, was used as a recipient for microcell-mediated chromosome transfer from 4 strains of mouse A9 cells, 3 of which carried a human X/11 recombinant chromosome containing various regions of chromosome 11, while the other carried an intact X chromosome. HAT-resistant microcell hybrids were isolated and examined for their radiosensitivity and chromosome constitution. The microcell hybrid clones obtained from the transfer of an intact X chromosome or an X/11 chromosome bearing the pter----q13 region of chromosome 11 did not show a difference in radiosensitivity from parental AT cells, while those obtained from the transfer of X/11 chromosomes bearing either the p11----qter or the pter----q23 region of chromosome 11 exhibited a marked radioresistance which was comparable to normal human fibroblasts. A HAT-resistant but radiosensitive variant was further obtained from the microcell fusion with an A9 cell strain carrying an X/11 chromosome bearing the 11p11----qter region, in which a deletion at the 11q23 region was found. The results indicate that the gene which complements a radiosensitive phenotype of AT is located at the q23 region of chromosome 11.
Chromosomal in situ suppression (CISS) hybridization of biotin-labeled DNA libraries for human chromosomes 1, 2 and 4 was used to investigate chromosome homology between human being and rhesus monkey. The results demonstrate that chromosome 1 in human being and rhesus monkey is homologous, of which the 1pter-->1q33 of rhesus monkey is highly homologous with a cognate region of chromosome 1 in human, while the 1q33-->1qter is relatively low; Chromosome 2 in human shows homology with the long arm of chromosome 13 as well as the long arm and the partial short arm of chromosome 9 in the rhesus, and chromosome 4 in human is identical to chromosome 2 in rhesus monkey. Combined with a comparative analysis of banding patterns of chromosomes, derivation relationships of chromosomes between man and the rhesus are discussed. Our present data provide a definitive proof that chromosomal rearrangements may be a major mechanism of chromosomal evolution in primates.
Chromosomal aberrations in colonic tumourigenesis were investigated by fluorescence in situ hybridization (FISH) with centromere-specific DNA probes and correlated to flow cytometry (FCM) results in a series of tissues including normal colonic epithelium, adenomas, and carcinomas, as well as adenomas adjacent to carcinomas. No numerical chromosome aberrations were detected in normal colonic epithelium, except for an extra chromosome X in one case. In the adenomas, the most frequently occurring chromosome aberration was a trisomy for chromosome 7, occurring in 37 per cent of the cases. In the carcinomas, two distinct routes of genetic aberration could be established on the basis of correlation with FCM: one with and one without endoreduplication. In the carcinomas without endoreduplication, trisomy or tetrasomy for chromosome 7 was detected in 12 out of 15 cases (80 per cent). In three of these cases, trisomy 7 was found in combination with loss of chromosome 17 and/or chromosome 18. In 87 per cent of the carcinomas with endoreduplication, loss of chromosome 17 and/or 18 was found, while in only one case was gain of chromosome 7 detected. In the adenomas adjacent to carcinomas, trisomy 7 was found in 36 per cent of the cases. In these cases, the concomitant adenocarcinomas showed the same numerical chromosome 7 aberration, plus extra aberrations for other chromosomes. In only two cases the carcinoma demonstrated trisomy 7 with a normal adjacent adenoma. These results suggest that gain of chromosome 7 is a significant aberration in the tumourigenesis of colonic carcinomas in which no endoreduplication has occurred. No marked clinico-pathological differences were observed between tumours of either route of tumourigenesis in this series.
Visual karyotyping and visual classification of isolated chromosomes was carried out by seven investigators on 22 trypsin banded metaphases of average quality. The karyotyping experiment resulted in an average error rate of 0-1% (zero-0-4%) and the classification of isolated chromosomes resulted in an error rate of 3% (2-5%). The B and F group chromosomes were found to be most difficult to classify when isolated, while no errors were made of the no. 1 and the X chromosome. Large differences were seen in the resulting error pattern for the individual investigators both with regard to their total error rate and also the chromosome types which they most frequently misclassified. Based upon these error patterns it is suggested that more than 95% of the chromosomes in an average quality material contain features upon which a reliable visual classification can be made. Thus there may be a potential possibility that these chromosomes may be classified by computer on the basis of these features. The fact that visual karyotyping is much more reliable than visual classification of isolated chromosomes indicated that computer classification of chromosomes should include programming capable of making appropriate comparison between the chromosomes in the metaphase and at the same time take into account the expected presence of 23 chromosome pairs for normal cells. This would simulate the human performance of visual karyotyping and make a classification possible of at least some of the remaining 5% difficult chromosomes.
Chromosome painting using commercially available human chromosome-specific DNA libraries was performed to elucidate chromosomal rearrangements in lemur evolution. Human-specific probes for chromosomes 3, 14, 15, and 21 were used to paint chromosomes of six species: Eulemur fulvus mayottensis, Varecia variegata, Lemur catta, Hapalemur simus, H. griseus griseus, and H. aureus. All human chromosome libraries hybridized specifically to chromosome segments of varying length or to whole arms of Lemur chromosomes. The labeling was clearly visualized and permitted precise delineation of the hybridized Lemur chromosomal segments. The use of commercial probes of human chromosomes for chromosome painting appears efficient enough to investigate homology in different species of Lemur. In general, the results obtained by chromosome painting in this study confirm results previously obtained by the R-banding technique but modify the location of some chromosomal rearrangements on different branches of the evolutionary tree of the Lemuridae and reveal some new rearrangements that were not detectable with banding techniques. These results show that chromosome painting with human chromosome-specific DNA libraries can provide useful information in comparative studies on karyotypes of distantly related mammalian species, providing a powerful tool for evolutionary studies, especially in phylogeny.