Mosaic trisomy 17 in amniocytes: phenotypic outcome, tissue distribution, and uniparental disomy studies.
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Mosaicism for trisomy 17 in amniocyte cultures is a rare finding, whilst postnatal cases are exceptional. In order to gain insight into the possible effects of the distribution of the trisomic line and of uniparental disomy (UPD) on embryofoetal development, we have performed follow-up clinical, cytogenetic and molecular investigations into three newly detected prenatal cases of trisomy 17 mosaicism identified in cultured amniotic fluid. In the first case, the pregnancy ended normally with the birth of a healthy girl, and analysis of newborn lymphocytes and of multiple extra-embryonic tissues was indicative of confined placental mosaicism. The second case was also associated with a normal pregnancy outcome and postnatal development, and only euploid cells were found in peripheral blood after birth. However, maternal isodisomy 17 consequent to a meiosis II error and loss of a chromosome 17 homologue was detected in peripheral lymphocytes postnatally. In the third case, pathological examination after termination of pregnancy showed growth retardation and minor dysmorphisms, and the trisomic line was detected in foetal skin fibroblasts. In addition, biparental derivation of chromosome 17 was demonstrated in the euploid lineage. These results, together with previously reported data, indicate that true amniotic trisomy 17 mosaicism is more commonly of extra-embryonic origin and associated with normal foetal development. Phenotypic consequences may arise when the trisomic line is present in foetal tissues. Case 2 also represents the first observation of maternal UPD involving chromosome 17; the absence of phenotypic anomalies in the child suggests that chromosome 17 is not likely to be subject to imprinting in maternal gametes. (+info)
Centrosome abnormalities in pancreatic ductal carcinoma.
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The centrosome plays an important role in microtubule nucleation and organization, ensuring the establishment of cell polarity and balanced chromosome segregation. Recent studies have suggested that the loss of cell polarity and/or chromosome missegregation (aneuploidy) in human malignant tumors could result from defects in centrosome function. Using immunofluorescence analysis with an antibody to gamma-tubulin (a well-characterized centrosomal component), we examined surgically resected human pancreatic tissues for centrosome abnormalities. The tissues included ductal carcinomas (n = 13), adenomas (n = 3), endocrine tumors (n = 3), chronic pancreatitis (n = 5), and normal pancreatic tissues (n = 12). We found that most (85%) carcinomas and some adenomas displayed abnormal centrosome profiles, characterized by an increase in size and number of centrosomes, and by their irregular distribution. In contrast, none of normal ductal and stromal tissues showed these abnormalities. These findings suggest that centrosome abnormalities may develop at a relatively early stage of pancreatic ductal carcinogenesis. (+info)
Comparison of features of human lung cancer cell lines and their corresponding tumors.
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Although human lung tumor-derived cell lines play an important role in the investigation of lung cancer biology and genetics, there is no comprehensive study comparing the genotypic and phenotypic properties of lung cancer cell lines with those of the individual tumors from which they were derived. We compared a variety of properties of 12 human non-small cell lung carcinoma (NSCLC) cell lines (cultured for a median period of 39 months; range, 12-69) and their corresponding archival tumor tissues. There was, in general, an excellent concordance between the lung tumor cell lines and their corresponding tumor tissues for morphology (100%), the presence of aneuploidy (100%), immunohistochemical expression of HER2/neu (100%) and p53 proteins (100%), loss of heterozygosity at 13 chromosomal regions analyzed (97%) using 37 microsatellite markers, microsatellite alterations (MAs, 75%), TP53 (67%), and K-ras (100%) gene mutations. In addition, there was 100% concordance for the parental allele lost in all 115 comparisons of allelic losses. Some discrepancies were found; more aneuploid subpopulations of cells were detected in the cell lines as well as higher incidences of TP53 mutations (4 of 10 mutations not found in the tumors) and microsatellite alterations (two cell lines with MAs not detected in the tumors). Similar loss of heterozygosity frequencies by chromosomal regions and mean fractional allelic loss index were detected between successfully cultured and 40 uncultured lung tumors (0.45 and 0.49, respectively), indicating that both groups were similar. Our findings indicate that the NSCLC cell lines in the large majority of instances retain the properties of their parental tumors for lengthy culture periods. NSCLC cell lines appear very representative of the lung cancer tumor from which they were derived and thus provide suitable model systems for biomedical studies of this important neoplasm. (+info)
How aneuploidy affects metabolic control and causes cancer.
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The complexity and diversity of cancer-specific phenotypes, including de-differentiation, invasiveness, metastasis, abnormal morphology and metabolism, genetic instability and progression to malignancy, have so far eluded explanation by a simple, coherent hypothesis. However, an adaptation of Metabolic Control Analysis supports the 100-year-old hypothesis that aneuploidy, an abnormal number of chromosomes, is the cause of cancer. The results demonstrate the currently counter-intuitive principle that it is the fraction of the genome undergoing differential expression, not the magnitude of the differential expression, that controls phenotypic transformation. Transforming the robust normal phenotype into cancer requires a twofold increase in the expression of thousands of normal gene products. The massive change in gene dose produces highly non-linear (i.e. qualitative) changes in the physiology and metabolism of cells and tissues. Since aneuploidy disrupts the natural balance of mitosis proteins, it also explains the notorious genetic instability of cancer cells as a consequence of the perpetual regrouping of chromosomes. In view of this and the existence of non-cancerous aneuploidy, we propose that cancer is the phenotype of cells above a certain threshold of aneuploidy. This threshold is reached either by the gradual, stepwise increase in the level of aneuploidy as a consequence of the autocatalysed genetic instability of aneuploid cells or by tetraploidization followed by a gradual loss of chromosomes. Thus the initiation step of carcinogenesis produces aneuploidy below the threshold for cancer, and the promotion step increases the level of aneuploidy above this threshold. We conclude that aneuploidy offers a simple and coherent explanation for all the cancer-specific phenotypes. Accordingly, the gross biochemical abnormalities, abnormal cellular size and morphology, the appearance of tumour-associated antigens, the high levels of secreted proteins responsible for invasiveness and loss of contact inhibition, and even the daunting genetic instability that enables cancer cells to evade chemotherapy, are all the natural consequence of the massive over- and under-expression of proteins. (+info)
Specific chromosome alterations in fluconazole-resistant mutants of Candida albicans.
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The exposure of Candida albicans to fluconazole resulted in the nondisjunction of two specific chromosomes in 17 drug-resistant mutants, each obtained by an independent mutational event. The chromosomal changes occurred at high frequencies and were related to the duration of the drug exposure. The loss of one homologue of chromosome 4 occurred after incubation on a fluconazole medium for 7 days. A second change, the gain of one copy of chromosome 3, was observed after exposure for 35 or 40 days. We found that the mRNA levels of ERG11, CDR1, CDR2, and MDR1, the candidate fluconazole resistance genes, remained either the same or were diminished. The lack of overexpression of putative drug pumps or the drug target indicated that some other mechanism(s) may be operating. The fluconazole resistance phenotype, electrophoretic karyotypes, and transcript levels of mutants were stable after growth for 112 generations in the absence of fluconazole. This is the first report to demonstrate that resistance to fluconazole can be dependent on chromosomal nondisjunction. Furthermore, we suggest that a low-level resistance to fluconazole arising during the early stages of clinical treatment may occur by this mechanism. These results support our earlier hypothesis that changes in C. albicans chromosome number is a common means to control a resource of potentially beneficial genes that are related to important cellular functions. (+info)
A proposal for a simple way to distinguish aneugens from clastogens in the in vitro micronucleus test.
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In our previous in vitro micronucleus (MN) study, we showed that aneugens, in addition to inducing micronuclei, induce a higher frequency of polynuclear (PN) and mitotic (M) cells than clastogens. We hypothesized that the frequency of PN and M cells induced can distinguish aneugens from clastogens. To test the hypothesis, we conducted the micronucleus tests with mitomycin C (MMC), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), vincristine (VINC) and diazepam in a Chinese hamster cell line (CHL) and VINC, benzo[a]pyrene (BP) and 7,12-dimethylbenz[a]anthracene (DMBA) in a subclone of V79 cells (V79-MZ). All chemicals increased the frequency of M cells with statistical significance. All chemicals except diazepam increased the frequency of PN cells with statistical significance. Three of the aneugens (VINC, BP and DMBA) induced >/=200 PN cells/1000 cells while the clastogens (MNNG and MMC) induced 100 PN cells at most. All the aneugens but no clastogens significantly increased the frequency of M cells. We propose that micronucleus test-positive chemicals that induce >/=200 PN cells/1000 cells and significantly increase the frequency of M cells are aneugens and those that induce at most 100 PN cells/1000 cells and do not significantly increase the frequency of M cells in our MN test protocol are clastogens. Diazepam, however, did not induce PN cells, although it increased the frequency of M cells dose dependently. We explain this fact in relation to diazepam's mode of action. Our proposal suggests a quick, easy and practical way to distinguish aneugens from clastogens for screening purposes. (+info)
c-erbB2/neu gene and chromosome 17 analysis in breast cancer by FISH on archival cytological fine-needle aspirates.
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The detection of specific genetic alterations in breast cancer is useful for diagnosing, predicting prognosis and planning preoperative treatment. c-erbB2/neu overexpression is usually detected by immunocytochemistry (ICC), although this technique is neither completely reproducible nor highly reliable, owing to specimen and methodologic variability and antibody sensitivity. Here, we combine two well-established techniques, fine-needle aspiration (FNA) and fluorescence in situ hybridization (FISH), to detect c-erbB2/neu amplification in patients candidate to primary chemotherapy and, in part, previously analysed for c-erbB2/neu overexpression. Sixty smears from FNA were used to simultaneously detect c-erbB2/neu and chromosome 17 centromere. FISH was successful in 58 cases and detected 24 amplified cases, three of which were negative by immunophenotyping, 28 negative cases, with evidence of two normal c-erbB2/neu/signals, two cases with deletion of c-erbB2/neu, and four cases with polysomy, thus providing more reliable and informative results than ICC. This study underlines the advantages offered by the FNA and FISH combination which are two rapid, reliable, simple and informative techniques, to analyse one of the most important genetic markers for predicting prognosis and chemotherapy planning for breast carcinoma in particular in the light of the recently proposed trials of primary chemotherapy. (+info)
Chromosomal gains and losses in primary colorectal carcinomas detected by CGH and their associations with tumour DNA ploidy, genotypes and phenotypes.
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Comparative genomic hybridization (CGH) is used to detect amplified and/or deleted chromosomal regions in tumours by mapping their locations on normal metaphase chromosomes. Forty-five sporadic colorectal carcinomas were screened for chromosomal aberrations using direct CGH. The median number of chromosomal aberrations per tumour was 7.0 (range 0-19). Gains of 20q (67%) and losses of 18q (49%) were the most frequent aberrations. Other recurrent gains of 5p, 6p, 7, 8q, 13q, 17q, 19, X and losses of 1p, 3p, 4, 5q. 6q, 8p, 9p, 10, 15q, 17p were found in > 10% of colorectal tumours. High-level gains (ratio > 1.5) were seen only on 8q, 13q, 20 and X, and only in DNA aneuploid tumours. DNA aneuploid tumours had significantly more chromosomal aberrations (median number per tumour of 9.0) compared to diploid tumours (median of 1.0) (P < 0.0001). The median numbers of aberrations seen in DNA hyperdiploid and highly aneuploid tumours were not significantly different (8.5 and 11.0 respectively; P = 0.58). Four tumours had no detectable chromosomal aberrations and these were DNA diploid. A higher percentage of tumours from male patients showed Xq gain and 18q loss compared to tumours from female patients (P = 0.05 and 0.01 respectively). High tumour S phase fractions were associated with gain of 20q13 (P = 0.03), and low tumour apoptotic indices were associated with loss of 4q (P = 0.05). Tumours with TP53 mutations had more aberrations (median of 9.0 per tumour) compared to those without (median of 2.0) (P = 0.002), and gain of 8q23-24 and loss of 18qcen-21 were significantly associated with TP53 mutations (P = 0.04 and 0.02 respectively). Dukes' C/D stage tumours tended to have a higher number of aberrations per tumour (median of 10.0) compared to Dukes' B tumours (median of 3.0) (P = 0.06). The low number of aberrations observed in DNA diploid tumours compared to aneuploid tumours suggests that genomic instability and possible growth advantages in diploid tumours do not result from acquisition of gross chromosomal aberrations but rather from selection for other types of mutations. Our study is consistent with the idea that these two groups of tumours evolve along separate genetic pathways and that gross genomic instability is associated with TP53 gene aberrations. (+info)