Evolution of a normal karyotype in a mouse bladder epithelial cell line transformed in vitro.
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Animals↗
Biomedical subjects
J K Cowell
Publications and source records attributed to J K Cowell.
Chromosome abnormalities associated with salivary gland epithelial cell lines transformed in vitro and in vivo with evidence of a role for genetic imbalance in transformation.
Chromosomal abnormalities associated with five in vitro-transformed male mouse salivary gland epithelial cell lines were compared with those in three cell lines derived from in vivo-induced tumors. All cell lines were hypotetraploid. Structural chromosome abnormalities were found in all cell lines, but no consistent aberration was detected. Nevertheless, losses of chromosomes 1, 4, 7, 9, and 14 were observed in all of the in vitro-transformed cell lines. With the possible exception of chromosome 1, the same chromosome losses were noted in the in vivo-transformed cell lines. In addition, a consistent feature of both in vitro- and in vivo-transformed cell lines was the presence of double minute chromosomes and homogeneously staining regions. Where both of these chromosome types were present in the same cell line, they were mutually exclusive. The Y chromosome was absent in nearly all of the cell lines. These findings are consistent with the view that, in salivary gland epithelium, the malignant phenotype may result from a genetic imbalance caused by specific chromosome losses from tetraploid cells.
9,10-Dimethyl-1,2-benzanthracene↗
Modification of the DNA content in translocated regions of Drosophila polytene chromosomes.
The DNA content of translocated polytene chromosome regions in Drosophila melanogaster is affected by heterochromatic position effect. Microdensitometric studies on wm258-21 translocation heterozygotes showd (Hartmann-Goldstein and Cowell, 1976; Cowell and Hartmann-Goldstein, 1980) that band region 3D1-E2, adjacent to the breakpoint, contained less DNA than the homologous non-translocated region whereas the neighbouring 3C1-10 region contained more DNA than its non-translocated counterpart. In the nuclei selected for measurement the translocated X chromosome was morphologically euchromatic, but both regions undergo heterochromatisation in other nuclei within the same salivary gland. To explore the relationship between changes in DNA content and heterochromatisation, the effect on DNA content of two known modifiers of heterochromatisation has now been studied. Larvae cultured at 15 degrees C, which exhibit more heterochromatisation than those grown in 25 degrees C, have the same relative DNA contents as at the higher temperature. The addition of a Y chromosome markedly reduced heterochromatisation; in XXY larvae there was no difference between the DNA contents of translocated and non-translocated 3D1-E2 regions, and in region 3C1-10 the percentage excess of DNA in the translocated homolgue was approximately double that found in XX larvae. The relationship between replication behaviour and compaction suggested by these results is discussed.
Animals↗
Contrasting response of euchromatin and heterochromatin to translocation in polytene chromosomes of Drosophila melanogaster.
Studies on Feulgen-DNA content in the polytene chromosomes of D. melanogaster T(1:4)wm258-21 heterozygotes showed that when the euchromatic region 3D1-E2 is located next to the heterochromatic breakpoint it contains less DNA than in the non-translocated homologue (Hartmann-Goldstein and Cowell, 1976). In contrast to the region adjacent to the breakpoint, region 3C1-10, which contains intercalary heterochromatin, shows more DNA in the translocated than in the non-translocated chromosome. Transposition may induce morphologically euchromatic regions containing putatively underreplicated sequences to undergo additional replication cycles. Region 2E1-3A4, distal to 3C1 and at some distance from the heterochromatic breakpoint is apparently unaffected. Extended replication and reduced DNA content in regions which have undergone chromosomal rearrangement could be accounted for by varying degrees of blockage of replication in individual strands of the polytene chromosome.
Animals↗
Changes in DNA content during in vitro transformation of mouse salivary gland epithelium.
DNA content was measured in single cells in situ during the in vitro development of neoplastic transformation in epithelial cells from mouse salivary glands. The earliest change in DNA content was found in stage III of the transformation process (a preneoplastic stage). In foci of these cells, the percentage of tetraploid (4C) cells was 30--60% compared with the starting tissue and early primary cultures, which were diploid. The stage III foci eventually gave rise to subtetraploid tumorigenic cell lines. The studies suggested that during in vitro development of neoplastic transformation in salivary gland epithelium, tetraploids were generated that then underwent a period of chromosome instability and loss. Evidence was also presented that a similar mechanism may be operating in transformation of salivary gland epithelium in vivo. A possible mechanism for transformation on the basis of chromosome imbalance was discussed.
Animals↗
A new chromosome region possibly derived from double minutes in an in vitro transformed epithelial cell line.
Double minute chromosomes (DMs) are reported for the first time in in vitro transformed mouse epithelial cells. In one cell line, CSG 122/17, DMs persisted through numerous passages. A subpopulation appeared in this line at passage 23, in which the DMs had disappeared but were replaced by a finely banded chromosome region possibly associated with the distal end of chromosome 5. In a second cell line, CSG 120/7, there was no evidence of DMs in the earliest frozen stock available. However, a finely banded region similar to that found in CSG 122/17 was present and was again associated with chromosome 5, in this case with the proximal end. The possible evolution of these new chromosome regions from DMs is discussed.
Animals↗
A rapid method for accurate DNA measurements in single cells in situ using a simple microfluorimeter and Hoechst 33258 as a quantitative fluorochrome.
A method is described for the rapid, accurate measurement of single cells in situ using microfluorimetry. This method involves a shutter system, which allows irradiation of single cells for fractions of a second and a peak fluorescence intensity recording device. In this way errors due to fluorochrome fading are almost eliminated and standard deviations of less than 5% are obtained. Hoechst 33258 has been used as a quantitative fluorochrome. Optimum fixation and staining conditions on glass and plastic tissue culture vessels are described.
Animals↗
Consistent chromosome abnormalities associated with mouse bladder epithelial cell lines transformed in vitro.
Nine epithelial tumor cell lines that were derived from inbred C57BL/lcrf-at adult male mouse bladder and were transformed in vitro were cytogenetically analyzed. Most cell lines were near-diploid and showed only minor karyotypic deviations from normal. Tetraploid cell lines showed duplication of chromosome markers, which suggested that they arose originally as near-diploid cell lines with minor karyotypic changes. Chromosome abnormalities were consistent among different cell lines and involved chromosomes #6, #3, and #15. The Y-chromosome was frequently missing. Identical chromosome abnormalities were present in cell lines that arose in control, dimethyl sulfoxide-treated, or 7, 12-dimethylbenz[a]anthracene-treated cultures. The most frequent abnormality was was the presence of three copies (trisomy) of chromosome #6. Few structural chromosome abnormalities were detected, although a marker chromosome derived from chromosome #3 was present in several cell lines. Two cell lines had excesses of chromosome #15. These results suggest that excesses of individual chromosomes or parts of chromosomes, particularly chromosome #6, may be important in the expression of the malignant phenotype in mouse bladder epithelium.
9,10-Dimethyl-1,2-benzanthracene↗
Assignment of an anonymous DNA sequence IB/D22 (DXS371) to XP11.1-11.4.
In densely mapped and characterized chromosomes such as the X chromosome there are still regions which have a paucity of markers. One of these areas lies in the Xp11 region. Using human-rodent somatic cell hybrids we have assigned a newly isolated clone IB/D22 to the Xp11.1-p11.4 region.
Cell Line, Transformed↗