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Biomedical subjects

R L Davidson

Publications and source records attributed to R L Davidson.

At least 73 records · Page 4Linked to original sources
PubMed1978

Bromodeoxyuridine mutagenesis in mammalian cells: mutagenesis is independent of the amount of bromouracil in DNA.

Studies were undertaken to determine how a line of mutant Syrian hamster melanoma cells (HAB-2E) that displays unlimited growth potential when all of the thymine residues in nuclear DNA are replaced by bromouracil (BrUra) could avoid the deleterious effects of bromodeoxyuridine (BrdUrd) mutagenicity. It was found that BrdUrd could be mutagenic to these cells. However, there was a nonlinear relationship between mutagenicity and the amount of BrUra in the DNA of the HAB-2E cells. With these cells, mutagenicity apparently is determined by the concentration of BrdUrd to which the cells are exposed rather than the amount of BrUra in DNA. These results were obtained with both the induction of ouabain resistance and thioguanine resistance as markers for mutagenesis. The dependence of BrdUrd mutagenicity on BrdUrd concentration was also observed for the parental melanoma cells.

Bromodeoxyuridine↗
PubMed1978

Altered pattern of replication of human chromosomes in a human fibroblast-mouse cell hybrid.

The pattern of terminal replication of the human chromosomes in a clone of hybrids between diploid human fibroblasts and mouse cells was analyzed by autoradiography. An average of 10 human chromosomes was present in the hybrid cells. Several of these chromosomes were found to terminate replication in a different order from the same chromosomes in the parental human fibroblasts. Chromosomes 4 and 5 completed replication later in the hybrid than in the fibroblasts (relative to the other human chromosomes). In contrast, chromosomes 7, 12, and 15 completed replication earlier in the hybrid than in the fibroblasts. These results suggest that the sequence of terminal chromosome replication in human fibroblasts is not irreversibly programmed into each chromosome.

Animals↗
PubMed1978

Genetics of cultured mammalian cells, as studied by somatic cell hybridization.

In the past 10 years, the technique of somatic cell hybridization has been used extensively in studies on mammalian somatic cell genetics. Much of the work with hybrid cells has focused on the problems of gene regulation and gene mapping; these two areas and the consideration of new techniques are discussed in this article. The types of genetic manipulations than can be used to investigate these problems are the central theme of the review.

Animals↗
PubMed1977

Expression of nervous system antigen-3 by lines of mouse fibroblasts and kidney cells and continued expression in hybrid cells.

In a survey of the expression on cultured mouse cells of the cell surface antigen known as nervous system antigen-3 (NS-3), it was found that RAG, a renal adenocarcinoma line, expressed that antigen. It was also observed that 3T3, a fibroblast line of unknown tissue origin, expressed NS-3. Cells of these two lines were hybridized with cells of two mouse L cell lines that did not express NS-3. Four hybrid clones were tested for both the 3T3 X L cell cross and the RAG X L cell cross, and all the hybrids were found to be NS-3 positive. All the hybrids had at least 40% as much activity as the NS-3 positive parent. Of the four parental mouse cell lines used, only 3T3 expressed Thy-1.2 antigen on the cell surface. In contrast to the continued expression of NS-3 on hybrid cells, Thy-1.2 antigen was not detectable on two clones of 3T3 X L cell hybrids that were tested.

Adenocarcinoma↗
PubMed1977

Effects of thymidine analogs on Syrian hamster melanoma cells: phenotypes arising from selection for analog resistance.

In order to compare the biological effects of different thymidine (dT) analogs, two unusual cell lines (B-4 and HAB) previously isolated from a Syrian hamster melanoma line by selection with 5-bromodeoxyuridine (BrdU) were analyzed for their response to other analogs. B-4 cells require high concentrations of BrdU for optimal growth, and it was seen that the requirement for BrdU could be satisfied partially by 5-chlorodeoxyuridine (CldU) but not by the other dT analogs tested. HAB cells are able to grow with all the dT residues in nuclear DNA replaced by BrdU, and it was found that they could also grow with essentially all the dT residues in nuclear DNA replaced by CldU but not by other analogs. New cell lines resistant to 100 micrometer concentrations of CldU, 5-iododeoxyuridine (IdU), and 5-hydroxymethyldeoxyuridine (HMdU) were isolated from the melanoma line and tested for cross-resistance to the other dT analogs. A high level of cross-resistance was observed only with BrdU and CldU. The ability of the cell lines resistant to BrdU, CldU, and IdU to incorporate these analogs into nuclear DNA also was determined. BrdU and CldU were incorporated efficiently by all of the lines tested, but the IdU-resistant cells seemed to preferentially exclude IdU.

Aminopterin↗
PubMed1977

A new dimension in suspension fusion techniques with polyethylene glycol.

Polyethylene glycol (PEG) induces the hybridization of mammalian cells at a much higher frequency when the cells are attached to a substrate during treatment than when the cells are treated in suspension. Since many cell types, e.g., lymphocytes, cannot attach to a substrate, a new technique for the PEG-induced fusion of cells in suspension was developed. This technique, referred to as "pancake fusion," is based on the centrifugation of suspended cells onto a coverslip and the PEG treatment of the cells on the coverslip as if they were attached to a substrate. With this technique, the frequency of hybridization of human white blood cells, which are incapable of attaching to a substrate, can be greatly increased.

Cell Fusion↗
PubMed1977

Increased dexamethasone resistance of cystic fibrosis fibroblasts.

We demonstrate previously that fibroblasts from cystic fibrosis (CF) patients are significantly more resistant to the toxic effects of ouabain than normal human fibroblasts are. Ouabain is generally assumed to act primarily at the level of the cell membrane and to cause killing of cells by inhibiting ion transport. We have therefore examined the ability of normal and CF cells to survive exposure to ethacrynic acid, another inhibitor of ion transport, and to survive colchicine and aminopterin, resistance to which has been associated with membrane alterations in other cells. The effect of dexamethasone, which has a sterol nucleus similar to that of ouabain but is thought to have a different site of cellular action, was also tested. Exposure of the cells to ethacrynic acid, colchicine, or aminopterin did not reveal any differences in survival between normal and CF fibroblasts. However, CF cells survived exposure to dexamethasone significantly better than normal cells did. These results suggest that normal and CF cells do not differ in terms of a generalized resistance to ion transport inhibitors or to drugs that must pass through the membrane to be active. Instead, the results raise the possibility that CF cells have an enhanced resistance to drugs that have the sterol nucleus found in ouabain and dexamethasone.

Aminopterin↗
PubMed1977

Differences in the order of termination of DNA replication in human chromosomes in peripheral blood lymphocytes and skin fibroblasts from the same individual.

A comparison of the sequence of terminal replication of DNA in human chromosomes has been made between skin fibroblasts and peripheral blood lymphocytes from the same adult male individual. The chromosomes were identified by quinacrine-banding, and the order of termination of replication was determined by autoradiography. Chromosomes 4, 5, 8, and 13 were found to terminate DNA replication later in lymphocytes than in fibroblasts, wheres chromosomes 15, 19, 20, and 22 were found to terminate their replication earlier in lymphocytes than in fibroblasts.

Adult↗
PubMed1976

Polyethylene glycol-induced mammalian cell hybridization: effect of polyethylene glycol molecular weight and concentration.

The effects of polyethylene glycol (PEG) molecular weight and concentration on mammalian cell hybridization were studied. The peak hybridization-inducing activity with all grades of PEG from 400-6000 was found to occur in the concentration range of 50-55%. However, changes in concentration were seen to have different quantitative effects with different grades of PEG. For monolayer fusions, PEG 1000 at 50% seems to be the optimal combination of PEG molecular weight and concentration, in terms of both efficiency of hybridization and relative insensitivity to dilution effects.

Cell Fusion↗
PubMed1976

33258 Hoechst enhancement of the photosensitivity of bromodeoxyuridine-substituted cells.

Cells that have incorporated 5-bromodeoxyuridine (BrdU) into their DNA become extremely sensitive to photoinduced killing after treatment with the dye, 33258 Hoechst. Under appropriate conditions the dye increases the efficiency of killing by a factor of approximately 10(4). This enhanced photosensitivity suggests that the combination of BrdU, dye, and light can be used to select conditional lethal mutants.

Benzimidazoles↗
PubMed1976

Nucleotide analysis of DNA and RNA in cells with thymidine totally replaced by bromodeoxyuridine.

The nucleotide composition of nuclear DNA has been determined in a cell line (HAB) that has grown for 275 generations with complete substitution of bromodeoxyuridine (BrdU) for thymidine in nuclear DNA. Within 50 generations there is a approximately 3% decrease in the G content and an equivalent increase in the BrdU content of DNA, relative to the unsubstituted parent cell line. However, these alterations do not continue to accumulate when the cells are grown for up to 275 generations with fully substituted DNA, suggesting that they are not brought about by BrdU-induced base transitions due to mispairing. RNA transcription has been examined both in vivo and in vitro to determine whether or not BrdU substitution in DNA results in large-scale transcriptional errors. The nucleotide composition of 18S and 28S rRNA from cells 0, 60%, and 100% substituted with BrdU does not significantly differ. Further, when DNA from these cells is transcribed in vitro with E. coli RNA polymerase, there is no evidence for altered incorporation of nucleotides into RNA made from the substituted templates.

Bromodeoxyuridine↗
PubMed1976

Improved techniques for the induction of mammalian cell hybridization by polyethylene glycol.

Modifications in the techniques for the induction of mammalian somatic cell hybridization by polyethylene glycol (PEG) have led to procedures that are rapid, simple, and effective. The basic improvements, for both monolayer and suspension fusions, are a short exposure to PEG and a rapid dilution of PEG following treatment. There is a marked effect of PEG concentration on cell hybridization, and there seem to be inherent differences between cells in terms of the extent of cell fusion induced by PEG.

Cell Fusion↗
PubMed1976

Inhibition of biological effects of bromodeoxyuridine by deoxycytidine: correlation with decreased incorporation of bromodeoxyuridine into DNA.

The effects of 5-bromodeoxyuridine (BrdU) on pigmentation, contact inhibition, cell morphology, and tumorogenicity of Syrian hamster melanoma cells are inhibited in the presence of deoxycytidine (dC). The inhibition of these biological effects of BrdU by dC is correlated with a decrease in the incorporation of BrdU into nuclear DNA. The results suggest that the intracellular changes resulting from the addition of dC to cells in the presence of BrdU are comparable to those resulting from a decrease in the concentration of BrdU in the medium.

Animals↗