Biomedical subjects
Publications and source records attributed to W F Morgan.
The incidence of sister chromatid exchanges in smokers and nonsmokers was investigated. There was no difference in the SCE rate between smokers and nonsmokers, nor was there any difference between heavy (greater than 10 per day) and light (less than 10 per day) smokers.
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The incidence of Sister-Chromatid Exchanges (SCEs) due to beta-radiation was investigated in cultured human lymphocytes using the BrdU/Giemsa technique. Cultures treated continuously with 0.001 and 0.01 microCi of [3H]uridine showed no increase in either chromosome abnormalities or SCEs. Continuous treatment with 0.1 microCi resulted in a significant increase in chromosome aberrations but no increase in SCEs, while treatment with 0.2 microCi gave both an increase in chromosome aberrations and SCEs. Cultures given a 4-h pulse with 1.0 microCi showed a significant increase in both SCEs and chromosome aberrations. The results indicate that low levels of beta-radiation do not cause an increase in SCEs in human lymphocytes, and, that a number, if not all the exchanges observed at low levels of beta-radiation with autoradiography, may be spontaneous events.
Fifty-seven herbicide and pesticide sprayers were studied for the incidence of sister chromatid exchanges (SCEs) in peripheral blood lymphocyte chromosomes. Overall there was no difference between the control group and the sprayers. Five sprayers had an SCE rate three standard deviations outside the mean of the control group. Possible factors contributing to this elevated SCE rate were (1) the failure to use protective clothing and (2) the length of time spraying. Many sprayers failed to take adequate protective measures when mixing and spraying and chemicals were often improperly stored. It is recommended that all persons using herbicides and pesticides take adequate protective measures so that the risk of fatal poisoning and possible long-term genetic hazard be reduced.
Human lymphocytes were cultured for 40, 42 and 44 h and analysed for the number of 1st and 2nd division metaphases using the Brd U-Giemsa technique. The most suitable time to obtain the majority of cells in their 1st division concommittant with an adequate mitotic index was 42 h. It is recommended that laboratories use sister chromatid differential staining to determine the most suitable culture time for the analysis of 1st division metaphases. This will permit accurate comparisons between individuals and laboratories to be made.
The distribution of sister chromatid exchanges (SCEs) both between and within chromosomes was studied in cultured human lymphocytes using the BRDU-Giemsa technique. In general, the distribution of SCEs between chromosomes was a function of chromosome length. However, chromosomes of the B group had more exchanges than expected on this basis, while the E, F, and G groups had less than expected. Analysis of cells showing both G-banding and sister chromatid differential staining indicates that the distribution of exchanges within the chromosomes is non-random and possible reasons for the observed distribution pattern are discussed.
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The incidence of sister chromatid exchanges (SCE) in cultured human lymphocytes from 50 normal individuals was studied using the BUdR-Giemsa technique. The mean SCE frequency per metaphase was 7.9 with a standard deviation of 1.36 and a range of 1-21. The incidence of exchanges was not influenced by the age of the donor nor did the exchange rate differ between sexes. The results of this study are compared with those of previous reports and reasons for the wide variation between results discussed.
Poly(ADP-ribose) is a nuclear polymer that is synthesized in response to DNA-strand breaks and covalently modifies numerous nuclear proteins. Inhibition of poly(ADP-ribose) polymerase by 3-amino-benzamide in cells exposed to DNA-damaging agents has a variety of cellular effects, including increases in cell killing, frequency of single-strand breaks, repair replication, and sister-chromatid exchange. These increases have been interpreted as an indication that poly(ADP-ribose) polymerization regulates the rate of ligation. Because of slow ligation, continued repair polymerization should therefore generate longer repair patches. Direct measurement of the rate of ligation of intracellular repair patches and of the size of repair patches indicates that they are unchanged when poly(ADP-ribose) polymerization is inhibited. We therefore conclude that poly(ADP-ribose) does not regulate the ligation stage of repair but instead may regulate the activity of intracellular nucleases and other enzymes that can cause additional DNA damage and changes in chromatin structure.
Restriction endonucleases that make either blunt- or cohesive-end DNA double-strand breaks can induce chromosome aberrations. We have used cell electroporation with great success to permeabilize Chinese hamster ovary cells for the introduction of restriction enzymes. The introduction of restriction enzymes by this method resulted in extremely high frequencies (greater than 90%) of aberrant metaphase cells and also a dramatic decrease in cell survival, as measured by subsequent colony formation. Cell electroporation by itself caused no increase in aberrant chromosomes and had only a slight effect on cell survival.