Biomedical subjects

C H Ockey

Publications and source records attributed to C H Ockey.

At least 37 records · Page 2Linked to original sources

PubMed1980

Differences between "spontaneous" and induced sister-chromatid exchanges with fixation time and their chromosome localization.

Mean "spontaneous" SCE values have been investigated in synchronized CHO and S3/4 fibroblasts and in phytostimulated human peripheral lymphocytes. Significant increases were found at progressive fixation times following BrdU introduction in all cultures. Similar increases were observed with fixation times in SCEs induced by pulse treatment with methyl methane sulphonate (MMS) at various stages in the S period in CHO cells. In the fibroblast cultures these increases ranged from 20 to 80% with an 8-h interval between fixations. The percentage increase depended on the real proliferation occurring during this fixation interval. In the lymphocyte cultures, fixation intervals raning from 22 to 54 h yielded increases of 40 to 80%. It is proposed that when SCE yields are compared in the SCE test for potentially damaging agents, the stages in cell proliferation expressed as frequencies of first, second, and third mitoses after BrdU incorporation should be taken into account. The distribution of "spontaneous" and MMS-induced SCE's have been examined in marker chromosomes of the CHO cells. Although "spontaneous" SCE's are nonrandomly distributed, they do not appear to show a high incidence over any specific type of banded region. MMS-induced SCEs, on the other hand, are preferentially located over those chromosome sites in replication at the time of pulse treatment.

Animals↗

PubMed1979

Quantitative replicon analysis of DNA synthesis in cancer-prone conditions and the defects in Bloom's syndrome.

A quantitative method of replicon analysis of DNA fibre autoradiographs has been used to study the relationship between mean rate of DNA chain growth (R) and distance between adjacent replicons (ID) in fibroblasts from cancer-prone conditions. Results are expressed in terms of the mean linear regression R = delta +(K.ID)10-2. When replicon behaviour was examined in cells from patients with ataxia telangiectasia, basal cell naevus and Bloom's syndromes grown at high density after 48 h in culture, no significant differences could be found in replicon behaviour between these syndromes and normal cultures. However when Bloom's cells were grown at low density and examined 24 h earlier, the mean rate of chain growth R was reduced compared to normal cells at the same density. Both cell types at high densities at 24 h showed equal but lower R values than at 48 h after plating the cultures. The lower rate of chain growth in Bloom's was accompanied by a longer S-period and cell cycle. Studies of cell proliferation kinetics using consecutive mitoses after bromodeoxyuridine (BUdR) incorporation and harlequin banding showed that Bloom's cells at low cell density require a longer period to recover a normal cell cycle length after plating than do normal cells at the same density. Plating densities and using conditioned media shorten the recovery period in Bloom's cells, and when foetal calf serum/MEM is replaced by human AB serum/McCoy 5a medium as the growth media, cell cycle behaviour of low density Bloom's and normal cells are equal at a much earlier time. It is concluded that the slow rate of DNA chain growth in Bloom's cells is an artefact introduced by culture conditions and also may be present in normal cells at an earlier period. The behaviour of replicons during this recovery period appears to be similar in Bloom's and normal cells except for the time lag. As recovery proceeds, the DNA chain growth in the associated replicon pairs recover progressively. This alters both the mean R value from 0.4 to 0.8 micron/min, the slope of the regression K from less than 1.0 to approximately 1.0 while the distance between initiation sites (ID) remains constant throughout. Pretreatment of all cultures with fluorodeoxyuridine (FUdR) produced the same differential effect on release from DNA synthesis inhibition, that is a similar increase in the activation of normally inactive replicons and a slightly slower rate of chain growth over all replicons. No evidence of a substance released by Bloom's cells in culture capable of increasing the sister-chromatid frequency in normal cells could be found. Since SCE frequencies were found to increase with fixation time after BUdR introduction it is concluded that some of the reported changes could be due to differences in cell cycle kinetics brought about by the different media conditions.

Autoradiography↗

PubMed1978

Changes in replicon behaviour during the S period in Sorex araneus cells in culture.

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Cell Cycle↗

PubMed1978

Fluorescein excitation and emission polarization spectra in living cells: changes during the cell cycle.

Changes in the fluorescein fluorescence emission and excitation polarization spectra in synchronized cultured S3 fibroblasts at G1, mid-S, and mitosis, as well as in human lymphocytes before and after stimulation with mitogens, were studied. In contrast to those measured in aqueous solutions the emission and excitation polarization spectra in living cells exhibit a wavelength dependence characteristic for the state of the cell cycle. Changes in the temperature and in the amount of intracellular water result in quantitative wavelength-independent changes in the polarization spectra. Possible mechanisms for the qualitative wavelength-dependent changes in the fluorescein emission and excitation polarization spectra during the cell cycle are discussed.

Cell Cycle↗

PubMed1977

Analysis of karyotype variation following carcinogen treatment of Chinese hamster primary cell lines.

Chinese hamster primary fibroblasts derived from several embryos were treated with the carcinogens benzo(a)pyrene, 7,12-dimethylbenz(a)anthracene or N-methyl-N'-nitro-N-nitrosoguanidine. Karyotype analysis, sister chromatid exchange frequency, evidence of transformation by growth in agar, cell morphology and reaction to cytocholasin B were tested at regular intervals over many culture passages. Carcinogen treatment was found to shorten the time period before onset of permanent karyotypically changed stem and side lines and in vitro transformation. Chromosomes X, 6 and 10 were more frequently involved in all cultures in these karyotype changes which were usually preceded by a period of chromosome variation. Spontaneous chromatid aberrations and aneuploidy increased in frequency with time in culture and generally appeared prior to the expression of transformation. No specific chromosomes were involved with the different carcinogens. There was no correlation between in vitro transformation and karyotype evolution and the criteria for transformation were present independently of one another. It is suggested that the lack of correlation between the parameters tested indicates that the expression of in vitro transformation is a result of selection for growth advantage from a cell population expressing an increasing degree of genetic instability and variation with time in culture.

Aneuploidy↗

PubMed1976