[Reorganization of DNA replicating system induced by 5-fluorodeoxyuridine and caffeine as the basis for radiosensitivity in human calls].

Treatment of diploid human fibroblasts with 5-fluorodeoryuridine (FUdR) and caffeine results in the increase in cellular radiosensitivity in terms of survival and chromosomal aberrations, on the one hand, and in radioresistant DNA synthesis (RDS), on the other hand, i.e. rather mimics those in mutant cells from patients with AT, XPII, Down syndrome, and others.

[Down syndrome: pathogenesis, radioresistant DNA synthesis and chromosomal instability].

Down syndrome (DS) is a frequent chromosomal aberration. Triplication of the fragment 21q22 of chromosome 21 is sufficient to cause the DS phenotype including immunodeficiency, premature aging, mental retardation, and an increased risk of leukemia. Chromosomal aberrations caused by X-ray irradiation were observed in DS lymphocytes and DS fibroblasts, but the correlation between chromosomal sensitivity, repair deficiency, and radioresistant DNA synthesis was not clear.

[Decreased frequency of activation of replicon clusters in Down syndrome lymphocytes].

Human blood lymphocytes from two normal and seven Down syndrome (DS) subjects were examined to determine rates of synthesis of individual replicon and adjacent clusters of replicons, using DNA fiber autoradiography. Lymphocytes in 6 of 7 DS patients were shown to have significantly slower synthesis of simultaneously active adjacent replicon clusters compared to normal controls. Rates of synthesis of individual replicons were the same in lymphocytes from all the subjects investigated.

[Morphofunctional characteristics of fibroblasts in basal cell nevus and Cockayne syndrome].

Some morphofunctional characters of fibroblasts in two genetic disorders--Cockayne syndrome (CS) and Basal cell naevus syndrome (BCNS) have been examined. The size of nucleus in BCN1SP line has been shown to be about 1.5 times less as well as the total size of nucleoli per nucleus, while the number of nucleoli was 2 times more compared with other cell lines investigated.

[The mechanism of radioresistant DNA synthesis in ataxia telangiectasia].

Using DNA fiber autoradiography, DNA replication in cells of healthy donors and in those of patients with ataxia telangiectasia (AT) was estimated. A new fact has been demonstrated showing a decreased number of simultaneously operating in tandem groups of replicon clusters in AT cells compared to that in normal cells. The data obtained suggest a reduced frequency of activation in the adjacent replicon clusters in AT cells.