RESUMEN
A study of the asynchronous culture of Chinese hamster fibroblasts by autoradiography has shown that the pulse (15 min) incorporation of 3H-thymidine in nuclear DNA influences the kinetics of labeled cell proliferation. The results obtained suggest that one of the early biological effects of the pulse incorporation of 3H-thymidine is a delay in the occurrence of the first mitosis. With the concentration of 3H-thymidine 37 kBq/ml the slowing down of of the movement of labeled cells in the cycle is detected by a shift and overlapping of waves of labeled and unlabeled mitotic cells. In an increase of the concentration up to 370-925 kBq/ml the pattern of the curves of labeled mitotic cells is distorted. These distortions are well interpreted by the nature of change of the index of labeled and unlabeled mitotic cells. A lowered index of labeled nuclei points to a decrease in the proliferative activity of labeled cells. After an increase in 3H-thymidine concentration from 37 up to 370-925 kBq/ml the mitotic activity of cells labeled at the end of S-phase decreases from 1 to 0.6-0.1% respectively. With the concentration of 925 kBq/ml for these cells incorporating 3H-thymidine at the end of S-phase, a delay of the entry into mitosis reaches 6-8 h. Autoradiography data with the assessment of granule density suggest that mitotic activity and the period of delay in the occurrence of mitosis depend on the dose of irradiation with intranuclear tritium. Thus the tritium dose rate after 15 min of incubation with 3H-thymidine is 0.03, 0.27 and 0.69 Gy/h for concentrations 37,370 and 925 kBq/ml respectively.
Asunto(s)
División Celular/efectos de la radiación , Timidina/farmacología , Tritio/farmacología , Animales , División Celular/efectos de los fármacos , Línea Celular , Cricetinae , Cricetulus , Relación Dosis-Respuesta en la Radiación , Femenino , Cinética , Índice Mitótico/efectos de los fármacos , Índice Mitótico/efectos de la radiaciónRESUMEN
A study was made of the unscheduled synthesis of DNA in gamma-irradiated nuclei of human lymphocytes 10, 15 and 20 hr following PHA-stimulation. It was shown that the unscheduled DNA synthesis is a function of radiation dose and time after PHA-stimulation.
Asunto(s)
Reparación del ADN , Interfase , Linfocitos/efectos de la radiación , Radioisótopos de Cobalto , Rayos gamma , Humanos , Activación de LinfocitosRESUMEN
A comparative study was made of the yield of chromosome aberrations in human lymphocyte culture exposed to 60Co-gamma-rays (2 Gy) at different mitotic cycle stages the cells being fixed after 52 and 60 hr. It was shown that with the latter fixation time (60 hr) the frequency of chromosome aberrations after irradiation in G1 stage was substantially lower than that with the former one (52 hr) and, vice versa, it was higher after irradiation in S and G2 stages. The authors discuss the probable causes of the distinctions observed.
Asunto(s)
Aberraciones Cromosómicas , Linfocitos/efectos de la radiación , Radioisótopos de Cobalto , Técnicas Citológicas , Rayos gamma , Humanos , Mitosis , Factores de TiempoRESUMEN
The salivary chromosomes of the l(3)tl mutant of D. melanogaster are considerably thicker and shorter than those of normal larvae. In most nuclei, chromosome shortening is associated with morphological changes of two types. a) The bands lose their distinctive pattern and become loose. The chromosome appears as a granular mass. In extreme cases pompon-like chromosomes arise. Most frequently male X-chromosomes undergo such changes and begin to shorten as early as in the middle of third larval instar. "Pompon" transformation is not associated with a change in the relative intensity of RNA synthesis: the ratio of silver grain number over the male X-chromosome to that over regions 61A-63F is the same in pompon-like l(3)tl chromosomes and in the male and female X-chromosomes of the normal lines. b) Shortened chromosomes occassionally retain distinct band organization and, in these cases, chromosome shortening is observed to be due to the condensation of the chromatin of many puffs and interbands resulting in the fusion of a large number of bands into "new" chromatin blocks. In regions of fused bands, transcriptional activity is decreased as compared with regions where this union does not occur. The chromosomes of l(3)tl larvae lack ecdysone-stimulated puffs and other prominent puffs. In 144-192 hour larvae, puffs can be induced by ecdysone and until 384 hours by temperature shock. The capacity of puff induction decreases with larval age.