Search

Ficoll-Hypaque-separated subpopulations of human peripheral blood T and B lymphocytes were exposed to 0, 0.5, 1.0, 2.5, or 5.0 Gy of gamma rays. Three parameters were examined: Survival, as measured by trypan blue dye exclusion in unstimulated cultures five days after irradiation; mitotic index, measured in phytohemagglutinin (PHA)-stimulated cultures 48 and 72 hours after irradiation; and chromosome aberration frequency, measured 48 or 60 hours after irradiation. Survival curves of T, B, and null cells are biphasic; the Do values for the radiosensitive populations of all three cell types are close to 0.6 Gy but are different for the radioresistant populations: 2.7 Gy for B cells, 4.77 Gy for T cells, and 6.03 Gy for null cells. B cells, as well as T cells, are stimulated to divide by PHA, and B cells comprise at least 10% of the mitotic figures seen in unirradiated cultures at 48 hours. The proportion of B lymphocytes in mitosis at any particular time after PHA stimulation decreases with increasing radiation dose, which reflects a higher mitotic radiosensitivity of B than of T cells. No significant difference, however, in chromosome aberration frequency was found between T and B cells.

Mitomycin C (MMC) induces acentric chromosome fragments in the neuroblast (Nb) of the grasshopper embryo (Chortophaga viridifasciata) after acute and chronic exposure to concentrations ranging from 10(-8) to 10(-4) M, the dose response being essentially linear up to 10(-5) M. Because Colcemid is not used in the Nb assay, it was possible to detect two additional effects of MMC: (1) Prolonged retardation of many cells occurs when they reach very late prophase; the chromosomes continue condensing and lose their orderly prophase orientation, and the nuclear envelope becomes increasingly fragile. Such cells, which were observed after both acute and chronic exposure, give the false impression of being c-metaphases when they are fixed and squashed. The frequency of retarded very late prophases and the duration of retardation are related to MMC concentration and time of exposure. A rationale is presented supporting the idea that the events associated with retarded very late prophase result from MMC effects on the nuclear envelope. (2) MMC significantly increases the frequency of Nb's with attenuated centromeres at the beginning of early anaphase, an effect that appears to be caused by a delay in the repulsion of sister chromatids that usually occurs immediately after centromere separation begins.

The dose-response for the induction of acentric chromosome fragments was determined in neuroblasts of the grasshopper embryo (Chortophaga viridifasciata De Geer, Orthoptera: Acrididae) exposed in vitro to four direct-acting chemical known to be mutagenic, clastogenic, and carcinogenic: 4-nitroquinoline-1-oxide (4NQO), N-methyl-N-nitro-N-nitrosoguanidine (MNNG), Adriamycin (ADM), and bleomycin (BLM). After a 1-hr exposure followed by a 3-hr recovery period (untreated cell cycle time is 4 hr), acentric fragments were observed at doses down to 1 microM 4NQO, 1.25 microM MNNG, and 0.125 microM ADM and BLM. After an 8-hr continuous exposure, acentric fragments were induced by 4NQO at a dose as low as 0.125 microM. These low concentrations also reduced the number of dividing cells. No chromosome aberrations or mitotic effects were observed in untreated embryos or in those exposed only to the solvent dimethyl sulfoxide. Because of the short cell cycle and the sensitivity of the neuroblast to the induction of acentric chromosome fragments by chemical clastogens, a minimum of time is needed to perform the test. From a comparison with the prominent clastogen test systems currently used, it is concluded that the grasshopper neuroblast test is the fastest and that it detects some agents that some systems do not. Grasshoppers have a worldwide distribution. If neuroblasts of other species prove to be as sensitive to mutagens as those of Chortophaga, investigators in many countries would have available a eukaryotic mutagen test system that is simple, fast, reproducible, and inexpensive.

Embryos of the grasshopper Chortophaga viridifasciata were exposed in vitro to formaldehyde (FA), as formalin, at concentrations ranging from 10(-8)M (0.0003 ppm) to 10(-3) M (30 ppm) at 38 degrees C. A low frequency of distinct acentric chromosome fragments (0.02-0.04/cell) was observed in the neuroblasts after 1 hr exposure to 7.5 X 10(-4) or 10(-3) M FA plus 3 hr recovery, but not at lower concentrations, even with 4 hr exposure. There was no obvious relation between distinct fragment frequency and concentration of FA. Neuroblasts with sticky chromosomes were observed at 10(-4), 7.5 X 10(-4), and 10(-3) M FA, the percent of cells with slight, moderate, or severe stickiness varying with FA concentrations. Fragments were associated with the sticky chromosomes. The frequency of these sticky fragments at the two higher concentrations (0.15-0.30/cell) was greater than the frequency of distinct fragments. It is concluded that the distinct acentric fragments induced by FA result from breakage at a single sticky point (slight stickiness) between separating sister chromatids. The chromosome effects observed probably result from the action of daughter products that are formed by the interaction of FA with culture medium components, especially the fetal calf serum.