Filamentous cells of Escherichia coli formed in the presence of mitomycin

The effects of mitomycin C on cell elongation of Escherichia coli B were studied. Filament formation was most marked in cultures treated with a moderate level (1 mug/ml) of the antibiotic, becoming less obvious at higher levels (10 mug/ml). Cells treated with a bacteriostatic concentration (0.1 mug/ml or less) of mitomycin C were also significantly elongated. The filamentous or elongated cells appeared to lack septa, since their spheroplasts were considerably larger than those formed from normal cells. The appearance of empty spheres also indicated some defects in the surfaces of the filamentous cells. Electron micrographs of the filaments revealed a characteristic difference in the arrangement of the nuclei in the filaments formed in the presence of low (0.1 mug/ml) and high (5 mug/ml) concentrations of mitomycin C. The filaments formed by the low level of mitomycin C had normal well-defined nuclear bodies distributed along the long axis, whereas those formed by the elevated level of the antibiotic contained smaller nuclei. The latter were characteristically confined to the center of the cells and did not extend out to the tips of the filaments.

The parathyroids in corticosteroid-treated pregnant rats and their offspring. I. Effect of cortisone

Geometrically increasing doses of cortisone (0.5, 1.5 and 4.5 mg twice daily) were injected into pregnant rats, and the volume, nuclear diameters and mitotic rate of the maternal parathyroids as well as the parathyroid volume and mitotic rate in the foetuses were determined. The nuclear diameters were if anything smaller and the mitotic rate tended to decrease in the cortisone treated groups. There were no significant differences between the parathyroid volumes of the foetuses in the control and cortisone-treated groups. Thus, it seems that the development of the rat foetal parathyroids and the morphology of the maternal parathyroids are little affected if at all, by cortisone.

The action of excess of vitamin A alcohol on the fine structure of rat dermal fibroblasts

Rat dermal fibroblasts were grown as monolayers, and changes in the fine structure of the cells that occurred during 12 hr incubation in a medium containing protein and excess of retinol (vitamin A alcohol) were studied by electron microscopy. There is little change during the first 6 hr, although some of the nuclei have highly convoluted membranes. During the subsequent 3 hr, there is some disorganization of the mitochondrial cristae; the cisternae of the rough-surfaced endoplasmic reticulum diminish in number; and the amount of smooth membranous material and free ribosomes increases. There is a rapid decline in the respiratory activity of the cells after 6 hr exposure to the vitamin. It is concluded that the primary action of excess of retinol is to cause alterations in the membranes of the cells and that these alterations affect the functions of the mitochondria and endoplasmic reticulum.

Combined effects of x-irradiation and 3'-methyl-4-dimethylaminoazobenzene on liver cell population

Livers of rats were exposed to 950 rads of X-irradiation. The liver cells were then induced to proliferate by the stimulus of partial hepatectomy. The regenerating livers consisted of two cell populations, one of colonies of ceils having normal amounts of DNA and the other having abnormal polyploid and aneuploid cells. Regeneration of the liver is attributed to the colonies with normal cells. When 3′-Me-DAB was fed to the X-irradiated animals, the behavior of these cell populations was reversed. The multiplication of abnormal cells was favored in the presence of the carcinogen. Changes in the percentage of mitotic irregularities, the mitotic rates, and the proportion of various stages of mitosis that resulted in the altered behavior of cell populations are discussed.