Changes in Surface Morphology Associated with Ethylnitrosourea-induced Malignant Transformation of Cultured Rat Brain Cells Studied by Scanning Electron Microscopy

Cultures of cells clonally derived from either normal adult rat brain or a culture of a mixed glioma induced by ethylnitrosourea (ENU) were studied by scanning electron microscopy. The two control lines, ARBOC9 and ARBOC11, were found to display very little surface activity. The cells were large, extremely flat with prominent nuclei and had few microvilli or ruffles. In contrast the two tumour lines A15A5 and A15A10 displayed a striking amount of surface activity which greatly exceeded that shown by the control cells grown and fixed under identical conditions. These cells were highly condensed and possessed large numbers of blebs, filopodia and microvilli. Cells derived from rat brains transplacentally exposed to either ENU or citrate buffer and cultured at 111-112 days after injection (when no tumour was visible) were also studied. Some of the cultures derived from ENU-exposed animals during the latent period were nevertheless tumorigenic (showing that malignant cells were already present). These cultures in general displayed features found in the tumour clones while control cultures did not. Preliminary results from one line suggest that cells exposed to ENU but which had not yet shown transformed properties such as growth in agar, tumorigenicity or high fibrinolytic activity displayed an intermediate morphology between control and tumorigenic lines. It subsequently became transformed and then displayed high surface activity.