Morphometric analysis of hyperthermia-induced nuclear and nucleolar size modifications in a human melanoma cell line

Although no prominent morphologic alterations were observed by light microscopy in a human melanoma cell line (M‐14) exposed at 42°C for 4 hr. the computerized image analysis demonstrated a significant enlargement of both nuclei and nucleoli. The mean nuclear and nucleolar areas were found to be 32% and 94% increased, respectively, in comparison with normal controls. The gaussian distribution of absolute frequency of the measures demonstrated that this nuclear and nucleolar enlargement was distributed among the whole cell population, taking place in clonogenic cells and in “sterilized” cells, ultimately doomed to die. This finding, not previously described in the context of the heat shock response, may be regarded as morphological evidence of an increase in the protein content of the nuclei of heat‐treated cells, as determined by biochemical methods.