Effect of bleomycin on the fine structure of mouse fibroblasts.

Asynchronously dividing mouse fibroblasts (L-cells) treated with the antitumor antibiotic Bleomycin show various rather specific morphological alterations. Many of the cells exposed to bleomycin assume a more or less epitheloid cell shape and are larger than untreated cells; in addition to an increase in nuclear size these cells often contain multiple nuclei. In most of the cells nuclei show an almost complete loss of peripheral condensed chromatin. The nucleolar hypertrophy initially observed is followed by a shrinkage and segregation of the nucleolar components.