Changes in chromatin morphology after infection of mouse embryo fibroblasts with polyoma virus, detected by image analysis.

Nuclear chromatin properties in control, SV40-infected and polyoma-infected cultures of mouse embryo fibroblasts were studied using quantitative image analysis. Distribution of Feulgen-DNA-content per nucleus was found to be similar in all three groups of cultures. No differences in nuclear area, mean optical density of chromatin and area of chromatin at different optical density thresholds were measurable between control and SV40-infected fibroblasts. Polyoma-infected fibroblasts were found to have smaller nuclei, more dense and less homogeneous chromatin than non-infected cells. The changes of chromatin in polyoma-infected cells occur in G1, middle S and G2 nuclei. The results are interpreted as an early manifestation of the cytopathic effect of polyoma virus.