Morphology of temperature-sensitive strains of viral-transformed 3T3 mouse fibroblasts in vitro as determined by SEM and STEM

Abstract

The morphological characteristics of BALB/c 3T3 mouse fibroblasts transformed with two temperature-sensitive strains of simian virus 40 (SV-40) were studied. When grown at the permissive temperature (32 degrees C, transformed phenotype) strains A7B4b and A209B4a both closely resemble the morphology described for wild-type SV-40 cells. Scanning electron images show numerous knobs and filopodia as characteristic surface features in both subconfluent and confluent cultures. Scanning-transmission electron images reveal that the two strains are also similar in intracellular structure. When grown at the restrictive temperature (39 degrees C, untransformed phenotype) the two strains differ from each other. The A209B4a strain is more elongated in subconfluent cultures, and shows interactions of filopodia at cell-cell interfaces when confluent similar to those described for wild-type 3T3 cells. This strain also shows intracellular accumulation of polymorphic material thought to be secondary lysosomes. The A7B4b cells are flattened but generally not elongated when subconfluent, and do not show any obvious interactions at confluency. Intracellularly, this strain also differs from A209B4a.