Comparison of surface material, cytoplasmic filaments, and intercellular junctions from untransformed and two mouse sarcoma virus-transformed cell lines.

Surface material, cytoplasmic filaments, and intercellular junctions of an untransformed normal rat kidney (NRK) cell line were compared to those of NRK cells transformed by a nonproductive mouse sarcoma virus and to NRK cells transformed by productive mouse sarcoma virus. Surface material was visualized by ruthenium red (RR) or by staining glycol methacrylate sections with acidic phosphotungstic acid. Normal and transformed cells were examined in subconfluent and confluent cultures. In subconfluent cultures where normal and transformed cells were dividing at equal rates, there was no difference in surface coats. With RR, there was a continuous, thin electron-dense layer at external surfaces of all cells while the staining of this layer by phosphotungstic acid was spotty. Differences in surface material were observed in confluent cultures, where untransformed cells were contact inhibited and did not increase in number while transformed cells continued to divide. Both lines of transformed cells exhibited surface coats similar to those observed in subconfluent cultures,.even where cells were closely apposed, while the NRK cells exhibited considerably more extracellular RR-positive mate rial, particularly at regions of cell contact. This material appeared to be involved in cell adhesion. Also in confluent cultures, the peripheral cytoplasm of NRK cells had many filaments which were aggregated into bundles and were most abundant near regions of cell-to-cell apposition. The filaments attached to material beneath plasma membranes at sites of intercellular junctions. Transformed cells were clearly deficient in cytoplasmic filaments and intercellular junctions. In this system, RR-positive material at cell surfaces and the presence of intercellular-junctions with associated cytoplasmic filaments may have a role in the regulation of cell growth and multiplication.