Carcinoma of the cervix: deficiency of nexus intercellular junctions

Intercellar junctions where cell membranes are in intimate contact (nexuses) are very abundant in the epithelium of normal human cervix. Squamous carcinoma cells are deficient in nexuses although a rare nexus is seen. Nexuses may be involved in normal growth regulation, while a deficiency of nexuses may be related to the invasive property of malignant growth.

Biochemical evidence for induction by polyoma virus of replication of the chromosomes of mouse kidney cells

It was shown earlier that in cultures of contact-inhibited mouse kidney cells infection with polyoma virus induces replication of the chromosomal DNA. In this paper we present evidence, based on analyses of isolated chromatin, that, parallel with and as a consequence of the virus-induced synthesis of cellular DNA, the chromosomal proteins are synthesized in the proportions characteristic of normal chromosome replication. These results are compatible with the hypothesis that polyoma virus activates (or derepresses) a regulatory system of the host cell which controls initiation of chromosome replication.

Surface-specific characteristics of a contact-inhibited cell line containing the SV40 viral genome

A cytoagglutinin purified from wheat germ lipase agglutinated five related murine fibroblast cell lines in the order of their saturation densities. One cell line, which was transformed by the oncogenic papova virus SV40 but which had a low saturation density, agglutinated poorly. Preincubation of cells with trypsin increased their agglutinability, but trypsin made no cell line more agglutinable than the cell line with the highest saturation density.

Metabolic co-operation between biochemically marked mammalian cells in tissue culture

Cells of a genetic variant of the hamster fibroblast line BHK 21 which lack inosinic pyrophosphorylase activity (IPP- cells) and therefore cannot normally incorporate [3H]hypoxanthine were grown in mixed culture with cells of BHK 21 sublines which have inosinic pyrophosphorylase activity (IPP+ cells). If not in contact with IPP+ cells, IPP- cells do not incorporate added [3H]hypoxanthine into nucleic acid. IPP+ cells always do incorporate [3H]hypoxanthine and IPP- cells when in direct or indirect contact with IPP+ cells also incorporate the isotope. Cell to cell contact appears to be essential for this gain of a metabolic function by IPP- cells.

The possible molecular basis and general implications of the phenomenon are discussed.

Local stimulation of growth in primary cultures of chick embryo fibroblasts

Confluent, slowly growing primary cultures of chick embryo fibroblasts were stimulated to grow more rapidly by making discontinuities in the monolayers by a "wounding" procedure. Growth was measured by mitotic index and by the fraction of cells synthesizing DNA as determined by autoradiography. Faster growth was confined to free cells at the edges of the discontinuities. Cells enclosed on all sides were not stimulated to renewed DNA synthesis, even when within 0.2 mm of the discontinuities. The time of appearance of increased rate of growth induced by wounding was measured and found to be similar to the time of a transient growth stimulation among enclosed cells induced by a change of medium. The increased rate of growth among free cells was not transient, however, and persisted as long as it was examined. To rule out possible artifacts incurred in wounding, a free edge was created by seeding trypsinized cells as a confluent sheet in a confined area of the tissue culture plate. Here also the growth rate of cells along the edge was much higher than in the confluent areas. It was concluded that interactions at short range between cells in culture can play an important role in regulating their growth.

A diffusible factor which sustains contact inhibition of replication

Confluent 3T3 cultures make and release into the medium a diffusible factor which sustains the state of contact inhibition of replication. Evidence is given that the factor is a specific and reversible inhibitor of the RNA synthesis which precedes cellular replication.

Basis for the acquisition of malignant potential by mouse cells cultivated in vitro

Balb/c mouse embryo lines maintained in culture for over 200 generations under conditions that minimize cell-cell contact do not become tumorigenic. Lines cultivated under conditions where there is extensive cell contact become tumor-producing within 30 generations. The tissue-culture property that correlates best with tumorigenicity is the loss of contact inhibition of cell division.