Spreading-independent growth of normal fibroblasts in three-dimensional cultures

Changes of cell shape resulting from cellular flattening on culture substratum have previously been demonstrated to correlate with mitotic activity of normal animal cells in monolayer cultures. Here, we compared the shapes and proliferation of chick embryo fibroblasts cultured either in multicellular, multilayered sheets extended between glass fibres, or in standard monolayers. Fibroblasts in sheets retained the mitotic activity characteristic of that observed in sparse monolayer cultures, i.e. considerably higher that in confluent monolayers. Morphometric analyses revealed, however, that the cells in sheets were considerably less flattened than in monolayer cultures. These observations indicate that the modulation of culture conditions resulting in multidirectional cell stretching leads to the dissociation of flattening and mitotic activity of normal animal cells, so long as an intracellular stress field, generated by contractile cytoskeleton and stabilised by intercellular contacts, is maintained.