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.