Observations on the social behaviour of cells in tissue culture: II. “Monolayering” of fibroblasts

Abstract

1. 1. Observations have been made on cell behaviour in the area between two embryonic chick heart explants, placed 0.5 to 1 mm apart in liquid medium tissue culture. 2. 2. The cell population in a given area in this situation rises steadily from zero as cells from both explants invade it, but then almost ceases to rise soon after the opposing outgrowths have met. There is no detectable diminution of rate of rise of population while the cells are approaching, before the outgrowths actually join. 3. 3. The velocity of individual cell movement after junction of the outgrowths is much slower between the explants than at either side of the explants. 4. 4. The direction of movements of cells in the region between the explants is predominantly outward from their respective explants until the two out-growths of cells join, when it becomes little more than randomly different from equal in all directions. 5. 5. It is concluded that outgrowth into the area between the two explants almost ceases soon after junction has been established between the opposing sheets of cells. After this junction, the number of cells in a radial strip joining the two explants becomes exceeded by the sum of two radial strips one at the side of each explant. Culture outgrowth therefore continues laterally after it has substantially ceased between the two explants. 6. 6. After junction the cells between the two explants tend to remain as a “monolayer”. The number of instances where one nucleus overlaps another is much fewer than is to be expected if the cells were randomly distributed. 7. 7. It is concluded that fibroblasts avoid moving over each other's surfaces. Such “contact-inhibition” of movement can explain why it is that fibroblasts normally migrate predominantly radially from an explant and that the whole culture tends rapidly to become circular in plan whatever its initial form.