Influence of cells number on directional migration of MO4 cells in vitro.

: The diameter of the circular area covered by MO4 cells explanted as a spheroid on glass is used as an index of directional migration. MO4 cells, the proliferation of which is inhibited by 5-fluorouracil or ionizing radiation can perform directional migration, indicating that directional migration and proliferation are basically unrelated cellular activities. In non-proliferating populations the distance of directional migration appears to increase with increasing volume of the original spheroid, indicating that directional migration is influenced by the cell number. Stimulation of directional migration is also obtained by explanting a second spheroid in the center of the area covered by cells from a first spheroid. Comparison of directional migration of cells from irradiated spheroids with that from spheroids in presence of 5-fluorouracil, shows that apart from the cell number, volume, degree of spread, number and type of intercellular contacts also influence directional migration.