The formation of contacts between HeLa cells. Directed mutual outgrowth of cell surface protrusions

The contacting behavior of HeLa cells in subconfluent monolayer cultures has been studied by phase contrast and scanning electron microscopy. We present further evidence that cells separated from each other by a cell-free space up to 20 micron width can simultaneously form directed and mutual protrusions against each other. A statistical analysis demonstrated that in more than half of the possible contact events a reciprocal outgrowth of cell surface protrusions had occurred. This suggests that contact formation is not just a random process, but may be influenced by so far unrecognized factors.