Cell locomotion within a contact-inhibited monolayer of chick embryonic liver parenchyma cells

Using time-lapse filming, the relative movement of cells (nuclei) within a contact-inhibited monolayer of chick embryonic liver parenchyma cells has been studied. Two techniques were employed to determine the amount of relative cell movement during a culture period of 6 h. Firstly, the number of neighbours lost or gained by each nucleus was counted. Secondly, the relative distance moved by each nucleus in relation to other nucleus in the monolayer was measured. (The numerical results obtained from these analyses and details of the methods used are given in the text). A considerable amount of relative movement of nuclei within the monolayer was found during this period of culture. Although some gaps were occasionally seen between the cells in the monolayer, it was observed that cells able both to "ruffle" and to translocate when no gap was detectable; i.e. the cells appeared able to move while entirely surrounded by other cells. Because of this, we suggest that the monolayering of these epitheloid cells on a surface may be due to restriction of overlapping between them rather than to inhibition of movement by mutual contact. We argue that the term "contact inhibition of overlapping" relates to this behaviour better than the term "contact inhibition of movement".