Rediscovering contact inhibition in the embryo.

The cellular reaction called contact inhibition of locomotion was initially characterised by Michael Abercrombie more than 60 years ago. In his most general definition, it is defined as the stopping of the continued locomotion of a cell in the direction which has produced a collision with another cell. This deceptively simple response has been widely studied in vitro in a number of cell types over the years, yet it is still often misunderstood by the scientific community. Abercrombie spent much of his life studying the failure of the response shown by cancer cell types and how this might lead to malignant invasion of normal tissue. However, since Abercrombie's time, a role for this response in living organisms has been left to the realm of speculation. Here, we discuss the history of contact inhibition research, clarify some of the misconceptions about the response and reclaim misused terminology. We will also highlight our recent work, which for the first time elucidates a functional role for contact inhibition in vivo during embryogenesis.