Emergence of embryonic pattern through contact inhibition of locomotion. Brian M Stramer, John Davis, Chieh-Yin Huang, Jennifer Zanet, Daniel Soong, Graham Dunn. Randall Division of Cell and Molecular Biophysics, King's College London, London, United Kingdom.

   The pioneering cell biologist, Michael Abercrombie, first described the process of contact inhibition of locomotion more than half a century ago when migrating fibroblasts were observed to rapidly change direction and migrate away upon collision. Since this initial observation, we have gleaned little understanding of how contact inhibition is regulated and only lately observed its occurrence in vivo. We recently revealed that Drosophila hemocytes require contact inhibition for their uniform embryonic dispersal (Stramer et al., J. Cell Biol. 2010). To investigate the role that contact inhibition plays in the patterning of this migration, we have now mathematically analyzed and computationally simulated their contact repulsion dynamics. Taking into account only the kinematics (i.e. acceleration and velocity) of freely moving and singly colliding cells, our data reveal that the final hexagonally arrayed pattern of hemocyte distribution, and the details and timing of its formation, can be explained entirely by contact inhibition dynamics within the geometry of the Drosophila embryo. This also highlights that the contact inhibition process is regulated by precise rules, and analysis of actin and microtubule dynamics around collisions suggests that there is a complex mechanical coupling between colliding cells allowing for the exact coordination of the response in colliding partners. These results have broader implications for morphological development suggesting that Michael Abercrombies social behavior of cells, in the absence of elaborate external cues, can be a significant driving force for embryonic pattern formation.