Epithelial cells cultured in a monolayer are very motile in isolation but reach a near-jammed state when mitotic division increases their number above a critical threshold. We have recently shown that a monolayer can be reawakened by over-expression of a single protein, RAB5A, a master regulator of endocytosis. This reawakening of motility was explained in term of a flocking transition that promotes the emergence of a large-scale collective migratory pattern. Here we focus on the impact of this reawakening on the structural properties of the monolayer. We find that the unjammed monolayer is characterised by a fluidisation at the single cell level and by enhanced non-equilibrium large-scale number fluctuations at a larger length scale. Also with the help of numerical simulations, we trace back the origin of these fluctuations to the self-propelled active nature of the constituents and to the existence of a local alignment mechanism, leading to the spontaneous breaking of the orientational symmetry.
Bibliographical noteWe thank S Henkes for useful discussions. FGia and RC acknowledge funding from the Italian Ministry of University and Scientific Research (MIUR) under the program Futuro in Ricerca—Project ANISOFT (RBFR125H0M) and from Regione Lombardia and CARIPLO foundation under the joint action Avviso congiunto per l'incremento dell'attrattivitá del sistema ricerca lombardo e della competitivitá dei ricercatori candidati su strumenti ERC—Project 2016-0998. CM, SC and GS acknowledge funding from Associazione Italiana per la Ricerca sul Cancro (AIRC 10168 and 18621), MIUR, the Italian Ministry of Health, Ricerca Finalizzata (RF0235844), Worldwide Cancer Research (AICR-14-0335), and the European Research Council (Advanced-ERC-268836). CM was also supported by Fondazione Umberto Veronesi and SC by an AIRC fellowship. FGin acknowledges support from the Marie Curie Career Integration Grant (CIG) PCIG13-GA-2013-618399, and wish to thank the University of Milan and LibrOsteria for their hospitality while this work was underway.
- active matter
- jamming transition
- collective cell migration
- non-equilibrium fluctuations