Scientists discover a new type of wave in living tissues

Researchers have shed new light on how the cells in our bodies collectively migrate, a critical process in positive events such as embryonic development and wound healing, but which is also integral to the development of cancer.

When an organism develops its shape or heals wounds, or when tumours metastasize, cells undergo massive collective movements. Despite decades of research, the mechanisms underpinning these movements remain poorly understood. Now, scientists at the Institute for Bioengineering of Catalonia (IBEC) have discovered that massive cell movements occur in a wave-like manner.

In studying the motion of cell clusters, the scientists detected evidence of wave-like crests of deformation launched at the edges of the clusters and propagating from cell to cell at roughly twice the speed at which cells were moving. “Imagine watching a traffic jam from above,” says Integrative Cell and Tissue Dynamics group leader Xavier Trepat, whose discovery is published in Nature Physics today and as a research highlight in Nature. “You’ll see a similar kind of wave effect as some cars edge forward and others follow after a slight delay to fill the gaps.  Unlike cars, however, cells in our study are able to push and pull from each other, so the phenomenon is much richer.”

Mechanical waves in inert matter have been well understood for a long time, but this is the first time they are observed in living matter. “These waves advance at roughly one millimeter per day, so they are among the slowest waves ever discovered,” adds Xavier.

The group’s findings establish a pattern of stress and strain reiterated in time and space across a multicellular tissue, something which has never before been observed, and which is a likely candidate for the driving force behind the activation of the networks responsible for the cellular invasion typical of cancer. “It’s already known that physical forces can act as intracellular signals to activate local regulatory protein networks – the processes that are needed for biological events to take place, good or bad,” says Xavier. “So our newly discovered ‘wave’ could play a leading role in triggering the required pathways.”

With these latest results, scientists are yet another step closer to understanding how cells migrate, and thus a stage nearer to understanding the dynamics of tumour cells and the physical mechanisms they use to break away and metastasize. ■

X. Serra-Picamal, V. Conte, R. Vincent, E. Anon, D. T. Tambe, E. Bazellieres, J. P. Butler, J. Fredberg, X. Trepat (2012). Mechanical waves during tissue expansion. Nature Physics, 8 July 2012