How do the cells of a developing embryo, initially mixed together, sort themselves into coherent tissues? An international study in Communications Physics, with the participation of Ignacio Bordeu of the Universidad de Chile's Physics Department, proposes an elegantly minimal answer: a change in the persistence of cell movement. When cells of different types touch, one can retain a kind of spatial memory of the encounter and move away in the opposite direction for a time, increasing its chances of rejoining its own kind.
The team tested the idea in vitro using genetically modified human HEK293 cells, pairing the experiments with theoretical modelling and numerical simulations. The striking result is sufficiency: this contact-triggered directional memory alone can produce cell segregation within hours, without invoking the more elaborate adhesion hierarchies that have dominated explanations of cell sorting since the mid-twentieth century. Small molecular changes at the scale of a single cell, the authors show, can scale up into significant changes in tissue structure.
The implications reach into several corners of biology and medicine. Embryonic development, tissue regeneration and ageing all depend on cells finding and keeping their proper neighbours, while cancer is in part a disease of lost tissue organisation. A physical mechanism this simple gives researchers a new dial to probe in each of those contexts, and illustrates the growing traction of biological physics, a field the Santiago group has made a point of cultivating.