A source and sink of cell flow

Kyogo Kawaguchi et al. show that particular sorts of defect structures in cultures of neural progenitor cells can act as ‘sources’ and ‘sinks’ of cell flow, depending on the direction of movement of cells around the defects. The alignment of cells around these defect structures (which correspond to topological defects) is similar to that seen in artificial extensile active nematic liquid-crystal systems. The authors observed that the cells either piled up into mounds or decreased in density around the defects, affecting the flow of the cells. The authors suggest that it is the interplay between the active forces from cell motility and frictional forces that lead to the changes in cell flow and density.