Mechanical worrying drives cell migration in crowded environments

Migratory cells navigate through crowded 3D microenvironments in vivo . Amoeboid cells, such as immune cells and some cancer cells, are thought to do so by deforming their bodies to squeeze through tight spaces.[1][1] Yet large populations of nearly spherical amoeboid cells migrate[2][2]–[4][3] in microenvironments too dense[5][4],[6][5] to move through without extensive shape deformations. How they do so is unknown. We used high-resolution light-sheet microscopy to visualize metastatic melanoma cells in dense environments, finding that cells maintain a round morphology as they migrate and create a path through which to move via bleb-driven mechanical degradation and subsequent macropinocytosis of extracellular matrix components. Proteolytic degradation of the extracellular matrix via matrix metalloproteinases is not required. Membrane blebs are short-lived relative to the timescale of migration, and thus persistence in their polarization is critical for productive ablation of the extracellular matrix. Interactions between small but long-lived cortical adhesions and collagen at the cell front induce PI-3 Kinase signaling that drive bleb enlargement via branched actin polymerization. Large blebs in turn abrade collagen, creating a feedback between extracellular matrix structure, cell morphology, and cell polarization that results in both path generation and persistent cell movement. ### Competing Interest Statement The authors have declared no competing interest. [1]: #ref-1 [2]: #ref-2 [3]: #ref-4 [4]: #ref-5 [5]: #ref-6