Blebs are cellular protrusions driven by intracellular pressure that typically retract within minutes after formation. It was recently reported that confined cells migrate by forming a single large stable bleb with fast cortical flows, by upregulating cortical contractility. Here, we report a new type of stable bleb protrusions that appears before cell-scale polarisation. Remarkably, stable blebs bear cortical flows and can self-fragment and migrate autonomously, constituting a simple system to study actomyosin-based motility. We propose a model for bleb morphogenesis in which the final phenotype — transient versus stable bleb — is due to the relative timing of cortex formation versus myosin contraction. Stress percolation and a sol-gel phase transition of the actin network at the leading edge determines bleb stability and shape. The description of a live cellular process explained by percolation theory at a molecular level constitutes a novel contribution to the cytoskeleton field.
In this archive, we included raw images, datasets, the original PhD thesis manuscript, and associated Supplementary videos.