blebbing

Blebbing is the formation of bulges, or blebs, on the plasma membrane of a cell. Blebs arise when the plasma membrane locally detaches from the underlying actin cortex, allowing cytoplasmic pressure to push the membrane outward. This process can occur during normal cellular activities as well as in response to stress or injury. Blebs are spheres that expand rapidly and can be transient or stable, depending on subsequent cortex reassembly and cytoskeletal regulation.

Mechanistically, blebbing begins with weakening or rupture of membrane-cortex connections, often at sites where RhoA-mediated actomyosin contractility increases intracellular pressure. Cytoplasmic flow inflates a bleb; the membrane expands while the cortex reforms beneath it. As actin filaments repolymerize, myosin-based contraction can retract the bleb, drawing the membrane back toward the cell body or stabilizing the bleb for locomotion. Blebbing is regulated by signaling pathways controlling actin dynamics and cortical tension.

Blebbing occurs in several biological contexts. Apoptotic blebbing accompanies programmed cell death and contributes to cell fragmentation into apoptotic bodies. Non-apoptotic blebbing supports amoeboid-type cell movement and invasion through soft extracellular matrices, as seen in some developmental processes and cancer cells. Blebs also appear during cytokinesis and various morphogenetic events.

In microscopy, blebs are visualized with fluorescent probes for the plasma membrane or the actin cortex, and time-lapse imaging tracks dynamic bleb formation and retraction. The phenomenon reflects the mechanical properties of the cell cortex and cytoplasm and serves as a model for studying cell motility, division, and death.