lamellipodes

Lamellipodes are broad, flattened, sheet-like extensions of the cell membrane that are characteristic of motile animal cells, particularly fibroblasts and some types of protozoa. They are dynamic structures that play a crucial role in cell locomotion and cell-cell adhesion. These structures are driven by the rapid polymerization of actin filaments at the leading edge of the cell. Actin monomers assemble into filaments, which then push the plasma membrane forward, creating the lamellipodium. This process is often regulated by a complex network of actin-binding proteins, including formins and Arp2/3 complex, which influence filament nucleation, elongation, and branching.

The formation and retraction of lamellipodes are essential for cell movement. As the lamellipodium extends, the cell adheres to the extracellular matrix or other cells at its leading edge, providing traction. Simultaneously, the rear of the cell retracts, allowing the cell body to move forward. This coordinated process of protrusion and retraction enables cells to migrate through tissues, a fundamental process in development, wound healing, and immune responses. Lamellipodes are also involved in phagocytosis, a process where cells engulf large particles, and in cell-cell recognition and adhesion. Their structure is highly organized, with a dense network of actin filaments often showing a branching or dendritic organization at the base, transitioning to more parallel arrays at the extending tip. The precise mechanisms governing the speed, directionality, and stability of lamellipodium extension are still areas of active research.