Filopodo

Filopodo is a slender, actin-rich cellular projection that extends from the surface of many cell types. Typically a few hundred nanometers in diameter and several micrometers long, filopodi are built from tight bundles of parallel actin filaments that push the membrane outward at the leading edge of migrating cells or growth cones in neurons.

The core actin is generally unbranched and stabilized by crosslinking proteins such as fascin and fimbrin. Actin polymerization at the tip is driven by formin-family nucleators (for example mDia) and enhanced by elongation factors like Ena/VASP, while the Arp2/3 complex plays a lesser role in the core structure compared with its prominent function in lamellipodia. Filopodia often arise from or during the maturation of lamellipodial regions and can serve as precursors to other protrusive structures.

Functions of filopodo include environmental sensing and guidance during cell migration. They act as sensory antennae, probing extracellular matrix components, chemokines, and other signaling cues. Through integrin-mediated adhesions, filopodi can anchor to substrates and contribute to directional movement. In the nervous system, filopodi contribute to growth cone navigation by exploring guidance cues critical for axon pathfinding.

Regulation is mediated by signaling pathways that control actin dynamics, notably small GTPases such as Cdc42, which promote filopodium formation and organization. Filopodia are dynamic, continually extending, retracting, and remodeling in response to intracellular and extracellular signals.

Pathological contexts include cancer, where altered filopodial dynamics can influence invasion and metastasis. Research areas span cell biology, developmental biology, and neurobiology, reflecting the broad relevance of filopodo in health and disease.