filopodium

180px|thumb|This electron micrograph shows exaggerated filopodia with club-like shape induced by formin mDia2 in cultured cells. These filopodia are filled with bundled microfilament|actin filaments which were born in and converged from the lamellipodial network.

Filopodia (: filopodium) are slender cytoplasmic projections that extend beyond the leading edge of lamellipodia in migrating cells. Within the lamellipodium, actin ribs are known as microspikes, and when they extend beyond the lamellipodia, they're known as filopodia. They contain microfilaments (also called actin filaments) cross-linked into bundles by actin-bundling proteins, such as fascin and fimbrin. Filopodia form focal adhesions with the substratum, linking them to the cell surface. Many types of migrating cells display filopodia, which are thought to be involved in both sensation of chemotropic cues, and resulting changes in directed locomotion.