Filopodia

[5] 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.

[6] Growth factors bind to receptor tyrosine kinases resulting in the polymerization of actin filaments, which, when cross-linked, make up the supporting cytoskeletal elements of filopodia.

[citation needed] The functions of filopodia have been attributed to pathfinding of neurons,[9] early stages of synapse formation,[10] antigen presentation by dendritic cells of the immune system,[11] force generation by macrophages[12] and virus transmission.

[34][35] A study deploying protein imaging of adult mice showed that filopodia in the explored regions were by an order of magnitude more abundant than previously believed, comprising about 30% of all dendritic protrusions.

At their tips, they contain "silent synapses" that are inactive until recruited as part of neural plasticity and flexible learning or memories, previously thought to be present mainly in the developing pre-adult brain and to die off with time.

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