Filopodia are F-actin-rich thread-like protrusions that form on the surface of moving animal cells. They are thought to `sense' the cell's environment somehow, but their exact role in the response to extracellular signals is poorly understood. David Soll and co-workers have therefore used a new computer-assisted 3D reconstruction and motion analysis system to study filopodia in Dictyostelium amoebae moving in buffer or in response to chemotactic signals (see ). Their analysis reveals that filopodia originate on pseudopodia – the temporary cytoplasmic extensions that allow the amoebae to move – and that their formation is regulated by chemotactic signals. The filopodia seem to stabilise pseudopodia on the substratum while the cell makes the decision to extend a lateral pseudopodium and turn up a chemoattractant gradient. The authors have also examined filopodia dynamics in Dictyostelium possessing mutations in myosin II heavy chain (MHC) phosphorylation sites. Their findings indicate that the formation and retraction of filopodia during chemotaxis are regulated by receptor-linked changes in MHC phosphorylation/dephosphorylation.
