Contributor: Dr Simon Moore, Columbia University, New York, USA Updated on: September 2012
Reviewer: Prof Alex Mogilner, University of California, Davis, USA
Reviewer: Prof Alex Mogilner, University of California, Davis, USA
Filopodia2.1 Basic DescriptionFilopodia (singular filopodium) are thin membrane protrusions that act as antennae for a cell to probe the surrounding environment [1, 2, 3]. Nonprotruding filopodia are mechanistically related to microspikes [4]. Filopodia are commonly found embedded within, or protruding from the lamelliopodium at the free front of migratory tissue sheets. Filopodia are also prominent in neurite growth cones and individual cells such as fibroblasts. These 60-200 nm diameter structures contain parallel bundles of 10-30 actin filaments held together by actin-binding proteins (e.g. fascin). Filopodia are oriented with the barbed end of the actin filaments directed towards the protruding membrane.Filopodia sense the extracellular environment at their tips using cell surface receptors [5, 6, 7]. Contact with an external target promotes the coupling of membrane-bound proteins to the backward (retrograde) flow of actin; this coupling produces the pulling forces needed for cell migration processes such as wound healing and neurite growth [8]. Contact differences between substrates or cell types influences the number of protruding filopodia [9]. A key set of proteins is involved in filopodia formation; however, the relative importance of each protein seems to vary between different organisms and their cell types. Three basic steps are involved in filopodial assembly: filament nucleation, sustained barbed end elongation and filament bundling.  Video: Filopodia probes precede amoeboid motility. Real-time differential interference contrast video of mouse spinal commisural neuron axon extending on a glass/polystyrene substrate. Actin protein is localized using a fluorescent probe. [Contributor: Simon Moore, Columbia Univ, New York.] |
