Filopodia

"Microspikes" redirects here. For the hiking footgear, see Crampons § Microspikes.
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.

Filopodia (sg.: filopodium) are slender cytoplasmic projections that extend beyond the leading edge of lamellipodia in migrating cells.[1] Within the lamellipodium, actin ribs are known as microspikes, and when they extend beyond the lamellipodia, they're known as filopodia.[2] They contain microfilaments (also called actin filaments) cross-linked into bundles by actin-bundling proteins,[3] such as fascin and fimbrin.[4] Filopodia form focal adhesions with the substratum, linking them to the cell surface.[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.

Activation of the Rho family of GTPases, particularly Cdc42 and their downstream intermediates, results in the polymerization of actin fibers by Ena/Vasp homology proteins.[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. Rho activity also results in activation by phosphorylation of ezrin-moesin-radixin family proteins that link actin filaments to the filopodia membrane.[6]

Filopodia have roles in sensing, migration, neurite outgrowth, and cell-cell interaction.[1][further explanation needed] To close a wound in vertebrates, growth factors stimulate the formation of filopodia in fibroblasts to direct fibroblast migration and wound closure.[7] In macrophages, filopodia act as phagocytic tentacles, pulling bound objects towards the cell for phagocytosis.[8]

  1. ^ a b Mattila PK, Lappalainen P (June 2008). "Filopodia: molecular architecture and cellular functions". Nature Reviews. Molecular Cell Biology. 9 (6): 446–454. doi:10.1038/nrm2406. PMID 18464790. S2CID 33533182.
  2. ^ Small JV, Stradal T, Vignal E, Rottner K (March 2002). "The lamellipodium: where motility begins". Trends in Cell Biology. 12 (3): 112–120. doi:10.1016/S0962-8924(01)02237-1. PMID 11859023.
  3. ^ Khurana S, George SP (September 2011). "The role of actin bundling proteins in the assembly of filopodia in epithelial cells". Cell Adhesion & Migration. 5 (5): 409–420. doi:10.4161/cam.5.5.17644. PMC 3218608. PMID 21975550.
  4. ^ Hanein D, Matsudaira P, DeRosier DJ (October 1997). "Evidence for a conformational change in actin induced by fimbrin (N375) binding". The Journal of Cell Biology. 139 (2): 387–396. doi:10.1083/jcb.139.2.387. PMC 2139807. PMID 9334343.
  5. ^ Lodish H, Berk A, Matsudaira P, Kaiser CA, Krieger M, Scott MP, Zipursky SL, Darnell J, eds. (2004). Molecular Cell Biology (fifth ed.). W.H. Freeman and Company. pp. 821, 823.
  6. ^ a b Ohta Y, Suzuki N, Nakamura S, Hartwig JH, Stossel TP (March 1999). "The small GTPase RalA targets filamin to induce filopodia". Proceedings of the National Academy of Sciences of the United States of America. 96 (5): 2122–2128. Bibcode:1999PNAS...96.2122O. doi:10.1073/pnas.96.5.2122. PMC 26747. PMID 10051605.
  7. ^ Cite error: The named reference pmid3773996 was invoked but never defined (see the help page).
  8. ^ Kress H, Stelzer EH, Holzer D, Buss F, Griffiths G, Rohrbach A (July 2007). "Filopodia act as phagocytic tentacles and pull with discrete steps and a load-dependent velocity". Proceedings of the National Academy of Sciences of the United States of America. 104 (28): 11633–11638. Bibcode:2007PNAS..10411633K. doi:10.1073/pnas.0702449104. PMC 1913848. PMID 17620618.