Filopodia 4102360 215778104 2008-05-29T17:48:01Z TimVickers 1635280 /* References */ del duplicate [[Image:Filopodia.jpg|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.|thumb]] The '''filopodia''' (also microspikes) are slender cytoplasmic projections, similar to [[lamellipodia]], which extend from the leading edge of migrating cells.<ref>{{cite journal |author=Mattila PK, Lappalainen P |title=Filopodia: molecular architecture and cellular functions |journal=Nat. Rev. Mol. Cell Biol. |volume=9 |issue=6 |pages=446–54 |year=2008 |month=June |pmid=18464790 |doi=10.1038/nrm2406}}</ref> They contain actin filaments cross-linked into bundles by actin-binding proteins, e.g. fimbrin.<ref name="pmid9334343">{{cite journal |author=Hanein D, Matsudaira P, DeRosier DJ |title=Evidence for a conformational change in actin induced by fimbrin (N375) binding |journal=J. Cell Biol. |volume=139 |issue=2 |pages=387–96 |year=1997 |month=October |pmid=9334343 |url=http://www.jcb.org/cgi/pmidlookup?view=long&pmid=9334343}}</ref> Filopodia form focal adhesions with the substratum, linking it to the cell surface (Lodish et al, 2004). A [[cell (biology)|cell]] migrates along a surface by extending filopodia at the leading edge. The filopodia attach to the substratum further down the migratory pathway, then contraction of stress fibres retracts the rear of the cell to move the cell forwards. Activation of the Rho family of small Ras-related [[GTPase]]s and their downstream intermediates results in the construction of actin fibers (Ohta et al, 1999). Growth factors bind to receptor tyrosine kinases resulting in the [[polymerization]] of [[actin]] filaments, which cross-linked, make up the supporting [[cytoskeleton|cytoskeletal]] elements of filopodia. Rho activity also results in the activation of the phosphorylation of the ezrin-moesin-radixin group promoting the binding of [[actin]] filaments to the filopodia membrane.<ref>{{cite journal |author=Ohta Y, Suzuki N, Nakamura S, Hartwig JH, Stossel TP |title=The small GTPase RalA targets filamin to induce filopodia |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=96 |issue=5 |pages=2122–8 |year=1999 |month=March |pmid=10051605 |url=http://www.pnas.org/cgi/pmidlookup?view=long&pmid=10051605}}</ref> To close a wound in vertebrates, growth factors stimulate the formation of filopodia in [[fibroblasts]] to direct [[fibroblast]] division and close the wound.<ref name="pmid3773996"/> In developing [[neurons]], filopodia extend from the [[growth cone]] at the leading edge. In neurons deprived of filopodia by the removal of [[actin|actin filaments]], growth cone extension continues as normal but direction of growth is disrupted and highly irregular.<ref name="pmid3773996">{{cite journal |author=Bentley D, Toroian-Raymond A |title=Disoriented pathfinding by pioneer neurone growth cones deprived of filopodia by cytochalasin treatment |journal=Nature |volume=323 |issue=6090 |pages=712–5 |year=1986 |pmid=3773996 |doi=10.1038/323712a0 |url=}}</ref> ==References== {{reflist}} *'''<u>Molecular Cell Biology Fifth Edition<u>''' Lodish, Berk, Matsudaira, Kaiser, Krieger, Scott, Zipursky, Darnell. pg. 821, 823 2004 by W.H. Freeman and Company. [[Category:Cytoskeleton]] [[Category:Cell biology]] [[de:Filopodium]] [[lt:Filopodija]]