Microheterogeneity controls the rate of gelation of actin filament networks

Yiider Tseng, Kwang M. An, Denis Wirtz

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53 Scopus citations


Rapid sol-gel transitions of the actin cytoskeleton are required for many key cellular processes, including cell spreading and cell locomotion. Actin monomers assemble into semiflexible polymers that rapidly intertwine into a network, a process that in vitro takes ∼1 min for an actin concentration of 1 mg/ml. The same actin filament network, however, takes ∼1 h to exhibit a steady-state elasticity. We hypothesize that the slow gelation of F-actin is due to the slow establishment of a homogeneous meshwork. Using a novel method, time-resolved multiple particle tracking, which monitors the range of thermally excited displacements of microspheres imbedded in the network, we show that the increase in elasticity in a polymerizing solution of actin parallels the progressive decline of the network microheterogeneity. The rates of gelation and network homogenization slightly decrease with actin concentration and in the presence of the F-actin cross-linking proteins α-actinin and fascin, whereas the rate of actin polymerization increases dramatically with actin concentration. Our measurements show that the slow spatial homogenization of the actin filament network, not actin polymerization or the formation of polymer overlaps, is the rate-limiting step in the establishment of an elastic actin network and suggest that a new activity of F-actin binding proteins may be required for the rapid formation of a homogeneous stiff gel.

Original languageEnglish (US)
Pages (from-to)18143-18150
Number of pages8
JournalJournal of Biological Chemistry
Issue number20
StatePublished - May 17 2002

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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