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. 2006 Mar 20;103(13):4906–4911. doi: 10.1073/pnas.0508269103

Fig. 4.

Fig. 4.

Star formation is observed when fascin is added to a solution of actin, VCA, and Arp2/3 complex. (a and b) Initial conditions were 7.28 μM actin monomer, 200 nM GST-VCA, 100 nM Arp2/3 complex, and 3 μM fascin; the [fascin]/[G actin] = 1/2. (a) After mixing for 2.5 min the star appears to be composed of a dense core surrounded by a low density cloud of actin. It is already possible to observe actin bundles in the cloudy regions. (b) After 7.5 min the cloudy corona turns into a fully developed star; the diffuse actin cloud disappears, turning into long actin bundles (10–30 μm) emanating from the dense core. (c) Addition of 40 nM CP results in inhibition of star formation. The number of stars is decreased and their bundles are shorter (≈2 μm). (d) Stars are not formed in the absence of Arp2/3 complex; instead, an entangled network of filament bundles is observed. Short white arrows mark branching points of actin bundles, and the long white arrow marks the bundling/splitting of several bundles. (e) The dynamic of star growth is followed in time steps of 20 s. Initial protein concentrations were 3.64 μM actin monomer, 200 nM GST-VCA, 100 nM Arp2/3 complex, and 1.5 μM fascin; [fascin]/[actin] = ½ as in a–d. The initial average growth rate of bundles is v̄ = 2.27 ± 0.80 μm/min. (f) Star pairs also form. Their bundles growth rate is the same as for individual stars.