March 26, 2015

The actin cytoskeleton at the leading edge of a crawling cell has been a source of both scientific fascination and stunning images for biologists. Today’s image is from a paper that sheds light on how that complex structure is generated. 

The outermost region of a crawling cell’s cortex is called the lamellipodium, and it depends on a complex actin cytoskeleton for its structure and rapid dynamics. The generation of branched actin filaments at lamellipodia requires the activity of the actin-nucleating Arp2/3 protein complex. In a recent study, Henson and colleagues use the very flat and Arp2/3-rich lamellipodia of sea urchin coelomocytes to visualize the actin cytoskeleton. As seen in the images above, treatment of coelomocytes with a drug that inhibits the Arp2/3 complex resulted in drastic changes to the actin cytoskeleton. Specifically, the densely-packed branched filaments of lamellipodia (left, control) were replaced with actin filament arcs that ran diagonal or parallel to the cell’s edge (30 and 60 seconds after drug treatment, middle and right images). These transverse actin arcs may act as mother/scaffold filaments from which more actin filaments are nucleated during organization of the cytoskeleton in lamellipodia.

Henson, J., Yeterian, M., Weeks, R., Medrano, A., Brown, B., Geist, H., Pais, M., Oldenbourg, R., & Shuster, C. (2015). Arp2/3 complex inhibition radically alters lamellipodial actin architecture, suspended cell shape, and the cell spreading process Molecular Biology of the Cell, 26 (5), 887-900 DOI: 10.1091/mbc.E14-07-1244

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