Dicing with dogma: de-branching the lamellipodium.
Bottom Line: The primary event in the movement of a migrating eukaryotic cell is the extension of cytoplasmic sheets termed lamellipodia composed of networks of actin filaments.Lamellipodia networks are thought to arise through the branching of new filaments from the sides of old filaments, producing a dendritic array.These findings signal a reconsideration of the structural basis of protrusion and about the roles of the different actin nucleating and elongating complexes involved in the process.
Affiliation: Institute of Molecular Biotechnology, Austrian Academy of Sciences, Dr Bohr-Gasse 3, Vienna, Austria. email@example.comShow MeSH
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Mentions: Advances in electron microscope technology have recently opened the way to electron tomography, also in combination with rapid freezing to avoid chemical fixation [33–35]. Early results of 3D imaging by this technique, with Dictyostelium amoeba, showed that actin filaments could be resolved in frozen cells , but the motile activity of the regions imaged was unknown. Electron tomography can be applied to those parts of cells thin enough to allow penetration of the electron beam. Lamellipodia, which vary from 0.1-0.3 μm in thickness, fall within this range, and tomograms of lamellipodia in cells frozen live and imaged in vitreous ice have been acquired recently . Tracking of actin filaments through the tomograms showed that the lamellipodium is composed mainly of overlapping actin filaments. The same result was obtained for cytoskeletons dried in negative stain, which retain a three dimensional organization, albeit with a collapse to around 50% of the thickness of frozen preparations. These recent findings, including data from four cell types , indicate that the Arp2/3 complex nucleates un-branched arrays of actin in lamellipodia (Figure 1).
Affiliation: Institute of Molecular Biotechnology, Austrian Academy of Sciences, Dr Bohr-Gasse 3, Vienna, Austria. firstname.lastname@example.org