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Gupton, S.L. et al. Cell migration without a lamellipodium: translation of actin dynamics into cell movement mediated by tropomyosin. J. Cell Biol. 168, 619-631

Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
The Journal of Cell Biology (Impact Factor: 9.69). 03/2005; 168(4):619-31. DOI: 10.1083/jcb.200406063
Source: PubMed

ABSTRACT The actin cytoskeleton is locally regulated for functional specializations for cell motility. Using quantitative fluorescent speckle microscopy (qFSM) of migrating epithelial cells, we previously defined two distinct F-actin networks based on their F-actin-binding proteins and distinct patterns of F-actin turnover and movement. The lamellipodium consists of a treadmilling F-actin array with rapid polymerization-dependent retrograde flow and contains high concentrations of Arp2/3 and ADF/cofilin, whereas the lamella exhibits spatially random punctae of F-actin assembly and disassembly with slow myosin-mediated retrograde flow and contains myosin II and tropomyosin (TM). In this paper, we microinjected skeletal muscle alphaTM into epithelial cells, and using qFSM, electron microscopy, and immunolocalization show that this inhibits functional lamellipodium formation. Cells with inhibited lamellipodia exhibit persistent leading edge protrusion and rapid cell migration. Inhibition of endogenous long TM isoforms alters protrusion persistence. Thus, cells can migrate with inhibited lamellipodia, and we suggest that TM is a major regulator of F-actin functional specialization in migrating cells.

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    • "FSM study: correlation of actin assembly with a green fluorescent protein (GFP)–p34 signal In biological systems, Arp2/3 is a protein complex that is thought to promote polymerization of networking filaments by aiding new filament creation from preexisting ones. This complex has been described in the literature as a mediator of actin, helping to regulate processes of polymerization and depolymerization in tandem [15] [16] [17]. It has been shown that Arp2/3 is present along the lamellipodium, the cytoskeletal actin at the mobile edge of cells. "
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    • "Because engagement of F-actin flow at FA is thought to limit the width of the lamellipodium and to establish a border between lamellipodium and lamellum (Ponti et al., 2004; Alexandrova et al., 2008; Shemesh et al., 2009), we sought to test whether vinculin affected the spatial organization of lamellipodium and lamellum. We localized F-actin and the lamellipodial protein cortactin or the lamellum protein phosphoserine19 myosin regulatory light chain-2 (pS19MLC2) in control and Vcl-KO MEF (Wu and Parsons, 1993; Ponti et al., 2004; Gupton et al., 2005; Lai et al., 2008). Line scans of staining intensity across the leading edge of control MEF revealed a sharply defined, narrow band of cortactin that colocalized with dense lamellipodial F-actin (Fig. 2, A [arrow], D, and E). "
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    • "Tropomyosin inhibits both the rate of polymerization and depolymerization of actin, regulates the actin-myosin interaction, and by the temporal and spatial regulation of its expression is involved with functional contributions to the actin cytoskeleton (Gunning et al. 2008). In addition, tropomyosin is a major regulator of F-actin functional specialization in migrating cells and is important for regionally defining the properties of the actin cytoskeleton in mediating changes in cell morphology (Gupton et al. 2005). Tropomyosin and troponin bind to actin and block myosin binding. "
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