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  • br Actin cytoskeleton in protrusion

    2024-05-15


    Actin cytoskeleton in protrusion Pushing force driving membrane protrusion is generated by polymerizing PF-4708671 filaments organized either into branched networks or parallel bundles. Branched networks are assembled through Arp2/3 complex-dependent actin nucleation and drive protrusion of lamellipodia, some membrane trafficking events, and formation of diverse cell–cell junctions. Parallel bundles are mostly known to drive protrusion of leading edge filopodia. Whereas basic principles of actin-based protrusion are well-established (reviewed in [1, 3]), recent efforts focused on understanding how specific geometry of polymerizing actin arrays is affected by biophysical and biochemical conditions.
    Actin cytoskeleton in contraction Pulling forces driving contraction are generated by mutual sliding of actin and myosin II filaments, as originally established for skeletal muscle. Nonmuscle cells use a combination of three NMII paralogs, NMIIA, NMIIB, and NMIIC, to generate contractile activity for migration, cytokinesis, and formation of cell–cell and cell–matrix junctions among other functions (reviewed in [32]). The most conspicuous contractile structures in nonmuscle cells are stress fibers—bundles of actin filaments interdigitating with bipolar NMII filaments. Cytokinetic contractile rings in dividing cells and non-aligned actin-NMII networks are other examples of contractile actin structures.
    Conclusions
    Conflict of interest statement
    References and recommended reading Papers of particular interest, published within the period of review, have been highlighted as:
    Acknowledgement This work was supported by the National Institutes of Health grant # R01 GM 095977.
    Introduction The cytoskeleton is a system of intracellular filaments crucial for cell shape, adhesion, growth, division and motility (Stossel, 1993; Wickstead and Gull, 2011). As one of the major component of cytoskeleton, actin filaments form a highly dynamic network composed of actin polymers and a large variety of associated proteins (Schmidt and Hall, 1998). The actin proteins exist within cells in either globular/monomer (G-actin) or filamentous (F-actin) form and thus in dynamic transitions between depolymerization and polymerization status (Ono, 2007). Actin depolymerization factor (ADF) cofilin is a family of actin binding proteins with actin filaments depolymerization function (Bamburg et al., 1980; Nishida et al., 1984). In mammals, the cofilin family consists of three highly similar paralogs: Cofilin-1 (CFL1, non-muscle cofilin, n-cofilin), Cofilin-2 (CFL2, muscle cofilin, m-cofilin) and destrin (DSTN). The activity of cofilins is regulated by phosphorylation, polyphosphoinositide interaction, pH and interaction with other actin binding proteins (Van Troys et al., 2008). Human bone marrow-derived stromal (Skeletal) stem cells (hMSCs) are a group of clonogenic and multipotent cells capable of differentiation into mesoderm-type cells e.g. osteoblast and adipocyte (Abdallah and Kassem, 2008). During lineage specific differentiation, hMSCs exhibit significant changes in morphology and actin cytoskeletal organization (McBeath et al., 2004; Treiser et al., 2010; Yourek et al., 2007). Previous studies have suggested that RhoA-ROCK (Ras homolog gene family member A-Rho-associated protein kinase) signaling mediates changes in cell shape and cytoskeletal tension regulating hMSC lineage commitment (McBeath et al., 2004). A spheroidal morphology associated with a dispersed actin cytoskeleton with few focal adhesions encourages MSC differentiate into adipocytes whereas a stiff, spread actin cytoskeleton with greater numbers of focal adhesions drives MSC differentiate into osteoblasts (Mathieu and Loboa, 2012). The changes in cell shape are caused by cytoskeletal changes due to actin synthesis and reorganization (Antras et al., 1989; Spiegelman and Farmer, 1982), and thus modification by mechanical forces or regulation of relative kinases that change actin cytoskeletal dynamics, can regulate cell differentiation (Arnsdorf et al., 2009; Kanzaki and Pessin, 2001; McBeath et al., 2004; Noguchi et al., 2007). However, this approach has not been widely utilized in differentiation studies of hMSCs.