Despite their near sequence identity, actin isoforms cannot completely replace each other in vivo and show marked differences in their tissue-specific and subcellular localization. Little is known about isoform-specific differences in their interactions with myosin motors and other actin-binding proteins. Mammalian cytoplasmic β- and γ-actin interact with nonsarcomeric conventional myosins such...

Specific messenger RNAs (mRNAs) can be sequestered within distinct cellular locations, but little is known about how this is accomplished. The participation of the three major cellular filaments in the localization of actin mRNA was studied in chicken embryo fibroblasts. Movement of actin mRNA to the cell periphery and maintenance of that regionalization required intact microfilaments (composed...

Actin nucleation is the key rate limiting step in the process of actin polymerization, and tight regulation of this process is critical to ensure actin filaments form only at specific times and at defined regions of the cell. Arp2/3 is a well-characterised protein complex that can promote nucleation of new filaments, though its activity requires additional nucleation promotion factors (NPFs). T...

Two ancient and highly divergent actin-based cytoskeletal systems have evolved in angiosperms. Plant genomes encode complex actin and actin binding protein (ABP) gene families, most of which are phylogenetically grouped into gene classes with distinct vegetative or constitutive and reproductive expression patterns. In Arabidopsis thaliana, ectopic expression of high levels of a reproductive cla...

Various concentrations of actin (0.3 or 1 mM MgCl2, 1 mM ATP, 1 mM EGTA) reached their final degree of polymerization (measured by a pyrene dye attached to actin) earlier in the presence of cytochalasin B than in its absence. The curves relating concentrations of polymeric F-actin to total actin concentration were under these conditions highly nonlinear making an unambiguous extrapolation to ze...

The tropomyosin family of proteins form end-to-end polymers along the actin filament. Tumour cells rely on specific tropomyosin-containing actin filament populations for growth and survival. To dissect out the role of tropomyosin in actin filament regulation we use the small molecule TR100 directed against the C terminus of the tropomyosin isoform Tpm3.1. TR100 nullifies the effect of Tpm3.1 on...

Changes in gene expression during reversible bud-hypha transitions of the opportunistic fungal pathogen Candida albicans permit adaptation to environmental conditions that are critical for proliferation in host tissues. Our previous work has shown that the hypha-specific adhesin gene HWP1 is up-regulated by the cyclic AMP (cAMP) signaling pathway. However, little is known about the potential in...

Cell-type-specific F-actin structures and myosin motors are key generators of the forces that drive tissue morphogenesis in developing organisms. These cytoskeletal elements mediate defined cell deformation and control the arrangement of cell-cell contacts. This SnapShot presents a selection of morphogenetic processes, the analysis of which has pioneered specific types of F-actin/myosin-mediate...

Skeletal alpha-actin (skA), a prominent fetal actin isoform that is re-expressed by adult cardiac myocytes after chronic overload in vivo, provides a model for studying cytoskeletal gene regulation by mechanical forces in vitro. We have determined the mechanisms by which perpendicular applied forces acting through integrins and the actin cytoskeleton regulate the expression of skA. Rat-2 fibrob...

In striated muscle tropomyosin (Tm) extends along the length of F-actin-containing thin filaments. Its location governs access of myosin binding sites on actin and, hence, force production. Intermolecular electrostatic associations are believed to mediate critical interactions between the proteins. For example, actin residues K326, K328, and R147 were predicted to establish contacts with E181 o...