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The actin cytoskeleton is one of the most important players in cell motility, adhesion, division, and functioning. The regulation of specific microfilament formation largely determines cellular functions. The main actin-binding protein in animal cells is tropomyosin (Tpm). The unique structural and functional diversity of microfilaments is achieved through the diversity of Tpm isoforms. In our work, we studied the properties of the cytoplasmic isoforms Tpm1.8 and Tpm1.9. The results showed that these isoforms are highly thermostable and differ in the stability of their central and C-terminal fragments. The properties of these isoforms were largely determined by the 6th exons. Thus, the strength of the end-to-end interactions, as well as the affinity of the Tpm molecule for F-actin, differed between the Tpm1.8 and Tpm1.9 isoforms. They were determined by whether an alternative internal exon, 6a or 6b, was included in the Tpm isoform structure. The strong interactions of the Tpm1.8 and Tpm1.9 isoforms with F-actin led to the formation of rigid actin filaments, the stiffness of which was measured using an optical trap. It is quite possible that the structural and functional features of the Tpm isoforms largely determine the appearance of these isoforms in the rigid actin structures of the cell cortex.

Microglia are the most prominent immune resident cell population in the central nervous system (CNS). In the healthy CNS, microglia survey their surrounding microenvironment, through recurrent extension and retraction of filopodia-like membrane protrusions, without evident cell body displacement. Microglia undergo dramatic transcriptomic and shape changes upon brain insults or neurodegenerative disease states and adopt a classical immune effector function (producing an extensive array of inflammatory mediators such as cytokines, chemokines, and reactive oxygen species) to re-establish tissue homeostasis. While the biophysical principles underlying microglia morphological changes remain elusive, several recent studies have highlighted the pivotal role of the actin and non-muscle myosin II filamentous cytoskeleton in this process. In this work, we discuss how subcellular topological patterning of the actin and myosin cytoskeleton can control microglial cell shape dynamics and how it can potentially feedback on their functional specialization, which is of great importance to understanding the mechanisms of microglial action in homeostatic conditions and CNS disease states.

A theory for diffusivity estimation for spatially extended activator–inhibitor dynamics modeling the evolution of intracellular signaling networks is developed in the mathematical framework of stochastic reaction–diffusion systems. In order to account for model uncertainties, we extend the results for parameter estimation for semilinear stochastic partial differential equations, as developed in Pasemann and Stannat (Electron J Stat 14(1):547–579, 2020), to the problem of joint estimation of diffusivity and parametrized reaction terms. Our theoretical findings are applied to the estimation of effective diffusivity of signaling components contributing to intracellular dynamics of the actin cytoskeleton in the model organism Dictyostelium discoideum. [ABSTRACT FROM AUTHOR]

Metabolons are dynamic associations of enzymes catalyzing consecutive reactions within a given pathway. Association results in enzyme stabilization and increased metabolic efficiency. Metabolons may use cytoskeletal elements, membranes and membrane proteins as scaffolds. The effects of glucose withdrawal on a putative glycolytic metabolon/F-actin system were evaluated in three Saccharomyces cerevisiae strains: a WT and two different obligate fermentative (OxPhos-deficient) strains, which obtained most ATP from glycolysis. Carbon source withdrawal led to inhibition of fermentation, decrease in ATP concentration and dissociation of glycolytic enzymes from F-actin. Depending on the strain, inactivation/reactivation transitions of fermentation took place in seconds. In addition, when ATP was very low, green fluorescent protein-labeled F-actin reorganized from highly dynamic patches to large, non-motile actin bodies containing proteins and enzymes. Glucose addition restored fermentation and cytoskeleton dynamics, suggesting that in addition to ATP concentration, at least in one of the tested strains, metabolon assembly/disassembly is a factor in the control of the rate of fermentation. Image 1 [ABSTRACT FROM AUTHOR]

Cell migration is a fundamental feature of tumour metastasis and angiogenesis. It is regulated by a variety of signalling molecules including H2O2 and Ca2+. Here, we asked whether the H2O2-sensitive transient receptor potential melastatin 2 (TRPM2) Ca2+ channel serves as a molecular link between H2O2 and Ca2+. H2O2-mediated activation of TRPM2 channels induced filopodia formation, loss of actin stress fibres and disassembly of focal adhesions, leading to increased migration of HeLa and prostate cancer (PC)-3 cells. Activation of TRPM2 channels, however, caused intracellular release of not only Ca2+ but also of Zn2+. Intriguingly, elevation of intracellular Zn2+ faithfully reproduced all of the effects of H2O2, whereas Ca2+ showed opposite effects. Interestingly, H2O2 caused increased trafficking of Zn2+-enriched lysosomes to the leading edge of migrating cells, presumably to impart polarisation of Zn2+ location. Thus, our results indicate that a reciprocal interplay between Ca2+ and Zn2+ regulates actin remodelling and cell migration; they call for a revision of the current notion that implicates an exclusive role for Ca2+ in cell migration [ABSTRACT FROM AUTHOR]

Actin cytoskeleton dynamics is critical for variety of cellular events including cell elongation, division and morphogenesis, and is tightly regulated by numerous groups of actin binding proteins. However it is not well understood how these actin binding proteins are modulated in a physiological condition by their interaction proteins. In this study, we describe that Arabidopsis 14-3-3 λ protein interacted with actin depolymerizing factor 1 (ADF1) in plant to regulate F-actin stability and dynamics. Loss of 14-3-3 λ in Arabidopsis resulted in longer etiolated hypocotyls in dark and changed actin cytoskeleton architecture in hypocotyl cells. Overexpression of ADF1 repressed 14-3-3 λ mutant hypocotyl elongation and actin dynamic phenotype. In addition, the phosphorylation level of ADF1 was increased and the subcellular localization of ADF1 was altered in 14-3-3 λ mutant. Consistent with these observations, the actin filaments were more stable in 14-3-3 λ mutant. Our results indicate that 14-3-3 λ protein mediates F-actin dynamics possibly through inhibiting ADF1 phosphorylation in vivo. [ABSTRACT FROM AUTHOR]

Microglia are the most prominent immune resident cell population in the central nervous system (CNS). In the healthy CNS, microglia survey their surrounding microenvironment, through recurrent extension and retraction of filopodia-like membrane protrusions, without evident cell body displacement. Microglia undergo dramatic transcriptomic and shape changes upon brain insults or neurodegenerative disease states and adopt a classical immune effector function (producing an extensive array of inflammatory mediators such as cytokines, chemokines, and reactive oxygen species) to re-establish tissue homeostasis. While the biophysical principles underlying microglia morphological changes remain elusive, several recent studies have highlighted the pivotal role of the actin and non-muscle myosin II filamentous cytoskeleton in this process. In this work, we discuss how subcellular topological patterning of the actin and myosin cytoskeleton can control microglial cell shape dynamics and how it can potentially feedback on their functional specialization, which is of great importance to understanding the mechanisms of microglial action in homeostatic conditions and CNS disease states. • Microglia morphodynamics is regulated by actin and actomyosin cytoskeleton. • Actin and actomyosin subcellular distribution decodes cell shape. • Myosin-II controls microglia function. [ABSTRACT FROM AUTHOR]

Fragile X Syndrome (FXS) is the most common form of inherited intellectual disability due to the silencing of the FMR1 gene encoding FMRP (Fragile X Mental Retardation Protein), an RNA-binding protein involved in different steps of RNA metabolism. Of particular interest is the key role of FMRP in translational regulation. Since the first functional characterizations of FMRP, its role has been underlined by its association with actively translating polyribosomes. Furthermore, a plethora of mRNA targets of FMRP have been identified. In the absence of FMRP the deregulation of translation/transport/stability of these mRNAs has a cascade effect on many pathways, resulting into the final phenotype. We review here a set of targets of FMRP (mRNAs and proteins) that may have an impact on the FXS phenotype by deregulating some key cellular processes, such as translation, cytoskeleton remodeling and oxidative stress. The manipulation of these abnormal pathways by specific drugs may represent new therapeutic opportunities for FXS patients. [ABSTRACT FROM AUTHOR]

Malfunction of the actin cytoskeleton is linked to numerous human diseases including neurological disorders and cancer. LIMK1 (LIM domain kinase 1) and its paralogue LIMK2 are two closely related kinases that control actin cytoskeleton dynamics. Consequently, they are potential therapeutic targets for the treatment of such diseases. In the present review, we describe the LIMK conformational space and its dependence on ligand binding. Furthermore, we explain the unique catalytic mechanism of the kinase, shedding light on substrate recognition and how LIMK activity is regulated. The structural features are evaluated for implications on the drug discovery process. Finally, potential future directions for targeting LIMKs pharmacologically, also beyond just inhibiting the kinase domain, are discussed. [ABSTRACT FROM AUTHOR]