Biology

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14 pages, 1183 KiB

Open AccessReview

Does the Actin Network Architecture Leverage Myosin-I Functions?

by Julien Pernier and Kristine Schauer

Biology 2022, 11(7), 989; https://doi.org/10.3390/biology11070989 - 29 Jun 2022

Cited by 2 | Viewed by 1977

The actin cytoskeleton plays crucial roles in cell morphogenesis and functions. The main partners of cortical actin are molecular motors of the myosin superfamily. Although our understanding of myosin functions is heavily based on myosin-II and its ability to dimerize, the largest and [...] Read more.

The actin cytoskeleton plays crucial roles in cell morphogenesis and functions. The main partners of cortical actin are molecular motors of the myosin superfamily. Although our understanding of myosin functions is heavily based on myosin-II and its ability to dimerize, the largest and most ancient class is represented by myosin-I. Class 1 myosins are monomeric, actin-based motors that regulate a wide spectrum of functions, and whose dysregulation mediates multiple human diseases. We highlight the current challenges in identifying the “pantograph” for myosin-I motors: we need to reveal how conformational changes of myosin-I motors lead to diverse cellular as well as multicellular phenotypes. We review several mechanisms for scaling, and focus on the (re-) emerging function of class 1 myosins to remodel the actin network architecture, a higher-order dynamic scaffold that has potential to leverage molecular myosin-I functions. Undoubtfully, understanding the molecular functions of myosin-I motors will reveal unexpected stories about its big partner, the dynamic actin cytoskeleton. Full article

(This article belongs to the Special Issue Reviews in Actin Cytoskeletal Dynamics)

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13 pages, 4505 KiB

Open AccessReview

Functional Remodeling of the Contractile Smooth Muscle Cell Cortex, a Provocative Concept, Supported by Direct Visualization of Cortical Remodeling

by Worawit Suphamungmee, William Lehman and Kathleen G. Morgan

Biology 2022, 11(5), 662; https://doi.org/10.3390/biology11050662 - 26 Apr 2022

Cited by 2 | Viewed by 2690

Abstract

Considerable controversy has surrounded the functional anatomy of the cytoskeleton of the contractile vascular smooth muscle cell. Recent studies have suggested a dynamic nature of the cortical cytoskeleton of these cells, but direct proof has been lacking. Here, we review past studies in [...] Read more.

Considerable controversy has surrounded the functional anatomy of the cytoskeleton of the contractile vascular smooth muscle cell. Recent studies have suggested a dynamic nature of the cortical cytoskeleton of these cells, but direct proof has been lacking. Here, we review past studies in this area suggesting a plasticity of smooth muscle cells. We also present images testing these suggestions by using the technique of immunoelectron microscopy of metal replicas to directly visualize the cortical actin cytoskeleton of the contractile smooth muscle cell along with interactions by representative cytoskeletal binding proteins. We find the cortical cytoskeletal matrix to be a branched, interconnected network of linear actin bundles. Here, the focal adhesion proteins talin and zyxin were localized with nanometer accuracy. Talin is reported in past studies to span the integrin–cytoplasm distance in fibroblasts and zyxin is known to be an adaptor protein between alpha-actinin and VASP. In response to activation of signal transduction with the alpha-agonist phenylephrine, we found that no movement of talin was detectable but that the zyxin-zyxin spacing was statistically significantly decreased in the smooth muscle cells examined. Contractile smooth muscle is often assumed to have a fixed cytoskeletal structure. Thus, the results included here are important in that they directly support the concept at the electron microscopic level that the focal adhesion of the contractile smooth muscle cell has a dynamic nature and that the protein–protein interfaces showing plasticity are protein-specific. Full article

(This article belongs to the Special Issue Reviews in Actin Cytoskeletal Dynamics)

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26 pages, 3231 KiB

Open AccessReview

To Stick or Not to Stick: Adhesions in Orofacial Clefts

by Angelo Antiguas, Brian J. Paul and Martine Dunnwald

Biology 2022, 11(2), 153; https://doi.org/10.3390/biology11020153 - 18 Jan 2022

Cited by 4 | Viewed by 3326

Abstract

Morphogenesis requires a tight coordination between mechanical forces and biochemical signals to inform individual cellular behavior. For these developmental processes to happen correctly the organism requires precise spatial and temporal coordination of the adhesion, migration, growth, differentiation, and apoptosis of cells originating from [...] Read more.

Morphogenesis requires a tight coordination between mechanical forces and biochemical signals to inform individual cellular behavior. For these developmental processes to happen correctly the organism requires precise spatial and temporal coordination of the adhesion, migration, growth, differentiation, and apoptosis of cells originating from the three key embryonic layers, namely the ectoderm, mesoderm, and endoderm. The cytoskeleton and its remodeling are essential to organize and amplify many of the signaling pathways required for proper morphogenesis. In particular, the interaction of the cell junctions with the cytoskeleton functions to amplify the behavior of individual cells into collective events that are critical for development. In this review we summarize the key morphogenic events that occur during the formation of the face and the palate, as well as the protein complexes required for cell-to-cell adhesions. We then integrate the current knowledge into a comprehensive review of how mutations in cell-to-cell adhesion genes lead to abnormal craniofacial development, with a particular focus on cleft lip with or without cleft palate. Full article

(This article belongs to the Special Issue Reviews in Actin Cytoskeletal Dynamics)

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12 pages, 1343 KiB

Open AccessReview

Dynamics of the Actin Cytoskeleton at Adhesion Complexes

by Nicholas M. Cronin and Kris A. DeMali

Biology 2022, 11(1), 52; https://doi.org/10.3390/biology11010052 - 30 Dec 2021

Cited by 9 | Viewed by 4413

Abstract

The shape of cells is altered to allow cells to adapt to their changing environments, including responding to internally generated and externally applied force. Force is sensed by cell surface adhesion proteins that are enriched in sites where cells bind to the extracellular [...] Read more.

The shape of cells is altered to allow cells to adapt to their changing environments, including responding to internally generated and externally applied force. Force is sensed by cell surface adhesion proteins that are enriched in sites where cells bind to the extracellular matrix (focal adhesions) and neighboring cells (cell–cell or adherens junctions). Receptors at these adhesion sites stimulate intracellular signal transduction cascades that culminate in dramatic changes in the actin cytoskeleton. New actin filaments form, and/or new and existing filaments can be cleaved, branched, or bundled. Here, we discuss the actin cytoskeleton and its functions. We will examine the current understanding for how the actin cytoskeleton is tethered to adhesion sites. Finally, we will highlight recent studies describing how the actin cytoskeleton at these adhesion sites is remodeled in response to force. Full article

(This article belongs to the Special Issue Reviews in Actin Cytoskeletal Dynamics)

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19 pages, 6268 KiB

Open AccessReview

The Central Role of the F-Actin Surface in Myosin Force Generation

by Matthew H. Doran and William Lehman

Biology 2021, 10(12), 1221; https://doi.org/10.3390/biology10121221 - 23 Nov 2021

Cited by 7 | Viewed by 3128

Abstract

Actin is one of the most abundant and versatile proteins in eukaryotic cells. As discussed in many contributions to this Special Issue, its transition from a monomeric G-actin to a filamentous F-actin form plays a critical role in a variety of cellular processes, [...] Read more.

Actin is one of the most abundant and versatile proteins in eukaryotic cells. As discussed in many contributions to this Special Issue, its transition from a monomeric G-actin to a filamentous F-actin form plays a critical role in a variety of cellular processes, including control of cell shape and cell motility. Once polymerized from G-actin, F-actin forms the central core of muscle-thin filaments and acts as molecular tracks for myosin-based motor activity. The ATP-dependent cross-bridge cycle of myosin attachment and detachment drives the sliding of myosin thick filaments past thin filaments in muscle and the translocation of cargo in somatic cells. The variation in actin function is dependent on the variation in muscle and non-muscle myosin isoform behavior as well as interactions with a plethora of additional actin-binding proteins. Extensive work has been devoted to defining the kinetics of actin-based force generation powered by the ATPase activity of myosin. In addition, over the past decade, cryo-electron microscopy has revealed the atomic-evel details of the binding of myosin isoforms on the F-actin surface. Most accounts of the structural interactions between myosin and actin are described from the perspective of the myosin molecule. Here, we discuss myosin-binding to actin as viewed from the actin surface. We then describe conserved structural features of actin required for the binding of all or most myosin isoforms while also noting specific interactions unique to myosin isoforms. Full article

(This article belongs to the Special Issue Reviews in Actin Cytoskeletal Dynamics)

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31 pages, 4138 KiB

Open AccessReview

A Layered View on Focal Adhesions

by Karin Legerstee and Adriaan B. Houtsmuller

Biology 2021, 10(11), 1189; https://doi.org/10.3390/biology10111189 - 16 Nov 2021

Cited by 40 | Viewed by 7554

Abstract

The cytoskeleton provides structure to cells and supports intracellular transport. Actin fibres are crucial to both functions. Focal Adhesions (FAs) are large macromolecular multiprotein assemblies at the ends of specialised actin fibres linking these to the extracellular matrix. FAs translate forces on actin [...] Read more.

The cytoskeleton provides structure to cells and supports intracellular transport. Actin fibres are crucial to both functions. Focal Adhesions (FAs) are large macromolecular multiprotein assemblies at the ends of specialised actin fibres linking these to the extracellular matrix. FAs translate forces on actin fibres into forces contributing to cell migration. This review will discuss recent insights into FA protein dynamics and their organisation within FAs, made possible by advances in fluorescence imaging techniques and data analysis methods. Over the last decade, evidence has accumulated that FAs are composed of three layers parallel to the plasma membrane. We focus on some of the most frequently investigated proteins, two from each layer, paxillin and FAK (bottom, integrin signalling layer), vinculin and talin (middle, force transduction layer) and zyxin and VASP (top, actin regulatory layer). Finally, we discuss the potential impact of this layered nature on different aspects of FA behaviour. Full article

(This article belongs to the Special Issue Reviews in Actin Cytoskeletal Dynamics)

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14 pages, 1106 KiB

Open AccessReview

New Insights into Cellular Functions of Nuclear Actin

by Malgorzata Kloc, Priyanka Chanana, Nicole Vaughn, Ahmed Uosef, Jacek Z. Kubiak and Rafik M. Ghobrial

Biology 2021, 10(4), 304; https://doi.org/10.3390/biology10040304 - 07 Apr 2021

Cited by 15 | Viewed by 4213

Abstract

Actin is one of the most abundant proteins in eukaryotic cells. There are different pools of nuclear actin often undetectable by conventional staining and commercial antibodies used to identify cytoplasmic actin. With the development of more sophisticated imaging and analytical techniques, it became [...] Read more.

Actin is one of the most abundant proteins in eukaryotic cells. There are different pools of nuclear actin often undetectable by conventional staining and commercial antibodies used to identify cytoplasmic actin. With the development of more sophisticated imaging and analytical techniques, it became clear that nuclear actin plays a crucial role in shaping the chromatin, genomic, and epigenetic landscape, transcriptional regulation, and DNA repair. This multifaceted role of nuclear actin is not only important for the function of the individual cell but also for the establishment of cell fate, and tissue and organ differentiation during development. Moreover, the changes in the nuclear, chromatin, and genomic architecture are preamble to various diseases. Here, we discuss some of the newly described functions of nuclear actin. Full article

(This article belongs to the Special Issue Reviews in Actin Cytoskeletal Dynamics)

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18 pages, 642 KiB

Open AccessReview

Fascin in Cell Migration: More Than an Actin Bundling Protein

by Maureen C. Lamb and Tina L. Tootle

Biology 2020, 9(11), 403; https://doi.org/10.3390/biology9110403 - 17 Nov 2020

Cited by 32 | Viewed by 6699

Abstract

Fascin, an actin-binding protein, regulates many developmental migrations and contributes to cancer metastasis. Specifically, Fascin promotes cell motility, invasion, and adhesion by forming filopodia and invadopodia through its canonical actin bundling function. In addition to bundling actin, Fascin has non-canonical roles in the [...] Read more.

Fascin, an actin-binding protein, regulates many developmental migrations and contributes to cancer metastasis. Specifically, Fascin promotes cell motility, invasion, and adhesion by forming filopodia and invadopodia through its canonical actin bundling function. In addition to bundling actin, Fascin has non-canonical roles in the cell that are thought to promote cell migration. These non-canonical functions include regulating the activity of other actin-binding proteins, binding to and regulating microtubules, mediating mechanotransduction to the nucleus via interaction with the Linker of the Nucleoskeleton and Cytoskeleton (LINC) Complex, and localizing to the nucleus to regulate nuclear actin, the nucleolus, and chromatin modifications. The many functions of Fascin must be coordinately regulated to control cell migration. While much remains to be learned about such mechanisms, Fascin is regulated by post-translational modifications, prostaglandin signaling, protein–protein interactions, and transcriptional means. Here, we review the structure of Fascin, the various functions of Fascin and how they contribute to cell migration, the mechanisms regulating Fascin, and how Fascin contributes to diseases, specifically cancer metastasis. Full article

(This article belongs to the Special Issue Reviews in Actin Cytoskeletal Dynamics)

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