scholarly journals Ordering of myosin II filaments driven by mechanical forces: experiments and theory

2018 ◽  
Vol 373 (1747) ◽  
pp. 20170114 ◽  
Author(s):  
Kinjal Dasbiswas ◽  
Shiqiong Hu ◽  
Frank Schnorrer ◽  
Samuel A. Safran ◽  
Alexander D. Bershadsky
Keyword(s):  
Actin Cytoskeleton ◽  
Actin Filament ◽  
Cell Biology ◽  
Striated Muscle ◽  
Myosin Ii ◽  
Muscle Cells ◽  
Self Organization ◽  
The Matrix ◽  
Filament Bundles ◽  
And Function

Myosin II filaments form ordered superstructures in both cross-striated muscle and non-muscle cells. In cross-striated muscle, myosin II (thick) filaments, actin (thin) filaments and elastic titin filaments comprise the stereotypical contractile units of muscles called sarcomeres. Linear chains of sarcomeres, called myofibrils, are aligned laterally in registry to form cross-striated muscle cells. The experimentally observed dependence of the registered organization of myofibrils on extracellular matrix elasticity has been proposed to arise from the interactions of sarcomeric contractile elements (considered as force dipoles) through the matrix. Non-muscle cells form small bipolar filaments built of less than 30 myosin II molecules. These filaments are associated in registry forming superstructures (‘stacks’) orthogonal to actin filament bundles. Formation of myosin II filament stacks requires the myosin II ATPase activity and function of the actin filament crosslinking, polymerizing and depolymerizing proteins. We propose that the myosin II filaments embedded into elastic, intervening actin network (IVN) function as force dipoles that interact attractively through the IVN. This is in analogy with the theoretical picture developed for myofibrils where the elastic medium is now the actin cytoskeleton itself. Myosin stack formation in non-muscle cells provides a novel mechanism for the self-organization of the actin cytoskeleton at the level of the entire cell. This article is part of the theme issue ‘Self-organization in cell biology’.

scholarly journals Molecular Architecture of Synaptic Actin Cytoskeleton in Hippocampal Neurons Reveals a Mechanism of Dendritic Spine Morphogenesis

2010 ◽  
Vol 21 (1) ◽  
pp. 165-176 ◽  
Author(s):  
Farida Korobova ◽  
Tatyana Svitkina
Keyword(s):  
Electron Microscopy ◽  
Actin Cytoskeleton ◽  
Actin Filament ◽  
Dendritic Spines ◽  
Dendritic Spine ◽  
Myosin Ii ◽  
Capping Protein ◽  
Dominant Feature ◽  
Presynaptic Boutons ◽  
Spine Morphogenesis

Excitatory synapses in the brain play key roles in learning and memory. The formation and functions of postsynaptic mushroom-shaped structures, dendritic spines, and possibly of presynaptic terminals, rely on actin cytoskeleton remodeling. However, the cytoskeletal architecture of synapses remains unknown hindering the understanding of synapse morphogenesis. Using platinum replica electron microscopy, we characterized the cytoskeletal organization and molecular composition of dendritic spines, their precursors, dendritic filopodia, and presynaptic boutons. A branched actin filament network containing Arp2/3 complex and capping protein was a dominant feature of spine heads and presynaptic boutons. Surprisingly, the spine necks and bases, as well as dendritic filopodia, also contained a network, rather than a bundle, of branched and linear actin filaments that was immunopositive for Arp2/3 complex, capping protein, and myosin II, but not fascin. Thus, a tight actin filament bundle is not necessary for structural support of elongated filopodia-like protrusions. Dynamically, dendritic filopodia emerged from densities in the dendritic shaft, which by electron microscopy contained branched actin network associated with dendritic microtubules. We propose that dendritic spine morphogenesis begins from an actin patch elongating into a dendritic filopodium, which tip subsequently expands via Arp2/3 complex-dependent nucleation and which length is modulated by myosin II-dependent contractility.

scholarly journals Alix Protein Is Substrate of Ozz-E3 Ligase and Modulates Actin Remodeling in Skeletal Muscle

2012 ◽  
Vol 287 (15) ◽  
pp. 12159-12171 ◽  
Author(s):  
Antonella Bongiovanni ◽  
Daniele P. Romancino ◽  
Yvan Campos ◽  
Gaetano Paterniti ◽  
Xiaohui Qiu ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Actin Cytoskeleton ◽  
Membrane Trafficking ◽  
Actin Polymerization ◽  
Myogenic Differentiation ◽  
E3 Ligase ◽  
Adaptor Protein ◽  
Muscle Cells ◽  
Endogenous Proteins ◽  
And Function

Alix/AIP1 is a multifunctional adaptor protein that participates in basic cellular processes, including membrane trafficking and actin cytoskeleton assembly, by binding selectively to a variety of partner proteins. However, the mechanisms regulating Alix turnover, subcellular distribution, and function in muscle cells are unknown. We now report that Alix is expressed in skeletal muscle throughout myogenic differentiation. In myotubes, a specific pool of Alix colocalizes with Ozz, the substrate-binding component of the muscle-specific ubiquitin ligase complex Ozz-E3. We found that interaction of the two endogenous proteins in the differentiated muscle fibers changes Alix conformation and promotes its ubiquitination. This in turn regulates the levels of the protein in specific subcompartments, in particular the one containing the actin polymerization factor cortactin. In Ozz−/− myotubes, the levels of filamentous (F)-actin is perturbed, and Alix accumulates in large puncta positive for cortactin. In line with this observation, we show that the knockdown of Alix expression in C2C12 muscle cells affects the amount and distribution of F-actin, which consequently leads to changes in cell morphology, impaired formation of sarcolemmal protrusions, and defective cell motility. These findings suggest that the Ozz-E3 ligase regulates Alix at sites where the actin cytoskeleton undergoes remodeling.

scholarly journals The Ringleaders: Understanding the Apicomplexan Basal Complex Through Comparison to Established Contractile Ring Systems

2021 ◽  
Vol 11 ◽  
Author(s):  
Alexander A. Morano ◽  
Jeffrey D. Dvorin
Keyword(s):  
Cell Biology ◽  
Myosin Ii ◽  
Ring Structure ◽  
Plastid Division ◽  
Contractile Ring ◽  
Ring Systems ◽  
Basal Complex ◽  
And Function

The actomyosin contractile ring is a key feature of eukaryotic cytokinesis, conserved across many eukaryotic kingdoms. Recent research into the cell biology of the divergent eukaryotic clade Apicomplexa has revealed a contractile ring structure required for asexual division in the medically relevant genera Toxoplasma and Plasmodium; however, the structure of the contractile ring, known as the basal complex in these parasites, remains poorly characterized and in the absence of a myosin II homolog, it is unclear how the force required of a cytokinetic contractile ring is generated. Here, we review the literature on the basal complex in Apicomplexans, summarizing what is known about its formation and function, and attempt to provide possible answers to this question and suggest new avenues of study by comparing the Apicomplexan basal complex to well-studied, established cytokinetic contractile rings and their mechanisms in organisms such as S. cerevisiae and D. melanogaster. We also compare the basal complex to structures formed during mitochondrial and plastid division and cytokinetic mechanisms of organisms beyond the Opisthokonts, considering Apicomplexan diversity and divergence.

Polarity sorting of actin filaments in cytochalasin-treated fibroblasts

1997 ◽  
Vol 110 (15) ◽  
pp. 1693-1704 ◽  
Author(s):  
A.B. Verkhovsky ◽  
T.M. Svitkina ◽  
G.G. Borisy
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Myosin Ii ◽  
Dynamic Network ◽  
Muscle Cells ◽  
Immunogold Labelling ◽  
Cultured Fibroblasts ◽  
Myosin S1 ◽  
Mixed Polarity ◽  
Myosin Interaction

The polarity of actin filaments is fundamental for the subcellular mechanics of actin-myosin interaction; however, little is known about how actin filaments are oriented with respect to myosin in non-muscle cells and how actin polarity organization is established and maintained. Here we approach these questions by investigating changes in the organization and polarity of actin relative to myosin II during actin filament translocation. Actin and myosin II reorganization was followed both kinetically, using microinjected fluorescent analogs of actin and myosin, and ultrastructurally, using myosin S1 decoration and immunogold labelling, in cultured fibroblasts that were induced to contract by treatment with cytochalasin D. We observed rapid (within 15 minutes) formation of ordered actin filament arrays: short tapered bundles and aster-like assemblies, in which filaments had uniform polarity with their barbed ends oriented toward the aggregate of myosin II at the base of a bundle or in the center of an aster. The resulting asters further interacted with each other and aggregated into bigger asters. The arrangement of actin in asters was in sharp contrast to the mixed polarity of actin filaments relative to myosin in non-treated cells. At the edge of the cell, actin filaments became oriented with their barbed ends toward the cell center; that is, the orientation was opposite to what was observed at the edge of nontreated cells. This rearrangement is indicative of relative translocation of actin and myosin II and of the ability of myosin II to sort actin filaments with respect to their polarity during translocation. The results suggest that the myosin II-actin system of non-muscle cells is organized as a dynamic network where actin filament arrangement is defined in the course of its interaction with myosin II.

The ultrastructure of the adult stage of Trichostrongylus colubriformis and Haemonchus placei

Parasitology ◽  
1972 ◽  
Vol 64 (2) ◽  
pp. 173-179 ◽  
Author(s):  
Kenneth Smith ◽  
Eric Harness
Keyword(s):  
Alimentary Tract ◽  
Striated Muscle ◽  
Adult Stage ◽  
Muscle Cells ◽  
Matrix Layer ◽  
The Matrix ◽  
Membrane Bound ◽  
Excretory Canals ◽  
Inner Cortex ◽  
Haemonchus Placei

The ultrastructure of the adult stage of T. colubriformis and H. placei was studied. The cuticle of both nematodes was composed of (1) a membrane-bound layer, (2) external cortex, (3) inner cortex, (4) matrix, (5)–(7) three fibre layers, and (8) a basal lamella. Pear-shaped bodies embedded in the matrix layer in H. placei occur, along the length of the animal, once per annulus. A thin hypodermis enlarged to form lateral, dorsal and ventral cords which contained hypodermal cells, nerves and excretory canals. The muscle cells were large and multilobular. Two sizes of myofilaments, present in the contractile part of the cell, conformed to the filament arrangement of obliquely striated muscle. The mouth, buccal cavity and oesophagus of the alimentary tract were lined with cuticle. The oesophagus contained gland cells, muscle cells and apical cells. The lumen of the intestinal cells of both species had a well-developed microvillar border. In H. placei each microvillus was encircled by a ring of apparently spirally orientated vesicles or tubules.The authors are grateful to Dr D. W. Brocklesby for his help and advice. They would also like to thank Dr D. L. Lee and Dr W. G. MacMillan for helpful discussions.

scholarly journals Myosin II filament assemblies in the active lamella of fibroblasts: their morphogenesis and role in the formation of actin filament bundles.

1995 ◽  
Vol 131 (4) ◽  
pp. 989-1002 ◽  
Author(s):  
A B Verkhovsky ◽  
T M Svitkina ◽  
G G Borisy
Keyword(s):  
Electron Microscopy ◽  
Actin Filament ◽  
Mammalian Cells ◽  
Myosin Ii ◽  
Myosin Filament ◽  
Actin Bundles ◽  
Fluorescence And Electron Microscopy ◽  
Myosin Filaments ◽  
Filament Bundles ◽  
Filament Network

The morphogenesis of myosin II structures in active lamella undergoing net protrusion was analyzed by correlative fluorescence and electron microscopy. In rat embryo fibroblasts (REF 52) microinjected with tetramethylrhodamine-myosin II, nascent myosin spots formed close to the active edge during periods of retraction and then elongated into wavy ribbons of uniform width. The spots and ribbons initially behaved as distinct structural entities but subsequently aligned with each other in a sarcomeric-like pattern. Electron microscopy established that the spots and ribbons consisted of bipolar minifilaments associated with each other at their head-containing ends and arranged in a single row in an "open" zig-zag conformation or as a "closed" parallel stack. Ribbons also contacted each other in a nonsarcomeric, network-like arrangement as described previously (Verkhovsky and Borisy, 1993. J. Cell Biol. 123:637-652). Myosin ribbons were particularly pronounced in REF 52 cells, but small ribbons and networks were found also in a range of other mammalian cells. At the edge of the cell, individual spots and open ribbons were associated with relatively disordered actin filaments. Further from the edge, myosin filament alignment increased in parallel with the development of actin bundles. In actin bundles, the actin cross-linking protein, alpha-actinin, was excluded from sites of myosin localization but concentrated in paired sites flanking each myosin ribbon, suggesting that myosin filament association may initiate a pathway for the formation of actin filament bundles. We propose that zig-zag assemblies of myosin II filaments induce the formation of actin bundles by pulling on an actin filament network and that co-alignment of actin and myosin filaments proceeds via folding of myosin II filament assemblies in an accordion-like fashion.

The capactins, a class of proteins that cap the ends of actin filaments

1982 ◽  
Vol 299 (1095) ◽  
pp. 263-273 ◽  
Keyword(s):  
Skeletal Muscle ◽  
Actin Filament ◽  
Actin Filaments ◽  
Muscle Cells ◽  
Preliminary Evidence ◽  
The Other ◽  
Cellular Regulation ◽  
Filament Assembly ◽  
Filament Bundles

A number of proteins that bind specifically to the barbed ends of actin filaments in a cytochalasin-like manner have been purified to various degrees from a variety of muscle and non-muscle cells and tissues. Preliminary evidence also indicates that proteins that interact with the pointed ends of filaments are present in skeletal muscle. Because of their ability to cap one or the other end of an actin filament, we have designated this class of proteins as the ‘capactins’. On the basis of their effect on actin filament assembly and interaction in vitro , we propose that the capactins play important roles in cellular regulation of actin-based cytoskeletal and contractile functions. Our finding that the disappearance of actin filament bundles in virally transformed fibroblasts can be correlated with an increase in capactin activity in the extracts of these cells is consistent with this hypothesis.

scholarly journals On the role of tubulin, plectin, desmin, and vimentin in the regulation of mitochondrial energy fluxes in muscle cells

2019 ◽  
Vol 316 (5) ◽  
pp. C657-C667 ◽  
Author(s):  
Kati Mado ◽  
Vladimir Chekulayev ◽  
Igor Shevchuk ◽  
Marju Puurand ◽  
Kersti Tepp ◽  
...  
Keyword(s):  
Striated Muscle ◽  
Adenine Nucleotides ◽  
Anion Channel ◽  
Muscle Cells ◽  
Eukaryotic Cell ◽  
Cytoskeletal Proteins ◽  
Energy Fluxes ◽  
Voltage Dependent Anion Channel ◽  
And Function

Mitochondria perform a central role in life and death of the eukaryotic cell. They are major players in the generation of macroergic compounds and function as integrated signaling pathways, including the regulation of Ca2+ signals and apoptosis. A growing amount of evidence is demonstrating that mitochondria of muscle cells use cytoskeletal proteins (both microtubules and intermediate filaments) not only for their movement and proper cellular positioning, but also to maintain their biogenesis, morphology, function, and regulation of energy fluxes through the outer mitochondrial membrane (MOM). Here we consider the known literature data concerning the role of tubulin, plectin, desmin and vimentin in bioenergetic function of mitochondria in striated muscle cells, as well as in controlling the permeability of MOM for adenine nucleotides (ADNs). This is of great interest since dysfunctionality of these cytoskeletal proteins has been shown to result in severe myopathy associated with pronounced mitochondrial dysfunction. Further efforts are needed to uncover the pathways by which the cytoskeleton supports the functional capacity of mitochondria and transport of ADN(s) across the MOM (through voltage-dependent anion channel).

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