Aggregation Of Actin Filaments Research Articles

LLGL2 Inhibits Ovarian Cancer Metastasis by Regulating Cytoskeleton Remodeling via ACTN1.

Epithelial ovarian cancer is the most lethal gynecological malignant tumor. Although debulking surgery, chemotherapy, and PARP inhibitors have greatly improved survival, the prognosis for patients with advanced EOC without HRD is still poor. LLGL2, as a cell polarity factor, is involved in maintaining cell polarity and asymmetric cell division. In the study of zebrafish development, LLGL2 regulated the proliferation and migration of epidermal cells and the formation of cortical F-actin. However, the role of LLGL2 in ovarian cancer has not been described. Our study found, through bioinformatics analysis, that low expression of LLGL2 was significantly associated with a more advanced stage and a higher grade of EOC and a poorer survival of patients. Functional experiments that involved LLGL2 overexpression and knockdown showed that LLGL2 inhibited the migration and invasion abilities of ovarian cancer cells in vitro, without affecting their proliferation. LLGL2-overexpressing mice had fewer metastatic implant foci than the controls in vivo. Mechanistically, immunoprecipitation combined with mass spectrometry analysis suggested that LLGL2 regulated cytoskeletal remodeling by interacting with ACTN1. LLGL2 altered the intracellular localization and function of ACTN1 without changing its protein and mRNA levels. Collectively, we uncovered that LLGL2 impaired actin filament aggregation into bundles by interacting with ACTN1, which led to cytoskeleton remodeling and inhibition of the invasion and metastasis of ovarian cancer cells.

Poria cocos Regulates Cell Migration and Actin Filament Aggregation in B35 and C6 Cells by Modulating the RhoA, CDC42, and Rho Signaling Pathways.

Poria is used as a traditional Chinese herbal medicine with anti-inflammatory, anticancer, and mood-stabilizing properties. Poria contains triterpenoids and polysaccharides, which are reported to regulate the cytoplasmic free calcium associated with the N-methyl-D-aspartate receptor and affect the cell function of neonatal rat nerve cells and hippocampal neurons. Although the modulatory effects of Poria on neuronal function have been widely reported, the molecular mechanism of these effects is unclear. Cell migration ability and the reorganization of actin filaments are important biological functions during neuronal development, and they can be regulated mainly by the Rho signaling pathway. We found that the cell migration ability and actin condensation in B35 cells enhanced by P. cocos (a water solution of P. cocos cum Radix Pini (PRP) or White Poria (WP)) might be caused by increased RhoA and CDC42 activity and increased expression of downstream ROCK1, p-MLC2, N-WASP, and ARP2/3 in B35 cells. Similar modulations of cell migration ability, actin condensation, and Rho signaling pathway were also observed in the C6 glial cell line, except for the PRP-induced regulation of RhoA and CDC42 activities. Ketamine-induced inhibition of cell migration and actin condensation can be restored by P. cocos. In addition, we observed that the increased expression of RhoA and ROCK1 or the decreased expression of CDC42 and N-WASP caused by ketamine in B35 cells could also be restored by P. cocos. The results of this study suggest that the regulatory effects of P. cocos on cell migration and actin filament aggregation are closely related to the regulation of RhoA, CDC42, and Rho signaling pathways in both B35 and C6 cells. PRP and WP have the potential to restore neuronal cell Rho signaling abnormalities involved in some mental diseases.

The effect of cadmium exposure on the cytoskeleton and morphology of the gill chloride cells in juvenile mosquito fish (Gambusia affinis)

One of the wide spread aquatic organisms in the rivers of Indonesia is the mosquito fish (Gambusia affinis (Baird and Girard, 1853)). Mosquito fish are invasive species that can adapt to environmental changes, also they act as bioindicator species for polluted environments. The study aims to determine the effects of the exposure to cadmium on the cytoskeleton and morphology of the gill’s Chloride Cells (CCs) in the mosquito fish. In cadmium treated mosquito fish (0.03 mg/L for 28 days), the immuno-fluorescent light microscope showed strong absorption of actin stain and strong primary MT antibody uptake in CC and apical epithelia. Scanning electron microscopy observations showed a change in microfilament organized at the CC's apex, with the appearance of some actin filament aggregates. Higher cadmium concentrations (0.03 and 0.015 mg/L) did not alter such reorganization. Microtubules weren’t significantly affected by similar exposures. SEM analysis showed that cadmium exposure induced a significant increase in CC's surface area. After 28 days, the density of CC also increased. It was observed that there is an increase of CC's surface area, although the CC density didn’t increase significantly. The results of this study confirmed the cytotoxic effects of cadmium on mosquito fish.

Localization of actin filaments and cortical microtubules in wood-forming tissues of conifers

ABSTRACT The aim of the present study was to investigate the orientation and localization of actin filaments and cortical microtubules in wood-forming tissues in conifers to understand wood formation. Small blocks were collected from the main stems of Abies firma, Pinus densiflora, and Taxus cuspidata during active seasons of the cambium. Bundles of actin filaments were oriented axially or longitudinally relative to the cell axis in fusiform and ray cambial cells. In differentiating tracheids, actin filaments were oriented longitudinally relative to the cell axis during primary and secondary wall formation. In contrast, the orientation of well-ordered cortical microtubules in tracheids changed from transverse to longitudinal during secondary wall formation. There was no clear relationship between the orientation of actin filaments and cortical microtubules in cambial cells and cambial derivatives. Aggregates of actin filaments and a circular band of cortical microtubules were localized around bordered pits and cross-field pits in differentiating tracheids. In addition, rope-like bands of actin filaments were observed during the formation of helical thickenings at the final stage of formation of secondary walls in tracheids. Actin filaments might not play a major role in changes in the orientation of cortical microtubules in wood-forming tissues. However, since actin filaments were co-localized with cortical microtubules during the formation of bordered pits, cross-field pits and helical thickenings at the final stage of formation of the secondary wall in tracheids, it seems plausible that actin filaments might be closely related to the localization of cortical microtubules during the development of these modifications of wood structure.

P.158Congenital-onset hypertrophic cardiomyopathy and skeletal myopathy with nemaline rods and actin filament aggregates due to likely pathogenic recessive variants in CFL2

P.158Congenital-onset hypertrophic cardiomyopathy and skeletal myopathy with nemaline rods and actin filament aggregates due to likely pathogenic recessive variants in CFL2

Mechanism of action of cytotoxic compounds from the seeds of Euphorbia lathyris

BackgroundThe seeds of Euphorbia lathyris are used in traditional Chinese medicines for the treatment of various medical conditions. E. lathyris contains many natural diterpenes with a lathyrane skeleton. Purpose and study designFive lathyrane-type diterpenoids named Euphorbia factors L1, L2, L3, L8, and L9 (1–5), were investigated for cytotoxicity against A549, MDA-MB-231, KB, and MCF-7 cancer cell lines and the KB-VIN multidrug resistant (MDR) cancer cell line. Also, a tetraol derivative (6) of Euphorbia factor L2 (2) was synthesized to assess the effect of hydroxy moieties. MethodsAn ethanolic extract of seeds of Euphorbia lathyris was prepared and separated into petroleum ether, EtOAc, n-butanol, and n-hexane extracts. The natural diterpenes were isolated by using silica gel and Sephadex LH-20 column chromatography as well as preparative thin-layer chromatography. Saponification of 2 gave tetraol derivative 6. Cytotoxic activity was determined by the sulforhodamine B (SRB) colorimetric assay. Mechanism of action studies focused on the impact of compounds on the cell cycle progression as well as cell morphology. ResultsCompound 5 exhibited the strongest cytotoxicity against all cell lines, while compound 2 showed selectivity against KB-VIN. In cells treated with 3 and 5, accumulation of G1 to early S phase cells was obvious, while no effect was seen on G2/M phase. ConclusionAnalysis of the screening data compared with compound structures suggested that the substitutions at C-3, C-5, C-7, and C-15 are critical for cytotoxicity, as well as cell type-selectivity. Furthermore, results of cytotoxic mechanism analysis demonstrated for the first time that compounds 3 and 5 disrupted normal cell cycle progression, whereas compounds 2‒5 induced obvious actin filament aggregation, as well as partial interference of the microtubule network.

PKB/Akt regulates the aggregation of actin by Girdin in mouse fertilized eggs

The purpose of this study is to reveal the role of Girdin in regulating the aggregation of actin filaments by studying the relationship between PKB/Akt and Girdin. First we used Scansite software (http://scansite.mit.edu) to predict relevant target sites of PKB/Akt on mouse Girdin. To gain insight into the role of phosphorylation of Girdin by PKB/Akt, we assessed the location of phosphorylated Girdin in fertilized eggs by staining with anti-P-Girdin 1 417 Ab. We detected a distinct increase in the fluorescence signal of F-actin and P-Girdin 1 417 after microinjection of Akt WT and myr-Akt. The addition of myr-Akt induced phosphorylation of Girdin in mouse fertilized eggs. In addition, siRNA-mediated Akt-knockdown blocked phosphorylation of Girdin. The distribution of actin filaments was obviously scattered. These results strongly suggest that PKB/Akt could directly phosphorylate Girdin on Ser1 417 and promote its function in mouse fertilized eggs.

Berberine induces dedifferentiation by actin cytoskeleton reorganization via phosphoinositide 3-kinase/Akt and p38 kinase pathways in rabbit articular chondrocytes.

Osteoarthritis is a nonrheumatologic joint disease characterized by progressive degeneration of the cartilage extracellular matrix. Berberine (BBR) is an isoquinoline alkaloid used in traditional Chinese medicine, the majority of which is extracted from Huang Lian (Coptis chinensis). Although numerous studies have revealed the anticancer activity of BBR, its effects on normal cells, such as chondrocytes, and the molecular mechanisms underlying its actions remain elusive. Therefore, we examined the effects of BBR on rabbit articular chondrocytes, and the underlying molecular mechanisms, focusing on actin cytoskeletal reorganization. BBR induced dedifferentiation by inhibiting activation of phosphoinositide-3(PI3)-kinase/Akt and p38 kinase. Furthermore, inhibition of p38 kinase and PI3-kinase/Akt with SB203580 and LY294002, respectively, accelerated the BBR-induced dedifferentiation. BBR also caused actin cytoskeletal architecture reorganization and, therefore, we investigated if these effects were involved in the dedifferentiation. Disruption of the actin cytoskeleton by cytochalasin D reversed the BBR-induced dedifferentiation by activating PI3-kinase/Akt and p38 kinase. In contrast, the induction of actin filament aggregation by jasplakinolide accelerated the BBR-induced dedifferentiation via PI3-kinase/Akt inhibition and p38 kinase activation. Taken together, these data suggest that BBR strongly induces dedifferentiation, and actin cytoskeletal reorganization is a crucial requirement for this effect. Furthermore, the dedifferentiation activity of BBR appears to be mediated via PI3-kinase/Akt and p38 kinase pathways in rabbit articular chondrocytes.

The indolinone MAZ51 induces cell rounding and G2/M cell cycle arrest in glioma cells without the inhibition of VEGFR-3 phosphorylation: involvement of the RhoA and Akt/GSK3β signaling pathways.

MAZ51 is an indolinone-based molecule originally synthesized as a selective inhibitor of vascular endothelial growth factor receptor (VEGFR)-3 tyrosine kinase. This study shows that exposure of two glioma cell lines, rat C6 and human U251MG, to MAZ51 caused dramatic shape changes, including the retraction of cellular protrusions and cell rounding. These changes were caused by the clustering and aggregation of actin filaments and microtubules. MAZ51 also induced G2/M phase cell cycle arrest. This led to an inhibition of cellular proliferation, without triggering significant cell death. These alterations induced by MAZ51 occurred with similar dose- and time-dependent patterns. Treatment of glioma cells with MAZ51 resulted in increased levels of phosphorylated GSK3β through the activation of Akt, as well as increased levels of active RhoA. Interestingly, MAZ51 did not affect the morphology and cell cycle patterns of rat primary cortical astrocytes, suggesting it selectively targeted transformed cells. Immunoprecipitation–western blot analyses indicated that MAZ51 did not decrease, but rather increased, tyrosine phosphorylation of VEGFR-3. To confirm this unanticipated result, several additional experiments were conducted. Enhancing VEGFR-3 phosphorylation by treatment of glioma cells with VEGF-C affected neither cytoskeleton arrangements nor cell cycle patterns. In addition, the knockdown of VEGFR-3 in glioma cells did not cause morphological or cytoskeletal alterations. Furthermore, treatment of VEGFR-3-silenced cells with MAZ51 caused the same alterations of cell shape and cytoskeletal arrangements as that observed in control cells. These data indicate that MAZ51 causes cytoskeletal alterations and G2/M cell cycle arrest in glioma cells. These effects are mediated through phosphorylation of Akt/GSK3β and activation of RhoA. The anti-proliferative activity of MAZ51 does not require the inhibition of VEGFR-3 phosphorylation, suggesting that it is a potential candidate for further clinical investigation for treatment of gliomas, although the precise mechanism(s) underlying its effects remain to be determined.

Dynamic assessment of Amyloid oligomers – cell membrane interaction by advanced impedance spectroscopy

The amyloid β (Aβ) peptides are believed to be pivotal in Alzheimer's disease (AD) pathogenesis and onset of vascular dysfunction. Recent studies indicate that Aβ1-42 treatment influences the expression of tight junction protein complexes, stress fibre formation, disruption and aggregation of actin filaments and cellular gap formation.Aiming for functional characterization of model cells upon Aβ1-42 treatment, we deployed an advanced Electric Cell-substrate Impedance Sensing for monitoring cell evolution. A precision Impedance Analyzer with a multiplexing module developed in house was used for recording individual electrode sets in the 40 Hz – 100 KHz frequency range. In a step forward from the classical ECIS assays, we report on a novel data analysis algorithm that enables access to cellular and paracellular electrical parameters and cell surface interaction with fully developed cell monolayers.The evolution of the impedance at selected frequencies provides evidence for a dual effect of Aβ42 exposure, at both paracellular permeability and cell adherence level, with intricate dynamics that open up new perspectives on Aβ1-42 oligomers – cell membrane interaction. Validation of electrical impedance assays of the amyloid fibrils effect on cell membrane structure is achieved by both AFM analysis and Surface Plasmon Resonance studies.The capabilities of this noninvasive, real time platform for cell analysis in a wider applicative context are outlined.

Large Gradient High Magnetic Fields Affect Osteoblast Ultrastructure and Function by Disrupting Collagen I or Fibronectin/αβ1 Integrin

The superconducting magnet generates a field and field gradient product that can levitate diamagnetic materials. In this study a specially designed superconducting magnet with a large gradient high magnetic field (LG-HMF), which can provide three apparent gravity levels (μ-g, 1-g, and 2-g), was used to simulate a space-like gravity environment. The effects of LG-HMF on the ultrastructure and function of osteoblast-like cells (MG-63 and MC3T3-E1) and the underlying mechanism were investigated by transmission electromicroscopy (TEM), MTT, and cell western (ICW) assays. Under LG-HMF significant morphologic changes in osteoblast-like cells occurred, including expansion of endoplasmic reticulum and mitochondria, an increased number of lysosomes, distorted microvilli, and aggregates of actin filaments. Compared to controls, cell viability and alkaline phosphatase (ALP) secretion were significantly increased, and collagen I (col I), fibronectin (FN), vinculin, integrin α3, αv, and β1 expression were changed under LG-HMF conditions. In conclusion, LG-HMF affects osteoblast ultrastructure, cell viability, and ALP secretion, and the changes caused by LG-HMF may be related to disrupting col I or FN/αβ1 integrin.

Kif5b controls the localization of myofibril components for their assembly and linkage to the myotendinous junctions

Controlled delivery of myofibril components to the appropriate sites of assembly is crucial for myofibrillogenesis. Here, we show that kinesin-1 heavy chain Kif5b plays important roles in anterograde transport of α-sarcomeric actin, non-muscle myosin IIB, together with intermediate filament proteins desmin and nestin to the growing tips of the elongating myotubes. Mice with Kif5b conditionally knocked out in myogenic cells showed aggregation of actin filaments and intermediate filament proteins in the differentiating skeletal muscle cells, which further affected myofibril assembly and their linkage to the myotendinous junctions. The expression of Kif5b in mutant myotubes rescued the localization of the affected proteins. Functional mapping of Kif5b revealed a 64-amino acid α-helix domain in the tail region, which directly interacted with desmin and might be responsible for the transportation of these proteins in a complex.

Vascular endothelial barrier dysfunction mediated by amyloid-beta proteins.

Neuronal inflammation is very common in Alzheimer's disease (AD). This inflammation can be caused by infiltration of neutrophils across the blood brain barrier. Endothelial permeability changes are required for the infiltration of high molecular weight components to the brain. Deposition of toxic amyloid-beta (A beta) fibrils in the cerebral vasculature, as well as in brain neurons, has been implicated in the development of AD. This study investigates the effect of A beta fibrils on the permeability of the endothelium and the mechanism for the observed permeability changes. A beta(1-40) and A beta(1-42) fibrils, but not monomers, were found to increase permeability of bovine pulmonary arterial endothelial cells in a dose- and time dependent manner as detected by transendothelial electrical resistance. This increase in permeability is only partially (25%) inhibited by catalase and is not associated with an increase in cytosolic Ca+2 or tyrosine phosphorylation. These results indicate that hydrogen peroxide is not the primary mediator for the permeability changes. Treatment of cells with both amyloid fibrils resulted in stress fiber formation, disruption and aggregation of actin filaments, and cellular gap formation. The results of this study reveal that A beta increases the permeability of endothelium by inducing change in the cytoskeleton network.

Actinopathies and myosinopathies.

The currently recognized two forms of "anabolic" protein aggregate myopathies, that is, defects in development, maturation and final formation of respective actin and myosin filaments encompass actinopathies and myosinopathies. The former are marked by mutations in the ACTA1 gene, largely of the de novo type. Aggregates of actin filaments are deposited within muscle fibers. Early clinical onset is often congenital; most patients run a rapidly progressive course and die during their first 2 years of life. Myosinopathies or myosin storage myopathies also commence in childhood, but show a much more protracted course owing to mutations in the myosin heavy chain gene MYH7. Protein aggregation consists of granular material in muscle fibers and few, if any, filaments.

Impaired Actin Assembly and Lamellipodia Formation in ATE1 Knockout Platelets.

In response to agonist stimulation, platelets undergo a rapid reorganization of their actin cytoskeleton. This process involves simultaneous disassembly and assembly of filamentous actin, and is one of the earliest events of platelet activation. Ex vivo flow models support the hypothesis that actin assembly is essential for stable in vivo platelet adhesion and thrombus formation under the shear conditions found within the arterial system. On the cellular level, the reorganization of actin that occurs during platelet activation involves the formation of an actin network similar to that found in lamellipodia at the leading edge of the locomoting fibroblasts. During lamellipod formation in fibroblasts, the predominant actin isoform of the cell leading edge is beta-actin. In these cells, beta-actin undergoes posttranslational arginylation (i.e., addition of arginine onto the N-terminus). We estimate that up to 40% of actin at the leading edge of fibroblasts is arginylated, and that the absence of this modification results in actin filament aggregation in vitro. Arginylation of actin is mediated by the arginyltransferase, ATE1. Embryos lacking ATE1 die between E12 and E17 due to severe cardiovascular defects and massive hemorrhage. Fibroblasts derived from knockout embryos collapse their extending lamella, potentially because their non-arginylated actin aggregates at the extending edge. The beta-isoform of actin is over 85% of the total actin in platelets. To gain insight into whether actin could undergo arginylation in platelets, we analyzed actin from resting and thrombin- or PMA-stimulated platelets fractionated on 2D gels. Our analysis indicates that platelet activation results in a prominent shift of a significant fraction of actin protein into the basic pI range, consistent with the addition of arginine onto the actin molecule. This result suggests that actin might be arginylated in platelets, and that this arginylation is activation-dependent. We hypothesized that if platelet actin reorganization indeed occurs by the mechanisms similar to those seen in fibroblasts, it should also be dependent on the arginylation. To test this hypothesis, we reconstituted the hematopoietic system of lethally irradiated mice with hematopoietic precursor cells collected from the livers of ATE1 null or wildtype embryos at day 13.5 of development. Platelets derived from ATE1 knockout radiation chimeric mice exhibited normal binding to fluorescently labeled fibrinogen in response to stimulation of the thrombin receptor or by PMA. However, in contrast to platelets derived from radiation chimeric mice rescued with normal hematopoietic cells, platelets derived from chimeric mice with ATE1 null hematopoietic cells spread poorly to immobilized fibrinogen (decreased 35.6%). When blood harvested from radiation chimeric mice was allowed to adhere to immobilized collagen under flow, wild type platelets adhered firmly, and rarely formed unstable adhesions (15 ± 10%). In contrast, ATE1 null platelets adhered less well, and frequently failed to form stable adhesions (50% ±15%). Together, these results suggest that beta-actin is rapidly arginylated in agonist-stimulated platelets, and that arginylation is required for actin reorganization during platelet adhesion and lamellipodia formation. We hypothesize that ATE1-mediated arginylation of platelet beta-actin is also essential for in vivo platelet adhesion and thrombosis.

Overexpression of RhoE in non-small cell lung cancer (NSCLC) is associated with smoking and correlates with DNA copy number changes

RhoE, a small G protein, is constitutively GTP bound within the cell and can regulate actin cytoskeleton reorganization, leading to the appearance of aggregates of actin filaments. Although emerging evidence suggests that RhoE is causally involved in cancer formation and progression, little is known about its significance in solid cancer, including lung cancer. In the present study, the expression of RhoE was analyzed using Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR), real-time RT-PCR, immunohistochemistry and western blot in 30 patients with Non-Small Cell Lung Cancer (NSCLC). Then the correlation of RhoE overexpression with clinical parameters was evaluated. Furthermore, the possible reasons contributing to the RhoE expression were examined by real-time genomic PCR and mutation analysis on DNA sequence and cDNA sequence. Our results revealed that RhoE expression was dramatically increased in lung cancer tissues compared with adjacent non-tumoral lung tissues (p

C-terminal fragments of thymopoietin favor formation of F-actin bundles: Electron microscopic data

Electron microscopy showed that PEP33, a synthetic peptide corresponding to the C-terminal part of the thymic hormone thymopoietin, favors bundling of F-actin filaments in the presence of 0.1 M KCl. The structure of PEP33 aggregates located within bundles between actin filaments is very similar to the structure of aggregates visible in preparations of pure PEP33. No changes were observed in the structure of G-actin in the presence of PEP33. A similar though weaker bundling effect was also detected for PEP5, or thymopentin, a fragment of PEP33. This peptide favors the formation of bundles of actin filaments of small size. The possible role of aggregation of actin filaments under the action of thymopoietin peptides is discussed in the light of the fact that the systematic release of thymopoietin from thymus leads to a phenomenon characteristic of the serious neuromuscular disease myasthenia gravis.

Nanotopographic Control of Cytoskeletal Organization

Growth of 3T3-L1 preadipocytes on a nanoscalar poly(ethylene terephthalate) (PET) surface produced an absence of the intracellular stress fibers characteristic of cell growth on "normal" planar surfaces. This phenomenon was consistently observed from time zero throughout 3 days of culture and was accompanied by changes in paxillin expression along with an approximately 50% decrease in the number of adherent cells in response to 500 dynes/cm(2) of shear stress. This suggests that the cytoskeleton in cells adherent to nanofibrillar surfaces does indeed form, but at a smaller, more difficult to observe scale. We propose a novel mechanism by which the growth and clustering of integrin-associated focal adhesions on surface nanofibrils regulates cytoskeletal development. The width of the extracellular matrix contacts is constrained by the width of the nanofibrils and the absence of any surface between them. The limited dimensions of these point contacts then constrain receptor polymerization and the associated aggregation of actin filaments. The existence of a topographic mechanism leading to growth-limited integrin clustering is hypothesized.

Gene-Related Protein Surplus Myopathies

Numerous muscular dystrophies, such as dystrophinopathies, sarcoglycanopathies, and emerino- and laminopathies, are marked by the absence or reduction of mutant transsarcolemmal or nuclear proteins. In addition to these recently identified minus-proteinopathies, there are a growing number of plus-proteinopathies among neuromuscular disorders marked by a surplus or excess of endogenous proteins within muscle fibers of different, i.e., nontranssarcolemmal and nonnuclear types. These proteins are often filamentous; for example, desmin and actin accrue in respective desmin-related myopathies, among which are entities marked by mutant desmin, true desminopathies, and actinopathy, the latter often seen as a subgroup in nemaline myopathies. Desmin-related myopathies consist largely of those marked by desmin-containing inclusions and those characterized by desmin-containing granulofilamentous material. When mutations in the desmin gene can be identified, the mutant desmin is thought to form the major myopathological lesion. Together with desmin, other proteins often accumulate. The spectrum of these proteins is quite diverse and encompasses such proteins as dystrophin, nestin, vimentin, αB-crystallin, ubiquitin, amyloid precursor protein, and β-amyloid epitopes, as well as gelsolin and α1-antichymotrypsin. Among these associated proteins, one, αB-crystallin, has been found mutant in one large family, justifying the term αB-crystallinopathy as a separate condition among the desmin-related myopathies. Other proteins accruing with desmin have not yet been identified as mutant in desmin-related myopathies. Mutations in the desmin gene entail missense mutations and small deletions. The formation of mutant actin may lead to aggregates of actin filaments which may or may not be associated with formation of sarcoplasmic and/or intranuclear nemaline bodies. A considerable number of missense mutations in the sarcomeric actin gene ACTA1 have been discovered in patients with nemaline myopathy and also in a few patients without myopathological evidence of nemaline bodies in biopsied skeletal muscle fibres. Apart from αB-crystallin, no other proteins coaggregating with actin in actin filament aggregates of actinopathy or the actin mutation type of nemaline myopathy have so far been identified. Two further candidates for protein surplus myopathies are hyaline body myopathy, which is marked by accumulation of granular nonfilamentous material within muscle fibers that is rich in myosin and adenosine triphosphatase activities, and hereditary inclusion body myopathies, which are marked by accumulation of tubulofilaments similar to the helical filaments of Alzheimer neurofibrillary tangles. These tubulofilaments consist of diverse proteins as well, though no mutant protein has yet been discovered. So far, no genes responsible for familial hyaline body and hereditary inclusion body myopathies have been identified. The discovery of mutant proteins, desmin, αB-crystallin, and actin, as components of surplus or excess proteins accumulating in muscle fibers in certain neuromuscular conditions is responsible for the recent emergence of this new concept of gene-related protein surplus myopathies.

Two distinct mechanisms of actin bundle formation.

Actin filaments (F-actin)-one of the major types of cytoskeletal filament-can be induced to form bundles by the addition of any of a number of polycations, including divalent metal ions, trivalent hexaminecobalt, or basic polypeptides. The general features of bundle formation, as detected by light scattering, centrifugation, optical and electron microscopy, are largely independent of the specific structure of the bundling agent used. The formation of lateral aggregates of actin filaments in response to polycations begins at a threshold concentration that varies strongly with the valence of the cation and increases with the ionic strength of the solution. Polyanions, such as nucleoside phosphates and acidic polypeptides, disperse actin bundles into single filaments. These features are similar to those associated with DNA condensation and