Ultrastructure of the actin cytoskeleton

Benefits and challenges of reconstituting the actin cortex

The cell's ability to change shape is a central feature in many cellular processes, including cytokinesis, motility, migration, and tissue formation. The cell constructs a network of contractile proteins underneath the cell membrane to form the cortex, and the reorganization of these components directly contributes to cellular shape changes. The desire to mimic these cell shape changes to aid in the creation of a synthetic cell has been increasing. Therefore, membrane-based reconstitution experiments have flourished, furthering our understanding of the minimal components the cell uses throughout these processes. Although biochemical approaches increased our understanding of actin, myosin II, and actin-associated proteins, using membrane-based reconstituted systems has further expanded our understanding of actin structures and functions because membrane-cortex interactions can be analyzed. In this review, we highlight the recent developments in membrane-based reconstitution techniques. We examine the current findings on the minimal components needed to recapitulate distinct actin structures and functions and how they relate to the cortex's impact on cellular mechanical properties. We also explore how co-processing of computational models with wet-lab experiments enhances our understanding of these properties. Finally, we emphasize the benefits and challenges inherent to membrane-based, reconstitution assays, ranging from the advantage of precise control over the system to the difficulty of integrating these findings into the complex cellular environment.

Actin dynamics switches two distinct modes of endosomal fusion in yolk sac visceral endoderm cells

Membranes undergo various patterns of deformation during vesicle fusion, but how this membrane deformation is regulated and contributes to fusion remains unknown. In this study, we developed a new method of observing the fusion of individual late endosomes and lysosomes by using mouse yolk sac visceral endoderm cells that have huge endocytic vesicles. We found that there were two distinct fusion modes that were differently regulated. In homotypic fusion, two late endosomes fused quickly, whereas in heterotypic fusion they fused to lysosomes slowly. Mathematical modeling showed that vesicle size is a critical determinant of these fusion types and that membrane fluctuation forces can overcome the vesicle size effects. We found that actin filaments were bound to late endosomes and forces derived from dynamic actin remodeling were necessary for quick fusion during homotypic fusion. Furthermore, cofilin played a role in endocytic fusion by regulating actin turnover. These data suggest that actin promotes vesicle fusion for efficient membrane trafficking in visceral endoderm cells.

Actin filament dynamics at barbed ends: New structures, new insights

The dynamic actin cytoskeleton contributes to many critical biological processes by providing the structural support underlying the morphology of most cells, facilitating intracellular transport, and generating forces required for cell motility and division. To execute many of these functions, actin monomers polymerize into polarized filaments that display different structural and biochemical properties at each end. Filament dynamics are regulated by diverse regulatory proteins which collaborate to dictate rates of elongation and disassembly, particularly at the fast-growing barbed (plus) end. This review highlights the biochemical mechanisms of six barbed end regulatory proteins: formin, profilin, capping protein, IQGAP1, cyclase-associated protein, and twinfilin. We discuss how individual proteins influence actin dynamics and how several intriguing complex assemblies influence the polymerization fate of actin filaments. Understanding these mechanisms offers insights into how actin is regulated in essential cell processes and dysregulated in disease.

GALNT9 enrichment attenuates MPP+-induced cytotoxicity by ameliorating protein aggregations containing α-synuclein and mitochondrial dysfunction

BACKGROUND

GALNTs (UDP-GalNAc; polypeptide N-acetylgalactosaminyltransferases) initiate mucin-type O-GalNAc glycosylation by adding N-GalNAc to protein serine/threonine residues. Abnormalities in O-GalNAc glycosylation are involved in various disorders such as Parkinson's disease (PD), a neurodegenerative disorder. GALNT9 is potentially downregulated in PD patients.

METHODS

To determine whether GALNT9 enrichment ameliorates cytotoxicity related to PD-like variations, a pcDNA3.1-GALNT9 plasmid was constructed and transfected into SH-SY5Y cells to establish a GALNT9-overexpressing cell model.

RESULTS

Downregulation of GALNT9 and O-GalNAc glycosylation was confirmed in our animal and cellular models of PD-like variations. GALNT9 supplementation greatly attenuated cytotoxicity induced by MPP+ (1-Methyl-4-phenylpyridinium iodide) since it led to increased levels of tyrosine hydroxylase and dopamine, reduced rates of apoptosis, and significantly ameliorated MPP+-induced mitochondrial dysfunction by alleviating abnormal levels of mitochondrial membrane potential and reactive oxygen species. A long-lasting mPTP (mitochondrial permeability transition pores) opening and calcium efflux resulted in significantly lower activity in the cytochrome C-associated apoptotic pathway and mitophagy process, signifying that GALNT9 supplementation maintained neuronal cell health under MPP+ exposure. Additionally, it was found that glycans linked to proteins influenced the formation of protein aggregates containing α-synuclein, and GALNT9 supplement dramatically reduced such insoluble protein aggregations under MPP+ treatment. Glial GALNT9 predominantly appears under pathological conditions like PD-like variations.

CONCLUSIONS

GALNT9 enrichment improved cell survival, and glial GALNT9 potentially represents a pathogenic index for PD patients. This study provides insights into the development of therapeutic strategies for the treatment of PD.

Transcriptome and single-cell analysis reveal disulfidptosis-related modification patterns of tumor microenvironment and prognosis in osteosarcoma

Osteosarcoma (OS) is the most common malignant bone tumor with high pathological heterogeneity. Our study aimed to investigate disulfidptosis-related modification patterns in OS and their relationship with survival outcomes in patients with OS. We analyzed the single-cell-level expression profiles of disulfidptosis-related genes (DSRGs) in both OS microenvironment and OS subclusters, and HMGB1 was found to be crucial for intercellular regulation of OS disulfidptosis. Next, we explored the molecular clusters of OS based on DSRGs and related immune cell infiltration using transcriptome data. Subsequently, the hub genes of disulfidptosis in OS were screened by applying multiple machine models. In vitro and patient experiments validated our results. Three main disulfidptosis-related molecular clusters were defined in OS, and immune infiltration analysis suggested high immune heterogeneity between distinct clusters. The in vitro experiment confirmed decreased cell viability of OS after ACTB silencing and higher expression of ACTB in patients with lower immune scores. Our study systematically revealed the underlying relationship between disulfidptosis and OS at the single-cell level, identified disulfidptosis-related subtypes, and revealed the potential role of ACTB expression in OS disulfidptosis.

Rhogef17: A novel target for endothelial barrier function

ARHGEF17 encodes the protein RhoGEF17, which is highly expressed in vascular endothelial cells. It is a guanine nucleotide exchange factor (GEF) that accelerates the exchange of GDP with GTP on many small GTPases through its Dbl homology (DH) domain, enabling the activation of Rho-GTPases such as RhoA, RhoB, and RhoC. Rho GTPase-regulated changes in the actin cytoskeleton and cell adhesion kinetics are the main mechanisms mediating many endothelial cell (EC) alterations, including cell morphology, migration, and division changes, which profoundly affect EC barrier function. This review focuses on ARHGEF17 expression, activation and biological functions in ECs, linking its regulation of cellular morphology, migration, mitosis and other cellular behaviors to disease onset and progression. Understanding ARHGEF17 mechanisms of action will contribute to the design of therapeutic approaches targeting RhoGEF17, a potential drug target for the treatment of various endothelium-related diseases, Such as vascular inflammation, carcinogenesis and transendothelial metastasis of tumors.

Proteomic analysis reveals the aging-related pathways contribute to pulmonary fibrogenesis

Aging usually causes lung-function decline and susceptibility to chronic lung diseases, such as pulmonary fibrosis. However, how aging affects the lung-fibrosis pathways and leads to the occurrence of pulmonary fibrosis is not completely understood. Here, mass spectrometry-based proteomics was used to chart the lung proteome of young and old mice. Micro computed tomography imaging, RNA immunoprecipitation, dual-fluorescence mRFP-GFP-LC3 adenovirus monitoring, transmission electron microscopy, and other experiments were performed to explore the screened differentially expressed proteins related to abnormal ferroptosis, autophagy, mitochondria, and mechanical force in vivo, in vitro, and in healthy people. Combined with our previous studies on pulmonary fibrosis, we further demonstrated that these biological processes and underlying molecular players were also involved in the aging process. Our work depicted a comprehensive cellular and molecular atlas of the aging lung and attempted to explain why aging is a risk factor for pulmonary fibrosis and the role that aging plays in the progression of pulmonary fibrosis. The abnormalities of aging triggered an increase in mechanical force and ferroptosis, autophagy blockade, and mitochondrial dysfunction, which often appear during pulmonary fibrogenesis. We hope that the elucidation of these anomalies will help to enhance our understanding of senescence-inducing pulmonary fibrosis, thereby guiding the use of anti-senescence as an entry point for early intervention in pulmonary fibrosis and age-related diseases.

Tuftelin1 drives experimental pulmonary fibrosis progression by facilitating stress fiber assembly

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease (ILD) with unknown etiology, characterized by sustained damage repair of epithelial cells and abnormal activation of fibroblasts, the underlying mechanism of the disease remains elusive.

METHODS

To evaluate the role of Tuftelin1 (TUFT1) in IPF and elucidate its molecular mechanism. We investigated the level of TUFT1 in the IPF and bleomycin-induced mouse models and explored the influence of TUFT1 deficiency on pulmonary fibrosis. Additionally, we explored the effect of TUFT1 on the cytoskeleton and illustrated the relationship between stress fiber and pulmonary fibrosis.

RESULTS

Our results demonstrated a significant upregulation of TUFT1 in IPF and the bleomycin (BLM)-induced fibrosis model. Disruption of TUFT1 exerted inhibitory effects on pulmonary fibrosis in both in vivo and in vitro. TUFT1 facilitated the assembly of microfilaments in A549 and MRC-5 cells, with a pronounced association between TUFT1 and Neuronal Wiskott-Aldrich syndrome protein (N-WASP) observed during microfilament formation. TUFT1 can promote the phosphorylation of tyrosine residue 256 (Y256) of the N-WASP (pY256N-WASP). Furthermore, TUFT1 promoted transforming growth factor-β1 (TGF-β1) induced fibroblast activation by increasing nuclear translocation of pY256N-WASP in fibroblasts, while wiskostatin (Wis), an N-WASP inhibitor, suppressed these processes.

CONCLUSIONS

Our findings suggested that TUFT1 plays a critical role in pulmonary fibrosis via its influence on stress fiber, and blockade of TUFT1 effectively reduces pro-fibrotic phenotypes. Pharmacological targeting of the TUFT1-N-WASP axis may represent a promising therapeutic approach for pulmonary fibrosis.

Identification of important genes associated with acute myocardial infarction using multiple cell death patterns

Acute myocardial infarction (AMI) is a global health threat, and programmed cell death (PCD) plays a crucial role in its occurrence and development. In this study, integrated bioinformatics tools were used to explore new biomarkers and therapeutic targets in AMI. Thirteen types of PCD-related genes were identified through literature review, KEGG, and GSEA pathways. Gene expression matrices and clinical data from AMI patients and healthy controls were obtained from the GEO database. Statistical analysis in R identified 377 differentially expressed genes in AMI patients. Intersection analysis between the differentially expressed genes and PCD-related genes revealed 24 genes positively correlated with immune cells such as Neutrophils and Monocytes, while negatively correlated with T cells CD4 memory resting and Plasma cells. Unsupervised clustering analysis divided patients into two groups (C1 and C2) based on the expression levels of these 24 genes. GSVA analysis showed that C2 patients were more active in pathways related to maintaining normal cell morphology and promoting phagocytosis, suggesting a lower programmed cell death rate and a higher tendency to maintain cell survival. Two hub genes, TNFAIP3 and TP53INP2, were identified through LASSO regression analysis and SVM-RFE, and were validated using an external dataset and RT-qPCR、Western blot and ELISA analysis. These hub genes showed significantly higher expression and protein secretion levels in AMI patients compared to healthy individuals. Overall, regulating and controlling PCD, particularly through the identified hub genes, TNFAIP3 and TP53INP2, may provide new therapeutic strategies for improving the prognosis of AMI patients and preventing heart failure.

The PI3K-AKT-mTOR signaling pathway mediates the cytoskeletal remodeling and epithelial-mesenchymal transition in bladder outlet obstruction

Objective

Partial bladder outlet obstruction(pBOO) is the most common cause of lower urinary tract symptoms (LUTS) and significantly affects the quality of life. Long-term pBOO can cause changes in bladder structure and function, referred to as bladder remodeling. The pathogenesis of pBOO-induced bladder remodeling has yet to be fully understood, so effective treatment options are lacking. Our study aimed to explore how pBOO-induced bladder remodeling brings new strategies for treating pBOO.

Methods

A rat model of pBOO was established by partial ligation of the bladder neck, and the morphological changes and fibrosis changes in the bladder tissues were detected by H&E and Masson trichrome staining. Furthermore, EMT(epithelial-mesenchymal transition) related indicators and related pathway changes were further examined after TGF- β treatment of urothelial cells SV-HUC-1. Finally, the above indicators were tested again after using the PI3K inhibitor. Subsequently, RNA sequencing of bladder tissues to identify differential genes and related pathways enrichment and validated by immunofluorescence and western blotting analysis.

Results

The pBOO animal model was successfully established by partially ligating the bladder neck. H&E staining showed significant changes in the bladder structure, and Masson trichrome staining showed significantly increased collagen fibers. RNA sequencing results significantly enriched in the cytoskeleton, epithelial-mesenchymal transformation, and the PI3K-AKT-mTOR signaling pathway. Immunofluorescence and western blotting revealed EMT and cytoskeletal remodeling in SV-HUC-1 cells after induction of TGF- β and in the pBOO bladder tissues. The western blotting showed significant activation of the PI3K-AKT-mTOR signaling pathway in SV-HUC-1 cells after induction of TGF-β and in pBOO bladder tissues. Furthermore, EMT and cytoskeletal damage were partially reversed after PI3K pathway inhibition using PI3K inhibitors.

Conclusions

In the pBOO rat model, the activation of the PI3K-AKT-mTOR signaling pathway can mediate the cytoskeletal remodeling and the EMT to induce fibrosis in the bladder tissues. PI3K inhibitors partially reversed EMT and cytoskeletal damage.

Uncovering the role of cytoskeleton proteins in the formation of neutrophil extracellular traps

Neutrophils are a type of lymphocyte involved in innate immune defense. In response to specific stimuli, these phagocytic cells undergo a unique form of cell death, NETosis, during which they release neutrophil extracellular traps (NETs) composed of modified chromatin structures decorated with cytoplasmic and granular proteins. Multiple proteins and pathways have been implicated in the formation of NETs. The cytoskeleton, an interconnected network of filamentous polymers and regulatory proteins, plays a crucial role in resisting deformation, transporting intracellular cargo, and changing shape during movement of eukaryotic cells. It may also have evolved to defend eukaryotic organisms against infection. Recent research focuses on understanding the mechanisms underlying NETs formation and how cytoskeletal networks contribute to this process, by identifying enzymes that trigger NETosis or interact with NETs and influence cellular behavior through cytoskeletal dynamics. An enhanced understanding of the complex relationship between the cytoskeleton and NET formation will provide a framework for future research and the development of targeted therapeutic strategies, and supports the notion that the long-lived cytoskeleton structures may have a lasting impact on this area of research.

Centralspindlin proteins Pavarotti and Tumbleweed along with WASH regulate nuclear envelope budding

Nuclear envelope (NE) budding is a nuclear pore-independent nuclear export pathway, analogous to the egress of herpesviruses, and required for protein quality control, synapse development, and mitochondrial integrity. The physical formation of NE buds is dependent on the Wiskott-Aldrich Syndrome protein, Wash, its regulatory complex (SHRC), and Arp2/3, and requires Wash's actin nucleation activity. However, the machinery governing cargo recruitment and organization within the NE bud remains unknown. Here, we identify Pavarotti (Pav) and Tumbleweed (Tum) as new molecular components of NE budding. Pav and Tum interact directly with Wash and define a second nuclear Wash-containing complex required for NE budding. Interestingly, we find that the actin-bundling activity of Pav is required, suggesting a structural role in the physical and/or organizational aspects of NE buds. Thus, Pav and Tum are providing exciting new entry points into the physical machineries of this alternative nuclear export pathway for large cargos during cell differentiation and development.

Septin and actin contributions to endothelial cell-cell junctions and monolayer integrity

Septins in endothelial cells (ECs) have important roles supporting the integrity of the endothelial monolayer. Cell-cell junctions in EC monolayers are highly dynamic, with continuous retractions and protrusions. Depletion of septins in ECs leads to disruption of cell-cell junctions, which are composed of VE-cadherin and other junctional proteins. In EC monolayers, septins are concentrated at the plasma membrane at sites of cell-cell contact, in curved- and scallop-shaped patterns. These membrane-associated septin accumulations are located in regions of positive membrane curvature, and those regions are often associated with and immediately adjacent to actin-rich protrusions with negative membrane curvature. EC septins associate directly with plasma membrane lipids, based on findings with site-specific mutations of septins in ECs, which is consistent with biochemical and cell biological studies in other systems. Loss of septins leads to disruption of the EC monolayer, and gaps form between cells. The number and breadth of cell-cell contacts and junctions decreases, and the number and frequency of retractions, ruffles, and protrusions at cell edges also decreases. In addition, loss of septins leads to decreased amounts of F-actin at the cortical membrane, along with increased amounts of F-actin in stress fibers of the cytoplasm. Endothelial monolayer disruption from loss of septins is also associated with decreased transendothelial electric resistance (TEER) and increased levels of transendothelial migration (TEM) by immune and cancer cells, owing to the gaps in the monolayer. A current working model is that assembly of septin filaments at regions of positive membrane curvature contributes to a mechanical footing or base for actin-based protrusive forces generated at adjoining regions of the membrane. Specific molecular interactions between the septin and actin components of the cytoskeleton may also be important contributors. Regulators of actin assembly may promote and support the assembly of septin filaments at the membrane, as part of a molecular feedback loop between the assembly of septin and actin filaments.

Visualization of Cell Membrane Tension Regulated by the Microfilaments as a "Shock Absorber" in Micropatterned Cells

The extracellular stress signal transmits along the cell membrane-cytoskeleton-focal adhesions (FAs) complex, regulating the cell function through membrane tension. However, the mechanism of the complex regulating membrane tension is still unclear. This study designed polydimethylsiloxane stamps with specific shapes to change the actin filaments' arrangement and FAs' distribution artificially in live cells, visualized the membrane tension in real time, and introduced the concept of information entropy to describe the order degree of the actin filaments and plasma membrane tension. The results showed that the actin filaments' arrangement and FAs' distribution in the patterned cells were changed significantly. The hypertonic solution resulted in the plasma membrane tension of the pattern cell changing more evenly and slowly in the zone rich in cytoskeletal filaments than in the zone lacking filaments. In addition, the membrane tension changed less in the adhesive area than in the non-adhesive area when destroying the cytoskeletal microfilaments. This suggested that patterned cells accumulated more actin filaments in the zone where FAs were difficult to generate to maintain the stability of the overall membrane tension. The actin filaments act as shock absorbers to cushion the alternation in membrane tension without changing the final value of membrane tension.

Antibacterial and anti-inflammatory effects of PGLa-loaded TiO2 nanotube arrays

Objectives: This study investigated the antimicrobial effect and anti-inflammatory activities of PGLa-loaded TiO₂ nanotube arrays (TiO₂ NTs) in osteoblast-like MG-63 cells. Methods: The surface morphology and roughness of three titanium (Ti) substrates (Ti, TiO₂ NTs, PGLa-loaded TiO₂ NTs) were evaluated by scanning electron microscopy (SEM) and atomic force microscope (AFM). The wettability of three titanium substrates was evaluated by contact angle. Biocompatibility of PGLa-loaded TiO₂ NTs were evaluated in MG-63 cells (cell adhesion, proliferation, cytoskeletal evaluation and alkaline phosphatase activity). Spread plate counting method was used to evaluate antibacterial abilities of the titanium substrates. The calcein AM/PI staining evaluated cell viability of MG-63 cells on the substrates with or without proinflammatory factors (TNF-α). Results: The average surface roughness of untreated Ti, TiO₂ NTs, PGLa-loaded TiO₂ NTs were found to be 135.8 ± 6.4 nm, 300.5 ± 10.5 nm, 348.9 ± 16.9 nm, respectively. The contact angle of the untreated Ti was 77.4° ± 6.6°. TiO₂ NTs displayed excellent wettability which of contact angle was 12.1° ± 2.9°. The contact angle of the PGLa-loaded TiO₂ NTs was 34.6° ± 4.9°. MG-63 cells on surface of PGLa-loaded TiO₂ NTs showed better cell adhesion, proliferation and osteogenic activity. The antibacterial rate of PGLa-loaded TiO₂ NTs group significantly increased (84.6% ± 5.5%, p < 0.05). The rate of dead cells on the surfaces of the PGLa-loaded TiO₂ NTs with TNF-α decreased significantly (4.49% ± 0.02, p < 0.01). Conclusion: PGLa-loaded TiO₂ NTs have multi-biofunctions including biocompatibility, antibacterial and anti-inflammatory properties.

Host factor DUSP5 potently inhibits dengue virus infection by modulating cytoskeleton rearrangement

Cytoskeleton has been reported to play an essential role in facilitating the viral life cycle. However, whether the host can exert its antiviral effects by modulating the cytoskeleton is not fully understood. In this study, we identified that host factor DUSP5 was upregulated after dengue virus (DENV) infection. In addition, we demonstrated that overexpression of DUSP5 remarkably inhibited DENV replication. Conversely, the depletion of DUSP5 led to an increase in viral replication. Moreover, DUSP5 was found to restrain viral entry into host cells by suppressing F-actin rearrangement via negatively regulating the ERK-MLCK-Myosin IIB signaling axis. Depletion of dephosphorylase activity of DUSP5 abolished its above inhibitory effects. Furthermore, we also revealed that DUSP5 exhibited broad-spectrum antiviral effects against DENV and Zika virus. Taken together, our studies identified DUSP5 as a key host defense factor against viral infection and uncovered an intriguing mechanism by which the host exerts its antiviral effects through targeting cytoskeleton rearrangement.

Bending actin filaments: twists of fate

In many cellular contexts, intracellular actomyosin networks must generate directional forces to carry out cellular tasks such as migration and endocytosis, which play important roles during normal developmental processes. A number of different actin binding proteins have been identified that form linear or branched actin, and that regulate these filaments through activities such as bundling, crosslinking, and depolymerization to create a wide variety of functional actin assemblies. The helical nature of actin filaments allows them to better accommodate tensile stresses by untwisting, as well as to bend to great curvatures without breaking. Interestingly, this latter property, the bending of actin filaments, is emerging as an exciting new feature for determining dynamic actin configurations and functions. Indeed, recent studies using in vitro assays have found that proteins including IQGAP, Cofilin, Septins, Anillin, α-Actinin, Fascin, and Myosins-alone or in combination-can influence the bending or curvature of actin filaments. This bending increases the number and types of dynamic assemblies that can be generated, as well as the spectrum of their functions. Intriguingly, in some cases, actin bending creates directionality within a cell, resulting in a chiral cell shape. This actin-dependent cell chirality is highly conserved in vertebrates and invertebrates and is essential for cell migration and breaking L-R symmetry of tissues/organs. Here, we review how different types of actin binding protein can bend actin filaments, induce curved filament geometries, and how they impact on cellular functions.

Unleashed Actin Assembly in Capping Protein-Deficient B16-F1 Cells Enables Identification of Multiple Factors Contributing to Filopodium Formation

Background: Filopodia are dynamic, finger-like actin-filament bundles that overcome membrane tension by forces generated through actin polymerization at their tips to allow extension of these structures a few microns beyond the cell periphery. Actin assembly of these protrusions is regulated by accessory proteins including heterodimeric capping protein (CP) or Ena/VASP actin polymerases to either terminate or promote filament growth. Accordingly, the depletion of CP in B16-F1 melanoma cells was previously shown to cause an explosive formation of filopodia. In Ena/VASP-deficient cells, CP depletion appeared to result in ruffling instead of inducing filopodia, implying that Ena/VASP proteins are absolutely essential for filopodia formation. However, this hypothesis was not yet experimentally confirmed. Methods: Here, we used B16-F1 cells and CRISPR/Cas9 technology to eliminate CP either alone or in combination with Ena/VASP or other factors residing at filopodia tips, followed by quantifications of filopodia length and number. Results: Unexpectedly, we find massive formations of filopodia even in the absence of CP and Ena/VASP proteins. Notably, combined inactivation of Ena/VASP, unconventional myosin-X and the formin FMNL3 was required to markedly impair filopodia formation in CP-deficient cells. Conclusions: Taken together, our results reveal that, besides Ena/VASP proteins, numerous other factors contribute to filopodia formation.

Actin Bundles Dynamics and Architecture

Cells use the actin cytoskeleton for many of their functions, including their division, adhesion, mechanosensing, endo- and phagocytosis, migration, and invasion. Actin bundles are the main constituent of actin-rich structures involved in these processes. An ever-increasing number of proteins that crosslink actin into bundles or regulate their morphology is being identified in cells. With recent advances in high-resolution microscopy and imaging techniques, the complex process of bundles formation and the multiple forms of physiological bundles are beginning to be better understood. Here, we review the physiochemical and biological properties of four families of highly conserved and abundant actin-bundling proteins, namely, α-actinin, fimbrin/plastin, fascin, and espin. We describe the similarities and differences between these proteins, their role in the formation of physiological actin bundles, and their properties-both related and unrelated to their bundling abilities. We also review some aspects of the general mechanism of actin bundles formation, which are known from the available information on the activity of the key actin partners involved in this process.

Nanomechanical Signatures in Glioma Cells Depend on CD44 Distribution in IDH1 Wild-Type but Not in IDH1R132H Mutant Early-Passage Cultures

Atomic force microscopy (AFM) recently burst into biomedicine, providing morphological and functional characteristics of cancer cells and their microenvironment responsible for tumor invasion and progression, although the novelty of this assay needs to coordinate the malignant profiles of patients' specimens to diagnostically valuable criteria. Applying high-resolution semi-contact AFM mapping on an extended number of cells, we analyzed the nanomechanical properties of glioma early-passage cell cultures with a different IDH1 R132H mutation status. Each cell culture was additionally clustered on CD44+/- cells to find possible nanomechanical signatures that differentiate cell phenotypes varying in proliferative activity and the characteristic surface marker. IDH1 R132H mutant cells compared to IDH1 wild-type ones (IDH1wt) characterized by two-fold increased stiffness and 1.5-fold elasticity modulus. CD44+/IDH1wt cells were two-fold more rigid and much stiffer than CD44-/IDH1wt ones. In contrast to IDH1 wild-type cells, CD44+/IDH1 R132H and CD44-/IDH1 R132H did not exhibit nanomechanical signatures providing statistically valuable differentiation of these subpopulations. The median stiffness depends on glioma cell types and decreases according to the following manner: IDH1 R132H mt (4.7 mN/m), CD44+/IDH1wt (3.7 mN/m), CD44-/IDH1wt (2.5 mN/m). This indicates that the quantitative nanomechanical mapping would be a promising assay for the quick cell population analysis suitable for detailed diagnostics and personalized treatment of glioma forms.

The cell biology of archaea

The past decade has revealed the diversity and ubiquity of archaea in nature, with a growing number of studies highlighting their importance in ecology, biotechnology and even human health. Myriad lineages have been discovered, which expanded the phylogenetic breadth of archaea and revealed their central role in the evolutionary origins of eukaryotes. These discoveries, coupled with advances that enable the culturing and live imaging of archaeal cells under extreme environments, have underpinned a better understanding of their biology. In this Review we focus on the shape, internal organization and surface structures that are characteristic of archaeal cells as well as membrane remodelling, cell growth and division. We also highlight some of the technical challenges faced and discuss how new and improved technologies will help address many of the key unanswered questions.

A Methylation Diagnostic Model Based on Random Forests and Neural Networks for Asthma Identification

Background

Asthma significantly impacts human life and health as a chronic disease. Traditional treatments for asthma have several limitations. Artificial intelligence aids in cancer treatment and may also accelerate our understanding of asthma mechanisms. We aimed to develop a new clinical diagnosis model for asthma using artificial neural networks (ANN).

Methods

Datasets (GSE85566, GSE40576, and GSE13716) were downloaded from Gene Expression Omnibus (GEO) and identified differentially expressed CpGs (DECs) enriched by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Random forest (RF) and ANN algorithms further identified gene characteristics and built clinical models. In addition, two external validation datasets (GSE40576 and GSE137716) were used to validate the diagnostic ability of the model.

Results

The methylation analysis tool (ChAMP) considered DECs that were up-regulated (n =121) and down-regulated (n =20). GO results showed enrichment of actin cytoskeleton organization and cell-substrate adhesion, shigellosis, and serotonergic synapses. RF (random forest) analysis identified 10 crucial DECs (cg05075579, cg20434422, cg03907390, cg00712106, cg05696969, cg22862094, cg11733958, cg00328720, and cg13570822). ANN constructed the clinical model according to 10 DECs. In two external validation datasets (GSE40576 and GSE137716), the Area Under Curve (AUC) for GSE137716 was 1.000, and AUC for GSE40576 was 0.950, confirming the reliability of the model.

Conclusion

Our findings provide new methylation markers and clinical diagnostic models for asthma diagnosis and treatment.

Unique and redundant functions of cytoplasmic actins and nonmuscle myosin II isoforms at epithelial junctions

The integrity and functions of epithelial barriers depend on the formation of adherens junctions (AJs) and tight junctions (TJs). A characteristic feature of AJs and TJs is their association with the cortical cytoskeleton composed of actin filaments and nonmuscle myosin II (NM-II) motors. Mechanical forces generated by the actomyosin cytoskeleton are essential for junctional assembly, stability, and remodeling. Epithelial cells express two different actin proteins and three NM-II isoforms, all known to be associated with AJs and TJs. Despite their structural similarity, different actin and NM-II isoforms have distinct biochemical properties, cellular distribution, and functions. The diversity of epithelial actins and myosin motors could be essential for the regulation of different steps of junctional formation, maturation, and disassembly. This review focuses on the roles of actin and NM-II isoforms in controlling the integrity and barrier properties of various epithelia. We discuss the effects of the depletion of individual actin isoforms and NM-II motors on the assembly and barrier function of AJs and TJs in model epithelial monolayers in vitro. We also describe the functional consequences of either total or tissue-specific gene knockout of different actins and NM-II motors, with a focus on the development and integrity of different epithelia in vivo.

Extraction of accurate cytoskeletal actin velocity distributions from noisy measurements

Dynamic remodeling of the actin cytoskeleton is essential for many cellular processes. Tracking the movement of individual actin filaments can in principle shed light on how this complex behavior arises at the molecular level. However, the information that can be extracted from these measurements is often limited by low signal-to-noise ratios. We developed a Bayesian statistical approach to estimate true, underlying velocity distributions from the tracks of individual actin-associated fluorophores with quantified localization uncertainties. We found that the motion of filamentous (F)-actin in fibroblasts and endothelial cells was better described by a statistical jump process than by models in which filaments undergo continuous, diffusive movement. In particular, a model with exponentially distributed jump length- and time-scales recapitulated actin filament velocity distributions measured for the cell cortex, integrin-based adhesions, and stress fibers, suggesting that a common physical model can potentially describe actin filament dynamics in a variety of cellular contexts.

High Concentrations of Genistein Decrease Cell Viability Depending on Oxidative Stress and Inflammation in Colon Cancer Cell Lines

Genistein could play a crucial role in modulating three closely linked physiological processes altered during cancer: oxidative stress, mitochondrial biogenesis, and inflammation. However, genistein’s role in colorectal cancer remains unclear. We aimed to determine genistein’s effects in two colon cancer cells: HT29 and SW620, primary and metastatic cancer cells, respectively. After genistein treatment for 48 h, cell viability and hydrogen peroxide (H₂O₂) production were studied. The cell cycle was studied by flow cytometry, mRNA and protein levels were analyzed by RT-qPCR and Western blot, respectively, and finally, cytoskeleton remodeling and NF-κB translocation were determined by confocal microscopy. Genistein 100 µM decreased cell viability and produced G₂/M arrest, increased H₂O₂, and produced filopodia in SW620 cells. In HT29 cells, genistein produced an increase of cell death, H₂O₂ production, and in the number of stress fibers. In HT29 cells, mitochondrial biogenesis was increased, however, in SW620 cells, it was decreased. Finally, the expression of inflammation-related genes increased in both cell lines, being greater in SW620 cells, where NF-κB translocation to the nucleus was higher. These results indicate that high concentrations of genistein could increase oxidative stress and inflammation in colon cancer cells and, ultimately, decrease cell viability.

F-actin bending facilitates net actomyosin contraction By inhibiting expansion with plus-end-located myosin motors

Contraction of actomyosin networks underpins important cellular processes including motility and division. The mechanical origin of actomyosin contraction is not fully-understood. We investigate whether contraction arises on the scale of individual filaments, without needing to invoke network-scale interactions. We derive discrete force-balance and continuum partial differential equations for two symmetric, semi-flexible actin filaments with an attached myosin motor. Assuming the system exists within a homogeneous background material, our method enables computation of the stress tensor, providing a measure of contractility. After deriving the model, we use a combination of asymptotic analysis and numerical solutions to show how F-actin bending facilitates contraction on the scale of two filaments. Rigid filaments exhibit polarity-reversal symmetry as the motor travels from the minus to plus-ends, such that contractile and expansive components cancel. Filament bending induces a geometric asymmetry that brings the filaments closer to parallel as a myosin motor approaches their plus-ends, decreasing the effective spring force opposing motor motion. The reduced spring force enables the motor to move faster close to filament plus-ends, which reduces expansive stress and gives rise to net contraction. Bending-induced geometric asymmetry provides both new understanding of actomyosin contraction mechanics, and a hypothesis that can be tested in experiments.

Comprehensively characterizing cellular changes and the expression of THSD7A and PLA2R1 under multiple in vitro models of podocyte injury

The unique morphology and gene expression of podocytes are critical for kidney function, and their abnormalities lead to nephropathies such as diabetic nephropathy and membranous nephropathy. Podocytes cultured in vitro are valuable tools to dissect the molecular mechanism of podocyte injury relative to nephropathy, however, these models have never been comprehensively compared. Here, we comprehensively compared the morphology, cytoskeleton, cell adhesion, cell spreading, cell migration, and lipid metabolism under five commonly used in vitro models including lipopolysaccharide (LPS), puromycin aminonucleoside (PAN), doxorubicin (Dox), high glucose, and glucose deprivation. Our results indicate that all stimulations significantly downregulate the expression of synaptopodin both in human and mouse podocytes. All stimulations affect podocyte morphology but show different intensity and phenotypes. In general, the five stimulations reduce cell adhesion, cell spreading, and cell migration, but the effect in human and mouse podocytes is slightly different. Human podocytes show high expression of genes enriched in the pentose phosphate pathway. Dox and PAN treatment show a strong effect on gene expression in lipid metabolism, while the other three stimulations show minimal effect. The expression of phospholipase A2 receptor (PLA2R1) and type-1 domain-containing protein 7 A (THSD7A) show opposite trends in given cells. Stimulations can dramatically affect the expression of PLA2R1 and THSD7A. Inhibition of super-enhancers reduces PLA2R1 and THSD7A expression, but ERK inhibition enhances their expression. Our results demonstrate distinctive responses in five commonly used in vitro podocyte injury models and the dynamic expression of PLA2R1 and THSD7A, which supply novel information to select suitable podocyte injury models.

Label-free monitoring of spatiotemporal changes in the stem cell cytoskeletons in time-lapse phase-contrast microscopy

Investigation of the dynamic structural changes in the actin cytoskeleton during cell migration provides crucial information about the physiological conditions of a stem cell during in-vitro culture. Here we proposed a quantitative analytical model associated with texture extraction with cell tracking techniques for in situ monitoring of the cytoskeletal density change of stem cells in phase-contrast microscopy without fluorescence staining. The reliability of the model in quantifying the texture density with different orientation was first validated using a series of simulated textural images. The capability of the method to reflect the spatiotemporal regulation of the cytoskeletal structure of a living stem cell was further proved by applying it to a set of 72 h phase-contrast microscopic video of the growth dynamics of mesenchymal stem cells in vitro culture.

Gelsolin impairs barrier function in pancreatic ductal epithelial cells by actin filament depolymerization in hypertriglyceridemia‑induced pancreatitis in vitro

Gelsolin (GSN) is a calcium-regulated actin-binding protein that can sever actin filaments. Notably, actin dynamics affect the structure and function of epithelial barriers. The present study investigated the role of GSN in the barrier function of pancreatic ductal epithelial cells (PDECs) in hypertriglyceridemia-induced pancreatitis (HTGP). The human PDEC cell line HPDE6-C7 underwent GSN knockdown and was treated with caerulein (CAE) + triglycerides (TG). Intracellular calcium levels and the actin filament network were analyzed under a fluorescence microscope. The expression levels of GSN, E-cadherin, nectin-2, ZO-1 and occludin were evaluated by reverse transcription-quantitative polymerase chain reaction and western blotting. Ultrastructural changes in tight junctions were observed by transmission electron microscopy. Furthermore, the permeability of PDECs was analyzed by fluorescein isothiocyanate-dextran fluorescence. The results revealed that CAE + TG increased intracellular calcium levels, actin filament depolymerization and GSN expression, and increased PDEC permeability by decreasing the expression levels of E-cadherin, nectin-2, ZO-1 and occludin compared with the control. Moreover, changes in these markers, with the exception of intracellular calcium levels, were reversed by silencing GSN. In conclusion, GSN may disrupt barrier function in PDECs by causing actin filament depolymerization in HTGP in vitro.

Cell and Tissue Nanomechanics: From Early Development to Carcinogenesis

Cell and tissue nanomechanics, being inspired by progress in high-resolution physical mapping, has recently burst into biomedical research, discovering not only new characteristics of normal and diseased tissues, but also unveiling previously unknown mechanisms of pathological processes. Some parallels can be drawn between early development and carcinogenesis. Early embryogenesis, up to the blastocyst stage, requires a soft microenvironment and internal mechanical signals induced by the contractility of the cortical actomyosin cytoskeleton, stimulating quick cell divisions. During further development from the blastocyst implantation to placenta formation, decidua stiffness is increased ten-fold when compared to non-pregnant endometrium. Organogenesis is mediated by mechanosignaling inspired by intercellular junction formation with the involvement of mechanotransduction from the extracellular matrix (ECM). Carcinogenesis dramatically changes the mechanical properties of cells and their microenvironment, generally reproducing the structural properties and molecular organization of embryonic tissues, but with a higher stiffness of the ECM and higher cellular softness and fluidity. These changes are associated with the complete rearrangement of the entire tissue skeleton involving the ECM, cytoskeleton, and the nuclear scaffold, all integrated with each other in a joint network. The important changes occur in the cancer stem-cell niche responsible for tumor promotion and metastatic growth. We expect that the promising concept based on the natural selection of cancer cells fixing the most invasive phenotypes and genotypes by reciprocal regulation through ECM-mediated nanomechanical feedback loop can be exploited to create new therapeutic strategies for cancer treatment.

WASp triggers mechanosensitive actin patches to facilitate immune cell migration in dense tissues

When crawling through the body, leukocytes often traverse tissues that are densely packed with extracellular matrix and other cells, and this raises the question: How do leukocytes overcome compressive mechanical loads? Here, we show that the actin cortex of leukocytes is mechanoresponsive and that this responsiveness requires neither force sensing via the nucleus nor adhesive interactions with a substrate. Upon global compression of the cell body as well as local indentation of the plasma membrane, Wiskott-Aldrich syndrome protein (WASp) assembles into dot-like structures, providing activation platforms for Arp2/3 nucleated actin patches. These patches locally push against the external load, which can be obstructing collagen fibers or other cells, and thereby create space to facilitate forward locomotion. We show in vitro and in vivo that this WASp function is rate limiting for ameboid leukocyte migration in dense but not in loose environments and is required for trafficking through diverse tissues such as skin and lymph nodes.

Membrane tension sensing molecule-FNBP1 is a prognostic biomarker related to immune infiltration in BRCA, LUAD and STAD

Background

Formin-binding protein 1/17 (FNBP1/FBP17), as a membrane-bound protein, is wildly expressed in eukaryotic cells and performs a critical role in tumor tumorigenesis and progression. However, the relationship between FNBP1 and immune infiltrating cells, prognostic value in patients still require comprehensive understanding. We purposed to explore the correlations of FNBP1 expression, prognosis and immune infiltration levels in various cancers.

Method

The expression and survival data of FNBP1 were collected from Oncomine, TIMER, GEPIA, Kaplan–Meier Plotter and PrognoScan databases. Correlations between FNBP1 and immune infiltrates were analyzed in TIMER and GEPIA databases.

Results

Compared with normal tissues, FNBP1 is significantly differentially expressed in a variety of tumor tissues. FNBP1 has significant and complex effects on the prognosis of kinds of cancers. High-expression was obviously correlated with better prognosis in breast carcinoma and lung adenocarcinoma, while worse prognosis in stomach adenocarcinoma. Besides, FNBP1 had a correlation with various immune infiltrating cells and diverse immune gene markers in breast invasive carcinoma (BRCA), lung adenocarcinoma (LUAD), and stomach adenocarcinoma (STAD). FNBP1 was also positively correlated with the adjustment of CD8+ cells, T cells, M2 macrophage, neutrophils, monocyte, Th1 cells, T regulatory cells (Treg) and Tumor-associated macrophages (TAMs). The expression level of FNBP1 is closely positively correlated with the expression level of multiple immune checkpoints in the three cancers. In addition, FNBP1 is significantly positively correlated with the expression levels of a variety of immunosuppressive molecules.

Conclusion

Our findings reveal FNBP1 can serve as a significant biomarker to influence the prognosis and the immune infiltrating levels in different cancers. The differential expression of FNBP1 might not only contribute to the judgment of metastatic and non-metastatic tumors but also in the immune escape by upregulating the expression of immune checkpoints.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12865-021-00475-z.

New twists in actin-microtubule interactions

Actin filaments and microtubules are cytoskeletal polymers that participate in many vital cell functions including division, morphogenesis, phagocytosis, and motility. Despite the persistent dogma that actin filament and microtubule networks are distinct in localization, structure, and function, a growing body of evidence shows that these elements are choreographed through intricate mechanisms sensitive to either polymer. Many proteins and cellular signals that mediate actin–microtubule interactions have already been identified. However, the impact of these regulators is typically assessed with actin filament or microtubule polymers alone, independent of the other system. Further, unconventional modes and regulators coordinating actin–microtubule interactions are still being discovered. Here we examine several methods of actin–microtubule crosstalk with an emphasis on the molecular links between both polymer systems and their higher-order interactions.

Two Motors and One Spring: Hypothetic Roles of Non-Muscle Myosin II and Submembrane Actin-Based Cytoskeleton in Cell Volume Sensing

Changes in plasma membrane curvature and intracellular ionic strength are two key features of cell volume perturbations. In this hypothesis we present a model of the responsible molecular apparatus which is assembled of two molecular motors [non-muscle myosin II (NMMII) and protrusive actin polymerization], a spring [a complex between the plasma membrane (PM) and the submembrane actin-based cytoskeleton (smACSK) which behaves like a viscoelastic solid] and the associated signaling proteins. We hypothesize that this apparatus senses changes in both the plasma membrane curvature and the ionic strength and in turn activates signaling pathways responsible for regulatory volume increase (RVI) and regulatory volume decrease (RVD). During cell volume changes hydrostatic pressure (HP) changes drive alterations in the cell membrane curvature. HP difference has opposite directions in swelling versus shrinkage, thus allowing distinction between them. By analogy with actomyosin contractility that appears to sense stiffness of the extracellular matrix we propose that NMMII and actin polymerization can actively probe the transmembrane gradient in HP. Furthermore, NMMII and protein-protein interactions in the actin cortex are sensitive to ionic strength. Emerging data on direct binding to and regulating activities of transmembrane mechanosensors by NMMII and actin cortex provide routes for signal transduction from transmembrane mechanosensors to cell volume regulatory mechanisms.

The roles of Cdc42 and Rac1 in the formation of plasma membrane protrusions in cancer epithelial HeLa cells

The inducible model of clones generated from the cervical cancer epithelial HeLa cell line has shown the role of DOCK10 as a guanine-nucleotide exchange factor for Rho GTPases Cdc42 and Rac1 and as an inducer of filopodia and plasma membrane (PM) ruffles. In this model, constitutively active (CA) mutants of Cdc42 and Rac1 promote filopodia and ruffles, respectively, as in other models. DOCK9 also induces filopodia and ruffles, although ruffling activity is less prominent. By exploiting this model further, the aim of this work is to provide a more complete understanding of the role of Cdc42 and Rac1, and their interactions with DOCK10 and DOCK9, in regulation of PM protrusions. New clones have been generated from HeLa, including single clones expressing one form of wild-type (WT) or dominant negative (DN) Cdc42 or Rac1, and double clones co-expressing one of them together with either DOCK10 or DOCK9. Expression of WT- and DN-Cdc42 induced filopodia. WT-Cdc42 and, especially, DN-Cdc42 also gave rise to veil protrusions, which were neutralized by DOCK10. Moreover, DN-Cdc42 stimulated the emergence of ruffles, further increased by DOCK10, and WT-Cdc42 also augmented ruffles in presence of DOCK9 and DOCK10. WT-Rac1 greatly increased PM blebbing, as did DN-Rac1 more moderately. In both cases, blebs were enhanced by DOCK10. DN-Rac1 and CA-Rac1 moderately raised filopodia, and DOCK10 and DOCK9 had opposed effects on filopodia (up and down, respectively) in presence of WT-Rac1. As conclusions, we highlight that Cdc42 promotes filopodia regardless of its conformational state, and Rac1 induces blebs in conformations other than CA, especially WT-Rac1, in the inducible HeLa clones. The model could be useful to learn more about the mechanisms underlying PM protrusions.

Mechanical Sensing Element PDLIM5 Promotes Osteogenesis of Human Fibroblasts by Affecting the Activity of Microfilaments

Human skin fibroblasts (HSFs) approximate the multidirectional differentiation potential of mesenchymal stem cells, so they are often used in differentiation, cell cultures, and injury repair. They are an important seed source in the field of bone tissue engineering. However, there are a few studies describing the mechanism of osteogenic differentiation of HSFs. Here, osteogenic induction medium was used to induce fibroblasts to differentiate into osteoblasts, and the role of the mechanical sensitive element PDLIM5 in microfilament-mediated osteogenic differentiation of human fibroblasts was evaluated. The depolymerization of microfilaments inhibited the expression of osteogenesis-related proteins and alkaline phosphatase activity of HSFs, while the polymerization of microfilaments enhanced the osteogenic differentiation of HSFs. The evaluation of potential protein molecules affecting changes in microfilaments showed that during the osteogenic differentiation of HSFs, the expression of PDLIM5 increased with increasing induction time, and decreased under the state of microfilament depolymerization. Lentivirus-mediated PDLIM5 knockdown by shRNA weakened the osteogenic differentiation ability of HSFs and inhibited the expression and morphological changes of microfilament protein. The inhibitory effect of knocking down PDLIM5 on HSF osteogenic differentiation was reversed by a microfilament stabilizer. Taken together, these data suggest that PDLIM5 can mediate the osteogenic differentiation of fibroblasts by affecting the formation and polymerization of microfilaments.

Kindlin3 regulates biophysical properties and mechanics of membrane to cortex attachment

Kindlin3 (K3), a FERM domain containing protein expressed in hematopoietic cells controls integrin activation and thus hemostatic and inflammatory responses. However, its role in the mechanics of plasma membrane remains unclear. Here, we show that genetic knockout of K3 in microglia and macrophages resulted in defective plasma membrane tension and membrane blebbing. Atomic force microscopy (AFM) of K3-deficient cells revealed a significant loss in membrane-to-cortex attachment (MCA), and consequently reduced membrane tension. This loss in MCA is amplified by the mislocalization of the cell cortex proteins-ezrin, radixin, and moesin (ERM)-to the plasma membrane of microglia and macrophages. Re-expression of K3 in K3-deficient macrophages rescued the defects and localization of ERMs implying a key role for K3 in MCA. Analysis of two K3 mutants, K3int affecting integrin binding and activation, and K3pxn/act disrupting binding to paxillin and actin but not integrin functions, demonstrated that the role of K3 in membrane mechanics is separate from integrin activation. The K3pxn/act mutant substantially diminished both membrane tension and Yes-associated protein (YAP) translocation to the nucleus, while preserving integrin activation, cell spreading, and migration. Together, our results show that K3 coordinates membrane mechanics, ERM protein recruitment to the membrane, and YAP translocation by linking integrin at the membrane to paxillin and actin of the cytoskeleton. This novel function of K3 is distinct from its role in integrin activation.

The intrinsically disordered protein SPE-18 promotes localized assembly of MSP in Caenorhabditis elegans spermatocytes

Many specialized cells use unconventional strategies of cytoskeletal control. Nematode spermatocytes discard their actin and tubulin following meiosis, and instead employ the regulated assembly/disassembly of the Major Sperm Protein (MSP) to drive sperm motility. However, prior to the meiotic divisions, MSP is sequestered through its assembly into paracrystalline structures called fibrous bodies (FBs). The accessory proteins that direct this sequestration process have remained mysterious. This study reveals SPE-18 as an intrinsically disordered protein that is essential for MSP assembly within FBs. In spe-18 mutant spermatocytes, MSP forms disorganized cortical fibers, and the cells arrest in meiosis without forming haploid sperm. In wild-type spermatocytes, SPE-18 localizes to pre-FB complexes and functions with the kinase SPE-6 to localize MSP assembly. Changing patterns of SPE-18 localization uncover previously unappreciated complexities in FB maturation. Later, within newly individualized spermatids, SPE-18 is rapidly lost, yet SPE-18 loss alone is insufficient for MSP disassembly. Our findings reveal an alternative strategy for sequestering cytoskeletal elements, not as monomers but in localized, bundled polymers. Additionally, these studies provide an important example of disordered proteins promoting ordered cellular structures.

Stress fibres are embedded in a contractile cortical network

Contractile actomyosin networks are responsible for the production of intracellular forces. There is increasing evidence that bundles of actin filaments form interconnected and interconvertible structures with the rest of the network. In this study, we explored the mechanical impact of these interconnections on the production and distribution of traction forces throughout the cell. By using a combination of hydrogel micropatterning, traction force microscopy and laser photoablation, we measured the relaxation of traction forces in response to local photoablations. Our experimental results and modelling of the mechanical response of the network revealed that bundles were fully embedded along their entire length in a continuous and contractile network of cortical filaments. Moreover, the propagation of the contraction of these bundles throughout the entire cell was dependent on this embedding. In addition, these bundles appeared to originate from the alignment and coalescence of thin and unattached cortical actin filaments from the surrounding mesh.

Membrane signalosome: where biophysics meets systems biology

We opine on the recent advances in experiments and modeling of modular signaling complexes assembled on mammalian cell membranes (membrane signalosomes) in the context of several applications including intracellular trafficking, cell migration, and immune response. Characterizing the individual components of the membrane assemblies at the nanoscale, ranging from protein-lipid and protein-protein interactions, to membrane morphology, and the energetics of emergent assemblies at the subcellular to cellular scales pose significant challenges. Overcoming these challenges through the iterative coupling of multiscale modeling and experiment can be transformative in terms of addressing the gaps between structural biology and super-resolution microscopy, as it holds the key to the discovery of fundamental mechanisms behind the emergence of function in the membrane signalosome.

Twinfilin uncaps filament barbed ends to promote turnover of lamellipodial actin networks

Coordinated polymerization of actin filaments provides force for cell migration, morphogenesis and endocytosis. Capping protein (CP) is a central regulator of actin dynamics in all eukaryotes. It binds to actin filament (F-actin) barbed ends with high affinity and slow dissociation kinetics to prevent filament polymerization and depolymerization. However, in cells, CP displays remarkably rapid dynamics within F-actin networks, but the underlying mechanism remains unclear. Here, we report that the conserved cytoskeletal regulator twinfilin is responsible for CP's rapid dynamics and specific localization in cells. Depletion of twinfilin led to stable association between CP and cellular F-actin arrays, as well as to its retrograde movement throughout leading-edge lamellipodia. These were accompanied by diminished F-actin turnover rates. In vitro single-filament imaging approaches revealed that twinfilin directly promotes dissociation of CP from filament barbed ends, while enabling subsequent filament depolymerization. These results uncover a bipartite mechanism that controls how actin cytoskeleton-mediated forces are generated in cells.

Coadministration of ARV (Atripla) and Topiramate disrupts quail cardiac neural crest cell migration

INTRODUCTION

Congenital anomalies such as ventricular septal defects and truncus communis have been reported with the prenatal use of antiretroviral therapy. The mechanism of antiretroviral therapy teratogenicity is unclear and is therefore the focus of this study. Some human immunodeficiency virus patients on antiretrovirals are placed on antiepileptic drugs which are also teratogenic. The interactive effects arising from this therapeutic combination may affect their teratogenic propensity through their effects on neural crest cell migration.

METHODS

Appropriately cultured neural crest cells from dissected neural tubes of 32-hr old quail embryos exposed to culture media containing peak plasma levels of Atripla, Topiramate and the combination of both were studied. Distance of migration of neural crest cells was measured using the migration assay and the cells were stained with rhodamine phalloidin to evaluate the cell actin. Also quail neural crest cells were brought into suspension and microinjected into chick hosts to determine the migration of the cells to the interventricular septum.

RESULTS

Migration of cultured neural crest cells was extensive in the control cultures, but inhibited in the treated groups. The experimental cultures showed a disarray of actin cytoskeleton contrary to normal distribution of actin filaments in controls. Significantly, few quail neural crest cells migrated to the interventricular septum of chick host embryos compared to the control cultures. The coadministration of topiramate with antiretroviral therapy does not seem to affect the activity of the antiretroviral drug.

CONCLUSION

These results indicate that Atripla and Topiramate cause ventricular septal defects by inhibiting the migration of cardiac neural crest cells.

An Integrative Computational Approach Based on Expression Similarity Signatures to Identify Protein-Protein Interaction Networks in Female-Specific Cancers

Breast, ovarian, and endometrial cancers have a major impact on mortality in women. These tumors share hormone-dependent mechanisms involved in female-specific cancers which support tumor growth in a different manner. Integrated computational approaches may allow us to better detect genomic similarities between these different female-specific cancers, helping us to deliver more sophisticated diagnosis and precise treatments. Recently, several initiatives of The Cancer Genome Atlas (TCGA) have encouraged integrated analyses of multiple cancers rather than individual tumors. These studies revealed common genetic alterations (driver genes) even in clinically distinct entities such as breast, ovarian, and endometrial cancers. In this study, we aimed to identify expression similarity signatures by extracting common genes among TCGA breast (BRCA), ovarian (OV), and uterine corpus endometrial carcinoma (UCEC) cohorts and infer co-regulatory protein-protein interaction networks that might have a relationship with the estrogen signaling pathway. Thus, we carried out an unsupervised principal component analysis (PCA)-based computational approach, using RNA sequencing data of 2,015 female cancer and 148 normal samples, in order to simultaneously capture the data heterogeneity of intertumors. Firstly, we identified tumor-associated genes from gene expression profiles. Secondly, we investigated the signaling pathways and co-regulatory protein-protein interaction networks underlying these three cancers by leveraging the Ingenuity Pathway Analysis software. In detail, we discovered 1,643 expression similarity signatures (638 downregulated and 1,005 upregulated genes, with respect to normal phenotype), denoted as tumor-associated genes. Through functional genomic analyses, we assessed that these genes were involved in the regulation of cell-cycle-dependent mechanisms, including metaphase kinetochore formation and estrogen-dependent S-phase entry. Furthermore, we generated putative co-regulatory protein-protein interaction networks, based on upstream regulators such as the ERBB2/HER2 gene. Moreover, we provided an ad-hoc bioinformatics workflow with a manageable list of intertumor expression similarity signatures for the three female-specific cancers. The expression similarity signatures identified in this study might uncover potential estrogen-dependent molecular mechanisms promoting carcinogenesis.

Haploid male germ cells-the Grand Central Station of protein transport

BACKGROUND

The precise movement of proteins and vesicles is an essential ability for all eukaryotic cells. Nowhere is this more evident than during the remarkable transformation that occurs in spermiogenesis-the transformation of haploid round spermatids into sperm. These transformations are critically dependent upon both the microtubule and the actin cytoskeleton, and defects in these processes are thought to underpin a significant percentage of human male infertility.

OBJECTIVE AND RATIONALE

This review is aimed at summarising and synthesising the current state of knowledge around protein/vesicle transport during haploid male germ cell development and identifying knowledge gaps and challenges for future research. To achieve this, we summarise the key discoveries related to protein transport using the mouse as a model system. Where relevant, we anchored these insights to knowledge in the field of human spermiogenesis and the causality of human male infertility.

SEARCH METHODS

Relevant studies published in English were identified using PubMed using a range of search terms related to the core focus of the review-protein/vesicle transport, intra-flagellar transport, intra-manchette transport, Golgi, acrosome, manchette, axoneme, outer dense fibres and fibrous sheath. Searches were not restricted to a particular time frame or species although the emphasis within the review is on mammalian spermiogenesis.

OUTCOMES

Spermiogenesis is the final phase of sperm development. It results in the transformation of a round cell into a highly polarised sperm with the capacity for fertility. It is critically dependent on the cytoskeleton and its ability to transport protein complexes and vesicles over long distances and often between distinct cytoplasmic compartments. The development of the acrosome covering the sperm head, the sperm tail within the ciliary lobe, the manchette and its role in sperm head shaping and protein transport into the tail, and the assembly of mitochondria into the mid-piece of sperm, may all be viewed as a series of overlapping and interconnected train tracks. Defects in this redistribution network lead to male infertility characterised by abnormal sperm morphology (teratozoospermia) and/or abnormal sperm motility (asthenozoospermia) and are likely to be causal of, or contribute to, a significant percentage of human male infertility.

WIDER IMPLICATIONS

A greater understanding of the mechanisms of protein transport in spermiogenesis offers the potential to precisely diagnose cases of male infertility and to forecast implications for children conceived using gametes containing these mutations. The manipulation of these processes will offer opportunities for male-based contraceptive development. Further, as increasingly evidenced in the literature, we believe that the continuous and spatiotemporally restrained nature of spermiogenesis provides an outstanding model system to identify, and de-code, cytoskeletal elements and transport mechanisms of relevance to multiple tissues.

Actin filaments mediated root growth inhibition by changing their distribution under UV-B and hydrogen peroxide exposure in Arabidopsis

BACKGROUND

UV-B signaling in plants is mediated by UVR8, which interacts with transcriptional factors to induce root morphogenesis. However, research on the downstream molecules of UVR8 signaling in roots is still scarce. As a wide range of functional cytoskeletons, how actin filaments respond to UV-B-induced root morphogenesis has not been reported. The aim of this study was to investigate the effect of actin filaments on root morphogenesis under UV-B and hydrogen peroxide exposure in Arabidopsis.

RESULTS

A Lifeact-Venus fusion protein was used to stain actin filaments in Arabidopsis. The results showed that UV-B inhibited hypocotyl and root elongation and caused an increase in H₂O₂ content only in the root but not in the hypocotyl. Additionally, the actin filaments in hypocotyls diffused under UV-B exposure but were gathered in a bundle under the control conditions in either Lifeact-Venus or uvr8 plants. Exogenous H₂O₂ inhibited root elongation in a dose-dependent manner. The actin filaments changed their distribution from filamentous to punctate in the root tips and mature regions at a lower concentration of H₂O₂ but aggregated into thick bundles with an abnormal orientation at H₂O₂ concentrations up to 2 mM. In the root elongation zone, the actin filament arrangement changed from lateral to longitudinal after exposure to H₂O₂. Actin filaments in the root tip and elongation zone were depolymerized into puncta under UV-B exposure, which showed the same tendency as the low-concentration treatments. The actin filaments were hardly filamentous in the maturation zone. The dynamics of actin filaments in the uvr8 group under UV-B exposure were close to those of the control group.

CONCLUSIONS

The results indicate that UV-B inhibited Arabidopsis hypocotyl elongation by reorganizing actin filaments from bundles to a loose arrangement, which was not related to H₂O₂. UV-B disrupted the dynamics of actin filaments by changing the H₂O₂ level in Arabidopsis roots. All these results provide an experimental basis for investigating the interaction of UV-B signaling with the cytoskeleton.

Cortactin in Epithelial-Mesenchymal Transition

Cortactin, a member of the actin-binding protein family, plays an important role in cell movement involving the cytoskeleton, as cell movement mediated by cortactin may induce the epithelial–mesenchymal transition. Cortactin participates in tumor proliferation, migration, and invasion and other related disease processes by binding to different proteins and participating in different pathways and mechanisms that induce the occurrence of these disease processes. Therefore, this article reviews the correlations between cortactin, the actin cytoskeleton, and the epithelial–mesenchymal transition and discusses its clinical importance in tumor therapy.

EPLIN-α and -β Isoforms Modulate Endothelial Cell Dynamics through a Spatiotemporally Differentiated Interaction with Actin

Actin-binding proteins are essential for linear and branched actin filament dynamics that control shape change, cell migration, and cell junction remodeling in vascular endothelium (endothelial cells [ECs]). The epithelial protein lost in neoplasm (EPLIN) is an actin-binding protein, expressed as EPLIN-α and EPLIN-β by alternative promoters; however, the isoform-specific functions are not yet understood. Aortic compared to cava vein ECs and shear stress-exposed cultured ECs express increased EPLIN-β levels that stabilize stress fibers. In contrast, EPLIN-α expression is increased in growing and migrating ECs, is targeted to membrane protrusions, and terminates their growth via interaction with the Arp2/3 complex. The data indicate that EPLIN-α controls protrusion dynamics while EPLIN-β has an actin filament stabilizing role, which is consistent with FRAP analyses demonstrating a lower EPLIN-β turnover rate compared to EPLIN-α. Together, EPLIN isoforms differentially control actin dynamics in ECs, essential in shear stress responses, cell migration, and barrier function.

Profilin choreographs actin and microtubules in cells and cancer

Actin and microtubules play essential roles in aberrant cell processes that define and converge in cancer including: signaling, morphology, motility, and division. Actin and microtubules do not directly interact, however shared regulators coordinate these polymers. While many of the individual proteins important for regulating and choreographing actin and microtubule behaviors have been identified, the way these molecules collaborate or fail in normal or disease contexts is not fully understood. Decades of research focus on Profilin as a signaling molecule, lipid-binding protein, and canonical regulator of actin assembly. Recent reports demonstrate that Profilin also regulates microtubule dynamics and polymerization. Thus, Profilin can coordinate both actin and microtubule polymer systems. Here we reconsider the biochemical and cellular roles for Profilin with a focus on the essential cytoskeletal-based cell processes that go awry in cancer. We also explore how the use of model organisms has helped to elucidate mechanisms that underlie the regulatory essence of Profilin in vivo and in the context of disease.

Regulation of the Actin Cytoskeleton in Podocytes

Podocytes are an integral part of the glomerular filtration barrier, a structure that prevents filtration of large proteins and macromolecules into the urine. Podocyte function is dependent on actin cytoskeleton regulation within the foot processes, structures that link podocytes to the glomerular basement membrane. Actin cytoskeleton dynamics in podocyte foot processes are complex and regulated by multiple proteins and other factors. There are two key signal integration and structural hubs within foot processes that regulate the actin cytoskeleton: the slit diaphragm and focal adhesions. Both modulate actin filament extension as well as foot process mobility. No matter what the initial cause, the final common pathway of podocyte damage is dysregulation of the actin cytoskeleton leading to foot process retraction and proteinuria. Disruption of the actin cytoskeleton can be due to acquired causes or to genetic mutations in key actin regulatory and signaling proteins. Here, we describe the major structural and signaling components that regulate the actin cytoskeleton in podocytes as well as acquired and genetic causes of actin dysregulation.