Regulation of actin cytoskeleton dynamics in cells

Postmitotic expansion of cell nuclei requires nuclear actin filament bundling by α-actinin 4

The actin cytoskeleton operates in a multitude of cellular processes including cell shape and migration, mechanoregulation, and membrane or organelle dynamics. However, its filamentous properties and functions inside the mammalian cell nucleus are less well explored. We previously described transient actin assembly at mitotic exit that promotes nuclear expansion during chromatin decondensation. Here, we identify non‐muscle α‐actinin 4 (ACTN4) as a critical regulator to facilitate F‐actin reorganization and bundling during postmitotic nuclear expansion. ACTN4 binds to nuclear actin filament structures, and ACTN4 clusters associate with nuclear F‐actin in a highly dynamic fashion. ACTN4 but not ACTN1 is required for proper postmitotic nuclear volume expansion, mediated by its actin‐binding domain. Using super‐resolution imaging to quantify actin filament numbers and widths in individual nuclei, we find that ACTN4 is necessary for postmitotic nuclear actin reorganization and actin filament bundling. Our findings uncover a nuclear cytoskeletal function for ACTN4 to control nuclear size and chromatin organization during mitotic cell division.

WD Repeat Domain 1 Deficiency Inhibits Neointima Formation in Mice Carotid Artery by Modulation of Smooth Muscle Cell Migration and Proliferation

The migration, dedifferentiation, and proliferation of vascular smooth muscle cells (VSMCs) are responsible for intimal hyperplasia, but the mechanism of this process has not been elucidated. WD repeat domain 1 (WDR1) promotes actin-depolymerizing factor (ADF)/cofilin-mediated depolymerization of actin filaments (F-actin). The role of WDR1 in neointima formation and progression is still unknown. A model of intimal thickening was constructed by ligating the left common carotid artery in Wdr1 deletion mice, and H&E staining showed that Wdr1 deficiency significantly inhibits neointima formation. We also report that STAT3 promotes the proliferation and migration of VSMCs by directly promoting WDR1 transcription. Mechanistically, we clarified that WDR1 promotes the proliferation and migration of VSMCs and neointima formation is regulated by the activation of the JAK2/STAT3/WDR1 axis.

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.

Genetic suppression of defective profilin by attenuated Myosin II reveals a potential role for Myosin II in actin dynamics in vivo in fission yeast

The actin cytoskeleton plays a variety of roles in eukaryotic cell physiology, ranging from cell polarity and migration to cytokinesis. Key to the function of the actin cytoskeleton is the mechanisms that control its assembly, stability, and turnover. Through genetic analyses in Schizosaccharomyces pombe, we found that myo2-S1 (myo2-G515D), a Myosin II mutant allele, was capable of rescuing lethality caused by partial defects in actin nucleation/stability caused, for example, through compromised function of the actin-binding protein Cdc3-profilin. The mutation in myo2-S1 affects the activation loop of Myosin II, which is involved in physical interaction with subdomain 1 of actin and in stimulating the ATPase activity of Myosin. Consistently, actomyosin rings in myo2-S1 cell ghosts were unstable and severely compromised in contraction on ATP addition. These studies strongly suggest a role for Myo2 in actin cytoskeletal disassembly and turnover in vivo, and that compromise of this activity leads to genetic suppression of mutants defective in actin filament assembly/stability at the division site.

Whole-blood dysregulation of actin-cytoskeleton pathway in adult spinal muscular atrophy patients

OBJECTIVE

Recent advances in therapeutics have improved prognosis for severely affected spinal muscular atrophy (SMA) type 1 and 2 patients, while the best method of treatment for SMA type 3 patients with later onset of disease is unknown. To better characterize the SMA type 3 population and provide potential therapeutic targets, we aimed to understand gene expression differences in whole blood of SMA type 3 patients (n = 31) and age- and gender-matched controls (n = 34).

METHODS

We performed the first large-scale whole blood transcriptomic screen with L1000, a rapid, high-throughput gene expression profiling technology that uses 978 landmark genes to capture a representation of the transcriptome and predict expression of 9196 additional genes.

RESULTS

The primary downregulated KEGG pathway in adult SMA type 3 patients was "Regulation of Actin Cytoskeleton," and downregulated expression of key genes in this pathway, including ROCK1, RHOA, and ACTB, was confirmed in the same whole blood samples using RT-qPCR. SMA type 3 patient-derived fibroblasts had lower expression of these genes compared to control fibroblasts from unaffected first-degree relatives. Overexpression of SMN levels using an AAV vector in fibroblasts did not normalize ROCK1, RHOA, and ACTB mRNA expression, indicating the involvement of additional genes in cytoskeleton dynamic regulation.

INTERPRETATION

Our findings from whole blood and patient-derived fibroblasts suggest SMA type 3 patients have decreased expression of actin cytoskeleton regulators. These observations provide new insights and potential therapeutic targets for SMA patients with longstanding denervation and secondary musculoskeletal pathophysiology.

Cytoskeletal Drugs Modulate Off-Target Protein Folding Landscapes Inside Cells

The dynamic cytoskeletal network of microtubules and actin filaments can be disassembled by drugs. Cytoskeletal drugs work by perturbing the monomer-polymer equilibrium, thus changing the size and number of macromolecular crowders inside cells. Changes in both crowding and nonspecific surface interactions ("sticking") following cytoskeleton disassembly can affect the protein stability, structure, and function directly or indirectly by changing the fluidity of the cytoplasm and altering the crowding and sticking of other macromolecules in the cytoplasm. The effect of cytoskeleton disassembly on protein energy landscapes inside cells has yet to be observed. Here we have measured the effect of several cytoskeletal drugs on the folding energy landscape of two FRET-labeled proteins with different in vitro sensitivities to macromolecular crowding. Phosphoglycerate kinase (PGK) was previously shown to be more sensitive to crowding, whereas variable major protein-like sequence expressed (VlsE) was previously shown to be more sensitive to sticking. The in-cell effects of drugs that depolymerize either actin filaments (cytochalasin D and latrunculin B) or microtubules (nocodazole and vinblastine) were compared. The crowding sensor protein CrH2-FRET verified that cytoskeletal drugs decrease the extent of crowding inside cells despite also reducing the overall cell volume. The decreased compactness and folding stability of PGK could be explained by the decreased extent of crowding induced by these drugs. VlsE's opposite response to the drugs shows that depolymerization of the cytoskeleton also changes sticking in the cellular milieu. Our results demonstrate that perturbation of the monomer-polymer cytoskeletal equilibrium, for example, during natural cell migration or stresses from drug treatment, has off-target effects on the energy landscapes of proteins in the cell.

Integrin crosstalk allows CD4+ T lymphocytes to continue migrating in the upstream direction after flow

In order to perform critical immune functions at sites of inflammation, circulatory T lymphocytes must be able to arrest, adhere, migrate and transmigrate on the endothelial surface. This progression of steps is coordinated by cellular adhesion molecules (CAMs), chemokines, and selectins presented on the endothelium. Two important interactions are between Lymphocyte Function-associated Antigen-1 (LFA-1) and Intracellular Adhesion Molecule-1 (ICAM-1) and also between Very Late Antigen-4 (VLA-4) and Vascular Cell Adhesion Molecule-1 (VCAM-1). Recent studies have shown that T lymphocytes and other cell types can migrate upstream (against the direction) of flow through the binding of LFA-1 to ICAM-1. Since upstream migration of T cells depends on a specific adhesive pathway, we hypothesized that mechanotransduction is critical to migration, and that signals might allow T-cells to remember their direction of migration after the flow is terminated. Cells on ICAM-1 surfaces migrate against the shear flow, but the upstream migration reverts to random migration after the flow is stopped. Cells on VCAM-1 migrate with the direction of flow. However, on surfaces that combine ICAM-1 and VCAM-1, cells crawl upstream at a shear rate of 800 s-1 and continue migrating in the upstream direction for at least 30 minutes after the flow is terminated-we call this 'migrational memory'. Post-flow upstream migration on VCAM-1/ICAM-1 surfaces is reversed upon the inhibition of PI3K, but conserved with cdc42 and Arp2/3 inhibitors. Using an antibody against VLA-4, we can block migrational memory on VCAM-1/ICAM-1 surfaces. Using a soluble ligand for VLA-4 (sVCAM-1), we can promote migrational memory on ICAM-1 surfaces. These results indicate that, while upstream migration under flow requires LFA-1 binding to immobilized ICAM-1, signaling from VLA-4 and PI3K activity is required for the migrational memory of CD4+ T cells. These results indicate that crosstalk between integrins potentiates the signal of upstream migration.

Exercise training reverses cancer-induced oxidative stress and decrease in muscle COPS2/TRIP15/ALIEN

OBJECTIVE

We tested the hypothesis that exercise training would attenuate metabolic impairment in a model of severe cancer cachexia.

METHODS

We used multiple in vivo and in vitro methods to explore the mechanisms underlying the beneficial effects induced by exercise training in tumor-bearing rats.

RESULTS

Exercise training improved running capacity, prolonged lifespan, reduced oxidative stress, and normalized muscle mass and contractile function in tumor-bearing rats. An unbiased proteomic screening revealed COP9 signalosome complex subunit 2 (COPS2) as one of the most downregulated proteins in skeletal muscle at the early stage of cancer cachexia. Exercise training normalized muscle COPS2 protein expression in tumor-bearing rats and mice. Lung cancer patients with low endurance capacity had low muscle COPS2 protein expression as compared to age-matched control subjects. To test whether decrease in COPS2 protein levels could aggravate or be an intrinsic compensatory mechanism to protect myotubes from cancer effects, we performed experiments in vitro using primary myotubes. COPS2 knockdown in human myotubes affected multiple cellular pathways, including regulation of actin cytoskeleton. Incubation of cancer-conditioned media in mouse myotubes decreased F-actin expression, which was partially restored by COPS2 knockdown. Direct repeat 4 (DR4) response elements have been shown to positively regulate gene expression. COPS2 overexpression decreased the DR4 activity in mouse myoblasts, and COPS2 knockdown inhibited the effects of cancer-conditioned media on DR4 activity.

CONCLUSIONS

These studies demonstrated that exercise training may be an important adjuvant therapy to counteract cancer cachexia and uncovered novel mechanisms involving COPS2 to regulate myotube homeostasis in cancer cachexia.

Tuning Cell Motility via Cell Tension with a Mechanochemical Cell Migration Model

Cell migration is orchestrated by a complicated mechanochemical system. However, few cell migration models take into account the coupling between the biochemical network and mechanical factors. Here, we construct a mechanochemical cell migration model to study the cell tension effect on cell migration. Our model incorporates the interactions between Rac-GTP, Rac-GDP, F-actin, myosin, and cell tension, and it is very convenient in capturing the change of cell shape by taking the phase field approach. This model captures the characteristic features of cell polarization, cell shape change, and cell migration modes. It shows that cell tension inhibits migration ability monotonically when cells are applied with persistent external stimuli. On the other hand, if random internal noise is significant, the regulation of cell tension exerts a nonmonotonic effect on cell migration. Because the increase of cell tension hinders the formation of multiple protrusions, migration ability could be maximized at intermediate cell tension under random internal noise. These model predictions are consistent with our single-cell experiments and other experimental results.

Putative Coiled-Coil Domain-Dependent Autoinhibition and Alternative Splicing Determine SHTN1's Actin-Binding Activity

The actin cytoskeleton plays a pivotal role in cell development, morphogenesis, and other cellular functions. Precise control of actin dynamics requires actin-binding proteins. Here, we characterize multifarious regulation of SHTN1 (shootin1) and show that, unlike known actin-binding proteins, SHTN1's actin binding activity is intrinsically inhibited by a putative coiled-coil domain (CCD) and the autoinhibition is overcome by alternative splicing regulation. We found SHTN1 contains a noncanonical WH2 domain and an upstream proline-rich region (PRR) that by themselves are sufficient for actin interaction. Alternative splicing of Shtn1 at the C terminus and downstream of the WH2-PRR domain produces a long (SHTN1L or shootin1b) and a short (SHTN1S or shootin1a) isoform, which both contain the described PRR and WH2 domains. However, SHTN1S does not interact with actin due to inhibition mediated by an N-terminal CCD. A SHTN1L-specific C-terminal motif counters the intramolecular inhibition and allows SHNT1L to bind actin. A nuclear localization signal is embedded between PRR and WH2 and is subject to similar autoinhibition. SHTN1 would be the first WH2-containing molecule that adopts CCD-dependent autoinhibition and alternative splicing-dependent actin interaction.

Hepatic Transcriptome Analysis Identifies Divergent Pathogen-Specific Targeting-Strategies to Modulate the Innate Immune System in Response to Intramammary Infection

Mastitis is one of the major risks for public health and animal welfare in the dairy industry. Two of the most important pathogens to cause mastitis in dairy cattle are Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). While S. aureus generally induces a chronic and subclinical mastitis, E. coli is an important etiological pathogen resulting in an acute and clinical mastitis. The liver plays a central role in both, the metabolic and inflammatory physiology of the dairy cow, which is particularly challenged in the early lactation due to high metabolic and immunological demands. In the current study, we challenged the mammary glands of Holstein cows with S. aureus or E. coli, respectively, mimicking an early lactation infection. We compared the animals' liver transcriptomes with those of untreated controls to investigate the hepatic response of the individuals. Both, S. aureus and E. coli elicited systemic effects on the host after intramammary challenge and seemed to use pathogen-specific targeting strategies to bypass the innate immune system. The most striking result of our study is that we demonstrate for the first time that S. aureus intramammary challenge causes an immune response beyond the original local site of the mastitis. We found that in the peripheral liver tissue defined biological pathways are switched on in a coordinated manner to balance the immune response in the entire organism. TGFB1 signaling plays a crucial role in this context. Important pathways involving actin and integrin, key components of the cytoskeleton, were downregulated in the liver of S. aureus infected cows. In the hepatic transcriptome of E. coli infected cows, important components of the complement system were significantly lower expressed compared to the control cows. Notably, while S. aureus inhibits the cell signaling by Rho GTPases in the liver, E. coli switches the complement system off. Also, metabolic hepatic pathways (e.g., lipid metabolism) are affected after mammary gland challenge, demonstrating that the liver restricts metabolic tasks in favor of the predominant immune response after infection. Our results provide new insights for the infection-induced modifications of the dairy cow's hepatic transcriptome following mastitis.

Prevalence of Cytoplasmic Actin Mutations in Diffuse Large B-Cell Lymphoma and Multiple Myeloma: A Functional Assessment Based on Actin Three-Dimensional Structures

Mutations in actins have been linked to several developmental diseases. Their occurrence across different cancers has, however, not been investigated. Using the cBioPortal database we show that human actins are infrequently mutated in patient samples of various cancers types. Nevertheless, ranking these studies by mutational frequency suggest that some have a higher percentage of patients with ACTB and ACTG1 mutations. Within studies on hematological cancers, mutations in ACTB and ACTG1 are associated with lymphoid cancers since none have currently been reported in myeloid cancers. Within the different types of lymphoid cancers ACTB mutations are most frequent in diffuse large B-cell lymphoma (DLBCL) and ACTG1 mutations in multiple myeloma. We mapped the ACTB and ACTG1 mutations found in these two cancer types on the 3D-structure of actin showing they are in regions important for actin polymer formation or binding to myosin. The potential effects of the mutations on actin properties imply that mutations in cytoplasmic actins deserve dedicated research in DLBCL and multiple myeloma.

Effects of Short-Term Inhibition of Rho Kinase on Dromedary Camel Oocyte In Vitro Maturation

Simple Summary

Our results revealed, for the first time, that short-term inhibition of Rho-associated protein kinases (ROCK) for 4 h prior to in vitro maturation (IVM) in a biphasic IVM approach improved oocyte nuclear maturation, producing more MII oocyte, through modulating the expression of cytokinesis- and antiapoptosis-related mRNA transcripts. This positive result suggests ROCK inhibitor as a potential candidate molecule to exploit in the control of oocyte meiotic maturation.

Abstract

This is the first report on a biphasic in vitro maturation (IVM) approach with a meiotic inhibitor to improve dromedary camel IVM. Spontaneous meiotic resumption poses a major setback for in vitro matured oocytes. The overall objective of this study was to improve in vitro maturation of dromedary camel oocytes using ROCK inhibitor (Y-27632) in a biphasic IVM to prevent spontaneous meiotic resumption. In the first experiment, we cultured immature cumulus–oocyte complexes (COCs, n = 375) in a prematuration medium supplemented with ROCK inhibitor (RI) for 2 h, 4 h, 6 h, and 24 h before submission to normal in vitro maturation to complete 28 h. The control was cultured for 28 h in the absence of RI. In the first phase of experiment two, we cultured COCs (n = 480) in the presence or absence (control) of RI for 2 h, 4 h, 6 h, and 24 h, and conducted real-time relative quantitative PCR (qPCR) on selected mRNA transcripts. The same was done in the second phase, but qPCR was done after completion of normal IVM. Assessment of nuclear maturation showed that pre-IVM for 4 h yielded an increase in MII oocyte (54.67% vs. 26.6% of control; p < 0.05). As expected, the same group showed the highest degree (2) of cumulus expansion. In experiment 2, qPCR results showed significantly higher expression of ACTB and BCL2 in the RI group treated for 4 h when compared with the other groups. However, their relative quantification after biphasic IVM did not reveal any significant difference, except for the positive response of BCL2 and BAX/BCL2 ratio after 4 and 6 h biphasic IVM. In conclusion, RI prevents premature oocyte maturation and gave a significantly positive outcome during the 4 h treatment. This finding is a paradigm for future investigation on dromedary camel biphasic IVM and for improving the outcome of IVM in this species.

Neuroinflammation Mediated by Glia Maturation Factor Exacerbates Neuronal Injury in an in vitro Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is the primary cause of death and disability affecting over 10 million people in the industrialized world. TBI causes a wide spectrum of secondary molecular and cellular complications in the brain. However, the pathological events are still not yet fully understood. Previously, we have shown that the glia maturation factor (GMF) is a mediator of neuroinflammation in neurodegenerative diseases. To identify the potential molecular pathways accompanying TBI, we used an in vitro cell culture model of TBI. A standardized injury was induced by scalpel cut through a mixed primary cell culture of astrocytes, microglia and neurons obtained from both wild type (WT) and GMF-deficient (GMF-KO) mice. Cell culture medium and whole-cell lysates were collected at 24, 48, and 72 h after the scalpel cuts injury and probed for oxidative stress using immunofluorescence analysis. Results showed that oxidative stress markers such as glutathione and glutathione peroxidase were significantly reduced, while release of cytosolic enzyme lactate dehydrogenase along with nitric oxide and prostaglandin E2 were significantly increased in injured WT cells compared with injured GMF-KO cells. In addition, injured WT cells showed increased levels of oxidation product 4-hydroxynonenal and 8-oxo-2'-deoxyguanosine compared with injured GMF-KO cells. Further, we found that injured WT cells showed a significantly increased expression of glial fibrillary acidic protein, ionized calcium binding adaptor molecule 1, and phosphorylated ezrin/radixin/moesin proteins, and reduced microtubule associated protein expression compared with injured GMF-KO cells after injury. Collectively, our results demonstrate that GMF exacerbates the oxidative stress-mediated neuroinflammation that could be brought about by TBI-induced astroglial activation.

Cellular and molecular aspects of oocyte maturation and fertilization: a perspective from the actin cytoskeleton

ABSTRACT

Much of the scientific knowledge on oocyte maturation, fertilization, and embryonic development has come from the experiments using gametes of marine organisms that reproduce by external fertilization. In particular, echinoderm eggs have enabled the study of structural and biochemical changes related to meiotic maturation and fertilization owing to the abundant availability of large and transparent oocytes and eggs. Thus, in vitro studies of oocyte maturation and sperm-induced egg activation in starfish are carried out under experimental conditions that resemble those occurring in nature. During the maturation process, immature oocytes of starfish are released from the prophase of the first meiotic division, and acquire the competence to be fertilized through a highly programmed sequence of morphological and physiological changes at the oocyte surface. In addition, the changes in the cortical and nuclear regions are essential for normal and monospermic fertilization. This review summarizes the current state of research on the cortical actin cytoskeleton in mediating structural and physiological changes during oocyte maturation and sperm and egg activation in starfish and sea urchin. The common denominator in these studies with echinoderms is that exquisite rearrangements of the egg cortical actin filaments play pivotal roles in gamete interactions, Ca2+ signaling, exocytosis of cortical granules, and control of monospermic fertilization. In this review, we also compare findings from studies using invertebrate eggs with what is known about the contributions made by the actin cytoskeleton in mammalian eggs. Since the cortical actin cytoskeleton affects microvillar morphology, movement, and positioning of organelles and vesicles, and the topography of the egg surface, these changes have impacts on the fertilization process, as has been suggested by recent morphological studies on starfish oocytes and eggs using scanning electron microscopy. Drawing the parallelism between vitelline layer of echinoderm eggs and the zona pellucida of mammalian eggs, we also discuss the importance of the egg surface in mediating monospermic fertilization.

GRAPHICAL ABSTRACT

IODVA1, a guanidinobenzimidazole derivative, targets Rac activity and Ras-driven cancer models

We report the synthesis and preliminary characterization of IODVA1, a potent small molecule that is active in xenograft mouse models of Ras-driven lung and breast cancers. In an effort to inhibit oncogenic Ras signaling, we combined in silico screening with inhibition of proliferation and colony formation of Ras-driven cells. NSC124205 fulfilled all criteria. HPLC analysis revealed that NSC124205 was a mixture of at least three compounds, from which IODVA1 was determined to be the active component. IODVA1 decreased 2D and 3D cell proliferation, cell spreading and ruffle and lamellipodia formation through downregulation of Rac activity. IODVA1 significantly impaired xenograft tumor growth of Ras-driven cancer cells with no observable toxicity. Immuno-histochemistry analysis of tumor sections suggests that cell death occurs by increased apoptosis. Our data suggest that IODVA1 targets Rac signaling to induce death of Ras-transformed cells. Therefore, IODVA1 holds promise as an anti-tumor therapeutic agent.

Roles of the actin cytoskeleton in aging and age-associated diseases

The integrity of the cytoskeleton is essential to diverse cellular processes such as phagocytosis and intracellular trafficking. Disruption of the organization and dynamics of the actin cytoskeleton leads to age-associated symptoms and diseases, ranging from cancer to neurodegeneration. In addition, changes in the integrity of the actin cytoskeleton disrupt the functioning of not only somatic and stem cells but also gametes, resulting in aberrant embryonic development. Strategies to preserve the integrity and dynamics of the cytoskeleton are, therefore, potentially therapeutic to age-related disorders. The objective of this article is to revisit the current understanding of the roles played by the actin cytoskeleton in aging, and to review the opportunities and challenges for the transition of basic research into intervention development. It is hoped that, with the snapshot of evidence regarding changes in actin dynamics with advanced age, insights into future research directions can be attained.

Regulation of actin isoforms in cellular and developmental processes

Actin is one of the most abundant and essential intracellular proteins that mediates nearly every form of cellular movement and underlies such key processes as embryogenesis, tissue integrity, cell division and contractility of all types of muscle and non-muscle cells. In mammals, actin is represented by six isoforms, which are encoded by different genes but produce proteins that are 95-99 % identical to each other. The six actin genes have vastly different functions in vivo, and the small amino acid differences between the proteins they encode are rigorously maintained through evolution, but the underlying differences behind this distinction, as well as the importance of specific amino acid sequences for each actin isoform, are not well understood. This review summarizes different levels of actin isoform-specific regulation in cellular and developmental processes, starting with the nuclear actin's role in transcription, and covering the gene-level, mRNA-level, and protein-level regulation, with a special focus on mammalian actins in non-muscle cells.

Mechanism of control of F-actin cortex architecture by SWAP-70

F-actin binding and bundling are crucial to a plethora of cell processes, including morphogenesis, migration, adhesion and many others. SWAP-70 was recently described as an in vitro F-actin-binding and -bundling protein. Fluorescence cross-correlation spectroscopy measurements with purified recombinant SWAP-70 confirmed that it forms stable oligomers that facilitate F-actin bundling. However, it remained unclear how SWAP-70 oligomerization and F-actin binding are controlled in living cells. We addressed this by biophysical approaches, including seFRET, FACS-FRET and FLIM-FRET. PIP3-mediated association with the cytoplasmic membrane and non-phosphorylated Y426 are required for SWAP-70 to dimerize and to bind F-actin. The dimerization region was identified near the C terminus where R546 is required for dimerization and, thus, F-actin bundling. The in vitro and in vivo data presented here reveal the functional relationship between the cytoplasm-to-membrane translocation and dimerization of SWAP-70, and F-actin binding and bundling, and demonstrate that SWAP-70 is a finely controlled modulator of membrane-proximal F-actin dynamics.This article has an associated First Person interview with the first author of the paper.

Dynamic actin remodeling in response to lysophosphatidic acid

Lysophosphatidic acid (LPA) is a multifunctional regulator of actin cytoskeleton that exerts a dramatic impact on the actin cytoskeleton to build a platform for diverse cellular processes including growth cone guidance, neurite retraction and cell motility. It has been implicated in the formation and dissociation of complexes between actin and actin binding proteins, supporting its role in actin remodeling. Several studies point towards its ability to facilitate formation of special cellular structures including focal adhesions and actin stress fibres by phosphoregulation of several actin associated proteins and their multiple regulatory kinases and phosphatases. In addition, multiple levels of crosstalk among the signaling cascades activated by LPA, affect actin cytoskeleton-mediated cell migration and chemotaxis which in turn play a crucial role in cancer metastasis. In the current review, we have attempted to highlight the role of LPA as an actin modulator which functions by controlling activities of specific cellular proteins that underlie mechanisms employed in cytoskeletal and pathophysiological events within the cell. Further studies on the actin affecting/remodeling activity of LPA in different cell types will no doubt throw up many surprises essential to gain a full understanding of its contribution in physiological processes as well as in diseases.Communicated by Ramaswamy H. Sarma.

Thymosin beta 4 attenuates PrP(106-126)-induced human brain endothelial cells dysfunction

The blood-brain barrier (BBB) is a highly selective permeability barrier that separates the circulating blood from the brain and extracellular fluid in the central nervous system (CNS). The BBB is formed by cerebral endothelial cells connected by tight junctions. Prion diseases are neurodegenerative pathologies characterized by the accumulation of altered forms of the prion protein (PrP), named PrP^Sc. Thymosin beta 4 (Tβ₄) is an actin-sequestering peptide known to bind monomeric actin and inhibit its polymerization, and it is known to have a neuroprotective effect. However, the effect of Tβ₄ on prion disease has not yet been investigated. Therefore, in this study, we investigated the effect of Tβ₄ on prion-induced BBB dysfunction in hCMEC/D3 human cerebral endothelial cells. We found that Tβ₄ increased the expression of tight junction protein, but reduced the ratio of F-actin to G-actin. Moreover, we showed that Tβ₄ significantly improved PrP (106-126)-induced vascular permeability dysfunction in hCMEC/D3 cells. Through human BBB in vitro model, we found that PrP (106-126) could disrupt tight junctions and cytoskeleton arrangement. These results suggest that Tβ₄ may play a critical role in barrier stabilization. Furthermore, Tβ₄ may prevent neurodegenerative diseases caused by prion-induced BBB dysfunction.

Behavioural and chronic toxicity of fullerene to Daphnia magna: Mechanisms revealed by transcriptomic analysis

Extensive application of fullerene nanoparticles (nC₆₀) leads to potential environmental pollution. The acute toxic effects of nC₆₀ have been largely investigated, but studies of behavioural and chronic toxicity at sublethal doses are still rare and the underlying molecular mechanisms remain unknown. The present study investigated behavioural and chronic toxicity of nC₆₀ to Daphnia magna. The results showed that, in response to nC₆₀ exposure, hopping, heartbeat frequencies and feeding ability of D. magna decreased significantly, displaying negative relationship with exposure time and dose. Chronic treatments with 0.1 mg/L or 1 mg/L nC₆₀ for 21 days significantly reduced survival and reproduction of D. magna. These harmful effects suggested negative impacts of nC₆₀ on aquatic ecosystems. Moreover, transcriptome analysis showed that the behavioural and chronic toxicity of nC₆₀ to D. magna might be related to physiological functions such as cell structural repair, protein degradation, energy metabolism and reproduction. We found that nC₆₀ accumulated in guts of D. magna, which should be responsible for the decrease of food ingestion and consequently inhibiting energy intake. Deficiency of energy not only affects behaviours but also declines reproduction in D. magna. Overall, this is the first study comprehensively considered the behavioral and chronic toxicity of nC₆₀ to aquatic organism. The results should be helpful to better understand the ecological consequences of C₆₀ released into water environments.

Circular RNA Expression Profiles in Vaginal Epithelial Tissue of Women With Lubrication Disorders

INTRODUCTION

Recently, circular RNA (circRNA) has been proved to occupy a vital pathological position in many diseases by acting as microRNAs sponges. However, the role of circRNA in female sexual dysfunction (FSD), especially in lubrication disorders (LDs), remains unclear.

AIM

The aim of this study was to detect circRNA expression in LDs, analyzed target genes, and pathways regulated by the differently expressed circRNAs.

METHODS

In this study, next-generation sequencing was first conducted to produce circRNA expression profiles of FSD groups and normal control groups. Furthermore, differences in expression of 6 randomly selected circRNAs were confirmed through real-time quantitative polymerase chain reaction. Kyoto Encyclopedia of Genes and Genomes biological pathway analysis and Gene Ontology showed that immune processes and infection could be involved in the development of FSDs.

MAIN OUTCOME MEASURE

CircRNA expression in vaginal epithelial tissue obtained from women with LDs have been detected. Gene Ontology, Kyoto Encyclopedia of Genes and Genomes biological pathway analysis, and circRNA-microRNA interaction predictions were investigated.

RESULTS

Totally, 7,746 circRNAs of vaginal epithelial tissue from women of 2 groups were sequenced. Preliminary judgment revealed that there were 73 circRNAs that have significant differential expression, including 53 downregulated circRNAs and 20 upregulated circRNAs. Research results also displayed that the majority of circRNAs has multiple binding sites of microRNAs, including miR-137, which has been reported to be linked to FSD.

CLINICAL IMPLICATIONS

We predicted 10 circRNAs paired with hsa-miR-137-5p, but the mechanism of circRNA involvement in disease development remains to be further explored.

STRENGTHS & LIMITATIONS

For the first time, the research disclosed the potential pathogenesis of LDs. However, we only analyzed the expression profile of circRNA in FSD, no specific mechanism was further confirmed or proposed. We still have a preliminary understanding, and more research is needed to explore the target of FSD treatment.

CONCLUSION

The results suggest that circRNAs have different expression in the FSD groups and play a vital part in the occurrence and development of FSD. Zhang J, Xia H, Zhang A, et al. Circular RNA Expression Profiles in Vaginal Epithelial Tissue of Women With Lubrication Disorders. J Sex Med 2019;16:1696-1707.

Early Alterations of Endothelial Nitric Oxide Synthase Expression Patterns in the Guinea Pig Cochlea After Noise Exposure

Constitutively expressed endothelial nitric oxide synthase (eNOS) is supposed to play a role in noise-induced nitric oxide (NO)-production. It is commonly known that intense noise exposure results in inducible NOS (iNOS) expression and increased NO-production, but knowledge about a contribution of the eNOS isoform is still lacking. Effects of noise exposure on eNOS immunolabeling were determined in male guinea pigs (n=24). For light microscopic analysis, 11 animals were exposed to 90 dB for 1 hr and 6 animals were used as controls. After exposure, eNOS immunostaining was performed on paraffin sections, and the staining intensities were quantified for 4 cochlear regions. For electron microscopic analysis, 2 animals were exposed for 2 hr to 90 dB and 5 animals were used as controls. The intensity of eNOS immunolabeling was found to be already comprehensively increased 1 hr after noise exposure to 90 dB. At the ultrastructural level, a clear increase in eNOS immunolabeling was found in microtubules-rich areas of cochlear cuticular structures. Hence, our findings indicate that the reticular lamina forming the endolymph-perilymph barrier at the apical side of the organ of Corti is involved in a fast intrinsic otoprotective mechanism of the cochlea.

Involvement of Actin in Autophagy and Autophagy-Dependent Multidrug Resistance in Cancer

Currently, autophagy in the context of cancer progression arouses a lot of controversy. It is connected with the possibility of switching the nature of this process from cytotoxic to cytoprotective and vice versa depending on the treatment. At the same time, autophagy of cytoprotective character may be one of the factors determining multidrug resistance, as intensification of the process is observed in patients with poorer prognosis. The exact mechanism of this relationship is not yet fully understood; however, it is suggested that one of the elements of the puzzle may be a cytoskeleton. In the latest literature reports, more and more attention is paid to the involvement of actin in the autophagy. The role of this protein is linked to the formation of autophagosomes, which are necessary element of the process. However, based on the proven effectiveness of manipulation of the actin pool, it seems to be an attractive alternative in breaking autophagy-dependent multidrug resistance in cancer.

Regulation of neuroblastoma migration, invasion, and in vivo metastasis by genetic and pharmacological manipulation of MDA-9/Syntenin

Despite multi-modality treatments, prognosis for advanced stage neuroblastoma (NB) remains challenging with residual long-term disabilities in survivors. Advanced stage NB is metastatic, which is a principal cause of cancer-related deaths. We presently document a primary role of MDA-9 in NB progression and define the molecular mechanisms by which MDA-9 promotes transformed phenotypes. NB cell lines and clinical samples display elevated MDA-9 expression and bioinformatic analysis supports an association between elevated MDA-9 and bone metastasis and poor prognosis. Genetic (shmda-9, mda-9 siRNA) or pharmacological (small molecule inhibitor of protein-protein interactions; PDZ1i) blockade of MDA-9 decreases NB migration, invasion, and metastasis. Blocking mda-9 expression or disrupting MDA-9 partner protein interactions downregulates integrin α6 and β4, diminishing Src activity and suppressing Rho-Rac-Cdc42 activity. These signaling changes inhibit cofilin and matrix metalloproteinases reducing in vitro and in vivo NB cell migration. Overexpression of integrin α6 and β4 rescues the invasion phenotype and increases Src activity, supporting integrins as essential regulators of MDA-9-mediated NB migration and invasion. We identify MDA-9 as a key contributor to NB pathogenesis and show that genetic or pharmacological inhibition suppresses NB pathogenesis by an integrin-mediated Src-disruption pathway.

JMJD3 regulates CD4 T cell trafficking by targeting actin cytoskeleton regulatory gene Pdlim4

Histone H3K27 demethylase, JMJD3 plays a critical role in gene expression and T-cell differentiation. However, the role and mechanisms of JMJD3 in T cell trafficking remain poorly understood. Here we show that JMJD3 deficiency in CD4+ T cells resulted in an accumulation of T cells in the thymus, and reduction of T cell number in the secondary lymphoid organs. We identified PDLIM4 as a significantly down-regulated target gene in JMJD3-deficient CD4+ T cells by gene profiling and ChIP-seq analyses. We further showed that PDLIM4 functioned as an adaptor protein to interact with S1P1 and filamentous actin (F-actin), thus serving as a key regulator of T cell trafficking. Mechanistically, JMJD3 bound to the promoter and gene body regions of Pdlim4 gene and regulated its expression by interacting with zinc finger transcription factor KLF2. Our findings have identified Pdlim4 as a JMJD3 target gene that affects T-cell trafficking by cooperating with S1P1, and provided insights into the molecular mechanisms by which JMJD3 regulates genes involved in T cell trafficking.

From isolated structures to continuous networks: A categorization of cytoskeleton-based motile engineered biological microstructures

As technology at the small scale is advancing, motile engineered microstructures are becoming useful in drug delivery, biomedicine, and lab-on-a-chip devices. However, traditional engineering methods and materials can be inefficient or functionally inadequate for small-scale applications. Increasingly, researchers are turning to the biology of the cytoskeleton, including microtubules, actin filaments, kinesins, dyneins, myosins, and associated proteins, for both inspiration and solutions. They are engineering structures with components that range from being entirely biological to being entirely synthetic mimics of biology and on scales that range from isotropic continuous networks to single isolated structures. Motile biological microstructures trace their origins from the development of assays used to study the cytoskeleton to the array of structures currently available today. We define 12 types of motile biological microstructures, based on four categories: entirely biological, modular, hybrid, and synthetic, and three scales: networks, clusters, and isolated structures. We highlight some key examples, the unique functionalities, and the potential applications of each microstructure type, and we summarize the quantitative models that enable engineering them. By categorizing the diversity of motile biological microstructures in this way, we aim to establish a framework to classify these structures, define the gaps in current research, and spur ideas to fill those gaps. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Nanotechnology Approaches to Biology > Cells at the Nanoscale Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Actin Cytoskeleton Straddling the Immunological Synapse between Cytotoxic Lymphocytes and Cancer Cells

The immune system is a fundamental part of the tumor microenvironment. In particular, cytotoxic lymphocytes, such as cytolytic T cells and natural killer cells, control tumor growth and disease progression by interacting and eliminating tumor cells. The actin cytoskeleton of cytotoxic lymphocytes engaged in an immunological synapse has received considerable research attention. It has been recognized as a central mediator of the formation and maturation of the immunological synapse, and its signaling and cytolytic activities. In comparison, fewer studies have explored the organization and function of actin filaments on the target cancer cell side of the immunological synapse. However, there is growing evidence that the actin cytoskeleton of cancer cells also undergoes extensive remodeling upon cytotoxic lymphocyte attack, and that such remodeling can alter physical and functional interactions at the immunological synapse. In this article, we review the current knowledge of actin organization and functions at both sides of the immunological synapse between cytotoxic lymphocytes and cancer cells, with particular focus on synapse formation, signaling and cytolytic activity, and immune evasion.

First passage of molecular motors on networks of cytoskeletal filaments

Molecular motors facilitate intracellular transport through a combination of passive motion in the cytoplasm and active transport along cytoskeletal filaments. Although the motion of motors on individual filaments is often well characterized, it remains a challenge to understand their transport on networks of filaments. Here we use computer simulations of a stochastic jump process to determine first-passage times (FPTs) of a molecular motor traversing an interval containing randomly distributed filaments of fixed length. We characterize the mean first-passage time (MFPT) as a function of the number and length of filaments. Intervals containing moderate numbers of long filaments lead to the largest MFPTs with the largest relative standard deviation; in this regime, some filament configurations lead to anomalously large FPTs due to spatial regions where motors become trapped for long times. For specific filament configurations, we systematically reverse the directionality of single filaments and determine the MFPT of the perturbed configuration. Surprisingly, altering a single filament can dramatically impact the MFPT, and filaments leading to the largest changes are commonly found in different regions than the traps. We conclude by analyzing the mean square displacement of motors in unconfined systems with a large density of filaments and show that they behave diffusively at times substantially less than the MFPT to traverse the interval. However, the effective diffusion coefficient underestimates the MFPT across the bounded interval, emphasizing the importance of local configurations of filaments on first-passage properties.

Protective effects of gelsolin in acute pulmonary thromboembolism and thrombosis in the carotid artery of mice

The present study provides first evidence on the role of plasma gelsolin in protecting pulmonary thromboembolism and thrombosis in a mouse model. Gelsolin is the most abundant actin depolymerizing protein in plasma and its significantly depleted values have been reported in metabolic disorders including cardiovascular diseases and myocardial infarction. Though gelsolin replacement therapy (GRT) has been shown to be effective in some animal models, no such study has been reported for thrombotic diseases that are acutely in need of bio-therapeutics for immediate and lasting relief. Here, using mice model and recombinant human gelsolin (rhuGSN), we demonstrate the antithrombotic effect of gelsolin in ferric chloride induced thrombosis in carotid artery and thrombin induced acute pulmonary thromboembolism. In thrombosis model, arterial occlusion time was significantly enhanced upon subcutaneous (SC) treatment with 8 mg of gelsolin per mice viz. 15.83 minutes vs. 8 minutes in the placebo group. Pertinently, histopathological examination showed channel formation within the thrombi in the carotid artery following injection of gelsolin. Fluorescence molecular tomography imaging further confirmed that administration of gelsolin reduced thrombus formation following carotid artery injury. In thrombin-induced acute pulmonary thromboembolism, mice pretreated with aspirin or gelsolin showed 100 and 83.33% recovery, respectively. In contrast, complete mortality of mice was observed in vehicle treated group within 5 minutes of thrombin injection. Overall, our studies provide conclusive evidence on the thrombo-protective role of plasma gelsolin in mice model of pulmonary thromboembolism and thrombosis.

A 19‑miRNA Support Vector Machine classifier and a 6‑miRNA risk score system designed for ovarian cancer patients

Ovarian cancer (OC) is the most common gynecologic malignancy with high incidence and mortality. The present study aimed to develop approaches for determining the recurrence type and identify potential miRNA markers for OC prognosis. The miRNA expression profile of OC (the training set, including 390 samples with recurrence information) was downloaded from The Cancer Genome Atlas database. The validation sets GSE25204 and GSE27290 were obtained from the Gene Expression Omnibus database. Prescreening of clinical factors was conducted using the survival package, and the differentially expressed miRNAs (DE-miRNAs) were identified using the limma package. Using the Caret package, the optimal miRNA set was selected to build a Support Vector Machine (SVM) classifier. The miRNAs and clinical factors independently related to prognosis were analyzed using the survival package, and the risk score system was constructed. Finally, the miRNA-target regulatory network was built by Cytoscape software, and enrichment analysis was performed. There were 46 DE-miRNAs between the recurrent and non-recurrent samples. After the optimal 19-miRNA set was selected for constructing the SVM classifier, 6 DE-miRNAs (miR-193b, miR-211, miR-218, miR-505, miR-508 and miR-514) independently related to prognosis were further extracted to build the risk score system. The neoplasm cancer status was independently correlated with the prognosis and conducted with stratified analysis. Additionally, the target genes in the regulatory network were enriched in the regulation of actin cytoskeleton and the TGF-β signaling pathway. The 6-miRNA signature may serve as a potential biomarker for OC prognosis, particularlyfor recurrence.

Nuclear Actin and Actin-Binding Proteins in DNA Repair

Nuclear actin has been implicated in a variety of DNA-related processes including chromatin remodeling, transcription, replication, and DNA repair. However, the mechanistic understanding of actin in these processes has been limited, largely due to a lack of research tools that address the roles of nuclear actin specifically, that is, distinct from its cytoplasmic functions. Recent findings support a model for homology-directed DNA double-strand break (DSB) repair in which a complex of ARP2 and ARP3 (actin-binding proteins 2 and 3) binds at the break and works with actin to promote DSB clustering and homology-directed repair. Further, it has been reported that relocalization of heterochromatic DSBs to the nuclear periphery in Drosophila is ARP2/3 dependent and actin-myosin driven. Here we provide an overview of the role of nuclear actin and actin-binding proteins in DNA repair, critically evaluating the experimental tools used and potential indirect effects.

Discovery of functional interactions among actin regulators by analysis of image fluctuations in an unperturbed motile cell system

Cell migration is driven by propulsive forces derived from polymerizing actin that pushes and extends the plasma membrane. The underlying actin network is constantly undergoing adaptation to new mechano-chemical environments and intracellular conditions. As such, mechanisms that regulate actin dynamics inherently contain multiple feedback loops and redundant pathways. Given the highly adaptable nature of such a system, studies that use only perturbation experiments (e.g. knockdowns, overexpression, pharmacological activation/inhibition, etc.) are challenged by the nonlinearity and redundancy of the pathway. In these pathway configurations, perturbation experiments at best describe the function(s) of a molecular component in an adapting (e.g. acutely drug-treated) or fully adapted (e.g. permanent gene silenced) cell system, where the targeted component now resides in a non-native equilibrium. Here, we propose how quantitative live-cell imaging and analysis of constitutive fluctuations of molecular activities can overcome these limitations. We highlight emerging actin filament barbed-end biology as a prime example of a complex, nonlinear molecular process that requires a fluctuation analytic approach, especially in an unperturbed cellular system, to decipher functional interactions of barbed-end regulators, actin polymerization and membrane protrusion.This article is part of the theme issue 'Self-organization in cell biology'.

Intracellular dynamics of actin affects Borna disease virus replication in the nucleus

Borna disease virus (BoDV) is a nonsegmented, negative-strand RNA virus that uniquely replicates and establishes persistent infection in cell nucleus. Recent studies have demonstrated the presence of actin in the nucleus and its role in intranuclear phenomena such as transcription and DNA repair. Although nuclear actin is involved in the life cycle of some intranuclear DNA viruses, the interaction between BoDV and nuclear actin has not been reported. In this study, we show that the inhibition of the nucleocytoplasmic transport of actin affects the replication of BoDV in the nucleus. The knockdown of a nuclear export factor of actin, exportin 6, results in the induction of structural aberration in intranuclear viral factories of BoDV. Furthermore, the inhibition of the nuclear export of actin promotes accumulation of viral matrix protein in the cytoplasm and periphery of the infected cells. These results suggest that the dynamics of actin affect the replication of BoDV by disturbing the structure of viral factories in the nucleus.

Phosphatidylinositol-3-phosphate-mediated actin domain formation linked to DNA synthesis upon insulin treatment in rat hepatoma-derived H4IIEC3 cells

Phosphatidylinositol-3-phosphate (PI3P) is a lipid that accumulates in the early endosomal membrane, and acts as a scaffold to recruit proteins that contain a PI3P-binding domain, such as the FYVE domain. In this study, we examined the effect of PI3P depletion on the insulin response in rat hepatoma-derived H4IIEC3 cells. We found that insulin treatment induced the transient formation of an actin domain structure, a mesh-like tangled network of actin filaments where phosphorylated Akt, endosomal proteins, and PI3P accumulated. Actin domain formation was repressed by the depletion of PI3P by SAR405, an inhibitor of the class III PI3 kinase, Vps34, by the inhibition of PI3P function by the competitive binding of an excess amount of GST-fused 2xFYVE protein to intracellular PI3P, and by the use of diabetic model cells, in which PI3P was depleted. SAR405 did not affect the phosphorylation level of Akt, and the transcriptional regulation of gluconeogenic and cholesterol synthetic genes after insulin treatment. Interestingly, insulin-induced DNA synthesis was specifically inhibited by SAR405, cytochalasin B, and also in diabetic model cells. These results suggest that PI3P is required for the formation of actin domains, which affected a signaling pathway downstream of Akt associated with DNA synthesis in H4IIEC3 cells.

Unraveling the Mechanobiology of the Immune System

Cells respond and actively adapt to environmental cues in the form of mechanical stimuli. This extends to immune cells and their critical role in the maintenance of tissue homeostasis. Multiple recent studies have begun illuminating underlying mechanisms of mechanosensation in modulating immune cell phenotypes. Since the extracellular microenvironment is critical to modify cellular physiology that ultimately determines the functionality of the cell, understanding the interactions between immune cells and their microenvironment is necessary. This review focuses on mechanoregulation of immune responses mediated by macrophages, dendritic cells, and T cells, in the context of modern mechanobiology.

Discovery profiling and bioinformatics analysis of serum microRNA in Mitochondrial NeuroGastroIntestinal Encephalomyopathy (MNGIE)

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare and fatal inherited metabolic disorder due to mutations in the nuclear TYMP gene and leads to a deficiency in the enzyme thymidine phosphorylase. This results in an accumulation of the deoxynucleosides, thymidine and deoxyuridine in the cellular and extracellular compartments, ultimately leading to mitochondrial failure. The understanding of the precise molecular mechanisms that underlie the disease pathology is limited, being hampered by the rarity of the disorder. Expression profiling of serum based mircoRNAs and subsequent bioinformatical analyses provide an approach to facilitate the identity of dysregulated genes and signalling pathways potentially involved in the pathogenesis of MNGIE.

β-actin regulates a heterochromatin landscape essential for optimal induction of neuronal programs during direct reprograming

During neuronal development, β-actin serves an important role in growth cone mediated axon guidance. Consistent with this notion, in vivo ablation of the β-actin gene leads to abnormalities in the nervous system. However, whether β-actin is involved in the regulation of neuronal gene programs is not known. In this study, we directly reprogramed β-actin^+/+ WT, β-actin^+/- HET and β-actin^-/- KO mouse embryonic fibroblast (MEFs) into chemically induced neurons (CiNeurons). Using RNA-seq analysis, we profiled the transcriptome changes among the CiNeurons. We discovered that induction of neuronal gene programs was impaired in KO CiNeurons in comparison to WT ones, whereas HET CiNeurons showed an intermediate levels of induction. ChIP-seq analysis of heterochromatin markers demonstrated that the impaired expression of neuronal gene programs correlated with the elevated H3K9 and H3K27 methylation levels at gene loci in β-actin deficient MEFs, which is linked to the loss of chromatin association of the BAF complex ATPase subunit Brg1. Together, our study shows that heterochromatin alteration in β-actin null MEFs impedes the induction of neuronal gene programs during direct reprograming. These findings are in line with the notion that H3K9Me3-based heterochromatin forms a major epigenetic barrier during cell fate change.

Although β-actin plays an important role in growth cone mediated axon guidance in neurons, the potential role of β-actin in controlling neuron differentiation remains unknown. Here, we converted β-actin^+/+ WT, β-actin^+/- HET and β-actin^-/- KO mouse embryonic fibroblast (MEFs) into chemically induced neurons (CiNeurons) by direct reprograming. We found that the up-regulation of neuronal programs was impaired in β-actin^-/- CiNeurons in comparison to WT ones. β-actin^+/- HET CiNeurons showed an intermediate level of neuronal program expression, suggesting that β-actin dosage plays an important role during direct neuronal reprograming. Importantly, the impaired up-regulation of neuron-related genes was associated with the elevated H3K9 and H3K27 methylation levels at gene loci in KO MEFs. These epigenetic changes were accompanied by the impaired chromatin association of Brg1-containing chromatin remodeling BAF complex in β-actin null cells. Together our study demonstrates that β-actin is required for the optimal induction of neuronal gene programs during direct reprograming by presetting a favorable chromatin status.

Transcriptomic characterization elucidates a signaling network that controls antler growth

Deer antlers are amazing appendages with the fastest growth rate among mammalian organs. Antler growth is driven by the growth center through a modified endochondral ossification process. Thus, identification of signaling pathways functioning in antler growth center would help us to uncover the underlying molecular mechanism of rapid antler growth. Furthermore, exploring and dissecting the molecular mechanism that regulates antler growth is extremely important and helpful for identifying methods to enhance long bone growth and treat cartilage- and bone-related diseases. In this study, we build a comprehensive intercellular signaling network in antler growth centers from both the slow growth stage and rapid growth stage using a state-of-art RNA-Seq approach. This network includes differentially expressed genes that regulate the activation of multiple signaling pathways, including the regulation of actin cytoskeleton, calcium signaling, and adherens junction. These signaling pathways coordinately control multiple biological processes, including chondrocyte proliferation and differentiation, matrix homeostasis, mechanobiology, and aging processes, during antler growth in a comprehensive and efficient manner. Therefore, our study provides novel insights into the molecular mechanisms regulating antler growth and provides valuable and powerful insight for medical research on therapeutic strategies targeting skeletal disorders and related cartilage and bone diseases.

Attenuation of murine and human airway contraction by a peptide fragment of the cytoskeleton regulatory protein gelsolin

We have previously reported that mice genetically deficient in the actin binding protein gelsolin exhibit impaired airway smooth muscle (ASM) relaxation. Primary cultured ASM cells from these mice demonstrate enhanced inositol triphosphate (IP₃) synthesis and increased intracellular calcium in response to G_q-coupled agonists. We hypothesized that this was due to increased intracellular availability of unbound phosphatidylinositol 4,5-bisphosphate (PIP₂), based on the fact that gelsolin contains a short peptide region that binds PIP₂, presumably making it a less available substrate. We now questioned whether a peptide that corresponds to the PIP₂ binding region of gelsolin could modulate ASM signaling and contraction. The 10 amino acid sequence of the gelsolin peptide within the PIP₂-binding region was incubated with primary cultures of human ASM cells, and IP₃ synthesis was measured in response to a G_q-coupled agonist. Gelsolin peptide-treated cells generated less IP₃ under basal and bradykinin or acetylcholine (G_q-coupled) conditions. Acetylcholine-induced contractile force measured in isolated tracheal rings from mice and human tracheal muscle strips in organ baths was attenuated in the presence of the gelsolin peptide. The gelsolin peptide also attenuated methacholine-induced airway constriction in murine precision-cut lung slices. Furthermore, this peptide fragment delivered to the respiratory system of mice via nebulization attenuated subsequent methacholine-induced increases in airway resistance in vivo. The current study demonstrates that introduction of this small gelsolin peptide into the airway may be a novel therapeutic option in bronchoconstrictive diseases.

A proteomics study to explore the role of adsorbed serum proteins for PC12 cell adhesion and growth on chitosan and collagen/chitosan surfaces

The aim of this article is to apply proteomics in the comparison of the molecular mechanisms of PC12 cell adhesion and growth mediated by the adsorbed serum proteins on the surfaces of chitosan and collagen/chitosan films. First, the chitosan and the collagen/chitosan films were prepared by spin coating; and their surface morphologies were characterized by scanning electron microscopy, X-ray energy dispersive spectroscopy, contact angle measurement and Fourier transform infrared spectroscopy. Subsequently, cell proliferation experiments on two materials were performed and the dynamic curves of protein adsorption on their surfaces were measured. Then, proteomics and bioinformatics were used to analyze and compare the adsorbed serum proteins on the surfaces of two biomaterials; and their effects on cell adhesion were discussed. The results showed that the optimum concentration of chitosan film was 2% w/v. When compared with chitosan film, collagen/chitosan film promoted the growth and proliferation of PC12 cells more significantly. Although the dynamic curves showed no significant difference in the total amount of the adsorbed proteins on both surfaces, proteomics and bioinformatics analyses revealed a difference in protein types: the chitosan surface adsorbed more vitronectin whereas collagen/chitosan surface adsorbed more fibronectin 1 and contained more cell surface receptor binding sites and more Leu-Asp-Val sequences in its surface structure; the collagen/chitosan surface were more conducive to promoting cell adhesion and growth.

NOSTRIN: A novel modulator of trophoblast giant cell differentiation

Differentiation-dependent expression of NOSTRIN in murine trophoblast cells prompted investigation on NOSTRIN's function in trophoblast differentiation. We show here that NOSTRIN levels increased in both mouse and rat placenta during gestation. NOSTRIN expression was not co-related to expression of eNOS precluding its eNOS mediated function. NOSTRIN transcripts were identified in trophoblast cells of the placenta, predominantly in trophoblast giant cells (TGC). Precocious over-expression of NOSTRIN during differentiation of trophoblast stem cells led to up-regulation of genetic markers associated with invasion (Prl4a1, Prl2a1) and TGC formation (Prl2c2, Prl3d1, Prl3b1). The functional consequence of NOSTRIN over-expression was increased TGC formation and trophoblast cell invasion. Furthermore, number of polyploid TGCs that arise by endoreduplication, were higher in presence of NOSTRIN. Early induction of NOSTRIN was associated with substantial decrease in G/F actin ratio and augmentation of N-WASP-Dynamin-NOSTRIN ternary complex formation that might be partially responsible for nucleation of actin filaments. NOSTRIN also formed a complex with Cdk1 and increased phosphorylation of T14 and Y15 residues that inhibits cytokinesis. Interestingly, SH3 domain deleted NOSTRIN was ineffective in eliciting NOSTRIN's function in differentiating trophoblast cells. These findings demonstrate that NOSTRIN potentiates trophoblast differentiation towards TGC trajectory that is critical for hemochorial placentation.

Eukaryotic Cell Dynamics from Crawlers to Swimmers

Movement requires force transmission to the environment, and motile cells are robustly, though not elegantly, designed nanomachines that often can cope with a variety of environmental conditions by altering the mode of force transmission used. As with humans, the available modes range from momentary attachment to a substrate when crawling, to shape deformations when swimming, and at the cellular level this involves sensing the mechanical properties of the environment and altering the mode appropriately. While many types of cells can adapt their mode of movement to their microenvironment (ME), our understanding of how they detect, transduce and process information from the ME to determine the optimal mode is still rudimentary. The shape and integrity of a cell is determined by its cytoskeleton (CSK), and thus the shape changes that may be required to move involve controlled remodeling of the CSK. Motion in vivo is often in response to extracellular signals, which requires the ability to detect such signals and transduce them into the shape changes and force generation needed for movement. Thus the nanomachine is complex, and while much is known about individual components involved in movement, an integrated understanding of motility in even simple cells such as bacteria is not at hand. In this review we discuss recent advances in our understanding of cell motility and some of the problems remaining to be solved.

WDR1 Promotes Cell Growth and Migration and Contributes to Malignant Phenotypes of Non-small Cell Lung Cancer through ADF/cofilin-mediated Actin Dynamics

The characteristic of carcinoma is cell migration and invasion, which involve in strong actin dynamics. Regulations of actin dynamics have been implicated in cancer cell migration and tumor progression. WDR1 (WD-repeat domain 1) is a major cofactor of the actin depolymerizing factor (ADF)/cofilin, strongly accelerating ADF/cofilin-mediated actin disassembly. The role of WDR1 in non-small cell lung cancer (NSCLC) progression has been unknown. Here, we show that the expression levels of WDR1 are increased in human NSCLC tissues compared with adjacent non-tumor tissues, and high WDR1 level correlates with poor prognosis in NSCLC patients. Knockdown of WDR1 in NSCLC cells significantly inhibits cell migration, invasion, EMT process and tumor cell growth in vitro and in vivo. Otherwise, overexpression of WDR1 promotes NSCLC cell proliferation and migration. Mechanically, our data suggested WDR1 regulated tumor cells proliferation and migration might through actin cytoskeleton-mediated regulation of YAP, and we demonstrated that WDR1 contributes to NSCLC progression through ADF/cofilin-mediated actin disassembly. Our findings implicate that the ADF/cofilin-WDR1-actin axis as an activator of malignant phenotype that will be a promising therapeutic target in lung cancer.

Retinal microglia - A key player in healthy and diseased retina

Microglia, the resident immune cells of the brain and retina, are constantly engaged in the surveillance of their surrounding neural tissue. During embryonic development they infiltrate the retinal tissues and participate in the phagocytosis of redundant neurons. The contribution of microglia in maintaining the purposeful and functional histo-architecture of the adult retina is indispensable. Within the retinal microenvironment, robust microglial activation is elicited by subtle changes caused by extrinsic and intrinsic factors. When there is a disturbance in the cell-cell communication between microglia and other retinal cells, for example in retinal injury, the activated microglia can manifest actions that can be detrimental. This is evidenced by activated microglia secreting inflammatory mediators that can further aggravate the retinal injury. Microglial activation as a harbinger of a variety of retinal diseases is well documented by many studies. In addition, a change in the microglial phenotype which may be associated with aging, may predispose the retina to age-related diseases. In light of the above, the focus of this review is to highlight the role played by microglia in the healthy and diseased retina, based on findings of our own work and from that of others.

Abnormalities in Skeletal Muscle Myogenesis, Growth, and Regeneration in Myotonic Dystrophy

Myotonic dystrophy type 1 (DM1) and 2 (DM2) are autosomal dominant degenerative neuromuscular disorders characterized by progressive skeletal muscle weakness, atrophy, and myotonia with progeroid features. Although both DM1 and DM2 are characterized by skeletal muscle dysfunction and also share other clinical features, the diseases differ in the muscle groups that are affected. In DM1, distal muscles are mainly affected, whereas in DM2 problems are mostly found in proximal muscles. In addition, manifestation in DM1 is generally more severe, with possible congenital or childhood-onset of disease and prominent CNS involvement. DM1 and DM2 are caused by expansion of (CTG•CAG)n and (CCTG•CAGG)n repeats in the 3' non-coding region of DMPK and in intron 1 of CNBP, respectively, and in overlapping antisense genes. This critical review will focus on the pleiotropic problems that occur during development, growth, regeneration, and aging of skeletal muscle in patients who inherited these expansions. The current best-accepted idea is that most muscle symptoms can be explained by pathomechanistic effects of repeat expansion on RNA-mediated pathways. However, aberrations in DNA replication and transcription of the DM loci or in protein translation and proteome homeostasis could also affect the control of proliferation and differentiation of muscle progenitor cells or the maintenance and physiological integrity of muscle fibers during a patient's lifetime. Here, we will discuss these molecular and cellular processes and summarize current knowledge about the role of embryonic and adult muscle-resident stem cells in growth, homeostasis, regeneration, and premature aging of healthy and diseased muscle tissue. Of particular interest is that also progenitor cells from extramuscular sources, such as pericytes and mesoangioblasts, can participate in myogenic differentiation. We will examine the potential of all these types of cells in the application of regenerative medicine for muscular dystrophies and evaluate new possibilities for their use in future therapy of DM.