Although more difficult to detect than in the cytoplasm, it is now clear that actin polymerization occurs in the nucleus and that it plays a role in the specific processes of the nucleus such as transcription, replication, and DNA repair. A number of studies suggest that nuclear actin polymerization is promoting precise DNA repair by homologous recombination, which could potentially be of help for precise genome editing and gene therapy. This review summarizes the findings and describes the challenges and chances in the field.

Cells need to migrate along gradients of chemicals (chemotaxis) in the course of development, wound healing, or immune responses. Neutrophils are prototypical migratory cells that are rapidly recruited to injured or infected tissues from the bloodstream. Their chemotaxis to these inflammatory sites involves changes in cytoskeletal dynamics in response to gradients of chemicals produced therein. Neutrophil chemotaxis has been largely studied in vitro; few assays have been developed to monitor gradient responses in complex living tissues. Here, we describe a laser-wound assay to generate focal injury in zebrafish larvae and monitor changes in behaviour and cytoskeletal dynamics. The first step is to cross adult fish and collect and rear embryos expressing a relevant fluorescent reporter (for example, Lifeact-mRuby, which labels dynamic actin) to an early larval stage. Subsequently, larvae are mounted and prepared for live imaging and wounding under a two-photon microscope. Finally, the resulting data are processed and used for cell segmentation and quantification of actin dynamics. Altogether, this assay allows the visualisation of cellular dynamics in response to acute injury at high resolution and can be combined with other manipulations, such as genetic or chemical perturbations. Key features • This protocol is designed to trigger laser wound in zebrafish larvae using two-photon intravital microscopy. • The ability to wound while imaging makes it possible to monitor the behaviour and actin changes of the cells immediately after gradient exposure. • The protocol requires a two-photon microscope for best results. Compared with one-photon laser wounding, the injury is more precise and has better tissue penetration. • The focal nature of the wounds is suitable for studies of neutrophil swarming/aggregation and can be further adapted to infectious settings.

The serine/threonine kinase, PINK1, and the E3 ubiquitin ligase, PRKN/Parkin facilitate LC3-dependent autophagosomal encasement and lysosomal clearance of dysfunctional mitochondria, and defects in this pathway contribute to the pathogenesis of numerous cardiometabolic and neurological diseases. Although dynamic actin remodeling has recently been shown to play an important role in governing spatiotemporal control of mitophagy, the mechanisms remain unclear. We recently found that the RhoGAP, ARHGAP26/GRAF1 is a PRKN-binding protein that is rapidly recruited to damaged mitochondria where upon phosphorylation by PINK1 it serves to coordinate phagophore capture by regulating mitochondrial-associated actin remodeling and by facilitating PRKN-LC3 interactions. Because ARHGAP26 phosphorylation on PINK1-dependent sites is dysregulated in human heart failure and ARHGAP26 depletion in mouse hearts blunts mitochondrial clearance and attenuates compensatory metabolic adaptations to stress, this enzyme may be a tractable target to treat the many diseases associated with mitochondrial dysfunction.

Dysregulation of cancer cell motility is a key driver of invasion and metastasis. High dysadherin expression in cancer cells is correlated with invasion and metastasis. Here, we found the molecular mechanism by which dysadherin regulates the migration and invasion of colon cancer (CC). Comprehensive analysis using single-cell RNA sequencing data from CC patients revealed that high dysadherin expression in cells is linked to cell migration-related gene signatures. We confirmed that the deletion of dysadherin in tumor cells hindered local invasion and distant migration using in vivo tumor models. In this context, by performing cell morphological analysis, we found that aberrant cell migration resulted from impaired actin dynamics, focal adhesion turnover and protrusive structure formation upon dysadherin expression. Mechanistically, the activation of focal adhesion kinase (FAK) was observed in dysadherin-enriched cells. The dysadherin/FAK axis enhanced cell migration and invasion by activating the FAK downstream cascade, which includes the Rho family of small GTPases. Overall, this study illuminates the role of dysadherin in modulating cancer cell migration by forcing actin dynamics and protrusive structure formation via FAK signaling, indicating that targeting dysadherin may be a potential therapeutic strategy for CC patients.

Quantum dots (QDs) are a novel type of nanomaterial that has unique optical and physical characteristics. As such, QDs are highly desired because of their potential to be used in both biomedical and industrial applications. However, the mass adoption of QDs usage has raised concerns among the scientific community regarding QDs\' toxicity. Although many papers have reported the negative impact of QDs on a cellular level, the exact mechanism of the QDs\' toxicity is still unclear. In this investigation, we study the adverse effects of QDs by focusing on one of the most important cellular processes: actin polymerization and depolymerization. Our results showed that QDs act in a biphasic manner where lower concentrations of QDs stimulate the polymerization of actin, while high concentrations of QDs inhibit actin polymerization. Furthermore, we found that QDs can bind to filamentous actin (F-actin) and cause bundling of the filament while also promoting actin depolymerization. Through this study, we found a novel mechanism in which QDs negatively influence cellular processes and exert toxicity.

The eukaryotic cytoskeleton is a complex scaffold consisting of actin filaments, intermediate filaments, and microtubules. Although fungi and plants lack intermediate filaments, their dynamic structural network of actin filaments and microtubules regulates cell shape, division, polarity, and vesicular trafficking. However, the specialized functions of the cytoskeleton during plant-fungus interactions remain elusive. Recent reports demonstrate that the plant cytoskeleton responds to signal cues and pathogen invasion through remodeling, thereby coordinating immune receptor trafficking, membrane microdomain formation, aggregation of organelles, and transport of defense compounds. Emerging evidence also suggests that cytoskeleton remodeling further regulates host immunity by triggering salicylic acid signaling, reactive oxygen species generation, and pathogenesis-related gene expression. During host invasion, fungi undergo systematic cytoskeleton remodeling, which is crucial for successful host penetration and colonization. Furthermore, phytohormones act as an essential regulator of plant cytoskeleton dynamics and are frequently targeted by fungal effectors to disrupt the host\'s growth-defense balance. This review discusses recent advances in the understanding of cytoskeleton dynamics during plant-fungus interactions and provides novel insights into the relationship between phytohormones and cytoskeleton remodeling upon pathogen attack. We also highlight the importance of fungal cytoskeleton rearrangements during host colonization and suggest directions for future investigations in this field.

Airway remodeling is a cardinal feature of asthma, associated with increased airway smooth muscle (ASM) cell mass and upregulation of extracellular matrix deposition. Exaggerated ASM cell migration contributes to excessive ASM mass. Previously, we demonstrated the alleviating role of Kp (kisspeptin) receptor (KISS1R) activation by Kp-10 in mitogen (PDGF [platelet-derived growth factor])-induced human ASM cell proliferation in vitro and airway remodeling in vivo in a mouse model of asthma. Here, we examined the mechanisms by which KISS1R activation regulates mitogen-induced ASM cell migration. KISS1R activation using Kp-10 significantly inhibited PDGF-induced ASM cell migration, further confirmed using KISS1R shRNA. Furthermore, KISS1R activation modulated F/G actin dynamics and the expression of promigration proteins like CDC42 (cell division control protein 42) and cofilin. Mechanistically, we observed reduced ASM RhoA-GTPAse with KISS1R activation. The antimigratory effect of KISS1R was abolished by PKA (protein kinase A)-inhibitory peptide. Conversely, KISS1R activation significantly increased cAMP and phosphorylation of CREB (cAMP-response element binding protein) in PDGF-exposed ASM cells. Overall, these results highlight the alleviating properties of Kp-10 in the context of airway remodeling.

Synapses change their weights in response to neuronal activity and in turn, neuronal networks alter their response properties and ultimately allow the brain to store information as memories. As for memories, not all events are maintained over time. Maintenance of synaptic plasticity depends on the interplay between functional changes at synapses and the synthesis of plasticity-related proteins that are involved in stabilizing the initial functional changes. Different forms of synaptic plasticity coexist in time and across the neuronal dendritic area. Thus, homosynaptic plasticity refers to activity-dependent synaptic modifications that are input-specific, whereas heterosynaptic plasticity relates to changes in non-activated synapses. Heterosynaptic forms of plasticity, such as synaptic cooperation and competition allow neurons to integrate events that occur separated by relatively large time windows, up to one hour. Here, we show that activation of Cdc42, a Rho GTPase that regulates actin cytoskeleton dynamics, is necessary for the maintenance of long-term potentiation (LTP) in a time-dependent manner. Inhibiting Cdc42 activation does not alter the time-course of LTP induction and its initial expression but blocks its late maintenance. We show that Cdc42 activation is involved in the phosphorylation of cofilin, a protein involved in modulating actin filaments and that weak and strong synaptic activation leads to similar levels on cofilin phosphorylation, despite different levels of LTP expression. We show that Cdc42 activation is required for synapses to interact by cooperation or competition, supporting the hypothesis that modulation of the actin cytoskeleton provides an activity-dependent and time-restricted permissive state of synapses allowing synaptic plasticity to occur. We found that under competition, the sequence in which synapses are activated determines the degree of LTP destabilization, demonstrating that competition is an active destabilization process. Taken together, we show that modulation of actin cytoskeleton by Cdc42 activation is necessary for the expression of homosynaptic and heterosynaptic forms of plasticity. Determining the temporal and spatial rules that determine whether synapses cooperate or compete will allow us to understand how memories are associated.

Alzheimer\'s disease (AD) is distinguished by extracellular accumulation of amyloid-beta plaques and intracellular neurofibrillary tangles of Tau. Pathogenic Tau species are also known to display \"prion-like propagation,\" which explains their presence in extracellular spaces as well. Glial population, especially microglia, tend to proclaim neuroinflammatory condition, disrupted signaling mechanisms, and cytoskeleton deregulation in AD. Omega-3 fatty acids play a neuroprotective role in the brain, which can trigger the anti-inflammatory pathways as well as actin dynamics in the cells. Improvement of cytoskeletal assembly mechanism by omega-3 fatty acids would regulate the other signaling cascades in the cells, leading to refining clearance of extracellular protein burden in AD. In this study, we focused on analyzing the ability of α-linolenic acid (ALA) as a regulator of actin dynamics to balance the signaling pathways in microglia, including endocytosis of extracellular Tau burden in AD.

Vision is formed by the transmission of light stimuli to the brain through axons extending from photoreceptor cells. Damage to these axons leads to loss of vision. Despite research on neural circuit regeneration through transplantation, achieving precise axon projection remains challenging. To achieve optic nerve regeneration by transplantation, we employed the Drosophila visual system. We previously established a transplantation method for Drosophila utilizing photoreceptor precursor cells extracted from the eye disc. However, little axonal elongation of transplanted cells into the brain, the lamina, was observed. We verified axonal elongation to the lamina by modifying the selection process for transplanted cells. Moreover, we focused on N-cadherin (Ncad), a cell adhesion factor, and Twinstar (Tsr), which has been shown to promote actin reorganization and induce axon elongation in damaged nerves. Overexpression of Ncad and tsr promoted axon elongation to the lamina, along with presynaptic structure formation in the elongating axons. Furthermore, overexpression of Neurexin-1 (Nrx-1), encoding a protein identified as a synaptic organizer, was found to not only promote presynapse formation but also enhance axon elongation. By introducing Ncad, tsr, and Nrx-1, we not only successfully achieved axonal projection of transplanted cells to the brain beyond the retina, but also confirmed the projection of transplanted cells into a deeper ganglion, the medulla. The present study offers valuable insights to realize regeneration through transplantation in a more complex nervous system.