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Developmental Biology Jun 2024In most mollusks (conchiferans), the early tissue responsible for shell development, namely, the shell field, shows a common process of invagination during...
In most mollusks (conchiferans), the early tissue responsible for shell development, namely, the shell field, shows a common process of invagination during morphogenesis. Moreover, lines of evidence indicated that shell field invagination is not an independent event, but an integrated output reflecting the overall state of shell field morphogenesis. Nevertheless, the underlying mechanisms of this conserved process remain largely unknown. We previously found that actomyosin networks (regularly organized filamentous actin (F-actin) and myosin) may play essential roles in this process by revealing the evident aggregation of F-actin in the invaginated region and demonstrating that nonmuscle myosin II (NM II) is required for invagination in the gastropod Lottia peitaihoensis (= Lottia goshimai). Here, we investigated the roles of the Rho family of small GTPases (RhoA, Rac1, and Cdc42) to explore the upstream regulators of actomyosin networks. Functional assays using small molecule inhibitors suggested that Cdc42 modulates key events of shell field morphogenesis, including invagination and cell rearrangements, while the roles of RhoA and Rac1 may be nonspecific or negligible. Further investigations revealed that the Cdc42 protein was concentrated on the apical side of shell field cells and colocalized with F-actin aggregation. The aggregation of these two molecules could be prevented by treatment with Cdc42 inhibitors. These findings suggest a possible regulatory cascade of shell field morphogenesis in which Cdc42 recruits F-actin (actomyosin networks) on the apical side of shell field cells, which then generates resultant mechanical forces that mediate correct shell field morphogenesis (cell shape changes, invagination and cell rearrangement). Our results emphasize the roles of the cytoskeleton in early shell development and provide new insights into molluscan shell evolution.
PubMed: 38942110
DOI: 10.1016/j.ydbio.2024.06.012 -
Journal of Cell Science Jun 2024Desmosomes are relatives of ancient cadherin-based junctions, which emerged late in evolution to ensure the structural integrity of vertebrate tissues by coupling the... (Review)
Review
Desmosomes are relatives of ancient cadherin-based junctions, which emerged late in evolution to ensure the structural integrity of vertebrate tissues by coupling the intermediate filament cytoskeleton to cell-cell junctions. Their ability to dynamically counter the contractile forces generated by actin-associated adherens junctions is particularly important in tissues under high mechanical stress, such as the skin and heart. Much more than the simple cellular 'spot welds' depicted in textbooks, desmosomes are in fact dynamic structures that can sense and respond to changes in their mechanical environment and external stressors like ultraviolet light and pathogens. These environmental signals are transmitted intracellularly via desmosome-dependent mechanochemical pathways that drive the physiological processes of morphogenesis and differentiation. This Cell Science at a Glance article and the accompanying poster review desmosome structure and assembly, highlight recent insights into how desmosomes integrate chemical and mechanical signaling in the epidermis, and discuss desmosomes as targets in human disease.
Topics: Desmosomes; Humans; Animals; Epidermis
PubMed: 38940346
DOI: 10.1242/jcs.261899 -
Journal of Integrative Neuroscience Jun 2024Alcohol abuse, a prevalent global health issue, is associated with the onset of cognitive impairment and neurodegeneration. Actin filaments (F-actin) and microtubules...
BACKGROUND
Alcohol abuse, a prevalent global health issue, is associated with the onset of cognitive impairment and neurodegeneration. Actin filaments (F-actin) and microtubules (MTs) polymerized from monomeric globular actin (G-actin) and tubulin form the structural basis of the neuronal cytoskeleton. Precise regulation of the assembly and disassembly of these cytoskeletal proteins, and their dynamic balance, play a pivotal role in regulating neuronal morphology and function. Nevertheless, the effect of prolonged alcohol exposure on cytoskeleton dynamics is not fully understood. This study investigates the chronic effects of alcohol on cognitive ability, neuronal morphology and cytoskeleton dynamics in the mouse hippocampus.
METHODS
Mice were provided access to 5% (v/v) alcohol in drinking water and were intragastrically administered 30% (v/v, 6.0 g/kg/day) alcohol for six weeks during adulthood. Cognitive functions were then evaluated using the Y maze, novel object recognition and Morris water maze tests. Hippocampal histomorphology was assessed through hematoxylin-eosin (HE) and Nissl staining. The polymerized and depolymerized states of actin cytoskeleton and microtubules were separated using two commercial assay kits and quantified by Western blot analysis.
RESULTS
Mice chronically exposed to alcohol exhibited significant deficits in spatial and recognition memory as evidenced by behavioral tests. Histological analysis revealed notable hippocampal damage and neuronal loss. Decreased ratios of F-actin/G-actin and MT/tubulin, along with reduced levels of polymerized F-actin and MTs, were found in the hippocampus of alcohol-treated mice.
CONCLUSIONS
Our findings suggest that chronic alcohol consumption disrupted the assembly of the actin cytoskeleton and MTs in the hippocampus, potentially contributing to the cognitive deficits and pathological injury induced by chronic alcohol intoxication.
Topics: Animals; Hippocampus; Microtubules; Actin Cytoskeleton; Male; Ethanol; Mice; Mice, Inbred C57BL; Central Nervous System Depressants; Disease Models, Animal; Behavior, Animal
PubMed: 38940085
DOI: 10.31083/j.jin2306118 -
Nature Communications Jun 2024Flowering plants rely on the polarized growth of pollen tubes to deliver sperm cells (SCs) to the embryo sac for double fertilization. In pollen, the vegetative nucleus...
Flowering plants rely on the polarized growth of pollen tubes to deliver sperm cells (SCs) to the embryo sac for double fertilization. In pollen, the vegetative nucleus (VN) and two SCs form the male germ unit (MGU). However, the mechanism underlying directional transportation of MGU is not well understood. In this study, we provide the first full picture of the dynamic interplay among microtubules, actin filaments, and MGU during pollen germination and tube growth. Depolymerization of microtubules and inhibition of kinesin activity result in an increased velocity and magnified amplitude of VN's forward and backward movement. Pharmacological washout experiments further suggest that microtubules participate in coordinating the directional movement of MGU. In contrast, suppression of the actomyosin system leads to a reduced velocity of VN mobility but without a moving pattern change. Moreover, detailed observation shows that the direction and velocity of VN's movement are in close correlations with those of the actomyosin-driven cytoplasmic streaming surrounding VN. Therefore, we propose that while actomyosin-based cytoplasmic streaming influences on the oscillational movement of MGU, microtubules and kinesins avoid MGU drifting with the cytoplasmic streaming and act as the major regulator for fine-tuning the proper positioning and directional migration of MGU in pollen.
Topics: Microtubules; Actin Cytoskeleton; Kinesins; Pollen; Actomyosin; Pollen Tube; Cell Nucleus; Arabidopsis; Cytoplasmic Streaming; Germination
PubMed: 38937444
DOI: 10.1038/s41467-024-49323-9 -
Cellular Signalling Jun 2024Tumor-associated macrophages (TAMs) secrete cytokines, chemokines, and growth factors in the tumor microenvironment (TME) to support cancer progression. Higher TAM...
Tumor-associated macrophages (TAMs) secrete cytokines, chemokines, and growth factors in the tumor microenvironment (TME) to support cancer progression. Higher TAM infiltration in the breast TME is associated with a poor prognosis. Previous studies have demonstrated the role of macrophages in stimulating long-range intercellular bridges referred to as tunneling nanotubes (TNTs) in cancer cells. Intercellular communication between cancer cells via TNTs promotes cancer growth, invasion, metastasis, and therapy resistance. Given the important role of TNTs and macrophages in cancer, the role of macrophage-induced TNTs in chemotherapy drug doxorubicin resistance is not known. Furthermore, the mechanism of macrophage-mediated TNT formation is elusive. In this study, it is shown that the macrophage-conditioned medium (MΦCM) partially mimicked inflammatory TME, induced an EMT phenotype, and increased migration in MCF-7 breast cancer cells. Additionally, secreted proteins in MΦCM induced TNT formation in MCF-7 cells, which led to increased resistance to doxorubicin. Transcriptomic analysis of MΦCM-treated MCF-7 cells showed enrichment of the NF-κB and focal adhesion pathways, as well as upregulation of genes involved in EMT, extracellular remodeling, and actin cytoskeleton reorganization. Interestingly, inhibitors of PKC, Src, NF-κB, and p38 decreased macrophage-induced TNT formation in MCF-7 cells. These results reveal the novel role of PKC and Src in inducing TNT formation in cancer cells and suggest that inhibition of PKC and Src activity may likely contribute to reduced macrophage-breast cancer cell interaction and the potential therapeutic strategy of cancer.
PubMed: 38936787
DOI: 10.1016/j.cellsig.2024.111274 -
Naunyn-Schmiedeberg's Archives of... Jun 2024The dreaded nosocomial pathogen Clostridioides difficile causes diarrhea and severe inflammation of the colon, especially after the use of certain antibiotics. The...
The dreaded nosocomial pathogen Clostridioides difficile causes diarrhea and severe inflammation of the colon, especially after the use of certain antibiotics. The bacterium releases two deleterious toxins, TcdA and TcdB, into the gut, which are mainly responsible for the symptoms of C. difficile-associated diseases (CDADs). Both toxins are capable of entering independently into various host cells, e.g., intestinal epithelial cells, where they mono-O-glucosylate and inactivate Rho and/or Ras GTPases, important molecular switches for various cellular functions. We have shown recently that the cellular uptake of the Clostridioides difficile toxins TcdA and TcdB (TcdA/B) is inhibited by the licensed class III antiarrhythmic drug amiodarone (Schumacher et al. in Gut Microbes 15(2):2256695, 2023). Mechanistically, amiodarone delays the cellular uptake of both toxins into target cells most likely by lowering membrane cholesterol levels and by interfering with membrane insertion and/or pore formation of TcdA/B. However, serious side effects, such as thyroid dysfunction and severe pulmonary fibrosis, limit the clinical use of amiodarone in patients with C. difficile infection (CDI). For that reason, we aimed to test whether dronedarone, an amiodarone derivative with a more favorable side effect profile, is also capable of inhibiting TcdA/B. To this end, we tested in vitro with various methods the impact of dronedarone on the intoxication of Vero and CaCo-2 cells with TcdA/B. Importantly, preincubation of both cell lines with dronedarone for 1 h at concentrations in the low micromolar range rendered the cells less sensitive toward TcdA/B-induced Rac1 glucosylation, collapse of the actin cytoskeleton, cell rounding, and cytopathic effects, respectively. Our study points toward the possibility of repurposing the already approved drug dronedarone as the preferable safer-to-use alternative to amiodarone for inhibiting TcdA/B in the (supportive) therapy of CDADs.
PubMed: 38935126
DOI: 10.1007/s00210-024-03248-8 -
Biochemical Society Transactions Jun 2024Macropinocytosis is a broadly conserved endocytic process discovered nearly 100 years ago, yet still poorly understood. It is prominent in cancer cell feeding, immune...
Macropinocytosis is a broadly conserved endocytic process discovered nearly 100 years ago, yet still poorly understood. It is prominent in cancer cell feeding, immune surveillance, uptake of RNA vaccines and as an invasion route for pathogens. Macropinocytic cells extend large cups or flaps from their plasma membrane to engulf droplets of medium and trap them in micron-sized vesicles. Here they are digested and the products absorbed. A major problem - discussed here - is to understand how cups are shaped and closed. Recently, lattice light-sheet microscopy has given a detailed description of this process in Dictyostelium amoebae, leading to the 'stalled-wave' model for cup formation and closure. This is based on membrane domains of PIP3 and active Ras and Rac that occupy the inner face of macropinocytic cups and are readily visible with suitable reporters. These domains attract activators of dendritic actin polymerization to their periphery, creating a ring of protrusive F-actin around themselves, thus shaping the walls of the cup. As domains grow, they drive a wave of actin polymerization across the plasma membrane that expands the cup. When domains stall, continued actin polymerization under the membrane, combined with increasing membrane tension in the cup, drives closure at lip or base. Modelling supports the feasibility of this scheme. No specialist coat proteins or contractile activities are required to shape and close cups: rings of actin polymerization formed around PIP3 domains that expand and stall seem sufficient. This scheme may be widely applicable and begs many biochemical questions.
PubMed: 38934501
DOI: 10.1042/BST20231426 -
Viruses May 2024Hepatitis delta virus (HDV), an RNA virus with two forms of the delta antigen (HDAg), relies on hepatitis B virus (HBV) for envelope proteins essential for hepatocyte...
Hepatitis delta virus (HDV), an RNA virus with two forms of the delta antigen (HDAg), relies on hepatitis B virus (HBV) for envelope proteins essential for hepatocyte entry. Hepatocellular carcinoma (HCC) ranks third in global cancer deaths, yet HDV's involvement remains uncertain. Among 300 HBV-associated HCC serum samples from Taiwan's National Health Research Institutes, 2.7% (8/300) tested anti-HDV positive, with 62.7% (5/8) of these also HDV RNA positive. Genotyping revealed HDV-2 in one sample, HDV-4 in two, and two samples showed mixed HDV-2/HDV-4 infection with RNA recombination. A mixed-genotype infection revealed novel mutations at the polyadenylation signal, coinciding with the ochre termination codon for the L-HDAg. To delve deeper into the possible oncogenic properties of HDV-2, the predominant genotype in Taiwan, which was previously thought to be less associated with severe disease outcomes, an HDV-2 cDNA clone was isolated from HCC for study. It demonstrated a replication level reaching up to 74% of that observed for a widely used HDV-1 strain in transfected cultured cells. Surprisingly, both forms of HDV-2 HDAg promoted cell migration and invasion, affecting the rearrangement of actin cytoskeleton and the expression of epithelial-mesenchymal transition markers. In summary, this study underscores the prevalence of HDV-2, HDV-4, and their mixed infections in HCC, highlighting the genetic diversity in HCC as well as the potential role of both forms of the HDAg in HCC oncogenesis.
Topics: Carcinoma, Hepatocellular; Hepatitis Delta Virus; Humans; Liver Neoplasms; Genetic Variation; Genotype; Male; Middle Aged; Carcinogenesis; Female; Taiwan; Evolution, Molecular; Virus Replication; Phylogeny; RNA, Viral; Hepatitis D; Aged; Hepatitis B virus
PubMed: 38932110
DOI: 10.3390/v16060817 -
Plants (Basel, Switzerland) Jun 2024Abiotic stress significantly affects plant growth and has devastating effects on crop production. Drought stress is one of the main abiotic stressors. Actin is a major...
Abiotic stress significantly affects plant growth and has devastating effects on crop production. Drought stress is one of the main abiotic stressors. Actin is a major component of the cytoskeleton, and actin-depolymerizing factors (ADFs) are conserved actin-binding proteins in eukaryotes that play critical roles in plant responses to various stresses. In this study, we found that , an gene from the soybean , showed drastic upregulation under drought stress. Subcellular localization experiments in tobacco epidermal cells and tobacco protoplasts showed that GmADF13 was localized in the nucleus and cytoplasm. We characterized its biological function in transgenic and hairy root composite soybean plants. plants transformed with displayed a more robust drought tolerance than wild-type plants, including having a higher seed germination rate, longer roots, and healthy leaves under drought conditions. Similarly, -overexpressing (OE) soybean plants generated via the -mediated transformation of the hairy roots showed an improved drought tolerance. Leaves from OE plants showed higher relative water, chlorophyll, and proline contents, had a higher antioxidant enzyme activity, and had decreased malondialdehyde, hydrogen peroxide, and superoxide anion levels compared to those of control plants. Furthermore, under drought stress, OE activated the transcription of several drought-stress-related genes, such as , , , , and . Thus, is a positive regulator of the drought stress response, and it may play an essential role in plant growth under drought stress conditions. These results provide new insights into the functional elucidation of soybean . They may be helpful for breeding new soybean cultivars with a strong drought tolerance and further understanding how help plants adapt to abiotic stress.
PubMed: 38931083
DOI: 10.3390/plants13121651 -
International Journal of Molecular... Jun 2024Arc (also known as Arg3.1) is an activity-dependent immediate early gene product enriched in neuronal dendrites. Arc plays essential roles in long-term potentiation,...
Arc (also known as Arg3.1) is an activity-dependent immediate early gene product enriched in neuronal dendrites. Arc plays essential roles in long-term potentiation, long-term depression, and synaptic scaling. Although its mechanisms of action in these forms of synaptic plasticity are not completely well established, the activities of Arc include the remodeling of the actin cytoskeleton, the facilitation of AMPA receptor (AMPAR) endocytosis, and the regulation of the transcription of AMPAR subunits. In addition, Arc has sequence and structural similarity to retroviral Gag proteins and self-associates into virus-like particles that encapsulate mRNA and perhaps other cargo for intercellular transport. Each of these activities is likely to be influenced by Arc's reversible self-association into multiple oligomeric species. Here, we used mass photometry to show that Arc exists predominantly as monomers, dimers, and trimers at approximately 20 nM concentration in vitro. Fluorescence fluctuation spectroscopy revealed that Arc is almost exclusively present as low-order (monomer to tetramer) oligomers in the cytoplasm of living cells, over a 200 nM to 5 μM concentration range. We also confirmed that an α-helical segment in the N-terminal domain contains essential determinants of Arc's self-association.
Topics: Protein Multimerization; Humans; Cytoskeletal Proteins; Nerve Tissue Proteins; Animals
PubMed: 38928159
DOI: 10.3390/ijms25126454