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Development (Cambridge, England) Oct 2023Myosins are evolutionarily conserved motor proteins that interact with actin filaments to regulate organelle transport, cytoplasmic streaming and cell growth....
Myosins are evolutionarily conserved motor proteins that interact with actin filaments to regulate organelle transport, cytoplasmic streaming and cell growth. Plant-specific class XI myosin proteins direct cell division and root organogenesis. However, the roles of plant-specific class VIII myosin proteins in plant growth and development are less understood. Here, we investigated the function of an auxin-regulated class VIII myosin, Arabidopsis thaliana MYOSIN 1 (ATM1), using genetics, transcriptomics and live cell microscopy. ATM1 is associated with the plasma membrane and plasmodesmata within the root apical meristem (RAM). Loss of ATM1 function results in decreased RAM size and reduced cell proliferation in a sugar-dependent manner. Auxin signaling and transcriptional responses were dampened in atm1-1 roots. Complementation of atm1-1 with a tagged ATM1 driven under the native ATM1 promoter restored root growth and cell cycle progression. Genetic analyses of atm1-1 seedlings with HEXOKINASE 1 (HXK1) and TARGET OF RAPAMYCIN COMPLEX 1 (TORC1) overexpression lines indicate that ATM1 is downstream of TOR. Collectively, these results provide previously unreported evidence that ATM1 functions to influence cell proliferation in primary roots in response to auxin and sugar cues.
Topics: Arabidopsis; Arabidopsis Proteins; Gene Expression Regulation, Plant; Indoleacetic Acids; Meristem; Myosins; Plant Roots; Sugars
PubMed: 37306290
DOI: 10.1242/dev.201762 -
The Journal of Cell Biology Sep 2023Apical constriction is a cell shape change that drives key morphogenetic events during development, including gastrulation and neural tube formation. The forces driving...
Apical constriction is a cell shape change that drives key morphogenetic events during development, including gastrulation and neural tube formation. The forces driving apical constriction are primarily generated through the contraction of apicolateral and/or medioapical actomyosin networks. In the Drosophila ventral furrow, the medioapical actomyosin network has a sarcomere-like architecture, with radially polarized actin filaments and centrally enriched non-muscle myosin II and myosin activating kinase. To determine if this is a broadly conserved actin architecture driving apical constriction, we examined actomyosin architecture during C. elegans gastrulation, in which two endodermal precursor cells internalize from the surface of the embryo. Quantification of protein localization showed that neither the non-muscle myosin II NMY-2 nor the myosin-activating kinase MRCK-1 is enriched at the center of the apex. Further, visualization of barbed- and pointed-end capping proteins revealed that actin filaments do not exhibit radial polarization at the apex. Our results demonstrate that C. elegans endodermal precursor cells apically constrict using a mixed-polarity actin filament network and with myosin and a myosin activator distributed throughout the network. Taken together with observations made in other organisms, our results demonstrate that diverse actomyosin architectures are used in animal cells to accomplish apical constriction.
Topics: Animals; Actin Cytoskeleton; Actomyosin; Caenorhabditis elegans; Constriction; Morphogenesis; Myosin Type II; Myosins; Caenorhabditis elegans Proteins
PubMed: 37351566
DOI: 10.1083/jcb.202302102 -
The Journal of Cell Biology Oct 2023Myosins are required for clathrin-mediated endocytosis, but their precise molecular roles in this process are not known. This is, in part, because the biophysical...
Myosins are required for clathrin-mediated endocytosis, but their precise molecular roles in this process are not known. This is, in part, because the biophysical properties of the relevant motors have not been investigated. Myosins have diverse mechanochemical activities, ranging from powerful contractility against mechanical loads to force-sensitive anchoring. To better understand the essential molecular contribution of myosin to endocytosis, we studied the in vitro force-dependent kinetics of the Saccharomyces cerevisiae endocytic type I myosin called Myo5, a motor whose role in clathrin-mediated endocytosis has been meticulously studied in vivo. We report that Myo5 is a low-duty-ratio motor that is activated ∼10-fold by phosphorylation and that its working stroke and actin-detachment kinetics are relatively force-insensitive. Strikingly, the in vitro mechanochemistry of Myo5 is more like that of cardiac myosin than that of slow anchoring myosin-1s found on endosomal membranes. We, therefore, propose that Myo5 generates power to augment actin assembly-based forces during endocytosis in cells.
Topics: Actins; Clathrin; Myosin Type I; Myosins; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins
PubMed: 37549220
DOI: 10.1083/jcb.202303095 -
Science Advances Jul 2023Hypertrophic cardiomyopathy (HCM) is a primary myocardial disorder characterized by left ventricular hypertrophy, hyperdynamic contraction, and impaired relaxation of... (Review)
Review
Hypertrophic cardiomyopathy (HCM) is a primary myocardial disorder characterized by left ventricular hypertrophy, hyperdynamic contraction, and impaired relaxation of the heart. These functional derangements arise directly from altered sarcomeric function due to either mutations in genes encoding sarcomere proteins, or other defects such as abnormal energetics. Current treatment options do not directly address this causal biology but focus on surgical and extra-sarcomeric (sarcolemmal) pharmacological symptomatic relief. Mavacamten (formerly known as MYK-461), is a small molecule designed to regulate cardiac function at the sarcomere level by selectively but reversibly inhibiting the enzymatic activity of myosin, the fundamental motor of the sarcomere. This review summarizes the mechanism and translational progress of mavacamten from proteins to patients, describing how the mechanism of action and pharmacological characteristics, involving both systolic and diastolic effects, can directly target pathophysiological derangements within the cardiac sarcomere to improve cardiac structure and function in HCM. Mavacamten was approved by the Food and Drug Administration in April 2022 for the treatment of obstructive HCM and now goes by the commercial name of Camzyos. Full information about the risks, limitations, and side effects can be found at www.accessdata.fda.gov/drugsatfda_docs/label/2022/214998s000lbl.pdf.
Topics: United States; Humans; Precision Medicine; Cardiomyopathy, Hypertrophic; Benzylamines; Myosins
PubMed: 37506209
DOI: 10.1126/sciadv.abo7622 -
Proceedings of the National Academy of... Dec 2023Mutations in atrial-enriched genes can cause a primary atrial myopathy that can contribute to overall cardiovascular dysfunction. encodes myosin-binding protein H-like...
Mutations in atrial-enriched genes can cause a primary atrial myopathy that can contribute to overall cardiovascular dysfunction. encodes myosin-binding protein H-like (MyBP-HL), an atrial sarcomere protein that shares domain homology with the carboxy-terminus of cardiac myosin-binding protein-C (cMyBP-C). The function of MyBP-HL and the relationship between MyBP-HL and cMyBP-C is unknown. To decipher the roles of MyBP-HL, we used structured illumination microscopy, immuno-electron microscopy, and mass spectrometry to establish the localization and stoichiometry of MyBP-HL. We found levels of cMyBP-C, a major regulator of myosin function, were half as abundant compared to levels in the ventricle. In genetic mouse models, loss of MyBP-HL doubled cMyBP-C abundance in the atria, and loss of cMyBP-C doubled MyBP-HL abundance in the atria. Structured illumination microscopy showed that both proteins colocalize in the C-zone of the A-band, with MyBP-HL enriched closer to the M-line. Immuno-electron microscopy of mouse atria showed MyBP-HL strongly localized 161 nm from the M-line, consistent with localization to the third 43 nm repeat of myosin heads. Both cMyBP-C and MyBP-HL had less-defined sarcomere localization in the atria compared to ventricle, yet areas with the expected 43 nm repeat distance were observed for both proteins. Isometric force measurements taken from control and null single atrial myofibrils revealed that loss of accelerated the linear phase of relaxation. These findings support a mechanism where MyBP-HL regulates cMyBP-C abundance to alter the kinetics of sarcomere relaxation in atrial sarcomeres.
Topics: Mice; Animals; Myocytes, Cardiac; Carrier Proteins; Protein Binding; Sarcomeres; Myosins; Myocardium
PubMed: 38091294
DOI: 10.1073/pnas.2314920120 -
Frontiers in Physiology 2023Having characterized actin from (Weihing and Korn, Biochemistry, 1971, 10, 590-600) and knowing that myosin had been isolated from the slime mold (Hatano and Tazawa,... (Review)
Review
Having characterized actin from (Weihing and Korn, Biochemistry, 1971, 10, 590-600) and knowing that myosin had been isolated from the slime mold (Hatano and Tazawa, Biochim. Biophys. Acta, 1968, 154, 507-519; Adelman and Taylor, Biochemistry, 1969, 8, 4976-4988), we set out in 1969 to find myosin in . We used K-EDTA-ATPase activity to assay myosin, because it is a unique feature of muscle myosins. After slightly less than 3 years, we purified a K-EDTA ATPase that interacted with actin. Actin filaments stimulated the Mg-ATPase activity of the crude enzyme, but this was lost with further purification. Recombining fractions from the column where this activity was lost revealed a "cofactor" that allowed actin filaments to stimulate the Mg-ATPase of the purified enzyme. The small size of the heavy chain and physical properties of the purified myosin were unprecedented, so many were skeptical, assuming that our myosin was a proteolytic fragment of a larger myosin similar to muscle or myosin. Subsequently our laboratories confirmed that myosin-I is a novel unconventional myosin that interacts with membrane lipids (Adams and Pollard, Nature, 1989, 340 (6234), 565-568) and that the cofactor is a myosin heavy chain kinase (Maruta and Korn, J. Biol. Chem., 1977, 252, 8329-8332). Phylogenetic analysis (Odronitz and Kollmar, Genome Biology, 2007, 8, R196) later established that class I myosin was the first myosin to appear during the evolution of eukaryotes.
PubMed: 38046947
DOI: 10.3389/fphys.2023.1324623 -
Current Opinion in Cardiology Sep 2023Cardiac myosin inhibitors (CMIs) represent a major milestone in the treatment of patients with symptomatic obstructive hypertrophic cardiomyopathy. The objective of this... (Review)
Review
PURPOSE OF REVIEW
Cardiac myosin inhibitors (CMIs) represent a major milestone in the treatment of patients with symptomatic obstructive hypertrophic cardiomyopathy. The objective of this review is to discuss the mechanisms of action, clinical trial evidence, safety profile and monitoring of CMIs, which are important to the implementation of these drugs in clinical practice.
RECENT FINDINGS
Mavacamten and aficamten have both been shown to substantially improve left ventricular outflow tract gradients, biomarkers and symptoms in patients with obstructive hypertrophic cardiomyopathy. Both agents are well tolerated with few adverse events in clinical trial follow up. Transient reductions in left ventricular ejection fraction may be associated with both mavacamten and aficamten but respond to dose reduction.
SUMMARY
There is now robust clinical trial evidence base to support the use of mavacamten for patients with symptomatic obstructive hypertrophic cardiomyopathy. Generation of long-term safety and efficacy data and exploring applications of CMI to nonobstructive cardiomyopathy and heart failure with preserved ejection fraction represent important next steps.
Topics: Humans; Stroke Volume; Ventricular Function, Left; Cardiac Myosins; Cardiomyopathy, Hypertrophic
PubMed: 37382090
DOI: 10.1097/HCO.0000000000001068 -
Annual Review of Physiology Feb 2024Force generation in striated muscle is primarily controlled by structural changes in the actin-containing thin filaments triggered by an increase in intracellular... (Review)
Review
Force generation in striated muscle is primarily controlled by structural changes in the actin-containing thin filaments triggered by an increase in intracellular calcium concentration. However, recent studies have elucidated a new class of regulatory mechanisms, based on the myosin-containing thick filament, that control the strength and speed of contraction by modulating the availability of myosin motors for the interaction with actin. This review summarizes the mechanisms of thin and thick filament activation that regulate the contractility of skeletal and cardiac muscle. A novel dual-filament paradigm of muscle regulation is emerging, in which the dynamics of force generation depends on the coordinated activation of thin and thick filaments. We highlight the interfilament signaling pathways based on titin and myosin-binding protein-C that couple thin and thick filament regulatory mechanisms. This dual-filament regulation mediates the length-dependent activation of cardiac muscle that underlies the control of the cardiac output in each heartbeat.
Topics: Humans; Actins; Muscle, Skeletal; Myocardium; Myosins; Actin Cytoskeleton; Calcium
PubMed: 37931167
DOI: 10.1146/annurev-physiol-042222-022728 -
The Journal of Biological Chemistry Dec 2023Cardiac MyBP-C (cMyBP-C) interacts with actin and myosin to fine-tune cardiac muscle contractility. Phosphorylation of cMyBP-C, which reduces the binding of cMyBP-C to...
Cardiac MyBP-C (cMyBP-C) interacts with actin and myosin to fine-tune cardiac muscle contractility. Phosphorylation of cMyBP-C, which reduces the binding of cMyBP-C to actin and myosin, is often decreased in patients with heart failure (HF) and is cardioprotective in model systems of HF. Therefore, cMyBP-C is a potential target for HF drugs that mimic its phosphorylation and/or perturb its interactions with actin or myosin. We labeled actin with fluorescein-5-maleimide (FMAL) and the C0-C2 fragment of cMyBP-C (cC0-C2) with tetramethylrhodamine (TMR). We performed two complementary high-throughput screens (HTS) on an FDA-approved drug library, to discover small molecules that specifically bind to cMyBP-C and affect its interactions with actin or myosin, using fluorescence lifetime (FLT) detection. We first excited FMAL and detected its FLT, to measure changes in fluorescence resonance energy transfer (FRET) from FMAL (donor) to TMR (acceptor), indicating binding. Using the same samples, we then excited TMR directly, using a longer wavelength laser, to detect the effects of compounds on the environmentally sensitive FLT of TMR, to identify compounds that bind directly to cC0-C2. Secondary assays, performed on selected modulators with the most promising effects in the primary HTS assays, characterized the specificity of these compounds for phosphorylated versus unphosphorylated cC0-C2 and for cC0-C2 versus C1-C2 of fast skeletal muscle (fC1-C2). A subset of identified compounds modulated ATPase activity in cardiac and/or skeletal myofibrils. These assays establish the feasibility of the discovery of small-molecule modulators of the cMyBP-C-actin/myosin interaction, with the ultimate goal of developing therapies for HF.
Topics: Humans; Actins; Drug Discovery; Heart Failure; Myocardium; Myosins; Phosphorylation; Protein Binding; Small Molecule Libraries; Drug Evaluation, Preclinical; Myofibrils; Carrier Proteins; Biosensing Techniques; Adenosine Triphosphatases; Muscle, Skeletal; Recombinant Proteins; Enzyme Activation; Fluorescence Resonance Energy Transfer
PubMed: 37865311
DOI: 10.1016/j.jbc.2023.105369 -
Circulation Research Jun 2024Autoimmunity significantly contributes to the pathogenesis of myocarditis, underscored by its increased frequency in autoimmune diseases such as systemic lupus... (Review)
Review
Autoimmunity significantly contributes to the pathogenesis of myocarditis, underscored by its increased frequency in autoimmune diseases such as systemic lupus erythematosus and polymyositis. Even in cases of myocarditis caused by viral infections, dysregulated immune responses contribute to pathogenesis. However, whether triggered by existing autoimmune conditions or viral infections, the precise antigens and immunologic pathways driving myocarditis remain incompletely understood. The emergence of myocarditis associated with immune checkpoint inhibitor therapy, commonly used for treating cancer, has afforded an opportunity to understand autoimmune mechanisms in myocarditis, with autoreactive T cells specific for cardiac myosin playing a pivotal role. Despite their self-antigen recognition, cardiac myosin-specific T cells can be present in healthy individuals due to bypassing the thymic selection stage. In recent studies, novel modalities in suppressing the activity of pathogenic T cells including cardiac myosin-specific T cells have proven effective in treating autoimmune myocarditis. This review offers an overview of the current understanding of heart antigens, autoantibodies, and immune cells as the autoimmune mechanisms underlying various forms of myocarditis, along with the latest updates on clinical management and prospects for future research.
Topics: Myocarditis; Humans; Autoimmune Diseases; Animals; Autoantibodies; Autoimmunity; T-Lymphocytes; Autoantigens; Cardiac Myosins
PubMed: 38843292
DOI: 10.1161/CIRCRESAHA.124.323816