scholarly journals The cytoskeletal architecture of the presynaptic terminal and molecular structure of synapsin 1.

1989 ◽  
Vol 108 (1) ◽  
pp. 111-126 ◽  
Author(s):  
N Hirokawa ◽  
K Sobue ◽  
K Kanda ◽  
A Harada ◽  
H Yorifuji
Keyword(s):  
Molecular Structure ◽  
Actin Filaments ◽  
Synaptic Vesicles ◽  
Plasma Membranes ◽  
Electric Organ ◽  
Main Element ◽  
Spherical Head ◽  
Spherical Structures ◽  
Synapsin 1

We have examined the cytoskeletal architecture and its relationship with synaptic vesicles in synapses by quick-freeze deep-etch electron microscopy (QF.DE). The main cytoskeletal elements in the presynaptic terminals (neuromuscular junction, electric organ, and cerebellar cortex) were actin filaments and microtubules. The actin filaments formed a network and frequently were associated closely with the presynaptic plasma membranes and active zones. Short, linking strands approximately 30 nm long were found between actin and synaptic vesicles, between microtubules and synaptic vesicles. Fine strands (30-60 nm) were also found between synaptic vesicles. Frequently spherical structures existed in the middle of the strands between synaptic vesicles. Another kind of strand (approximately 100 nm long, thinner than the actin filaments) between synaptic vesicles and plasma membranes was also observed. We have examined the molecular structure of synapsin 1 and its relationship with actin filaments, microtubules, and synaptic vesicles in vitro using the low angle rotary shadowing technique and QF.DE. The synapsin 1, approximately 47 nm long, was composed of a head (approximately 14 nm diam) and a tail (approximately 33 nm long), having a tadpole-like appearance. The high resolution provided by QF.DE revealed that a single synapsin 1 cross-linked actin filaments and linked actin filaments with synaptic vesicles, forming approximately 30-nm short strands. The head was on the actin and the tail was attached to the synaptic vesicle or actin filament. Microtubules were also cross-linked by a single synapsin 1, which also connected a microtubule to synaptic vesicles, forming approximately 30 nm strands. The spherical head was on the microtubules and the tail was attached to the synaptic vesicles or to microtubules. Synaptic vesicles incubated with synapsin 1 were linked with each other via fine short fibrils and frequently we identified spherical structures from which two or three fibril radiated and cross-linked synaptic vesicles. We have examined the localization of synapsin 1 using ultracryomicrotomy and colloidal gold-immunocytochemistry of anti-synapsin 1 IgG. Synapsin 1 was exclusively localized in the regions occupied by synaptic vesicles. Statistical analyses indicated that synapsin 1 is located mostly at least approximately 30 nm away from the presynaptic membrane. These data derived via three different approaches suggest that synapsin 1 could be a main element of short linkages between actin filaments and synaptic vesicles, and between microtubules and synaptic vesicles, and between synaptic vesicles in the nerve terminals.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Palladin Is a Regulator of Actin Filament Bundles at the Ectoplasmic Specialization in Adult Rat Testes

Endocrinology ◽  
2013 ◽  
Vol 154 (5) ◽  
pp. 1907-1920 ◽  
Author(s):  
Xiaojing Qian ◽  
Dolores D. Mruk ◽  
Elissa W. P. Wong ◽  
Pearl P. Y. Lie ◽  
C. Yan Cheng
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Plasma Membranes ◽  
Permeability Barrier ◽  
Protein Distribution ◽  
Filament Bundles ◽  
Ectoplasmic Specialization ◽  
Blood Testis Barrier

Abstract In rat testes, the ectoplasmic specialization (ES) at the Sertoli-Sertoli and Sertoli-spermatid interface known as the basal ES at the blood-testis barrier and the apical ES in the adluminal compartment, respectively, is a testis-specific adherens junction. The remarkable ultrastructural feature of the ES is the actin filament bundles that sandwiched in between the cisternae of endoplasmic reticulum and apposing plasma membranes. Although these actin filament bundles undergo extensive reorganization to switch between their bundled and debundled state to facilitate blood-testis barrier restructuring and spermatid adhesion/transport, the regulatory molecules underlying these events remain unknown. Herein we report findings of an actin filament cross-linking/bundling protein palladin, which displayed restrictive spatiotemporal expression at the apical and the basal ES during the epithelial cycle. Palladin structurally interacted and colocalized with Eps8 (epidermal growth factor receptor pathway substrate 8, an actin barbed end capping and bundling protein) and Arp3 (actin related protein 3, which together with Arp2 form the Arp2/3 complex to induce branched actin nucleation, converting bundled actin filaments to an unbundled/branched network), illustrating its role in regulating actin filament bundle dynamics at the ES. A knockdown of palladin in Sertoli cells in vitro with an established tight junction (TJ)-permeability barrier was found to disrupt the TJ function, which was associated with a disorganization of actin filaments that affected protein distribution at the TJ. Its knockdown in vivo also perturbed F-actin organization that led to a loss of spermatid polarity and adhesion, causing defects in spermatid transport and spermiation. In summary, palladin is an actin filament regulator at the ES.

scholarly journals Bassoon controls synaptic vesicle pools via regulation of presynaptic phosphorylation and cAMP homeostasis

2021 ◽  
Author(s):  
Carolina Montenegro-Venegas ◽  
Debarpan Guhathakurta ◽  
Eneko Pina-Fernandez ◽  
Maria Andres-Alonso ◽  
Florian Plattner ◽  
...  
Keyword(s):  
Neurotransmitter Release ◽  
Synaptic Vesicles ◽  
Molecular Mechanisms ◽  
Cultured Neurons ◽  
Glutamatergic Synapses ◽  
Vesicle Pools ◽  
Downstream Effectors ◽  
Synapsin 1

Neuronal presynaptic terminals contain hundreds of neurotransmitter-filled synaptic vesicles (SVs). The morphologically uniform SVs differ in their release competence segregating into functional pools that differentially contribute to neurotransmission. The presynaptic scaffold bassoon is required for neurotransmission, but the underlying molecular mechanisms are unknown. We report that glutamatergic synapses lacking bassoon featured a decreased SV release competence and increased resting pool of SV as observed by imaging of SV release in cultured neurons. Further analyses in vitro and in vivo revealed a dysregulation of CDK5/calcineurin and cAMP/PKA presynaptic signalling resulting in an aberrant phosphorylation of their downstream effectors synapsin 1 and SNAP25, which are well-known regulators of SV release competence. An acute pharmacological restoration of physiological CDK5 and cAMP/PKA activity fully normalised the SV pools in neurons lacking bassoon. Finally, we demonstrated that CDK5-dependent regulation of PDE4 activity controls SV release competence by interaction with cAMP/PKA signalling. These data reveal that bassoon organises SV pools via regulation of presynaptic phosphorylation and indicate an involvement of PDE4 in the control of neurotransmitter release.

scholarly journals Molecular Structure Study on the Polyelectrolyte Properties of Actin Filaments

2022 ◽  
Author(s):  
Santiago M Bedoya ◽  
Marcelo Marucho
Keyword(s):  
Molecular Structure ◽  
Actin Filaments ◽  
Surrounding Medium ◽  
Electrical Potential ◽  
Finite Size ◽  
Electrolyte Solutions ◽  
Structure Study ◽  
Structure Model ◽  
The Impact

An accurate characterization of the polyelectrolyte properties of actin filaments might provide a deeper understanding of the fundamental mechanisms governing the intracellular ionic wave packet propagation in neurons. Infinitely long cylindrical models for actin filaments and approximate electrochemical theories for the electrolyte solutions were recently used to characterize these properties in in-vitro and intracellular conditions. This article uses a molecular structure model for actin filaments to investigate the impact of roughness and finite size on the mean electrical potential, ionic density distributions, currents, and conductivities. We solved the electrochemical theories numerically without further approximations. Our findings bring new insights into the electrochemical interactions between a filament′s irregular surface charge density and the surrounding medium. The irregular shape of the filament structure model generated pockets, or hot spots, where the current density reached higher or lower magnitudes than those in neighboring areas throughout the filament surface. It also revealed the formation of a well-defined asymmetric electrical double layer with a thickness larger than that commonly used for symmetric models.

scholarly journals Isolation of pure cholinergic nerve endings from Torpedo electric organ. Evaluation of their metabolic properties.

1977 ◽  
Vol 75 (1) ◽  
pp. 43-55 ◽  
Author(s):  
N Morel ◽  
M Israel ◽  
R Manaranche ◽  
P Mastour-Frachon
Keyword(s):  
Synaptic Vesicles ◽  
Morphological Analysis ◽  
Electric Organ ◽  
Nerve Endings ◽  
Cholinergic Nerve ◽  
Membrane Attachment ◽  
Biochemical Measurements ◽  
Torpedo Electric Organ ◽  
Metabolic Properties

Pure cholinergic nerve endings (synaptosomes) were isolated from the electric organ of Torpedo by a rapid procedure. These synaptosomes are approximately 3 micron in diameter. They contain an occasional mitochondrion, numerous synaptic vesicles, and sometimes an active zone is observed. No postynaptic membrane attachment is found. This nerve ending fraction is extremely pure as shown by morphological controls and biochemical data. It is rich in choline acetyltransferase (450 nmol/h per mg protein) and acetylcholine (ACh) (130 nmol/mg protein). The isolated endings retain their cytoplasmic components and they synthesize ACh and are stable in vitro for several hours, as shown by biochemical measurements and morphological analysis.

scholarly journals Platelet Shape Changes during Thrombus Formation: Role of Actin-Based Protrusions

2021 ◽  
Vol 41 (01) ◽  
pp. 014-021
Author(s):  
Markus Bender ◽  
Raghavendra Palankar
Keyword(s):  
Blood Loss ◽  
Actin Filaments ◽  
Thrombus Formation ◽  
Short Review ◽  
Critical Component ◽  
Clot Retraction ◽  
Shape Changes ◽  
Platelet Shape

AbstractPlatelet activation and aggregation are essential to limit blood loss at sites of vascular injury but may also lead to occlusion of diseased vessels. The platelet cytoskeleton is a critical component for proper hemostatic function. Platelets change their shape after activation and their contractile machinery mediates thrombus stabilization and clot retraction. In vitro studies have shown that platelets, which come into contact with proteins such as fibrinogen, spread and first form filopodia and then lamellipodia, the latter being plate-like protrusions with branched actin filaments. However, the role of platelet lamellipodia in hemostasis and thrombus formation has been unclear until recently. This short review will briefly summarize the recent findings on the contribution of the actin cytoskeleton and lamellipodial structures to platelet function.

Myofibrillar degeneration with diphtheria toxin

2020 ◽  
Vol 45 (4) ◽  
pp. 351-357
Author(s):  
Bilge Özerman Edis ◽  
Muhammet Bektaş ◽  
Rüstem Nurten
Keyword(s):  
Protein Synthesis ◽  
Actin Filaments ◽  
Diphtheria Toxin ◽  
Cardiac Tissue ◽  
Culture Conditions ◽  
Bacterial Toxin ◽  
Filamentous Actin ◽  
Cardiac Damage ◽  
Tissue Samples

AbstractObjectivesCardiac damage in patient with diphtheritic myocarditis is reported as the leading cause of mortality. Diphtheria toxin (DTx) is a well-known bacterial toxin inducing various cytotoxic effects. Mainly, catalytic fragment inhibits protein synthesis, induces cytotoxicity, and depolymerizes actin filaments. In this study, we aimed to demonstrate the extent of myofibrillar damage under DTx treatment to porcine cardiac tissue samples.MethodsTissue samples were incubated with DTx for 1–3 h in culture conditions. To analyze whole toxin (both fragments) distribution, conjugation of DTx with FITC was performed. Measurements were carried out with fluorescence spectrophotometer before and after dialysis. Immunofluorescence microscopy was used to show localization of DTx-FITC (15 nM) on cardiac tissue incubated for 2 h. Ultrastructural characterization of cardiac tissue samples treated with DTx (15 or 150 nM) was performed with transmission electron microscopy.ResultsDTx exerts myofibrillar disorganization. Myofilament degeneration, mitochondrial damage, vacuolization, and abundant lipid droplets were determined with 150 nM of DTx treatment.ConclusionsThis finding is an addition to depolymerization of actin filaments as a result of the DTx-actin interactions in in vitro conditions, indicating that myofilament damage can occur with DTx directly besides protein synthesis inhibition. Ultrastructural results support the importance of filamentous actin degeneration at diphtheritic myocarditis.

scholarly journals Glycan-to-Glycan Binding: Molecular Recognition through Polyvalent Interactions Mediates Specific Cell Adhesion

Molecules ◽  
2021 ◽  
Vol 26 (2) ◽  
pp. 397
Author(s):  
Gradimir Misevic ◽  
Emanuela Garbarino
Keyword(s):  
Cell Adhesion ◽  
Plasma Membranes ◽  
Specific Cell ◽  
Cellular Interactions ◽  
New Paradigm ◽  
Tumor Cell Adhesion ◽  
Self Recognition ◽  
Structural And Functional Properties ◽  
Low Valent

Glycan-to-glycan binding was shown by biochemical and biophysical measurements to mediate xenogeneic self-recognition and adhesion in sponges, stage-specific cell compaction in mice embryos, and in vitro tumor cell adhesion in mammals. This intermolecular recognition process is accepted as the new paradigm accompanying high-affinity and low valent protein-to-protein and protein-to-glycan binding in cellular interactions. Glycan structures in sponges have novel species-specific sequences. Their common features are the large size >100 kD, polyvalency >100 repeats of the specific self-binding oligosaccharide, the presence of fucose, and sulfated and/or pyruvylated hexoses. These structural and functional properties, different from glycosaminoglycans, inspired their classification under the glyconectin name. The molecular mechanism underlying homophilic glyconectin-to-glyconectin binding relies on highly polyvalent, strong, and structure-specific interactions of small oligosaccharide motifs, possessing ultra-weak self-binding strength and affinity. Glyconectin localization at the glycocalyx outermost cell surface layer suggests their role in the initial recognition and adhesion event during the complex and multistep process. In mammals, Lex-to-Lex homophilic binding is structure-specific and has ultra-weak affinity. Cell adhesion is achieved through highly polyvalent interactions, enabled by clustering of small low valent structure in plasma membranes.

scholarly journals A sodium-activated potassium channel supports high-frequency firing and reduces energetic costs during rapid modulations of action potential amplitude

2013 ◽  
Vol 109 (7) ◽  
pp. 1713-1723 ◽  
Author(s):  
Michael R. Markham ◽  
Leonard K. Kaczmarek ◽  
Harold H. Zakon
Keyword(s):  
Action Potential ◽  
High Frequency ◽  
Electric Fish ◽  
Electric Organ Discharge ◽  
Electric Organ ◽  
Weakly Electric Fish ◽  
Energetic Costs ◽  
Dynamic Regulation ◽  
Voltage Gated

We investigated the ionic mechanisms that allow dynamic regulation of action potential (AP) amplitude as a means of regulating energetic costs of AP signaling. Weakly electric fish generate an electric organ discharge (EOD) by summing the APs of their electric organ cells (electrocytes). Some electric fish increase AP amplitude during active periods or social interactions and decrease AP amplitude when inactive, regulated by melanocortin peptide hormones. This modulates signal amplitude and conserves energy. The gymnotiform Eigenmannia virescens generates EODs at frequencies that can exceed 500 Hz, which is energetically challenging. We examined how E. virescens meets that challenge. E. virescens electrocytes exhibit a voltage-gated Na+current ( INa) with extremely rapid recovery from inactivation (τrecov= 0.3 ms) allowing complete recovery of Na+current between APs even in fish with the highest EOD frequencies. Electrocytes also possess an inwardly rectifying K+current and a Na+-activated K+current ( IKNa), the latter not yet identified in any gymnotiform species. In vitro application of melanocortins increases electrocyte AP amplitude and the magnitudes of all three currents, but increased IKNais a function of enhanced Na+influx. Numerical simulations suggest that changing INamagnitude produces corresponding changes in AP amplitude and that KNachannels increase AP energy efficiency (10–30% less Na+influx/AP) over model cells with only voltage-gated K+channels. These findings suggest the possibility that E. virescens reduces the energetic demands of high-frequency APs through rapidly recovering Na+channels and the novel use of KNachannels to maximize AP amplitude at a given Na+conductance.

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