scholarly journals Cytoskeletal organization of axons in vertebrates and invertebrates

2020 ◽  
Vol 219 (7) ◽  
Author(s):  
Andreas Prokop
Keyword(s):  
Initial Segment ◽  
Growth Cones ◽  
Axon Initial Segment ◽  
Electron Microscopic ◽  
Cytoskeletal Organization ◽  
Ultrastructural Studies ◽  
Microscopic Studies ◽  
Different Dimensions ◽  
Plastic Changes ◽  
Axon Initial Segments

The maintenance of axons for the lifetime of an organism requires an axonal cytoskeleton that is robust but also flexible to adapt to mechanical challenges and to support plastic changes of axon morphology. Furthermore, cytoskeletal organization has to adapt to axons of dramatically different dimensions, and to their compartment-specific requirements in the axon initial segment, in the axon shaft, at synapses or in growth cones. To understand how the cytoskeleton caters to these different demands, this review summarizes five decades of electron microscopic studies. It focuses on the organization of microtubules and neurofilaments in axon shafts in both vertebrate and invertebrate neurons, as well as the axon initial segments of vertebrate motor- and interneurons. Findings from these ultrastructural studies are being interpreted here on the basis of our contemporary molecular understanding. They strongly suggest that axon architecture in animals as diverse as arthropods and vertebrates is dependent on loosely cross-linked bundles of microtubules running all along axons, with only minor roles played by neurofilaments.

scholarly journals Improvements of glycol methacrylate. I. Its use as an embedding medium for electron microscopic studies.

1977 ◽  
Vol 25 (3) ◽  
pp. 163-174 ◽  
Author(s):  
R C Spaur ◽  
G C Moriarty
Keyword(s):  
Electron Beam ◽  
Water Soluble ◽  
Cross Linking ◽  
Electron Microscopic ◽  
Glycol Methacrylate ◽  
Ultrastructural Studies ◽  
Tissue Morphology ◽  
Methacrylate Monomer ◽  
Microscopic Studies ◽  
Embedding Medium

The technique for using the water-soluble embedding medium glycol methacrylate has been improved for ultrastructural studies by the simplification of the method of formation of prepolymers used in embedding the tissue, by the addition of a cross-linking agent so that sections are stable in the electron beam, and by improving the softness of the blocks by the addition of a plasticizing agent. The preservation of tissue morphology has been improved by complete dehydration in glycol methacrylate monomer prior to infiltration with the prepolymer. Preservations of tissue morphology is further enhanced by complete dehydration in ethanols and embedding in the improved glycol methacrylate medium.

scholarly journals Tailoring of the axon initial segment shapes the conversion of synaptic inputs into spiking output in OFF-α T retinal ganglion cells

2020 ◽  
Vol 6 (37) ◽  
pp. eabb6642
Author(s):  
Paul Werginz ◽  
Vineeth Raghuram ◽  
Shelley I. Fried
Keyword(s):  
Retinal Ganglion Cells ◽  
Initial Segment ◽  
Ganglion Cells ◽  
Axon Initial Segment ◽  
Retinal Ganglion ◽  
Light Responses ◽  
Synaptic Inputs ◽  
Dorsal Cells ◽  
Axon Initial Segments ◽  
Dorsal Retina

Recently, mouse OFF-α transient (OFF-α T) retinal ganglion cells (RGCs) were shown to display a gradient of light responses as a function of position along the dorsal-ventral axis; response differences were correlated to differences in the level of excitatory presynaptic input. Here, we show that postsynaptic differences between cells also make a strong contribution to response differences. Cells in the dorsal retina had longer axon initial segments (AISs)—the greater number of Nav1.6 channels in longer AISs directly mediates higher rates of spiking and helps avoid depolarization block that terminates spiking in ventral cells with shorter AISs. The pre- and postsynaptic specializations that shape the output of OFF-α T RGCs interact in different ways: In dorsal cells, strong inputs and the long AISs are both necessary to generate their strong, sustained spiking outputs, while in ventral cells, weak inputs or the short AISs are both sufficient to limit the spiking signal.

Glomerular Mesangial Fibrosis in Hatchery-Reared Rainbow Trout (Salmo gairdneri)

1976 ◽  
Vol 33 (11) ◽  
pp. 2551-2559 ◽  
Author(s):  
David E. Hinton ◽  
Raymond T. Jones ◽  
Roger Lee Herman
Keyword(s):  
Rainbow Trout ◽  
Mesangial Cells ◽  
Salmo Gairdneri ◽  
Unknown Etiology ◽  
Electron Microscopic ◽  
Glomerular Lesion ◽  
Ultrastructural Studies ◽  
Glomerular Lesions ◽  
Microscopic Studies ◽  
Rate Comparison

Light and electron microscopic studies were performed on tissues of hatchery-reared rainbow trout (Salmo gairdneri) having a disease of currently unknown etiology with external symptoms of severe edema which causes increased mortality rate. Comparison with unaffected trout tissues revealed loss of cellularity in glomerular tufts with a replacement of mesangial cells by connective tissue. Ultrastructural studies showed the material to be collagen and established the diagnosis of glomerular mesangial fibrosis. The glomerular lesion was associated with alterations in lining epithelium of proximal tubules and extensive debris within tubule lumens. The findings are compared to glomerular lesions in mammalian and amphibian kidney.

Ultrastructure of Septa from the Filamentous Fungus Aspergillus Nidulans

1998 ◽  
Vol 4 (S2) ◽  
pp. 1142-1143
Author(s):  
Elizabeth A. Richardson ◽  
Michelle Momany
Keyword(s):  
Aspergillus Nidulans ◽  
Filamentous Fungus ◽  
Freeze Substitution ◽  
Uranyl Acetate ◽  
Temperature Sensitive ◽  
Electron Microscopic ◽  
Genetic Studies ◽  
Ultrastructural Studies ◽  
Microscopic Studies ◽  
Dialysis Membranes

The filamentous fungus Aspergillus nidulans partitions its cells by laying down septa at regularly spaced intervals in response to nuclear division. Physiological and genetic studies of the temperature-sensitive sep mutants have been especially useful in dissecting the regulation of septation. Electron microscopic studies of the sep mutants should be equally useful in dissecting the structural intermediates of septation. In preparation for ultrastructural studies of the sep mutants, we have examined septa in wild-type A. nidulans fixed by freeze substitution.Dialysis membranes were placed on rich medium plates and inoculated with A. nidulans spore suspensions. After 12 hours at 30°C, the dialysis membranes with adhering fungal hyphae were cut into square pieces measuring approximately 5mm on each side. The pieces were plunged into liquid propane and processed according to the procedures of Hoch. Serial sections were cut using a diamond knife and post stained with uranyl acetate and lead citrate.

The distribution and movement of organelles in maturing growth cones: correlated video-enhanced and electron microscopic studies

1988 ◽  
Vol 17 (6) ◽  
pp. 783-795 ◽  
Author(s):  
Donald W. Burmeister ◽  
Mary Chen ◽  
Craig H. Bailey ◽  
Daniel J. Goldberg
Keyword(s):  
Growth Cones ◽  
Electron Microscopic ◽  
Microscopic Studies

scholarly journals NuMA1 promotes axon initial segment assembly through inhibition of endocytosis

2019 ◽  
pp. jcb.201907048 ◽  
Author(s):  
Tomohiro Torii ◽  
Yuki Ogawa ◽  
Cheng-Hsin Liu ◽  
Tammy Szu-Yu Ho ◽  
Hamdan Hamdan ◽  
...  
Keyword(s):  
Transient Expression ◽  
Action Potentials ◽  
Initial Segment ◽  
Axon Initial Segment ◽  
Neonatal Mouse ◽  
Scaffolding Protein ◽  
Differential Proteomics ◽  
Mitotic Apparatus ◽  
Axon Initial Segments ◽  
Protein 4.1B

Axon initial segments (AISs) initiate action potentials and regulate the trafficking of vesicles between somatodendritic and axonal compartments. However, the mechanisms controlling AIS assembly remain poorly defined. We performed differential proteomics and found nuclear mitotic apparatus protein 1 (NuMA1) is downregulated in AIS-deficient neonatal mouse brains and neurons. NuMA1 is transiently located at the AIS during development where it interacts with the scaffolding protein 4.1B and the dynein regulator lissencephaly 1 (Lis1). Silencing NuMA1 or protein 4.1B by shRNA disrupts AIS assembly, but not maintenance. Silencing Lis1 or overexpressing NuMA1 during AIS assembly increased the density of AIS proteins, including ankyrinG and neurofascin-186 (NF186). NuMA1 inhibits the endocytosis of AIS NF186 by impeding Lis1’s interaction with doublecortin, a potent facilitator of NF186 endocytosis. Our results indicate the transient expression and AIS localization of NuMA1 stabilizes the developing AIS by inhibiting endocytosis and removal of AIS proteins.

scholarly journals Polymerizing Microtubules Activate Site-directed F-Actin Assembly in Nerve Growth Cones

1999 ◽  
Vol 10 (7) ◽  
pp. 2309-2327 ◽  
Author(s):  
M. William Rochlin ◽  
Michael E. Dailey ◽  
Paul C. Bridgman
Keyword(s):  
Plasma Membrane ◽  
Actin Filaments ◽  
Cytochalasin B ◽  
Membrane Surface ◽  
Growth Cones ◽  
Actin Assembly ◽  
Electron Microscopic ◽  
Early Step ◽  
Microscopic Studies ◽  
Nerve Growth Cones

We identify an actin-based protrusive structure in growth cones termed “intrapodium.” Unlike filopodia, intrapodia are initiated exclusively within lamellipodia and elongate in a continuous (nonsaltatory) manner parallel to the plane of the dorsal plasma membrane causing a ridge-like protrusion. Intrapodia resemble the actin-rich structures induced by intracellular pathogens (e.g.,Listeria) or by extracellular beads. Cytochalasin B inhibits intrapodial elongation and removal of cytochalasin B produced a burst of intrapodial activity. Electron microscopic studies revealed that lamellipodial intrapodia contain both short and long actin filaments oriented with their barbed ends toward the membrane surface or advancing end. Our data suggest an interaction between microtubule endings and intrapodia formation. Disruption of microtubules by acute nocodazole treatment decreased intrapodia frequency, and washout of nocodazole or addition of the microtubule-stabilizing drug Taxol caused a burst of intrapodia formation. Furthermore, individual microtubule ends were found near intrapodia initiation sites. Thus, microtubule ends or associated structures may regulate these actin-dependent structures. We propose that intrapodia are the consequence of an early step in a cascade of events that leads to the development of F-actin-associated plasma membrane specializations.

scholarly journals Endogenously expressed Ranbp2 (Nup358) is not at the axon initial segment

2021 ◽  
pp. jcs.256180
Author(s):  
Yuki Ogawa ◽  
Matthew N. Rasband
Keyword(s):  
Nuclear Pore Complex ◽  
Nuclear Membrane ◽  
Initial Segment ◽  
Axon Initial Segment ◽  
Nuclear Pore ◽  
Cultured Neurons ◽  
Epitope Tag ◽  
Antibody Binding Site ◽  
Axon Initial Segments ◽  
Primary Cultured Neurons

Ranbp2 (also known as Nup358) is a member of the nucleoporin family that comprises the nuclear pore complex. Ranbp2 localizes at the nuclear membrane and was recently reported at the axon initial segment (AIS). However, we show the anti-Ranbp2 antibody used in previous studies is not specific for Ranbp2. We mapped the antibody binding site to the amino acid sequence KPLQG that is present in both Ranbp2 and Neurofascin, a well-known AIS protein. After silencing Neurofascin expression in neurons, the AIS was not stained by the antibody. Surprisingly, an exogenously expressed N-terminal fragment of Ranbp2 localizes at the AIS. We show this fragment interacts with stable microtubules. Finally, using CRISPR-Cas9 in primary cultured neurons, we inserted an HA-epitope tag at N-terminal, C-terminal, or internal sites of the endogenously expressed Ranbp2. No matter the location of the HA-epitope, endogenous Ranbp2 was found at the nuclear membrane but not the AIS. These results show that endogenously expressed Ranbp2 is not found at axon initial segments.

scholarly journals Pathological consequences of chronic olfactory inflammation on neurite morphology of olfactory bulb projection neurons

2021 ◽  
Author(s):  
Brandon Joseph LaFever ◽  
Yuka Imamura Kawasawa ◽  
Ayako Ito ◽  
Fumiaki Imamura
Keyword(s):  
Chronic Rhinosinusitis ◽  
Intranasal Administration ◽  
Initial Segment ◽  
Recovery Period ◽  
Axon Initial Segment ◽  
Projection Neurons ◽  
Inflammatory Cytokine Production ◽  
Response To Stress ◽  
Axon Initial Segments ◽  
Integrated Circuitry

Abstract Background : Chronic olfactory inflammation (COI) in conditions such as chronic rhinosinusitis significantly impairs the functional and anatomical components of the olfactory system. COI induced by intranasal administration of lipopolysaccharide (LPS) results in atrophy, gliosis, and pro-inflammatory cytokine production in the OB. Although chronic rhinosinusitis patients have smaller olfactory bulbs (OBs), the consequences of olfactory inflammation on OB neurons are largely unknown. Methods : In this study, we investigated the neurological consequence of COI on OB projection neurons, mitral cells (MCs) and tufted cells (TCs). To induce COI, we performed unilateral intranasal administration of LPS to mice for 4 and 10 weeks. Effects of COI on the OB were examined using RNA-sequencing approaches and immunohistochemical analyses. Results : We found that repeated LPS administration upregulated immune-related biological pathways in the OB after 4 weeks. We also determined that the length of TC lateral dendrites in the OB significantly decreased after 10 weeks of COI. The axon initial segment of TCs decreased in number and in length after 10 weeks of COI. The lateral dendrites and axon initial segments of MCs, however, were largely unaffected. In addition, dendritic arborization and axon initial segment reconstruction both took place following a 10-week recovery period. Conclusion : Our findings suggests that olfactory inflammation specifically affects TCs and their integrated circuitry, whereas MCs are potentially protected from this condition. This data demonstrates unique characteristics of the OBs ability to undergo neuroplastic changes in response to stress.

Transmission and Scanning Electron Microscopy of the Follicle in the Human Ovary

1974 ◽  
Vol 32 ◽  
pp. 142-143
Author(s):  
I. M. Baccarini
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Granulosa Cells ◽  
Osmium Tetroxide ◽  
Human Ovary ◽  
Scanning Microscope ◽  
Electron Microscopic ◽  
Ultrastructural Studies ◽  
Microscopic Studies ◽  
Scanning Electron

Several ultrastructural studies demonstrated that the granulosa cells changed the structure since their differentiation, maturation and degeneration. However, little is known about the organization of the granulosa cells in the follicle for instance, the connection between the cells and cellular interchanges.Fragments of ovary obtained from the surgery room were fixed in 3% buffered glutaraldehyde for scanning microscope and post-fixed in 1% buffered osmium tetroxide for electron microscopic studies.

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