scholarly journals Mechanism of formation, ultrastructure, and function of the cytoplasmic bridge system during morphogenesis in Volvox.

1981 ◽  
Vol 91 (3) ◽  
pp. 756-769 ◽  
Author(s):  
K J Green ◽  
G I Viamontes ◽  
D L Kirk
Keyword(s):  
Mechanism Of Formation ◽  
Cell Interior ◽  
Cytoplasmic Bridge ◽  
Transmission Electron ◽  
Actual Movement ◽  
Ultrastructure And Function ◽  
And Function ◽  
And Inversion ◽  
Isolated Cell ◽  
Bridge System

The cytoplasmic bridge system that links all cells of a Volvox embryo and plays a crucial role in morphogenesis is shown to form as a result of localized incomplete cytokinesis; sometimes bridge formation occurs before other regions of the cell have begun to divide. Vesicles, believed to be derived from the cell interior, align along the presumptive cleavage furrow in the bridge-forming region. Apparently it is where these vesicles fail to fuse that bridges are formed. Conventional and high voltage transmission electron microscopy analyses confirm that bridges are regularly spaced; they possess a constant, highly ordered structure throughout cleavage and inversion. Concentric cortical striations (similar to those observed previously in related species) ring each bridge throughout its length and continue out under the plasmalemma of the cell body to abut the striations of neighboring bridges. These striations are closely associated with an electron-dense material that coats the inner face of the membrane throughout the bridge region and appears to be thickest near the equator of each bridge. In addition to the parallel longitudinal arrays of cortical microtubules that traverse the cells, we observed microtubules that angle into and through the bridges during cleavage; however, the latter are not seen once inversion movements have begun. During inversion, bridge bands undergo relocation relative to the cell bodies without any loss of integrity or change in bridge spacing. Observation of isolated cell clusters reveals that it is the sequential movement of individual cells with respect to a stationary bridge system, and not actual movement of the bridges, that gives rise to the observed relocation.

scholarly journals Linking Ultrastructure and Function in Four Genera of Anaerobic Ammonium-Oxidizing Bacteria: Cell Plan, Glycogen Storage, and Localization of Cytochrome c Proteins

2007 ◽  
Vol 190 (2) ◽  
pp. 708-717 ◽  
Author(s):  
Laura van Niftrik ◽  
Willie J. C. Geerts ◽  
Elly G. van Donselaar ◽  
Bruno M. Humbel ◽  
Richard I. Webb ◽  
...  
Keyword(s):  
Electron Tomography ◽  
Glycogen Storage ◽  
Anammox Bacteria ◽  
Ammonium Oxidation ◽  
Intracytoplasmic Membrane ◽  
Transmission Electron ◽  
Cell Plan ◽  
Ultrastructure And Function ◽  
And Function ◽  
Common Cell

ABSTRACT Anaerobic ammonium oxidation (anammox) is an ecologically and industrially important process and is performed by a clade of deeply branching Planctomycetes. Anammox bacteria possess an intracytoplasmic membrane-bounded organelle, the anammoxosome. In the present study, the ultrastructures of four different genera of anammox bacteria were compared with transmission electron microscopy and electron tomography. The four anammox genera shared a common cell plan and contained glycogen granules. Differences between the four genera included cell size (from 800 to 1,100 nm in diameter), presence or absence of cytoplasmic particles, and presence or absence of pilus-like appendages. Furthermore, cytochrome c proteins were detected exclusively inside the anammoxosome. This detection provides further support for the hypothesis that this organelle is the locus of anammox catabolism.

scholarly journals Morphological changes in hepatocytes of rats deprived of dietary nucleotides

1996 ◽  
Vol 76 (4) ◽  
pp. 579-589 ◽  
Author(s):  
Ana T. Lopez-Navarro ◽  
Juan D. Bueno ◽  
Angel Gil ◽  
Antonio Sánchez-Pozo
Keyword(s):  
Morphological Changes ◽  
Chromatin Condensation ◽  
Negative Effects ◽  
Adult Rats ◽  
Transmission Electron ◽  
Dietary Nucleotides ◽  
Liver Morphology ◽  
Ultrastructure And Function ◽  
And Function ◽  
Ribosome Association

The aim of the present study was to investigate the influence of dietary nucleotides on liver morphology. Adult rats were fed for 21 d on a nucleotide-containing diet or the same diet free of nucleotides. Liver sections were examined by light and transmission electron microscopy, as well as for nucleic acid and protein contents. Morphometric analysis was performed for different variables. Deprivation of dietary nucleotides resulted in a reduction in hepatocyte nuclear and nucleolar areas as well as in nuclear chromatin condensation. In addition, the rough endoplasmic reticulum was reduced, as were ribosome association and abundance, whereas fat accumulated. These findings portray dietary nucleotides as required nutrients for the liver under normal physiological conditions and suggest that an inadequate supply of nucleotides for a certain period of time has transient negative effects on liver ultrastructure and function.

Structure of contact sites between the outer and inner mitochondrial membranes investigated by HVEM tomography

1996 ◽  
Vol 54 ◽  
pp. 966-967
Author(s):  
C.A. Mannella ◽  
K.F. Buttle ◽  
K.A. O‘Farrell ◽  
A. Leith ◽  
M. Marko
Keyword(s):  
Liver Mitochondrion ◽  
Adenine Nucleotide ◽  
Protein Complexes ◽  
Mitochondrial Membranes ◽  
Electron Microscopic ◽  
Contact Sites ◽  
Transmission Electron ◽  
Precursor Proteins ◽  
Membrane Contacts ◽  
And Function

Early transmission electron microscopy of plastic-embedded, thin-sectioned mitochondria indicated that there are numerous junctions between the outer and inner membranes of this organelle. More recent studies have suggested that the mitochondrial membrane contacts may be the site of protein complexes engaged in specialized functions, e.g., import of mitochondrial precursor proteins, adenine nucleotide channeling, and even intermembrane signalling. It has been suggested that the intermembrane contacts may be sites of membrane fusion involving non-bilayer lipid domains in the two membranes. However, despite growing interest in the nature and function of intramitochondrial contact sites, little is known about their structure.We are using electron microscopic tomography with the Albany HVEM to determine the internal organization of mitochondria. We have reconstructed a 0.6-μm section through an isolated, plasticembedded rat-liver mitochondrion by combining 123 projections collected by tilting (+/- 70°) around two perpendicular tilt axes. The resulting 3-D image has confirmed the basic inner-membrane organization inferred from lower-resolution reconstructions obtained from single-axis tomography.

scholarly journals Mice with cleavage-resistant N-cadherin exhibit synapse anomaly in the hippocampus and outperformance in spatial learning tasks

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
M. Asada-Utsugi ◽  
K. Uemura ◽  
M. Kubota ◽  
Y. Noda ◽  
Y. Tashiro ◽  
...  
Keyword(s):  
Memory Function ◽  
Three Dimensional ◽  
Excitatory Synapses ◽  
Missense Mutations ◽  
Glutamatergic Synapses ◽  
Learning Tasks ◽  
Transmission Electron ◽  
Nmdar Activation ◽  
And Function

AbstractN-cadherin is a homophilic cell adhesion molecule that stabilizes excitatory synapses, by connecting pre- and post-synaptic termini. Upon NMDA receptor (NMDAR) activation by glutamate, membrane-proximal domains of N-cadherin are cleaved serially by a-disintegrin-and-metalloprotease 10 (ADAM10) and then presenilin 1(PS1, catalytic subunit of the γ-secretase complex). To assess the physiological significance of the initial N-cadherin cleavage, we engineer the mouse genome to create a knock-in allele with tandem missense mutations in the mouse N-cadherin/Cadherin-2 gene (Cdh2R714G, I715D, or GD) that confers resistance on proteolysis by ADAM10 (GD mice). GD mice showed a better performance in the radial maze test, with significantly less revisiting errors after intervals of 30 and 300 s than WT, and a tendency for enhanced freezing in fear conditioning. Interestingly, GD mice reveal higher complexity in the tufts of thorny excrescence in the CA3 region of the hippocampus. Fine morphometry with serial section transmission electron microscopy (ssTEM) and three-dimensional (3D) reconstruction reveals significantly higher synaptic density, significantly smaller PSD area, and normal dendritic spine volume in GD mice. This knock-in mouse has provided in vivo evidence that ADAM10-mediated cleavage is a critical step in N-cadherin shedding and degradation and involved in the structure and function of glutamatergic synapses, which affect the memory function.

scholarly journals Structure and Function of Trypsin-Loaded Fibrinolytic Liposomes

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
Anna Tanka-Salamon ◽  
Attila Bóta ◽  
András Wacha ◽  
Judith Mihály ◽  
Miklós Lovas ◽  
...  
Keyword(s):  
Freeze Fracture ◽  
Product Concentration ◽  
Plasma Clot ◽  
Dynamic Conditions ◽  
X Ray Scattering ◽  
Transmission Electron ◽  
Ft Ir ◽  
And Function ◽  
Targeted Release ◽  
Fibrinolytic Action

Protease encapsulation and its targeted release in thrombi may contribute to the reduction of haemorrhagic complications of thrombolysis. We aimed to prepare sterically stabilized trypsin-loaded liposomes (SSLT) and characterize their structure and fibrinolytic efficiency. Hydrogenated soybean phosphatidylcholine-basedSSLTwere prepared and their structure was studied by transmission electron microscopy combined with freeze fracture (FF-TEM), Fourier transform infrared spectroscopy (FT-IR), and small-angle X-ray scattering (SAXS). Fibrinolytic activity was examined at 45, 37, or 24°C on fibrin or plasma clots with turbidimetric and permeation-driven lysis assays. Trypsin was shown to be attached to the inner surface of vesicles (SAXS and FF-TEM) close to the lipid hydrophilic/hydrophobic interface (FT-IR). The thermosensitivity ofSSLTwas evidenced by enhanced fibrinolysis at 45°C: time to reduce the maximal turbidity to 20% decreased by 8.6% compared to 37°C and fibrin degradation product concentration in the permeation lysis assay was 2-fold to 5-fold higher than that at 24°C.SSLTexerted its fibrinolytic action on fibrin clots under both static and dynamic conditions, whereas plasma clot dissolution was observed only in the permeation-driven assay. The improved fibrinolytic efficiency ofSSLTunder dynamic conditions suggests that they may serve as a novel therapeutic candidate for dissolution of intravascular thrombi, which are typically exposed to permeation forces.

scholarly journals Alterations in flight muscle ultrastructure and function in Drosophila tropomyosin mutants.

1996 ◽  
Vol 135 (3) ◽  
pp. 673-687 ◽  
Author(s):  
A J Kreuz ◽  
A Simcox ◽  
D Maughan
Keyword(s):  
Amino Acid ◽  
Power Output ◽  
Flight Muscle ◽  
Structure And Function ◽  
Wild Type ◽  
Muscle Tropomyosin ◽  
Ultrastructure And Function ◽  
And Function ◽  
Net Power Output ◽  
Current Report

Drosophila indirect flight muscle (IFM) contains two different types of tropomyosin: a standard 284-amino acid muscle tropomyosin, Ifm-TmI, encoded by the TmI gene, and two > 400 amino acid tropomyosins, TnH-33 and TnH-34, encoded by TmII. The two IFM-specific TnH isoforms are unique tropomyosins with a COOH-terminal extension of approximately 200 residues which is hydrophobic and rich in prolines. Previous analysis of a hypomorphic TmI mutant, Ifm(3)3, demonstrated that Ifm-TmI is necessary for proper myofibrillar assembly, but no null TmI mutant or TmII mutant which affects the TnH isoforms have been reported. In the current report, we show that four flightless mutants (Warmke et al., 1989) are alleles of TmI, and characterize a deficiency which deletes both TmI and TmII. We find that haploidy of TmI causes myofibrillar disruptions and flightless behavior, but that haploidy of TmII causes neither. Single fiber mechanics demonstrates that power output is much lower in the TmI haploid line (32% of wild-type) than in the TmII haploid line (73% of wild-type). In myofibers nearly depleted of Ifm-TmI, net power output is virtually abolished (< 1% of wild-type) despite the presence of an organized fibrillar core (approximately 20% of wild-type). The results suggest Ifm-TmI (the standard tropomyosin) plays a key role in fiber structure, power production, and flight, with reduced Ifm-TmI expression producing corresponding changes of IFM structure and function. In contrast, reduced expression of the TnH isoforms has an unexpectedly mild effect on IFM structure and function.

Essential thrombocythemia in a child: Platelet ultrastructure and function

1980 ◽  
Vol 8 (1) ◽  
pp. 87-107 ◽  
Author(s):  
Marion I. Barnhart ◽  
Tae H. Kim ◽  
Bruce L. Evatt ◽  
Abdelsalam H. Ragab ◽  
Victor K. Lui ◽  
...  
Keyword(s):  
Essential Thrombocythemia ◽  
Ultrastructure And Function ◽  
And Function

scholarly journals Ultrastructure and function of mitochondria in gametocytic stage ofPlasmodium falciparum

Parasite ◽  
2000 ◽  
Vol 7 (1) ◽  
pp. 19-26 ◽  
Author(s):  
J. Krungkrai ◽  
P. Prapunwattana ◽  
S.R. Krungkrai
Keyword(s):  
Ofplasmodium Falciparum ◽  
Ultrastructure And Function ◽  
And Function
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