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PubMed1997

Degeneration of spermatocytes during meiotic divisions in the golden hamster testis.

The appearance and morphology of spontaneously degenerating meiotic spermatocytes was studied in late pubertal golden hamster testes by high resolution light and electron microscopy. While degeneration of primary spermatocytes during the long prophase of meiosis I is chiefly confined to midpachytene cells in stages VII-VIII of the seminiferous cycle, the subsequent meiotic phases (and their degenerative disorders) appear side by side in stage XIII of the cycle. Degeneration regularly concerns, in decreasing order of frequency, midpachytene primary spermatocytes (prophase I), metaphases I/II, telophases I/II, prophase II, and anaphases I/II. This closely corresponds to the apparent durations of these respective phases. In all meiotic phases studied, degeneration follows the same morphological pattern, including an initial vacuolar transformation of the cytoplasm and accumulation of densely staining material along membranes and microtubules, a progressive condensation of all nuclear and cytoplasmic structures, and the final cellular disintegration. In meta- and anaphase cells, meiotic spindle fibres are often perceivable even in advanced stages of degeneration. Both the morphological uniformity of spermatocyte degeneration and the constant susceptibility of meiotic phases to degeneration throughout meiotic divisions point to a generally similar mechanism underlying the physiological loss of meiotic spermatocytes.

Animals↗
PubMed1997

Preassembly of annulate lamellae in egg extracts inhibits nuclear pore complex formation, but not nuclear membrane assembly.

Annulate lamellae (AL) are cytoplasmic structures containing pore complexes similar in composition and morphology to nuclear envelope pore complexes. We have tested the ability of Xenopus egg extract to support nuclear membrane and pore complex formation when chromatin is added to extract only after annulate lamellae had been allowed to assemble (preincubated extract). We have observed that preassembly of AL does not inhibit the formation of a double membrane surrounding sperm chromatin. However, these double membranes are often distended, do not support accumulation of karyophilic proteins, and do not possess immunologically or morphologically identifiable pore complexes. We have demonstrated that nuclear pore complex assembly and function can be rescued by adding isolated egg vesicles to the preincubated extract. Our data support the conclusion that multiple vesicle populations are utilized in the formation of a nuclear envelope, including: vesicle population(s) which are common to pore formation in nuclear envelopes and annulate lamellae, and vesicle population(s) which seem to be preferentially utilized for nuclear membrane assembly.

Animals↗
PubMed1996

In vivo and in vitro studies on the morphological change in the monkey epidermal Langerhans cells following exposure to dengue 2 (16681) virus.

A direct comparison of skin Langerhans cell (LC) morphologic change following in vivo and in vitro exposure to dengue-2 (DEN-2) virus (16681) was performed in the monkey to investigate any differences in functional activity profiles. Time-lapse study of skin biopsy at the intradermal (id) virus injection sites, and thin skin sheets removed from the monkey with exposure to virus in culture medium, revealed a highly active migration of epidermal LCs in both sets of experimental specimens. The migration led to a relatively higher number of dendritic cells (DC) which appeared in active migrational profiles, in the superficial dermis. Moreover, obvious cytoplasmic structural changes, corresponding to their immunologic function, were observed in these superficial dermal DCs 2 hours after exposure. Despite their similar changes, early and late endosomes with degraded virus-like particles could be seen in the skin sheets owing to lagging in cellular physiological process in vitro, but none in the skin biopsies. Existence of these endosomes, which was extremely difficult to visualize in vivo, highlighted the mode of antigen processing by the endocytic pathway. The present study showed that the epidermal LC was a potent antigen-presenting cell for eliciting the success of id immunization and carried out the immunological activity in vivo or in vitro in the like manner, in respect to the physiological conditions.

Animals↗
PubMed1997

Implication of mitochondria in apoptosis.

The induction phase of programmed cell death (PCD) or apoptosis is characterized by an extreme heterogeneity of potential PCD-triggering signal transduction pathways. During the subsequent effector phase, the numerous PCD-inducing stimuli converge into a few stereotypical pathways and cells pass a 'point of no return', thus becoming irreversibly committed to death. Evidence is accumulating that cytoplasmic structures, including mitochondria, participate in the critical effector stage and that alterations usually considered to define apoptosis, as nuclear chromatolysis and cytolysis, have to be ascribed to the late degradation phase. We and others have recently shown that nuclear features of apoptosis are preceded by alterations in mitochondrial function and structure. The importance of these alterations for the apoptotic process and also the possible link between, these observations, the permeability transition pore and the programmed cell death, are discussed.

Animals↗
PubMed1997

Ultrastructural studies of the effect of pentoxyfylline on the hepatic cell of the rat with simultaneous administration of cyclophosphamide.

Ultrastructural examinations carried out on liver specimens collected from Wistar rats revealed that single administration of cyclophosphamide in a dose of 150 mg/kg body weight produced changes in the cytoplasmic structures, particularly in the smooth endoplasmic reticulum and mitochondria. The changes were reversible and subsided 14 days following cyclophosphamide administration. Administration of pentoxyfylline to rats in a dose of 30 mg/kg b.w./day for 10 days induced structural alterations in the intracytoplasmic structures of hepatocytes, similar to those caused by cyclophosphamide, although more intensified in the vicinity of the vascular pole. The pentoxyfylline-induced changes in hepatocytes retreated already 4 days after its withdrawal and can be considered adaptative. Simultaneous administration of both drugs to rats resulted in enhanced metabolic disturbances in hepatocytes and dissociation of adaptative mechanisms manifesting themselves in irreversible morphological changes in the intracytoplasmic structures and in the occurrence of collagen in the intercellular spaces.

Animals↗
PubMed1998

Micromanipulation of retinal neurons by optical tweezers.

Micromanipulation by optical tweezers has been tested in cultures of mature isolated retinal cells to determine its potential for use in creating synaptic circuits in vitro. Rod and cone photoreceptors as well as other retinal nerve cell types could be optically trapped with a 980 nm diode laser mounted on an inverted light microscope using a 40x oil immersion objective numerical aperture of 1.3. Manipulation was done under sterile conditions using transparent culture dishes. To form cell groups, one half of a culture dish was made less adhesive by application of a thin layer of silicone elastomer. Unattached cells were trapped and relocated next to cells lying on an adhesive culture substrate. Optical trapping did not affect the ability of neurons to subsequently attach to the culture substrate. Up to 60% of trapped cells survived for 2 or more days. The pattern and rate of process outgrowth for manipulated cells was comparable to unmanipulated cells and by 2 days, cell-cell contacts were observed. Cultures were fixed at 2 and 5 days for electron microscopy. Organelle, nuclear and cytoplasmic structure of manipulated cells was completely normal and in photoreceptors, synaptic vesicles and ribbons were intact. Optical tweezers, therefore, provide a benign technique with which to micromanipulate whole neurons. The procedures also bestow increased precision to the study of cell-cell interactions by allowing the selection of potentially interacting cell types at a single cell level.

Ambystoma↗
PubMed1998

[Ultrastructural and immunocytochemical study of Listeria monocytogenes with varying levels of pathogenicity factor production].

Wild and mutant strains of Listeria monocytogenes are examined by electron and immunoelectron microscopy. The mutant strain was characterized as a strain with a high level of production of pathogenic factors. No essential morphological criteria permitting the differentiation between wild and mutant Listeria strains were detected. Addition of activated charcoal to nutrient medium resulted in similar morphological changes in both strains. Enlargement of cells, a thicker cell wall, and changes in the cytoplasm structure are objective morphological signs of functional activity of bacteria with a higher level of pathogenic factor production. Indirect immunocytochemical method demonstrated the localization of specific phosphatidyl inosityl phospholipase C.

Bacterial Proteins↗
PubMed1983

The presence of a histidine-aspartic acid pair in the active site of 2-hydroxyacid dehydrogenases. X-ray refinement of cytoplasmic malate dehydrogenase.

The structure of cytoplasmic malate dehydrogenase has been partially refined by crystallographic least squares methods. Using x-ray phases based on the refined coordinates, analysis of the resultant electron density maps has led to a new model of cytoplasmic malate dehydrogenase and a tentative "x-ray sequence." The two crystallographically independent subunits comprising the dimeric enzyme are nearly identical in structure and are related to each other by roughly 2-fold rotational symmetry. The best fit of the molecular structure of cytoplasmic malate dehydrogenase to that of lactate dehydrogenase has been obtained by least squares methods. The active sites of these two enzymes contain similarly oriented His-Asp pairs linked by a hydrogen bond which may function as a proton relay system during catalysis. This pair could also provide an explanation for the relatively stronger binding by cytoplasmic malate dehydrogenase and lactate dehydrogenase of NADH versus NAD. Similar His-Asp pairs have been observed in the serine proteases, thermolysin, and phospholipase A2, and the His-Asp pair may play a similar functional role in all of these enzymes.

Amino Acid Sequence↗
PubMed1999

Crystal structure of the cytoplasmic domain of the type I TGF beta receptor in complex with FKBP12.

Activation of the type I TGFbeta receptor (TbetaR-I) requires phosphorylation of a regulatory segment known as the GS region, located upstream of the serine/threonine kinase domain in the cytoplasmic portion of the receptor. The crystal structure of a fragment of unphosphorylated TbetaR-I, containing both the GS region and the catalytic domain, has been determined in complex with the FK506-binding protein FKBP12. TbetaR-I adopts an inactive conformation that is maintained by the unphosphorylated GS region. FKBP12 binds to the GS region of the receptor, capping the TbetaR-II phosphorylation sites and further stabilizing the inactive conformation of TbetaR-I. Certain structural features at the catalytic center of TbetaR-I are characteristic of tyrosine kinases rather than Ser/Thr kinases.

Activin Receptors, Type I↗
PubMed2001

Two crystal structures of the cytoplasmic molybdate-binding protein ModG suggest a novel cooperative binding mechanism and provide insights into ligand-binding specificity.

The X-ray structures of the cytoplasmic molybdate-binding protein ModG from Azotobacter vinelandii in two different crystal forms have been determined. For such a small protein it is remarkably complex. Each 14.3 kDa subunit contains two small beta-barrel domains, which display an OB-fold motif, also seen in the related structure of ModE, a molybdenum-dependent transcriptional regulator, and very recently in the Mop protein that, like ModG, has been implicated in molybdenum homeostasis within the cell. In contrast to earlier speculation, the functional unit of ModG is actually not a dimer (as in ModE), but a trimer capable of binding a total of eight molybdate molecules that are distributed between two disparate types of site. All the binding sites are located at subunit interfaces, with one type lying on a crystallographic 3-fold axis, whilst the other lies between pairs of subunits. The two types of site are linked by short hydrogen bond networks that may suggest a cooperative binding mechanism. A superposition of two subunits of the ModG trimer on the apo-ModE dimer allows the probable locations of the molybdate-binding sites of the latter to be assigned. Through structural comparisons with other oxyanion-binding proteins, including Mop and ModE, it is possible to speculate about ligand-binding affinities, selectivity and evolution.

Aldehyde Oxidoreductases↗
PubMed1957

The structure of some cytoplasmic components of plant cells in relation to the biochemical properties of isolated particles.

1. Electron micrographs of thin sections of material fixed with buffered osmium tetroxide have been used for comparison of the fine structure of isolated cytoplasmic particles from silver beet petioles and roots of germinating wheat with that of the cytoplasm of the intact cells. 2. Mitochondria of wheat roots have an external double membrane and poorly oriented internal double membranes. As compared with the structures seen in situ, the isolated mitochondria showed evidence of some disorganisation of the fine internal structure, probably due to osmotic effects. The possible influence of such changes on the enzymic properties of the isolated mitochondria is discussed. 3. The isolated plant microsomes are mainly spherical vesicular structures consisting of (a) an outer membrane enclosing (b) either an homogeneous slightly dense material (wheat root microsomes) or some granular dense material (silver beet microsomes) and (c) small dense particles, mostly associated with the vesicle membranes. 4. The cytoplasm of the wheat root cells does not contain any structures similar to the isolated microsomes but has a very dense reticular network, consisting of membranes with associated small dense particles, here called the endoplasmic reticulum. The observations indicate that the isolated microsomes arise mainly by rupture and transformation of the membranes of this structure. The effects of such extensive changes in the lipoprotein membranes on the enzymic activities of the endoplasmic reticulum, as studied in isolated microsomes, is discussed. 5. Meristematic wheat root cells contain structures which consist of smooth membranes with associated vacuoles and are similar to the Golgi zones of animal cells. The membranes of these zones probably contribute to the microsomal fraction under the conditions of preparation used for the enzymic and chemical studies previously reported.

Animals↗
PubMed2006

Crystal structure of the cytoplasmic domain of the chloride channel ClC-0.

Ion channels are frequently organized in a modular fashion and consist of a membrane-embedded pore domain and a soluble regulatory domain. A similar organization is found for the ClC family of Cl- channels and transporters. Here, we describe the crystal structure of the cytoplasmic domain of ClC-0, the voltage-dependent Cl- channel from T. marmorata. The structure contains a folded core of two tightly interacting cystathionine beta-synthetase (CBS) subdomains. The two subdomains are connected by a 96 residue mobile linker that is disordered in the crystals. As revealed by analytical ultracentrifugation, the domains form dimers, thereby most likely extending the 2-fold symmetry of the transmembrane pore. The structure provides insight into the organization of the cytoplasmic domains within the ClC family and establishes a framework for guiding future investigations on regulatory mechanisms.

Amino Acid Sequence↗
PubMed1987

Cytoplasmic bar-like structures of alveolar type II cells: an ultrastructural study in freshly isolated cells from rat lungs.

Bar-like structures are tubular cytoplasmic inclusions found in situ in pulmonary epithelial type II cells of several animal species. The physiological significance and mode of formation of these inclusions are not fully established. In this paper, we describe bar-like structures as found in freshly isolated type II cells from rat lungs. Pulmonary cells were dissociated from the tissue with elastase and separated on a discontinuous density gradient of Percoll. The complete isolation procedure yielded 17 X 10(6) type II cells per animal (purity = 80%). Either from the crude cell suspensions or the purified preparations, only a small fraction of the type II cell population harbored the inclusions (less than 5%). It is shown that the bounding membranes of the bar-like structures can derive from the endoplasmic reticulum, the nuclear membrane, or the Golgi apparatus. Occasional connections with lamellar bodies were observed, and different levels of complexity in the bar-like structures were also found. The apparent rigid conformation and the orientation of the bar-like structures were taken as evidence for a role of the cytoskeleton in their formation. Because the inclusions do not appear to be new organelles or cellular structures performing a specific function, we propose that their formation may be a transient and limited cellular event in normal cells. However, the stabilization and the generation of the osmiophilic structures, as well as their overproduction, may reflect alterations of the normal physiology of the type II cells.

Animals↗
PubMed1988

Isolation and characterization of interferon-resistant variants from S49 mouse lymphoma.

S49 mouse lymphoma cells were found to be extremely sensitive to the antiproliferative activity of interferon. These characteristics were studied to select for IFN-resistant cell variants. Some 0.6% of the parental S49 cell population were resistant to the antiproliferative and cytotoxic activities of IFN. The resistant cells were cloned and analyzed for their responses to several of the activities of IFN, namely, inhibition of encephalomyocarditis (EMC) virus, murine leukemia virus (MuLV) replications, and the induction of (2'-5') oligoadenylate synthetase. Among the clones selected some were highly resistant while others demonstrated only partial responsiveness to IFN. S49 cells demonstrate tubular structures in the cytoplasm. These structures were previously reported to be antigenically related to mouse mammary tumor virus (MMTV). We report here that IFN treatment decreases the expression of these cytoplasmic viral structures as revealed by electron microscopy. To correlate this novel antiviral activity to the more established functions of IFN we utilized the above mentioned S49 IFN-resistant variants. The anti-MMTV activity of IFN correlated with the other effects of IFN in both the highly resistant and partially responsive S49 clones. Our findings indicate that a relatively high proportion of S49 cells vary in their response to IFN. The defect in the resistant cells appears to affect a primary response to IFN which is common to its diverse activities. Furthermore, the effect of IFN on MMTV-related structures involves the usual pathway of IFN action.

2',5'-Oligoadenylate Synthetase↗
PubMed1993

Fractionation and identification of cytoplasmic tRNAS and structural characterization of a phenylalanine and a leucine tRNA from cucumber hypocotyls.

Total cytoplasmic tRNAs from cucumber hypocotyls were fractionated by two-dimensional polyacrylamide gel electrophoresis into about 56 species. Of these, 32 tRNA species were identified by aminoacylation as tRNA specific for 15 amino acids. Furthermore, cytoplasmic tRNA(Phe) and tRNA(Leu(NAA)) were purified to homogeneity by the combination of RPC-5 column chromatography and two-dimensional polyacrylamide gel electrophoresis. The primary structure of tRNA(Leu(NAA)) and the modified nucleotides of tRNA(Phe) have been determined. The sequence of cucumber cytoplasmic tRNA(Leu(NAA)) is identical to that of bean cytoplasmic tRNA(Leu(NAA)) except for three base differences in the variable loop.

Autoradiography↗
PubMed1999

Four-helical-bundle structure of the cytoplasmic domain of a serine chemotaxis receptor.

The bacterial chemotaxis receptors are transmembrane receptors with a simple signalling pathway which has elements relevant to the general understanding of signal recognition and transduction across membranes, how signals are relayed between molecules in a pathway, and how adaptation to a persistent signal is achieved. In contrast to many mammalian receptors which signal by oligomerizing upon ligand binding, the chemotaxis receptors are dimeric even in the absence of their ligands, and their signalling does not depend on a monomer-dimer equilibrium. Bacterial chemotaxis receptors are composed of a ligand-binding domain, a transmembrane domain consisting of two helices TM1 and TM2, and a cytoplasmic domain. All known bacterial chemotaxis receptors have a highly conserved cytoplasmic domain, which unites signals from different ligand domains into a single signalling pathway to flagella motors. Here we report the crystal structure of the cytoplasmic domain of a serine chemotaxis receptor of Escherichia coli, which reveals a 200 A-long coiled-coil of two antiparallel helices connected by a 'U-turn'. Two of these domains form a long, supercoiled, four-helical bundle in the cytoplasmic portion of the receptor.

Chemotaxis↗