Coxsackievirus can exploit LC3 in both autophagy-dependent and -independent manners in vivo

RNA viruses modify intracellular membranes to produce replication scaffolds. In pancreatic cells, coxsackievirus B3 (CVB3) hijacks membranes from the autophagy pathway, and in vivo disruption of acinar cell autophagy dramatically delays CVB3 replication. This is reversed by expression of GFP-LC3, indicating that CVB3 may acquire membranes from an alternative, autophagy-independent, source(s). Herein, using 3 recombinant CVB3s (rCVB3s) encoding different proteins (proLC3, proLC3(G120A), or ATG4B(C74A)), we show that CVB3 is, indeed, flexible in its utilization of cellular membranes. When compared with a control rCVB3, all 3 viruses replicated to high titers in vivo, and caused severe pancreatitis. Most importantly, each virus appeared to subvert membranes in a unique manner. The proLC3 virus produced a large quantity of LC3-I which binds to phosphatidylethanolamine (PE), affording access to the autophagy pathway. The proLC3(G120A) protein cannot attach to PE, and instead binds to the ER-resident protein SEL1L, potentially providing an autophagy-independent source of membranes. Finally, the ATG4B(C74A) protein sequestered host cell LC3-I, causing accumulation of immature phagophores, and massive membrane rearrangement. Taken together, our data indicate that some RNA viruses can exploit a variety of different intracellular membranes, potentially maximizing their replication in each of the diverse cell types that they infect in vivo.

Assembly of the Ebola Virus Nucleoprotein from a Chaperoned VP35 Complex

Ebolavirus NP oligomerizes into helical filaments found at the core of the virion, encapsidates the viral RNA genome, and serves as a scaffold for additional viral proteins within the viral nucleocapsid. We identified a portion of the phosphoprotein homolog VP35 that binds with high affinity to nascent NP and regulates NP assembly and viral genome binding. Removal of the VP35 peptide leads to NP self-assembly via its N-terminal oligomerization arm. NP oligomerization likely causes a conformational change between the NP N- and C-terminal domains, facilitating RNA binding. These functional data are complemented by crystal structures of the NP°-VP35 complex at 2.4 Å resolution. The interactions between NP and VP35 illuminated by these structures are conserved among filoviruses and provide key targets for therapeutic intervention.

Comprehensive bioimaging with fluorinated nanoparticles using breathable liquids

Fluorocarbons are lipophobic and non-polar molecules that exhibit remarkable biocompatibility, with applications in liquid ventilation and synthetic blood. The unique properties of these compounds have also enabled mass spectrometry imaging of tissues where the fluorocarbons act as a Teflon-like coating for nanostructured surfaces to assist in desorption/ionization. Here we report fluorinated gold nanoparticles (f-AuNPs) designed to facilitate nanostructure imaging mass spectrometry. Irradiation of f-AuNPs results in the release of the fluorocarbon ligands providing a driving force for analyte desorption. The f-AuNPs allow for the mass spectrometry analysis of both lipophilic and polar (central carbon) metabolites. An important property of AuNPs is that they also act as contrast agents for X-ray microtomography and electron microscopy, a feature we have exploited by infusing f-AuNPs into tissue via fluorocarbon liquids to facilitate multimodal (molecular and anatomical) imaging.

Structural rearrangement of ebola virus VP40 begets multiple functions in the virus life cycle

Proteins, particularly viral proteins, can be multifunctional, but the mechanisms behind multifunctionality are not fully understood. Here, we illustrate through multiple crystal structures, biochemistry, and cellular microscopy that VP40 rearranges into different structures, each with a distinct function required for the ebolavirus life cycle. A butterfly-shaped VP40 dimer traffics to the cellular membrane. Once there, electrostatic interactions trigger rearrangement of the polypeptide into a linear hexamer. These hexamers construct a multilayered, filamentous matrix structure that is critical for budding and resembles tomograms of authentic virions. A third structure of VP40, formed by a different rearrangement, is not involved in virus assembly but instead uniquely binds RNA to regulate viral transcription inside infected cells. These results provide a functional model for ebolavirus matrix assembly and the other roles of VP40 in the virus life cycle and demonstrate how a single wild-type, unmodified polypeptide can assemble into different structures for different functions.

ROS and Sympathetically Mediated Mitochondria Activation in Brown Adipose Tissue Contribute to Methamphetamine-Induced Hyperthermia

Methamphetamine (Meth) abuse has been shown to induce alterations in mitochondrial function in the brain as well as to induce hyperthermia, which contributes to neurotoxicity and Meth-associated mortality. Brown adipose tissue (BAT), a thermogenic site known to be important in neonates, has recently regained importance since being identified in significant amounts and in correlation with metabolic balance in human adults. Given the high mitochondrial content of BAT and its role in thermogenesis, we aimed to investigate whether BAT plays any role in the development of Meth-induced hyperthermia. By ablating or denervating BAT, we identified a partial contribution of this organ to Meth-induced hyperthermia. BAT ablation decreased temperature by 0.5°C and reduced the length of hyperthermia by 1 h, compared to sham-operated controls. BAT denervation also affected the development of hyperthermia in correlation with decreased the expression of electron transport chain molecules, and increase on PCG1a levels, but without affecting Meth-induced uncoupling protein 1 upregulation. Furthermore, in isolated BAT cells in culture, Meth, but not Norepinephrine, induced H2O2 upregulation. In addition, we found that in vivo Reactive Oxygen Species (ROS) play a role in Meth hyperthermia. Thus, sympathetically mediated mitochondrial activation in the BAT and Meth-induced ROS are key components to the development of hyperthermia in Meth abuse.

Pancreatic acinar cell-specific autophagy disruption reduces coxsackievirus replication and pathogenesis in vivo

Autophagy protects against many infections by inducing the lysosomal-mediated degradation of invading pathogens. However, previous in vitro studies suggest that some enteroviruses not only evade these protective effects but also exploit autophagy to facilitate their replication. We generated Atg5(f/f)/Cre(+) mice, in which the essential autophagy gene Atg5 is specifically deleted in pancreatic acinar cells, and show that coxsackievirus B3 (CVB3) requires autophagy for optimal infection and pathogenesis. Compared to Cre(-) littermates, Atg5(f/f)/Cre(+) mice had an ∼2,000-fold lower CVB3 titer in the pancreas, and pancreatic pathology was greatly diminished. Both in vivo and in vitro, Atg5(f/f)/Cre(+) acinar cells had reduced intracellular viral RNA and proteins. Furthermore, intracellular structural elements induced upon CVB3 infection, such as compound membrane vesicles and highly geometric paracrystalline arrays, which may represent viral replication platforms, were infrequently observed in infected Atg5(f/f)/Cre(+) cells. Thus, CVB3-induced subversion of autophagy not only benefits the virus but also exacerbates pancreatic pathology.

Fine-tuning of Drp1/Fis1 availability by AKAP121/Siah2 regulates mitochondrial adaptation to hypoxia

Defining the mechanisms underlying the control of mitochondrial fusion and fission is critical to understanding cellular adaptation to diverse physiological conditions. Here we demonstrate that hypoxia induces fission of mitochondrial membranes, dependent on availability of the mitochondrial scaffolding protein AKAP121. AKAP121 controls mitochondria dynamics through PKA-dependent inhibitory phosphorylation of Drp1 and PKA-independent inhibition of Drp1-Fis1 interaction. Reduced availability of AKAP121 by the ubiquitin ligase Siah2 relieves Drp1 inhibition by PKA and increases its interaction with Fis1, resulting in mitochondrial fission. High AKAP121 levels, seen in cells lacking Siah2, attenuate fission and reduce apoptosis of cardiomyocytes under simulated ischemia. Infarct size and degree of cell death were reduced in Siah2(-/-) mice subjected to myocardial infarction. Inhibition of Siah2 or Drp1 in hatching C. elegans reduces their life span. Through modulating Fis1/Drp1 complex availability, our studies identify Siah2 as a key regulator of hypoxia-induced mitochondrial fission and its physiological significance in ischemic injury and nematode life span.

Ultrastructural and biophysical characterization of hepatitis C virus particles produced in cell culture

We analyzed the biochemical and ultrastructural properties of hepatitis C virus (HCV) particles produced in cell culture. Negative-stain electron microscopy revealed that the particles were spherical (∼40- to 75-nm diameter) and pleomorphic and that some of them contain HCV E2 protein and apolipoprotein E on their surfaces. Electron cryomicroscopy revealed two major particle populations of ∼60 and ∼45 nm in diameter. The ∼60-nm particles were characterized by a membrane bilayer (presumably an envelope) that is spatially separated from an internal structure (presumably a capsid), and they were enriched in fractions that displayed a high infectivity-to-HCV RNA ratio. The ∼45-nm particles lacked a membrane bilayer and displayed a higher buoyant density and a lower infectivity-to-HCV RNA ratio. We also observed a minor population of very-low-density, >100-nm-diameter vesicular particles that resemble exosomes. This study provides low-resolution ultrastructural information of particle populations displaying differential biophysical properties and specific infectivity. Correlative analysis of the abundance of the different particle populations with infectivity, HCV RNA, and viral antigens suggests that infectious particles are likely to be present in the large ∼60-nm HCV particle populations displaying a visible bilayer. Our study constitutes an initial approach toward understanding the structural characteristics of infectious HCV particles.

Short-term fasting induces profound neuronal autophagy

Disruption of autophagy--a key homeostatic process in which cytosolic components are degraded and recycled through lysosomes--can cause neurodegeneration in tissue culture and in vivo. Upregulation of this pathway may be neuroprotective, and much effort is being invested in developing drugs that cross the blood brain barrier and increase neuronal autophagy. One well-recognized way of inducing autophagy is by food restriction, which upregulates autophagy in many organs including the liver; but current dogma holds that the brain escapes this effect, perhaps because it is a metabolically privileged site. Here, we have re-evaluated this tenet using a novel approach that allows us to detect, enumerate and characterize autophagosomes in vivo. We first validate the approach by showing that it allows the identification and characterization of autophagosomes in the livers of food-restricted mice. We use the method to identify constitutive autophagosomes in cortical neurons and Purkinje cells, and we show that short-term fasting leads to a dramatic upregulation in neuronal autophagy. The increased neuronal autophagy is revealed by changes in autophagosome abundance and characteristics, and by diminished neuronal mTOR activity in vivo, demonstrated by a reduction in levels of phosphorylated S6 ribosomal protein in Purkinje cells. The increased abundance of autophagosomes in Purkinje cells was confirmed using transmission electron microscopy. Our data lead us to speculate that sporadic fasting might represent a simple, safe and inexpensive means to promote this potentially therapeutic neuronal response.

A general strategy for the bacterial expression of amyloidogenic peptides using BCL-XL-1/2 fusions

Biophysical studies on amyloidogenic and aggregation-prone peptides often require large quantities of material. However, solid-phase synthesis, handling, and purification of peptides often present challenges on these scales. Recombinant expression is an attractive alternative because of its low cost, the ability to isotopically label the peptides, and access to sequences exceeding approximately 50 residues. However, expression systems that seek to solubilize amyloidogenic peptides suffer from low yields, difficult optimizations, and isolation challenges. We present a general strategy for expressing and isolating amyloidogenic peptides in Escherichia coli by fusion to a polypeptide that drives the expression of attached peptides into bacterial inclusion bodies. This scheme minimizes toxicity during bacterial growth and enables the processing and handling of the peptides in denaturing solutions. Immobilized metal affinity chromatography, reverse phase HPLC, and cyanogen bromide cleavage are used to isolate the peptide, followed by further reverse phase HPLC, which yields milligram quantities of the purified peptide. We demonstrate that driving the peptides into inclusion bodies using fusion to BCL-XL-1/2 is a general strategy for their expression and isolation, as exemplified by the production of 11 peptides species.

Talin 1 and 2 are required for myoblast fusion, sarcomere assembly and the maintenance of myotendinous junctions

Talin 1 and 2 connect integrins to the actin cytoskeleton and regulate the affinity of integrins for ligands. In skeletal muscle, talin 1 regulates the stability of myotendinous junctions (MTJs), but the function of talin 2 in skeletal muscle is not known. Here we show that MTJ integrity is affected in talin 2-deficient mice. Concomitant ablation of talin 1 and 2 leads to defects in myoblast fusion and sarcomere assembly, resembling defects in muscle lacking beta1 integrins. Talin 1/2-deficient myoblasts express functionally active beta1 integrins, suggesting that defects in muscle development are not primarily caused by defects in ligand binding, but rather by disruptions of the interaction of integrins with the cytoskeleton. Consistent with this finding, assembly of integrin adhesion complexes is perturbed in the remaining muscle fibers of talin 1/2-deficient mice. We conclude that talin 1 and 2 are crucial for skeletal muscle development, where they regulate myoblast fusion, sarcomere assembly and the maintenance of MTJs.

DNase I inhibits a late phase of reactive oxygen species production in neutrophils

Neutrophils kill bacteria on extracellular complexes of DNA fibers and bactericidal proteins known as neutrophil extracellular traps (NETs). The NET composition and the bactericidal mechanisms they use are not fully understood. Here, we show that treatment with deoxyribonuclease (DNase I) impairs a late oxidative response elicited by Gram-positive and Gram-negative bacteria and also by phorbol ester. Isoluminol-dependent chemiluminescence elicited by opsonized Listeria monocytogenes-stimulated neutrophils was inhibited by DNase I, and the DNase inhibitory effect was also evident when phagocytosis was blocked, suggesting that DNase inhibits an extracellular mechanism of reactive oxygen species (ROS) generation. The DNase inhibitory effect was independent of actin polymerization. Phagocytosis and cell viability were not impaired by DNase I. Immunofluorescence analysis shows that myeloperoxidase is present on NETs. Furthermore, granular proteins were detected in NETs from Rab27a-deficient neutrophils which have deficient exocytosis, suggesting that exocytosis and granular protein distribution on NETs proceed by independent mechanisms. NADPH oxidase subunits were also detected on NETs, and the detection of extracellular trap-associated NADPH oxidase subunits was abolished by treatment with DNase I and dependent on cell stimulation. In vitro analyses demonstrate that MPO and NADPH oxidase activity are not directly inhibited by DNase I, suggesting that its effect on ROS production depends on NET disassembly. Altogether, our data suggest that inhibition of ROS production by microorganism-derived DNase would contribute to their ability to evade killing.

Progressive myopathy and defects in the maintenance of myotendinous junctions in mice that lack talin 1 in skeletal muscle

The development and function of skeletal muscle depend on molecules that connect the muscle fiber cytoskeleton to the extracellular matrix (ECM). beta1 integrins are ECM receptors in skeletal muscle, and mutations that affect the alpha7beta1 integrin cause myopathy in humans. In mice, beta1 integrins control myoblast fusion, the assembly of the muscle fiber cytoskeleton, and the maintenance of myotendinous junctions (MTJs). The effector molecules that mediate beta1 integrin functions in muscle are not known. Previous studies have shown that talin 1 controls the force-dependent assembly of integrin adhesion complexes and regulates the affinity of integrins for ligands. Here we show that talin 1 is essential in skeletal muscle for the maintenance of integrin attachment sites at MTJs. Mice with a skeletal muscle-specific ablation of the talin 1 gene suffer from a progressive myopathy. Surprisingly, myoblast fusion and the assembly of integrin-containing adhesion complexes at costameres and MTJs advance normally in the mutants. However, with progressive ageing, the muscle fiber cytoskeleton detaches from MTJs. Mechanical measurements on isolated muscles show defects in the ability of talin 1-deficient muscle to generate force. Collectively, our findings show that talin 1 is essential for providing mechanical stability to integrin-dependent adhesion complexes at MTJs, which is crucial for optimal force generation by skeletal muscle.

Phage escape libraries for checkmate analysis

Ligand-binding epitopes of proteins can mutate rapidly, as shown by viral mutations that lead to escape from neutralizing antibodies. We have undertaken to recreate in vitro the evolutionary competition between viral mutations that allow escape from antibody binding and host mutations that generate new neutralizing antibodies to the mutated viral antigen. To examine this vital race, we describe a phage-based method that allows rapid analysis of molecules that perturb the binding of proteins to their ligands. Because the system can amplify by replication, single-molecule sensitivity can be achieved. When combinatorial protein or small-molecule libraries are studied, large numbers of binding events can be analyzed simultaneously. Such libraries may be used in a sequential phage escape format, where cycles of phage binding and release of mutants are driven by antibodies or small molecules and the difficulty of escape increases at each cycle. Ultimately, the sequencing of the viral mutants allows annotation of the allowed trajectory of escape. Likewise, sequencing of the antibody perturbants charts the chemistry of the immune system response to the viral challenge. We have termed such analysis of competing mutations a "checkmate analysis." When viral systems are studied, a checkmate analysis allows experimental evaluation of the evolutionary contest between viruses and the immune system and may predict which antibodies and small-molecule ligands should be generated in anticipation of viral mutations before these mutations create viral epidemics.

Osteopontin prevents monocyte recirculation and apoptosis

Cells of the monocyte/macrophage lineage have been shown to be the principal targets for productive HIV-1 replication within the CNS. In addition, HIV-1-associated dementia (HAD) has been shown to correlate with macrophage abundance in the brain. Although increased entry of monocytes into the brain is thought to initiate this process, mechanisms that prevent macrophage egress from the brain and means that prevent macrophage death may also contribute to cell accumulation. We hypothesized that osteopontin (OPN) was involved in the accumulation of macrophages in the brain in neuroAIDS. Using in vitro model systems, we have demonstrated the role of OPN in two distinct aspects of macrophage accumulation: prevention from recirculation and protection from apoptosis. In these unique mechanisms, OPN would aid in macrophage survival and accumulation in the brain, the pathological substrate of HAD.

Game performance and intermittent hypoxic training

Live high-train low altitude exposure simulated by hypoxic devices may improve athletic performance. In this study, intermittent normobaric hypoxia was achieved with the GO2altitude hypoxicator to determine its effects on sea level performance in rugby players. Ten players were randomly assigned to two groups. Players in each group received 14 sessions of either hypoxic (10-15% O(2)) or normoxic (21% O(2)) exposure at rest over 14 consecutive days in a single blind fashion. Various performance measures were obtained consecutively in a single testing session pre- and post-exposure. Effects of hypoxic exposure on maximum speed and sprint times were trivial (<1.0%) but unclear (90% likely range, +/-5% to +/-9%). In rugby simulation, hypoxic exposure produced impairments of peak power in two scrums (15%, +/-8%; 9%, +/-7%) and impairments of time in offensive sprints (7%, +/-8%) and tackle sprints (11%, +/-9%). Pending further research, rugby players would be unwise to use normobaric intermittent hypoxic exposure to prepare for games at sea level.

Cooperation between VEGF and beta3 integrin during cardiac vascular development

In the developing myocardium, vascular endothelial growth factor (VEGF)-dependent neovascularization occurs by division of existing vessels, a process that persists for several weeks following birth. During this remodeling phase, mRNA expression of beta3 integrin in the heart decreases significantly as vessel maturation progresses. However, in male mice lacking beta3, coronary capillaries fail to mature and continue to exhibit irregular endothelial thickness, endothelial protrusions into the lumen, and expanded cytoplasmic vacuoles. Surprisingly, this phenotype was not seen in female beta3-null mice. Enhanced VEGF signaling contributes to the beta3-null phenotype, because these vessels can be normalized by inhibitors of VEGF or Flk-1. Moreover, intravenous injection of VEGF induces a similar angiogenic phenotype in hearts of adult wild-type mice. These findings show a clear vascular phenotype in the hearts of mice lacking beta3 and suggest this integrin plays a critical role in coronary vascular development and the vascular response to VEGF.

N-(3-oxo-acyl)homoserine lactones signal cell activation through a mechanism distinct from the canonical pathogen-associated molecular pattern recognition receptor pathways

Innate immune system receptors function as sensors of infection and trigger the immune responses through ligand-specific signaling pathways. These ligands are pathogen-associated products, such as components of bacterial walls and viral nuclear acids. A common response to such ligands is the activation of mitogen-activated protein kinase p38, whereas double-stranded viral RNA additionally induces the phosphorylation of eukaryotic translation initiation factor 2alpha (eIF2alpha). Here we have shown that p38 and eIF2alpha phosphorylation represent two biochemical markers of the effects induced by N-(3-oxo-acyl)homoserine lactones, the secreted products of a number of Gram-negative bacteria, including the human opportunistic pathogen Pseudomonas aeruginosa. Furthermore, N-(3-oxo-dodecanoyl)homoserine lactone induced distension of mitochondria and the endoplasmic reticulum as well as c-jun gene transcription. These effects occurred in a wide variety of cell types including alveolar macrophages and bronchial epithelial cells, requiring the structural integrity of the lactone ring motif and its natural stereochemistry. These findings suggest that N-(3-oxo-acyl)homoserine lactones might be recognized by receptors of the innate immune system. However, we provide evidence that N-(3-oxo-dodecanoyl)homoserine lactone-mediated signaling does not require the presence of the canonical innate immune system receptors, Toll-like receptors, or two members of the NLR/Nod/Caterpillar family, Nod1 and Nod2. These data offer a new understanding of the effects of N-(3-oxo-dodecanoyl)homoserine lactone on host cells and its role in persistent airway infections caused by P. aeruginosa.

In vivo functional assay of a recombinant aquaporin in Pichia pastoris

The water channel protein PvTIP3;1 (alpha-TIP) is a member of the major intrinsic protein (MIP) membrane channel family. We overexpressed this eukaryotic aquaporin in the methylotrophic yeast Pichia pastoris, and immunogold labeling of cellular cryosections showed that the protein accumulated in the plasma membrane, as well as vacuolar and other intracellular membranes. We then developed an in vivo functional assay for water channel activity that measures the change in optical absorbance of spheroplasts following an osmotic shock. Spheroplasts of wild-type P. pastoris displayed a linear relationship between absorbance and osmotic shock level. However, spheroplasts of P. pastoris expressing PvTIP3;1 showed a break in this linear relationship corresponding to hypo-osmotically induced lysis. It is the difference between control and transformed spheroplasts under conditions of hypo-osmotic shock that forms the basis of our aquaporin activity assay. The aquaporin inhibitor mercury chloride blocked water channel activity but had no effect on wild-type yeast. Osmotically shocked yeast cells were affected only slightly by expression of the Escherichia coli glycerol channel GlpF, which belongs to the MIP family but is a weak water channel. The important role that aquaporins play in human physiology has led to a growing interest in their potential as drug targets for treatment of hypertension and congestive heart failure, as well as other fluid overload states. The simplicity of this assay that is specific for water channel activity should enable rapid screening for compounds that modulate water channel activity.

S1P3 receptor-induced reorganization of epithelial tight junctions compromises lung barrier integrity and is potentiated by TNF

Pulmonary pathologies including adult respiratory distress syndrome are characterized by disruption of pulmonary integrity and edema compromising respiratory function. Sphingosine 1-phosphate (S1P) is a lipid mediator synthesized and/or stored in mast cells, platelets, and epithelial cells, with production up-regulated by the proinflammatory cytokines IL-1 and TNF. S1P administration via the airways but not via the vasculature induces lung leakage. Using receptor-null mice, we show that S1P, acting on S1P3 receptor expressed on both type I and type II alveolar epithelial cells but not vascular endothelium, induces pulmonary edema by acute tight junction opening. WT but not S1P3-null mice showed disruption of pulmonary epithelial tight junctions and the appearance of paracellular gaps between epithelial cells by electron microscopy within 1 h of airways exposure to S1P. We further show by fluorescence microscopy that S1P induced rapid loss of ZO-1 reactivity, an essential component of the cytoplasmic plaque associated with tight junctions, as well as of the tetraspannin Claudin-18, an integral membrane organizer of tight junctions. S1P shows synergistic activity with the proinflammatory cytokine TNF, showing both pulmonary edema and mortality at subthreshold S1P doses. Specifically, preexposure of mice to subthreshold doses of TNF, which alone induced no lung edema, exacerbated S1P-induced edema and impaired survival. S1P, acting through S1P3, regulates epithelial integrity and acts additively with TNF in compromising respiratory barrier function. Because S1P3-null mice are resistant to S1P-induced pulmonary leakage, either alone or in the presence of TNF, S1P3 antagonism may be useful in protecting epithelial integrity in pulmonary disease.

GW182 is critical for the stability of GW bodies expressed during the cell cycle and cell proliferation

A novel cytoplasmic compartment referred to as GW bodies was initially identified using human autoantibodies to a 182 kDa protein named GW182. GW bodies are small, generally spherical, cytoplasmic domains that vary in number and size in several mammalian cell types examined to date. Based on our earlier studies, GW bodies were proposed to be cytoplasmic sites for mRNA storage and/or degradation. In the present study, immunogold electron microscopy identified electron dense structures of 100-300 nm diameter devoid of a lipid bilayer membrane. These structures appeared to comprise clusters of electron dense strands of 8-10 nm in diameter. By costaining with CENP-F and PCNA, and employing a double-thymidine block to synchronize HeLa cells, GW bodies were observed to be small in early S phase and larger during late S and G2 phases of the cell cycle. The majority of GW bodies disassembled prior to mitosis and small GW bodies reassembled in early G1. The analysis of GW bodies in two experimental models of cell proliferation using reversal of 3T3/serum-starvation and concanavalin A stimulation of mouse splenocytes and T cells, revealed that proliferating cells contained larger, brighter, and more numerous GW bodies as well as up to a fivefold more total GW182 protein than quiescent cells. In vitro gene knockdown of GW182 led to the disappearance of GW bodies demonstrating that GW182 is a critical component of GW bodies. The incremental expression of the GW182 protein in cells induced to proliferate and the cyclic formation and breakdown of GW bodies during mitosis are intriguing in view of the notion that GW bodies are specialized centers involved in maintaining stability and/or controlling degradation of mRNA.

Accessibility of nuclear chromatin by DNA binding polyamides

Pyrrole-imidazole polyamides bind DNA with affinities comparable to those of transcriptional regulatory proteins and inhibit the DNA binding activities of components of the transcription apparatus. If polyamides are to be useful for the regulation of gene expression in cell culture experiments, one pivotal issue is accessibility of specific sites in nuclear chromatin. We first determined the kinetics of uptake and subcellular distribution of polyamides in lymphoid and myeloid cells using fluorescent polyamide-bodipy conjugates and deconvolution microscopy. Then cells were incubated with a polyamide-chlorambucil conjugate, and the sites of specific DNA cleavage in the nuclear chromatin were assayed by ligation-mediated PCR. In addition, DNA microarray analysis revealed that two different polyamides generated distinct transcription profiles. Remarkably, the polyamides affected only a limited number of genes.

Students' anxiety in a senior thesis course

The State-Trait Anxiety Inventory was administered on Weeks 8, 12, and 15 of a semester to 16 students enrolled in a senior thesis course. State anxiety scores were elevated when oral presentations began and declined following the presentations. Trait anxiety scores remained constant across test administrations. The influence of situational variables on students' anxiety was discussed.

Hierarchy of Order in Liquid Crystalline Polycaps

When outfitted with long alkyl chains, polycaps, capsules along a polymer chain, spontaneously organize themselves into a two-dimensional liquid crystalline phase. Further organization results from shearing or pulling the liquid crystalline samples, producing three-dimensional assemblies of micrometer-wide, infinitely long fibers (see schematic representation).

The arginine taste receptor. Physiology, biochemistry, and immunohistochemistry

The amino acid, L-arginine (L-Arg), is a potent taste stimulus for the channel catfish, Ictalurus punctatus. Receptor binding studies demonstrated a high-affinity binding of L-Arg to putative taste receptor sites. This binding could be inhibited by preincubation of the tissue in the lectins Phaseolus vulgaris agglutinin (PHA) and Ricinus communis agglutinin I (RCA I). Neurophysiological studies demonstrated that the L-Arg receptor is a stimulus-gated ion channel type receptor whose conductance was stimulated by L-Arg and inhibited by D-arginine (D-Arg). To purify the receptor we subjected CHAPS solubilized partial membrane preparation from barbel epithelium to RCA I lectin affinity chromatography. The bound proteins were eluted with D-galactose. When these proteins were reconstituted into lipid bilayers, L-Arg activated single channel currents with conductances between 45 and 85 pS. Sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) of the eluted protein showed a distinct band at approximately 83 kDa. Polyclonal antibodies raised against this 83-kDa band in guinea pigs reacted with numerous small (approximately 1 micron) sites within the taste pore of every taste bud when applied to fixed nonpermeabilized barbels. This observation suggests that the antibodies recognize an externally-facing epitope of the putative Arg receptor. The antibodies also inhibited L-Arg-stimulated currents in reconstitution studies. Sephacryl S-300 HR chromatography of the eluant from the affinity column showed a high molecular weight peak (> 700 kDa) which was recognized by the antibodies. Reconstitution of the protein from this peak into a lipid bilayer resulted in L-Arg-stimulated channels that could be inhibited by D-Arg. This high molecular weight component may be aggregates of the arginine taste receptor.

SRC binding to the cytoskeleton, triggered by growth cone attachment to laminin, is protein tyrosine phosphatase-dependent

The interaction of the non-receptor tyrosine kinase, Src, with the cytoskeleton of adhesion sites was studied in nerve growth cones isolated from fetal rat brain. Of particular interest was the role of protein tyrosine phosphatases in the regulation of Src-cytoskeleton binding. Growth cones were found to contain a high level of protein tryrosine phosphatase activity, most of it membrane-associated and forming large, multimeric and wheat germ agglutinin-binding complexes. The receptor tyrosine phosphatase PTPalpha seems to be the most prevalent species among the membrane-associated enzymes. As seen by immunofluorescence, PTPalpha is present throughout the plasmalemma of the growth cone including filopodia, and it forms a punctate pattern consistent with that of integrin beta1. For adhesion site analysis, isolated growth cones were either plated onto the neurite growth substratum, laminin, or kept in suspension. Plating growth cones on laminin triggered an 8-fold increase in Src binding to the adherent cytoskeleton. This effect was blocked completely with the protein tyrosine phosphatase inhibitor, vanadate. Growth cone plating also increased the association with adhesion sites of tyrosine phosphatase activity (14-fold) and of PTPalpha immunoreactivity (6-fold). Vanadate blocked the enzyme activity but not the recruitment of PTPalpha to the adhesion sites. In conjunction with our previous results on growth cones, these data suggest that integrin binding to laminin triggers the recruitment of PTPalpha (and perhaps other protein tyrosine phosphatases) to adhesion sites, resulting in de-phosphorylation of Src's tyr 527. As a result Src unfolds, becomes kinase-active, and its SH2 domain can bind to an adhesion site protein. This implies a critical role for protein tyrosine phosphatase activity in the earliest phases of adhesion site assembly.

Targeting and modification of prokaryotic cell-cell junctions by tobacco mosaic virus cell-to-cell movement protein

The movement protein (MP) of tobacco mosaic virus (TMV) facilitates the cell-to-cell spread of infection by altering the structure and function of plasmodesmata, the intercellular communication channels in plants. Because the protein was shown to interfere with intercellular communication when expressed in the cyanobacterium Anabaena sp. strain PCC 7120, whether the ability of the protein to target and to modify intercellular communication channels in plants is conserved in this prokaryote was investigated. It was found that the MP localizes to the cell junctions and induces the formation of filamentous structures that traverse the septa. It is proposed that the protein interacts with host components that are similar between plants and Anabaena and that may be evolutionarily related. The observations in Anabaena suggest that the MP modifies plasmodesmata by forming a filamentous aggregate within the pore.

The effect of streptomycin, oxytetracycline, tilmicosin and phenylbutazone on spermatogenesis in bulls

To determine whether declining semen quality associated with health problems may be due to certain antibiotic or anti-inflammatory treatments, semen was collected 3 times per week for up to 42 d from 6 normal bulls after treatment with oxytetracycline, tilmicosin, dihydrostreptomycin, or phenylbutazone. No adverse effects on semen quality were observed.

Characterization of phospholipase A2 activity enriched in the nerve growth cone

Nerve growth cones isolated from fetal rat brain exhibit in their cytosol a robust level of phospholipase A2 activity hydrolyzing phosphatidylinositol (PI) and phosphatidylethanolamine (PE) but not phosphatidylcholine (PC). Western blot analysis with an antibody to the well-characterized cytosolic phospholipase A2 (mol wt 85,000) reveals only trace amounts of this PC- and PE-selective enzyme in growth cones. By gel filtration on Superose 12, growth cone phospholipase A2 activity elutes essentially as two peaks of high molecular mass, at approximately 65 kDa and at well over 100 kDa. Anion exchange chromatography completely separates a PI-selective from a PE-selective activity, indicating the presence of two different, apparently monoselective phospholipase A2 species. The PI-selective enzyme, the predominant phospholipase A2 activity in whole growth cones, is enriched greatly in these structures relative to their parent fractions from fetal brain. This phospholipase A2 is resistant to reducing agents and is found in the cytosol as well as membrane-associated in the presence of Ca2+. However, its catalytic activity is Ca(2+)-independent regardless of whether the enzyme is associated with pure substrate or mixed-lipid growth cone vesicles. The PE-selective phospholipase A2 in growth cones was studied in less detail but shares with the PI-selective enzyme several properties, including intracellular localization, the existence of cytosolic and membrane-associated forms, and Ca2+ independence. Our data indicate growth cones contain two high-molecular-weight forms of phospholipase A2 that share many properties with known, Ca(2+)-independent cytosolic phospholipase A2 species but that appear to be monoselective for PI and PE, respectively. In particular, the PI-selective enzyme may represent a new member of the growing family of cytoplasmic phospholipases A2. The enrichment of the PI-selective phospholipase A2 in growth cones suggests it plays a major role in the regulation of growth cone function.

Axonal origin and purity of growth cones isolated from fetal rat brain

The investigation of the molecular properties of nerve growth cones depends to a significant degree on their isolation from fetal brain in the form of 'growth cone particles' (GCPs). The availability of markers for developing axons and dendrites, as well as glial cells, has made it possible to characterize the GCP fraction in much greater detail than before and to optimize its yield. Marker analyses show that a member of the N-CAM family (5B4-CAM), synaptophysin, and especially GAP-43 and non-phosphorylated tau, are enriched in the GCP fraction. In contrast, MAP2 and, particularly, glial fibrillary acidic protein and vimentin are fractionated away from GCPs. Furthermore, GCP yield can be doubled relative to the original procedure, without compromising purity, by raising the sucrose concentration of the fractionation gradient's uppermost layer. The results indicate that GCPs are highly purified growth cone fragments with very little glial contamination, and that they are primarily of axonal origin.

Na+ channel changes in the growth cone and developing nerve terminal

Previous saxitoxin binding studies indicated two forms of the sodium channel in the fetal rat brain; a low-affinity precursor located in an internal membrane compartment, present exclusively in growth cones and a high-affinity mature form present in the plasmalemma of growth cones and characteristic of synapses. This raises the questions (1) of the presence or absence of the beta2 subunit in these channel forms and (2) of the developmental regulation of the the beta2 subunit. Antibodies against the alpha and beta2 channel subunits were used to probe Western blots of subcellular fractions from rat brains at embryonic day 18 (E18), pups at postnatal (P) days 7-25, and adults, as well as purified sodium channels from adult brain. In both synaptosomes and the purified sodium channel the beta2 antibody recognized the expected band at 38 kDa under reducing conditions. However, in contrast to the alpha subunit, this band was absent at E18 and became apparent only from P7 onwards. At the earlier time intervals a very prominent immunoreactive band of unknown identity was evident at 260--300kDa, which declined in intensity concomitant with the appearance of the 38 kDa beta2 band. These data indicate that beta2 subunits are regulated independently from alpha subunits, are absent in differentiating neurons, and hence are not necessary for insertion of the sodium channel into the plasmalemma, at least during early development of the neuron.

Synthesis and biological activity of novel cephalosporins containing a (Z)-vinyl dimethylphosphonate group

A series of cephalosporins containing a novel 7-[2-(Z)-(2-amino-thiazol-4- yl)-3-(dimethoxy-phosphoryl)-acryloylamino] group were prepared and their antibacterial activity measured against a range of pathogens. In general the compounds displayed a broad spectrum of activity against both Gram positive and Gram negative organisms, except Pseudomonas aeruginosa. Activity against the latter could be achieved by introducing a catechol moiety at the 3 position of the cephalosporin. The methyl phosphonates in general were stable to a wide range of beta-lactamases, including the TEM enzymes and the Enterobacter cloacae P99 chromosomal enzyme. In addition, they showed the advantage of being highly water soluble.

A chloride channel reconstituted from fetal rat brain growth cones

Chloride channels were reconstituted into planar lipid bilayers isolated from a preparation of growth cone particles (GCPs) isolated from fetal rat brain. One type of channel was predominantly seen and some of its biophysical and pharmacological properties were studied. The single channel i-V relationship was curvilinear with a chord conductance of 75 pS at +30 mV in symmetric 200 mM NaCl solutions buffered with phosphate. The channel was inactivated by depolarization, and this inactivation was reversed rapidly upon returning to -25 mV. The Cl- channel was significantly permeant to Na+ ions (PNa/PCl = 0.26), and the relative halide permeabilities were determined to be: I(1.92) > Br(1.73) > Cl(1.0) > F(0.34). The channel was inhibited by the common stilbene compounds (DIDS, SITS, DNDS), as well as by Zn2+ ions and an indanyloxyacetic acid derivative. A developmental role for the GCP Cl- channel is suggested by the observation that adult rat brain synaptosomal membranes were nearly devoid of this type of Cl- channel.

Plasmalemmal insertion and modification of sodium channels at the nerve growth cone

We have characterized voltage-dependent sodium channels in growth cones (GCPs) isolated from fetal rat brain using saxitoxin and TTX binding as well as recordings from channels reconstituted into lipid bilayer membranes. Both high- and low-affinity binding sites are present in GCP membranes. However, the two binding sites are segregated largely or completely, with the high-affinity binding sites in the plasmalemma, and the low-affinity sites in an internal membrane compartment. Plasmalemmal insertion of these internal sites can be triggered by high-potassium depolarization and depends on a metalloendoprotease-requiring mechanism. These observations indicate that a precursor-product relationship exists between the internal and external sodium channels of the growth cone, and therefore suggest that channel externalization causes conversion of low-affinity to high-affinity saxitoxin receptors. This conversion may represent a step of channel capacitation.

The value of stump split skin grafting following amputation for trauma in adult upper and lower limb amputees

One hundred and twenty adult patients were reviewed in whom split skin grafts were applied to the stump following traumatic amputation of the upper limb (44 amputees) or lower limb (76 amputees). The average follow-up period was seven and a half years after initial amputation. There was delay in prosthetic fitting in all patients. Approximately one third of patients complained of occasional minor ulceration, controlled by removing the prosthesis for a few days or modification of the prosthesis. Further revision surgery, including excision of the grafted skin often combined with proximal bone resection, but not removal of the proximal joint, was necessary in 29% of below-elbow amputees and approximately 50% of below and above-knee amputees. At the above-elbow level, use of skin grafts allowed prosthetic fitting because of preservation of sufficient length of the stump. Despite the fact that revision surgery may often be necessary, split skin grafting has a definite place in the early management of the stump following traumatic limb amputation in the adult. Preservation of stump length with the knee or elbow joint allows easier rehabilitation and lower energy expenditure when using the prosthesis. Partial foot amputation, when combined with skin grafting usually requires subsequent revision to a more proximal level to obtain a satisfactory result.

The value of revision surgery after initial amputation of an upper or lower limb

The value of revision surgery when carried out more than six weeks after initial amputation of the upper or lower limb was assessed. When performed for stump and/or phantom limb pain alone, only 33/95 (35%) obtained satisfactory results after one revision; 25/95 (26%) of the patients required four or more surgical procedures without relief of pain. However, when carried out for local specific pathology, the results of surgical revision were 100% successful, even if the procedure had to be repeated once in 15% (28/189) of this group of patients. Transcutaneous nerve stimulation appeared to offer no long lasting relief of pain following amputation surgery.

Electrophysiological and morphological correlates of axotomy-induced deafferentation of the goldfish Mauthner cell

Axotomy-induced changes in afferent synapses to the goldfish Mauthner cell have been analyzed with intracellular recordings and with electron microscopy. The studies encompassed 7-208 days after cervical spinal cord transection. The physiological findings suggest a persistent and specific reduction in excitatory chemical inputs to the soma and proximal lateral dendrite, with no changes in somatic inhibition or in the electrotonic and chemical inputs to the more distal regions of the lateral dendrite. Corroborative morphological evidence includes swelling of the M-cell soma, as indicated by a 35% increase in the length of its minor diameter, an increased spacing and a quantitatively lower density of terminals on the soma, and the appearance of astrocytic processes partially or completely engulfing the terminals in that region. Similar changes were observed on the inferior dendrites projecting from the ventral surface of the soma, although these dendrites do not exhibit the chromatolytic changes observed at the soma. In contrast, there are no noticeable changes in either the synaptic investment of the lateral dendrite or its ultrastructure. Quantitative and qualitative data support the conclusion that there is a restricted and specific reduction in the proximal excitatory inputs to the M-cell. The evidence also suggests that electrotonic junctions between afferents and the M-cell remain intact, functionally and structurally.

Localization of active sites along the myelinated goldfish Mauthner axon: morphological and pharmacological evidence for saltatory conduction

Injections of Lucifer Yellow (LY) and horseradish peroxidase (HRP) were made within the myelin sheath of the goldfish Mauthner axon to determine the domains of individual oligodendrocytes. Long segments of the myelin sheath were stained with both markers. The lengths and locations of these sheath segments were analyzed in whole mount preparations (LY) or in reconstructions of serial vibratome sections (HRP). The termination sites of individual myelin sheaths, relative to gross anatomical landmarks of the brain, were consistent within and between all fish studied. In particular, the average locations of the termination sites were separated by 2.2 to 2.6 mm and corresponded to the brain regions where active site foci have been previously localized electrophysiologically. Individual sheath segments generally spanned the entire distance between adjacent active sites. The node-internode-node structure of the Mauthner axon that is suggested by these findings was further tested by ejecting tetrodotoxin (TTX) at various discrete rostral-caudal locations just outside the fiber. Large all-or-nothing components of the antidromic action potential were rapidly blocked (within seconds) only when the TTX ejections were made within a few hundred micrometers of the active site foci. The amplitudes of these blocked components are also consistent with predictions based upon previous electrophysiological analyses which demonstrated an active site spacing of 2.2 to 2.6 mm, a space constant of 5.0 mm, and a safety factor of 6 for impulse propagation. It is concluded from these morphological, pharmacological, and electrophysiological observations that the Mauthner axon possesses nodes separated by 2.2 to 2.6 mm and that a single oligodendrocyte spans an internodal region. Although nodal ultrastructure remains to be described, these results rule out the possibility that each of the short (approximately 50 micron), closely spaced (average separation = 155 micron) axon collaterals is a site of action current production.

Organized projection of the goldfish saccular nerve onto the Mauthner cell lateral dendrite

Application of horseradish peroxidase (HRP) to the proximal end of the transected saccular nerve in the goldfish results in uptake by fibers projecting to the distal half of the Mauthner (M) cell's lateral dendrite. More discrete HRP injections reveal an organized projection from the saccular nerve onto the lateral dendrite, as small groups of stained fibers terminate there in restricted regions. The possibility that this represents a tonotopic projection onto the M-cell is considered.

Granular coated vesicles in the goldfish Mauthner cell following axotomy

Axotomy of the goldfish Mauthner cell induces a marked increase in the occurrence of granular coated vesicles in close association with axosomatic synapses. This phenomenon, which persists for over 200 days, is discussed in relation to other morphological and physiological changes which occur over the same time period.

Purification of carnosine synthetase from avian muscle by affinity chromatography and determination of its subunit structure

An extract of chick pectoral muscle was prepared in which the level of carnosine synthetase (L-histidine; beta-alanine ligase (AMP-forming), EC 6.3.2.11) activity was approx. 10-times that of previous preparations. In affinity chromatography studies, this material was applied to a Cibracon blue-agarose column, and elution of carnosine synthetase by carnosine was attempted. Results indicated that the elution was not specific as the eluate contained large amounts of myosin. An (NH4)2SO4 fraction (21--30% satn.) of the crude extract was prepared which, in comparison to the crude extract, had a higher specific activity, was more stable on storage at 4 degrees C and had much lower myosin content. On affinity chromatography of this fraction, apparently homogeneous carnosine synthetase was eluted with carnosine, and the specific activity of the preparation was 1700-times that of the fresh crude extract. Amino acid analysis of the preparation indicated that it had a very high histidine content (141 per 1000 residues). On analysis of the preparation by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS), a polypeptide of Mr 119 000 was observed, whereas gel permeation chromatography of the native enzyme indicated an Mr of 250 000, suggesting that the native enzyme is a dimer.

Synaptic regeneration and glial reactions in the transected spinal cord of the lamprey

We have examined axonal growth and synaptic regeneration in identified giant neurons of the transected lamprey spinal cord using intracellular injection of horseradish peroxidase. Wholemounts together with serial section light and electron microscopy, show that axons from identified Müller and Mauthner reticulospinal neurons grow across the lesion and regenerate new synaptic contacts. Relatively normal swimming returns in these animals by 3-4 weeks after spinal transection. This occurs despite the formation of regenerated synapses in regions of the cord that are not usually occupied by these neurons. The regenerating axons branch profusely in contrast to their unbranched state in the normal animal. In addition to showing the two synaptic configuration found normally, synapses may be formed by slender sprouts from the growing giant axon. These 'sprout' type synaptic contacts appear unique to the regenerating neuron. Only regenerated chemical synapses were seen; the morphologically mixed chemical and electrical (gap junction) synaptic complex common in the normal animal was not observed at regenerated synapses. The site of spinal transection in the functionally recovered animal shows an increase in the number of ependymal and glial cells. Ependymal-like cells appear in regions away from the central canal. The expanded ependymal and glial processes covering the peripheral surface of the injured cord become convoluted, in contrast to their normal smooth configuration. There is no collagen within the cord at the site of transection but a considerable deposition is seen external to the cord surface. Axonal growth across a spinal lesion and subsequent synaptic regeneration can be examined in single identifiable giant interneurons in the spinal cord of the larval lamprey. This preparation may be used as an assay to investigate factors that could contribute to functional recovery following central nervous system injury in the higher vertebrates.

A biomechanical study of the effects of growth hormone in experimental fracture healing

In 65 mature Wistar rats a Kirschner wire was introduced into the medullary cavity of each femur. A closed transverse mid-shaft fracture of one femur was produced by a three-point bending technique. Subsequently the mechanical characteristics of the healing fracture, including the torque and angle of twist required to take the callus to its yield point and to ultimate failure, were compared with those for the opposite femur of each rat. Controls were killed in groups at two, three, four, five and seven weeks. Test animals were given bovine growth hormone in a daily dose of five milligrams before being killed in groups at two, three and four weeks. A significant increase in torque index was found in the two-week group of test animals but not in subsequent groups. No evidence was found that growth hormone given alone could produce an overall shortening of the healing time in fresh fractures.