BACE1 interacts with nicastrin

Beta-amyloid peptide (Abeta) is generated through the proteolytic cleavage of beta-amyloid precursor protein (APP) by beta- and gamma-secretases. The beta-secretase, BACE1, initiates Abeta formation followed by gamma-cleavage within the APP transmembrane domain. Although BACE1 localizes in the transGolgi network (TGN), its physiological substrates and modulators are not known. In addition, the relationship to other secretase(s) also remains unidentified. Here, we demonstrate that BACE1 binds to nicastrin, a component of gamma-secretase complexes, in vitro, and that nicastrin activates beta-secretase activity in COS-7 cells.     

Phosphorylation of hUPF1 induces formation of mRNA surveillance complexes containing hSMG-5 and hSMG-7

Eukaryotic mRNAs containing premature termination codons (PTCs) are degraded by a process known as nonsense-mediated mRNA decay (NMD). NMD has been suggested to require the recognition of PTC by an mRNA surveillance complex containing UPF1/SMG-2. In multicellular organisms, UPF1/SMG-2 is a phosphoprotein, and its phosphorylation contributes to NMD. Here we show that phosphorylated hUPF1, the human ortholog of UPF1/SMG-2, forms a complex with human orthologs of the C. elegans NMD proteins SMG-5 and SMG-7. The complex also associates with protein phosphatase 2A (PP2A), resulting in dephosphorylation of hUPF1. Overexpression of hSMG-5 mutants that retain interaction with P-hUPF1 but which cannot induce its dephosphorylation impair NMD, suggesting that NMD requires P-hUPF1 dephosphorylation. We also show that P-hUPF1 forms distinct complexes containing different isoforms of hUPF3A. We propose that sequential phosphorylation and dephosphorylation of hUPF1 by hSMG-1 and PP2A, respectively, contribute to the remodeling of the mRNA surveillance complex.     

Difference in response by two cyprinid species to predatory threat from the nocturnal catfish Silurus asotus

Response to predators may not be identical between different prey species with different life histories and body sizes, particularly when the threat of predation is not great. To clarify this hypothesis, we introduced two prey species (10 Japanese dace, Tribolodon hakonensis, and 10 pale chub, Zacco platypus) into each experimental pond (in total, 8 ponds×4 trials) in which benthic algae had been allowed to grow. The presence or absence of Far Eastern catfish, Silurus asotus, and a refuge for prey fish was used to produce four treatments. The presence of catfish and/or a refuge did not affect either the feeding behavior or growth rate of Japanese dace. In contrast, when catfish were present and no refuge was available, the incidence of bottom feeding for pale chub greatly decreased. Pale chub growth rate was low when catfish were present and a refuge was available, indicating that pale chub spent more of their time in the refuge and lost opportunities of acquiring food. Japanese dace can reach a threshold size at which the prey are safe from predation, but pale chub cannot, and this may explain the differences in response to predators of the two species.     

Antimicrobial activity of essential oils against Helicobacter pylori

Background. Helicobacter pylori is an important pathogen responsible for gastroduodenal diseases in humans. Although the eradication of H. pylori using antibiotics often improves gastroduodenal diseases, resistance to the antibiotics is emerging. Materials and Methods. The antimicrobial effect of essential oils and the development of resistance to the essential oils were evaluated in vitro and in vivo. Results. Thirteen essential oils used in this study completely inhibited the growth of H. pylori in vitro at a concentration of 0.1% (v/v). Cymbopogon citratus (lemongrass) and Lippia citriodora (lemon verbena) were bactericidal against H. pylori at 0.01% at pH 4.0 and 5.0. Resistance to lemongrass did not develop even after 10 sequential passages, whereas resistance to clarithromycin developed under the same conditions. In in vivo studies, the density of H. pylori in the stomach of mice treated with lemongrass was significantly reduced compared with untreated mice. Conclusions. These results demonstrate that the essential oils are bactericidal against H. pylori without the development of acquired resistance, suggesting that essential oils may have potential as new and safe agents for inclusion in anti‐H. pylori regimens.     

A rapid BOD sensing system using luminescent recombinants of Escherichia coli

A biochemical oxygen demand (BOD) sensing system based on bacterial luminescence from recombinant Escherichia coli containing lux A-E genes from Vibrio fischeri has been developed. It was possible to use frozen cells of luminescent recombinants of E. coli as the bacterial reagents for measurement. Steady bioluminescence was observed during the incubation time between 90 and 150 min in the presence of a sole carbon source such as glucose, acetate, L-glutamate and BOD standard solution (GGA solution). This disposable bacterial reagent was applied to measure and detect organic pollution due to biodegradable substances in various wastewaters. The obtained values of this study showed a similar correlation with that of the conventional method for BOD determination (BOD5). Bacterial luminescence that was visualized with an imaging system using a charge coupled device (CCD) camera and a photomulti-counter demonstrated that this method could also be used for multi-sample detection of organic pollution due to biodegradable substances by using a microtiter plate. These results suggested for successful achievement of high-though-put detection of BOD in practical.     

Expression of placental lactogen and cytokeratin in bovine placental binucleate cells in culture

Binucleate cells are present in ruminant placenta and play an endocrine role in the production of many hormones during pregnancy. We isolated and cultured binucleate cells from bovine placenta at middle to late gestation and characterized these cells using immunofluorescence techniques. Enriched preparations of binucleate cells were obtained using Percoll density gradient centrifugation following collagenase digestion. Binucleate cells in culture preferentially attached to collagen-coated dishes rather than to noncoated plastic dishes. The cells gradually extended their edges on collagen substrata, and finally assumed a flattened morphology. Antibodies to placental lactogen (PL) and pregnancy-associated glycoprotein-1 (PAG-1) specifically stained the majority of round binucleate cells, but not the flat cells. We found that PL-positive binucleate cells were consistently devoid of cytokeratin. In contrast, cytokeratin was expressed in PL-negative binucleate cells as well as mononuclear epithelial cells. Furthermore, the PL-negative flat binucleate cells also developed intense cytokeratin networks in the cytoplasm. These results indicate that cytokeratin expression is inversely proportionate to that of PL in cultured binucleate cells. We conclude that downregulation of cytokeratin in binucleate cells is a function of the state of cellular differentiation.     

Metabolism of amyloid precursor protein in COS cells transfected with a β-secretase candidate

Thimet oligopeptidase (TOP) is a thiol- andmetallo-dependent peptidase and has been shown to beone of the -secretase candidates. TOPexpressed in COS cells cleaved amyloid precursorprotein (APP) at the -secretase site, and wefound a proteolytic product of APP called secretedform of APP by -secretase (sAPP) in theconditioned media. Here we demonstrate thatsAPP was increased in conditioned media whenTOP was coexpressed in COS cells with APP and treatedwith an ADAM inhibitor SI-27. In addition, althoughTOP expressed in COS cell was localized at nuclei orGolgi apparatus, it exclusively colocalized at Golgiapparatus when APP was coexpressed with TOP.     

Analysis of a muscular control system in human movements

In this work, we have studied a muscular control system under experimental conditions for analyzing the dynamic behavior of individual muscles and theoretical considerations for elucidating its control strategy. Movement of human limbs is achieved by joint torques and each torque is specified as the sum of torques generated by muscle forces. The behavior of individual muscles is controlled by the neural input which is estimated by means of an electromyogram (EMG). In this study, the EMGs for a flexor and an extensor are measured in elbow joint movements and the dynamic behavior of individual muscles is analyzed. As a result, it is verified that both a flexor and an extensor are activated throughout the entire movement and that the activation of muscles is controlled above a specific limit independent of the hand-held load. Subsequently, a system model for simulating elbow joint movements is developed which includes the muscle dynamic relationship between the neural input and the isometric force. The minimum limit of muscle activation that has been confirmed in experiments is provided as a constraint of the neural input and the criterion is defined by a derivative of the isometric force of individual muscles. The optimal trajectories formulated under these conditions are quantitatively compared with the experimentally observed trajectories, and the control strategy of a muscular control system is studied. Finally, a muscular control system in multi-joint arm movements is discussed with regard to the comparative analysis between observed and optimal trajectories. Received: 7 April 1999 / Accepted in revised form: 27 July 1999