Calcium-induced aggregation of archaeal bipolar tetraether liposomes derived from the thermoacidophilic archaeon Sulfolobus acidocaldarius

Previously, we showed that the proton permeability of small unilamellar vesicles (SUVs) composed of polar lipid fraction E (PLFE) from the thermoacidophilic archaeon Sulfolobus acidocaldarius was remarkably low and insensitive to temperature (Komatsu and Chong 1998). In this study, we used photon correlation spectroscopy to investigate the time dependence of PLFE SUV size as a function of Ca2+ concentration. In the absence of Ca2+, vesicle diameter changed little over 6 months. Addition of Ca2+, however, immediately induced formation of vesicle aggregates with an irregular shape, as revealed by confocal fluorescence microscopy. Aggregation was reversible upon addition of EDTA; however, the reversibility varied with temperature as well as incubation time with Ca2+. Freeze-fracture electron microscopy showed that, after a long period of incubation (2 weeks) with Ca2+, the PLFE vesicles had not just aggregated, but had fused or coalesced. The initial rate of vesicle aggregation varied sigmoidally with Ca2+ concentration. At pH 6.6, the threshold calcium concentration (Cr) for vesicle aggregation at 25 and 40 degrees C was 11 and 17 mM, respectively. At pH 3.0, the Cr at 25 degrees C increased to 25 mM. The temperature dependence of Cr may be attributable to changes in membrane surface potential, which was -22.0 and -13.2 mV at 25 and 40 degrees C, respectively, at pH 6.6, as determined by 2-(p-toluidinyl)naphthalene-6-sulfonic acid fluorescence. The variation in surface potential with temperature is discussed in terms of changes in lipid conformation and membrane organization.     

Transgenic mice expressing F3/contactin from the TAG-1 promoter exhibit developmentally regulated changes in the differentiation of cerebellar neurons

F3/contactin (CNTN1) and TAG-1 (CNTN2) are closely related axonal glycoproteins that are differentially regulated during development. In the cerebellar cortex TAG-1 is expressed first as granule cell progenitors differentiate in the premigratory zone of the external germinal layer. However, as these cells begin radial migration, TAG-1 is replaced by F3/contactin. To address the significance of this differential regulation, we have generated transgenic mice in which F3/contactin expression is driven by TAG-1 gene regulatory sequences, which results in premature expression of F3/contactin in granule cells. These animals (TAG/F3 mice) display a developmentally regulated cerebellar phenotype in which the size of the cerebellum is markedly reduced during the first two postnatal weeks but subsequently recovers. This is due in part to a reduction in the number of granule cells, most evident in the external germinal layer at postnatal day 3 and in the inner granular layer between postnatal days 8 and 11. The reduction in granule cell number is accompanied by a decrease in precursor granule cell proliferation at postnatal day 3, followed by an increase in the number of cycling cells at postnatal day 8. In the same developmental window the size of the molecular layer is markedly reduced and Purkinje cell dendrites fail to elaborate normally. These data are consistent with a model in which deployment of F3/contactin on granule cells affects proliferation and differentiation of these neurons as well as the differentiation of their synaptic partners, the Purkinje cells. Together, these findings indicate that precise spatio-temporal regulation of TAG-1 and F3/contactin expression is critical for normal cerebellar morphogenesis.     

Selection by phage display of a variant mustard trypsin inhibitor toxic against aphids

The mustard trypsin inhibitor, MTI-2, is a potent inhibitor of trypsin with no activity towards chymotrypsin. MTI-2 is toxic for lepidopteran insects, but has low activity against aphids. In an attempt to improve the activity of the inhibitor towards aphids, a library of inhibitor variants was constructed and cloned into the pRlac3 phagemid vector. The library of 9.3 x 107 independent colonies was created by randomisation of a stretch of five consecutive codons in the reactive site. Repeated selection rounds against bovine trypsin and chymotrypsin allowed the identification of novel, MTI-2 derived, antitrypsin and antichymotrypsin inhibitors. Chy8, the selected variant with highest affinity for bovine chymotrypsin (Ki = 32 nm versus >1000 nm for the wild-type) represents the strongest known recombinant chymotrypsin inhibitor of the MTI-2 family. It is highly toxic to nymphs of the aphid Acyrthosiphon pisum, and moderately toxic to nymphs of Aphis gossypii and Myzus persicae. The LC50 of 73 microg ml-1 towards A. pisum is the lowest value known among chymotrypsin inhibitors. The aphicidal activity of Chy8 was improved eightfold compared to the wild-type inhibitor. This demonstrates, for the first time, that bovine chymotrypsin provides a useful template to select engineered proteins highly toxic against these aphids. The selected gene will allow the development of transgenic crops that are protected against sucking insect pests.     

In vitro selection and characterization of hepatitis C virus serine protease variants resistant to an active-site peptide inhibitor

The hepatitis C virus (HCV) serine protease is necessary for viral replication and represents a valid target for developing new therapies for HCV infection. Potent and selective inhibitors of this enzyme have been identified and shown to inhibit HCV replication in tissue culture. The optimization of these inhibitors for clinical development would greatly benefit from in vitro systems for the identification and the study of resistant variants. We report the use HCV subgenomic replicons to isolate and characterize mutants resistant to a protease inhibitor. Taking advantage of the replicons' ability to transduce resistance to neomycin, we selected replicons with decreased sensitivity to the inhibitor by culturing the host cells in the presence of the inhibitor and neomycin. The selected replicons replicated to the same extent as those in parental cells. Sequence analysis followed by transfection of replicons containing isolated mutations revealed that resistance was mediated by amino acid substitutions in the protease. These results were confirmed by in vitro experiments with mutant enzymes and by modeling the inhibitor in the three-dimensional structure of the protease.     

A spatial mechanism with higher pairs for modelling the human knee joint

By generalizing a previous model proposed in the literature, a new spatial kinematic model of the knee joint passive motion is presented. The model is based on an equivalent spatial parallel mechanism which relies upon the assumption that fibers within the anterior cruciate ligament (ACL), the medial collateral ligament (MCL) and the posterior cruciate ligament (PCL) can be considered as isometric during the knee flexion in passive motion (virtually unloaded motion). The articular surfaces of femoral and tibial condyles are modelled as 3-D surfaces of general shapes. In particular, the paper presents the closure equations of the new mechanism both for surfaces represented by means of scalar equations that have the Cartesian coordinates of the points of the surface as variables and for surfaces represented in parametric form. An example of simulation is presented in the case both femoral condyles are modelled as ellipsoidal surfaces and tibial condyles as spherical surfaces. The results of the simulation are compared to those of the previous models and to measurements. The comparison confirms the expectation that a better approximation of the tibiofemoral condyle surfaces leads to a more accurate model of the knee passive motion.     

Conicamin, a novel histamine antagonist from the mediterranean tunicate Aplidium conicum

In addition to the known 6-bromo-hypaphorine (2) and plakohypaphorine-A (3), the methanol extract of the Mediterranean tunicate Aplidium conicum was shown to contain conicamin, a novel indole alkaloid having histamine-antagonistic activity which structure was determined to be 1 on the basis of the spectral data.     

What does it take to evolve behaviorally complex organisms?

What genotypic features explain the evolvability of organisms that have to accomplish many different tasks? The genotype of behaviorally complex organisms may be more likely to encode modular neural architectures because neural modules dedicated to distinct tasks avoid neural interference, i.e. the arrival of conflicting messages for changing the value of connection weights during learning. However, if the connection weights for the various modules are genetically inherited, this raises the problem of genetic linkage: favorable mutations may fall on one portion of the genotype encoding one neural module and unfavorable mutations on another portion encoding another module. We show that this can prevent the genotype from reaching an adaptive optimum. This effect is different from other linkage effects described in the literature and we argue that it represents a new class of genetic constraints. Using simulations we show that sexual reproduction can alleviate the problem of genetic linkage by recombining separate modules all of which incorporate either favorable or unfavorable mutations. We speculate that this effect may contribute to the taxonomic prevalence of sexual reproduction among higher organisms. In addition to sexual recombination, the problem of genetic linkage for behaviorally complex organisms may be mitigated by entrusting evolution with the task of finding appropriate modular architectures and learning with the task of finding the appropriate connection weights for these architectures.     

Expression of HER2/neu is uncommon in human neuroblastic tumors and is unrelated to tumor progression

Neuroblastic tumors (NT) are the most frequently occurring extracranial solid tumors during childhood. The overall 5-year survival is approximately 20% for patients with metastatic disease. Novel treatments are therefore intensively sought and tumor-targeted immuno- and chemotherapy appear promising. The HER2/neu oncogene, which is highly homologous to the EGF receptor, was initially isolated from rat neuroblastoma cells. HER2/neu over-expression is frequently detected in breast tumors and constitutes an important unfavorable prognostic factor. HER2/neu is a suitable target for antibody-based immunotherapy, as demonstrated by the clinical efficacy of the Herceptin monoclonal antibody (mAb), which reacts with its extracellular domain. Expression of HER2/neu has also been reported to be a negative prognostic factor in a small survey of NT tumors. Here, we have investigated HER2/neu expression in 14 human and 2 murine neuroblastoma (NB) cell lines by flow cytometric analysis and in 93 NT by means of a certified immunohistochemical system. HER2/neu over-expression was found in 2 human cell lines and 11 tumors (14% for both types of samples). No significant association was found between HER2/neu expression and stage, age, sex, ploidy, histological type or subtype. Moreover, log rank test indicated that overall and event-free survival was not significantly different in HER2/neu positive and negative patients. These data suggest that HER2/neu should not be considered as a relevant prognostic factor in NT, and that HER2/neu-based immunotherapy may be feasible only in a minority of NT patients.