Magnetically induced transparency of a quantum metamaterial composed of twin flux qubits.

Quantum theory is expected to govern the electromagnetic properties of a quantum metamaterial, an artificially fabricated medium composed of many quantum objects acting as artificial atoms. Propagation of electromagnetic waves through such a medium is accompanied by excitations of intrinsic quantum transitions within individual meta-atoms and modes corresponding to the interactions between them. Here we demonstrate an experiment in which an array of double-loop type superconducting flux qubits is embedded into a microwave transmission line. We observe that in a broad frequency range the transmission coefficient through the metamaterial periodically depends on externally applied magnetic field. Field-controlled switching of the ground state of the meta-atoms induces a large suppression of the transmission. Moreover, the excitation of meta-atoms in the array leads to a large resonant enhancement of the transmission. We anticipate possible applications of the observed frequency-tunable transparency in superconducting quantum networks.

Flux-dependent crossover between quantum and classical behavior in a dc SQUID.

In a coupled system of one classical and one quantum mechanical degree of freedom, the quantum degree of freedom can facilitate the escape of the whole system. Such unusual escape characteristics have been theoretically predicted as the "Münchhausen effect." We implement such a system by shunting one of the two junctions of a dc SQUID with an additional capacitance. In our experiments, we detect a crossover between quantum and classical escape processes related to the direction of escape. We find that, under varying external magnetic flux, macroscopic quantum tunneling periodically alternates with thermally activated escape, a hallmark of the "Münchhausen effect."

Multistability and switching in a superconducting metamaterial.

The field of metamaterial research revolves around the idea of creating artificial media that interact with light in a way unknown from naturally occurring materials. This is commonly achieved using sub-wavelength lattices of electronic or plasmonic structures, so-called meta-atoms. One of the ultimate goals for these tailored media is the ability to control their properties in situ. Here we show that superconducting quantum interference devices can be used as fast, switchable meta-atoms. We find that their intrinsic nonlinearity leads to simultaneously stable dynamic states, each of which is associated with a different value and sign of the magnetic susceptibility in the microwave domain. Moreover, we demonstrate that it is possible to switch between these states by applying nanosecond-long pulses in addition to the microwave-probe signal. Apart from potential applications for this all-optical metamaterial switch, the results suggest that multistability can also be utilized in other types of nonlinear meta-atoms.

A one-dimensional tunable magnetic metamaterial.

We present experimental data on a one-dimensional super-conducting metamaterial that is tunable over a broad frequency band. The basic building block of this magnetic thin-film medium is a single-junction (rf-) superconducting quantum interference device (SQUID). Due to the nonlinear inductance of such an element, its resonance frequency is tunable in situ by applying a dc magnetic field. We demonstrate that this results in tunable effective parameters of our metamaterial consisting of 54 rf-SQUIDs. In order to obtain the effective magnetic permeability µr,eff from the measured data, we employ a technique that uses only the complex transmission coefficient S21.

[Neurological lower torso function test. A new assessment]. / Neurologischer Funktionstest unterer Rumpf. Ein neues Assessment.

The neurological lower torso function test was developed in addition to the Berg Balance Scale as an assessment for diagnosis and follow-up of lower torso stability and functioning in neurological patients, used for example in subjects in the early rehabilitation phase or still showing low motoric recovery after suffering a stroke. Due to the ground effect for changes in severely affected neurological patients, other tests currently available do not provide an adequate level of sensitivity. The neurological function test was integrated into the study "Combined whole body vibration and balance training using Vibrosphere" with 66 inpatient/partial inpatient neurological subjects ≥ 60 years. Based on six tasks, a qualitative assessment of the selective function of movement and posture tone of the lower extremity, the muscular system around the hip, and the lower torso are performed. Analogous to the Berg Balance Scale, a 5 point scale is used. It shows a high degree of reliability and responsiveness and can be performed with little effort of time and personnel.

Combined whole body vibration and balance training using Vibrosphere®: improvement of trunk stability, muscle tone, and postural control in stroke patients during early geriatric rehabilitation.

Strokes are a leading cause of disability, immobility, and reduced ability to perform activities of daily living (ADLs) among the elderly. Balance and postural control are often affected in stroke patients. Physical therapy for the lower back to improve posture, mobility, and ADLs can be very time consuming. In this randomized, controlled study of 66 geriatric patients (mean age 74.5 years) with stroke-related paresis or hemiplegia, it was demonstrated that stroke patients may benefit more from 3 additional weeks of combined whole body vibration and balance training than from a comprehensive inpatient geriatric rehabilitation program in terms of trunk stability, postural control, and muscle tone.

Synaptotagmin VII as a plasma membrane Ca(2+) sensor in exocytosis.

Synaptotagmins I and II are Ca(2+) binding proteins of synaptic vesicles essential for fast Ca(2+)-triggered neurotransmitter release. However, central synapses and neuroendocrine cells lacking these synaptotagmins still exhibit Ca(2+)-evoked exocytosis. We now propose that synaptotagmin VII functions as a plasma membrane Ca(2+) sensor in synaptic exocytosis complementary to vesicular synaptotagmins. We show that alternatively spliced forms of synaptotagmin VII are expressed in a developmentally regulated pattern in brain and are concentrated in presynaptic active zones of central synapses. In neuroendocrine PC12 cells, the C(2)A and C(2)B domains of synaptotagmin VII are potent inhibitors of Ca(2+)-dependent exocytosis, but only when they bind Ca(2+). Our data suggest that in synaptic vesicle exocytosis, distinct synaptotagmins function as independent Ca(2+) sensors on the two fusion partners, the plasma membrane (synaptotagmin VII) versus synaptic vesicles (synaptotagmins I and II).

Beta-catenin is a major tyrosine-phosphorylated protein during mouse oocyte maturation and preimplantation development.

During mouse preimplantation development, the components of the E-cadherin-catenin complex are derived from both maternal and zygotic gene activity and the adhesion complex is increasingly accumulated and stored in a nonfunctional form, ready to be used for compaction and the formation of the trophectoderm cell layer (Ohsugi et al., Dev. Dyn. 206:391-402, 1996). Here, we show that beta-catenin is a major tyrosine-phosphorylated protein in oocytes and early cleavage-stage embryos and that the relative amount of phosphorylated beta-catenin is greatly reduced during the morula-blastocyst transition. Peptide-specific antibodies indicate that beta-catenin undergoes conformational changes and/or that the carboxy-terminal region of beta-catenin is blocked during preimplantation development. Moreover, the availability of a carboxy-terminal epitope seems to depend on the tyrosine phosphorylation state of beta-catenin and becomes unmasked when oocytes are treated with the tyrosine kinase inhibitor genistein. Our results suggest that tyrosine phosphorylation of beta-catenin represents a molecular mechanism to keep the accumulating E-cadherin adhesion complex in a nonfunctional form. Dev Dyn 1999;216:168-176.

The subcellular localizations of atypical synaptotagmins III and VI. Synaptotagmin III is enriched in synapses and synaptic plasma membranes but not in synaptic vesicles.

Multiple synaptotagmins are expressed in brain, but only synaptotagmins I and II have known functions in fast, synchronous Ca2+-triggered neurotransmitter release. Synaptotagmin III was proposed to regulate other aspects of synaptic vesicle exocytosis, particularly its slow component. Such a function predicts that synaptotagmin III should be an obligatory synaptic vesicle protein, as would also be anticipated from its high homology to synaptotagmins I and II. To test this hypothesis, we studied the distribution, developmental expression, and localization of synaptotagmin III and its closest homolog, synaptotagmin VI. We find that synaptotagmins III and VI are present in all brain regions in heterogeneous distributions and that their levels increase during development in parallel with synaptogenesis. Furthermore, we show by immunocytochemistry that synaptotagmin III is concentrated in synapses, as expected. Surprisingly, however, we observed that synaptotagmin III is highly enriched in synaptic plasma membranes but not in synaptic vesicles. Synaptotagmin VI was also found to be relatively excluded from synaptic vesicles. Our data suggest that synaptotagmins III and VI perform roles in neurons that are not linked to synaptic vesicle exocytosis but to other Ca2+-related nerve terminal events, indicating that the functions of synaptotagmins are more diverse than originally thought.

A tripartite protein complex with the potential to couple synaptic vesicle exocytosis to cell adhesion in brain.

We identify a complex of three proteins in brain that has the potential to couple synaptic vesicle exocytosis to neuronal cell adhesion. The three proteins are: (1) CASK, a protein related to MAGUKs (membrane-associated guanylate kinases); (2) Mint1, a putative vesicular trafficking protein; and (3) Veli1, -2, and -3, vertebrate homologs of C. elegans LIN-7. CASK, Mint1, and Velis form a tight, salt-resistant complex that can be readily isolated. CASK, Mint1, and Velis contain PDZ domains in addition to other modules. However, no PDZ domains are involved in complex formation, leaving them free to recruit cell adhesion molecules, receptors, and channels to the complex. We propose that the tripartite complex acts as a nucleation site for the assembly of proteins involved in synaptic vesicle exocytosis and synaptic junctions.

Thy-1 is a component common to multiple populations of synaptic vesicles.

Thy-1, a glycosylphosphatidylinositol-linked integral membrane protein of the immunoglobulin superfamily, is a component of both large dense-core and small clear vesicles in PC12 cells. A majority of this protein, formerly recognized only on the plasma membrane of neurons, is localized to regulated secretory vesicles. Thy-1 is also present in synaptic vesicles in rat central nervous system. Experiments on permeabilized PC12 cells demonstrate that antibodies against Thy-1 inhibit the regulated release of neurotransmitter; this inhibition appears to be independent of any effect on the Ca2+ channel. These findings suggest Thy-1 is an integral component of many types of regulated secretory vesicles, and plays an important role in the regulated vesicular release of neurotransmitter at the synapse.

M-cadherin-mediated cell adhesion and complex formation with the catenins in myogenic mouse cells.

M-cadherin is a member of the multigene family of calcium-dependent intercellular adhesion molecules, the cadherins, which are involved in morphogenetic processes. Amino acid comparisons between M-cadherin and E-, N-, and P-cadherin suggested that M-cadherin diverged phylogenetically very early from these classical cadherins. It has been shown that M-cadherin is expressed in prenatal and adult skeletal muscle. In the cerebellum, M-cadherin is present in an adherens-type junction which differs in its molecular composition from the E-cadherin-mediated adherens-type junctions. These and other findings raised the question of whether M-cadherin and the classical cadherins share basic biochemical properties, notably the calcium-dependent resistance to proteolysis, mediation of calcium-dependent intercellular adhesion, and the capability to form M-cadherin complexes with the catenins. Here we show that M-cadherin is resistant to trypsin digestion in the presence of calcium ions but at lower trypsin concentrations than E-cadherin. When ectopically expressed in LMTK- cells, M-cadherin mediated calcium-dependent cell aggregation. Finally, M-cadherin was capable of forming two distinct cytoplasmic complexes in myogenic cells, either with alpha-catenin/beta-catenin or with alpha-catenin/plakoglobin, as E-and N-cadherin, for example, have previously been shown to form. The relative amount of these complexes changed during differentiation from C2C12 myoblasts to myotubes, although the molecular composition of each complex was unaffected during differentiation. These results demonstrate that M-cadherin shares important features with the classical cadherins despite its phylogenetic divergence.

An alpha-E-catenin gene trap mutation defines its function in preimplantation development.

Catenins are proteins associated with the cytoplasmic domain of cadherins, a family of transmembrane cell adhesion molecules. The cadherin-catenin adhesion system is involved in morphogenesis during development and in the maintenance of the integrity of different tissue types. Using a gene trap strategy, we have isolated a mouse mutation for the gene encoding the alpha-E-catenin. This form of the alpha-catenin appears frequently coexpressed with E-cadherin in epithelial cell types. The mutation obtained eliminates the carboxyl-terminal third of the protein but nevertheless provokes a complete loss-of-function phenotype. Homozygous mutants show disruption of the trophoblast epithelium (the first differentiated embryonic tissue), and development is consequently blocked at the blastocyst stage. This phenotype parallels the defects observed in E-cadherin mutant embryos. Our results show the requirement of the alpha-E-catenin carboxy terminus for its function and represent evidence of the role of the alpha-E-catenin in vivo, identifying this molecule as the natural partner of the E-cadherin in trophoblast epithelium.

Tyrosine kinase receptors concentrated in caveolae-like domains from neuronal plasma membrane.

Recent evidence suggests that tyrosine kinases are highly organized in caveolae of tissue culture cells. We now report the isolation of a membrane domain from neuronal plasma membranes that has the biochemical characteristics of caveolae. A low density membrane (LDM) fraction with the same density as caveolae was highly enriched in tyrosine kinases such as insulin receptors, neurotrophin receptors, Eph family receptors, and Fyn. Grb2, Ras, heterotrimeric GTP-binding proteins, and Erk2 were also concentrated in the LDM. Incubation of the LDM fraction at 37 degrees C stimulated the phosphorylation on tyrosine of multiple, resident proteins, whereas the bulk membrane fraction was devoid of tyrosine kinase activity. The LDM, which makes up approximately 5-10% of the plasma membrane protein, appears to be organized for signal transduction.

Influence of norethisterone acetate and estradiol on the serotonin metabolism of postmenopausal women.

Previous studies have shown that estradiol increases urinary excretion of the main stable metabolite of serotonin, 5-hydroxyindole acetic acid (5-HIAA), reflecting an increase in serotonin production. In the present study, the effect of the progestin norethisterone acetate (NETA) on serotonin metabolism was investigated, both alone and in addition to estradiol replacement in 20 postmenopausal women. Urinary excretion of 5-HIAA was measured after treatment with NETA orally for 8 days, estradiol valerate orally for 9 days and a combination of both hormones for 12 days. 5-HIAA values, expressed as percentages of the pretreatment values, were significantly increased only after the estrogen treatment phase. NETA alone did not significantly alter the serotonin metabolite excretion; in combination with estradiol, the estradiol effect on serotonin metabolism was abolished. This indicates that adding norethisterone acetate to estradiol replacement therapy may have a negative impact on the effect of estradiol on serotonin metabolism.

A role for cadherins in tissue formation.

We have produced null mutant mouse embryonic stem cells for the cell adhesion molecule E-cadherin. Such E-cadherin-/- ES cells are defective in cell aggregation; this defect can be corrected by transfection with cDNA for either E-cadherin or N-cadherin driven by a constitutive promoter. The presence (or absence) of E-cadherin regulates the expression of the transcription factor T-brachyury, indicating that cadherins play a role in linking cell surface receptors and gene expression. Comparative analysis of the parental and the genetically altered ES cell lines was performed to examine cell differentiation and the capability to form organized tissues. While differentiating E-cadherin-/- ES cells are still able to express various early and late differentiation markers, they show a clear-cut deficiency in forming organized structures. This phenotype can be rescued by constitutive expression of E-cadherin, which results exclusively in formation of epithelia. In contrast, rescue transfectants expressing N-cadherin show no epithelial structures, instead forming neuroepithelium and cartilage. These results provide the first evidence that specific cadherins directly stimulate differentiation into certain types of tissues.

The proteolytic fragments generated by vertebrate proteasomes: structural relationships to major histocompatibility complex class I binding peptides.

Proteasomes are involved in the proteolytic generation of major histocompatibility complex (MHC) class I epitopes but their exact role has not been elucidated. We used highly purified murine 20S proteasomes for digestion of synthetic 22-mer and 41/44-mer ovalbumin partial sequences encompassing either an immunodominant or a marginally immunogenic epitope. At various times, digests were analyzed by pool sequencing and by semiquantitative electrospray ionization mass spectrometry. Most dual cleavage fragments derived from 22-mer peptides were 7-10 amino acids long, with octa- and nonamers predominating. Digestion of 41/44-mer peptides initially revealed major cleavage sites spaced by two size ranges, 8 or 9 amino acids and 14 or 15 amino acids, followed by further degradation of the latter as well as of larger single cleavage fragments. The final size distribution was slightly broader than that of fragments derived from 22-mer peptides. The majority of peptide bonds were cleaved, albeit with vastly different efficiencies. This resulted in multiple overlapping proteolytic fragments including a limited number of abundant peptides. The immunodominant epitope was generated abundantly whereas only small amounts of the marginally immunogenic epitope were detected. The frequency distributions of amino acids flanking proteasomal cleavage sites are correlated to that reported for corresponding positions of MHC class I binding peptides. The results suggest that proteasomal degradation products may include fragments with structural properties similar to MHC class I binding peptides. Proteasomes may thus be involved in the final stages of proteolytic epitope generation, often without the need for downstream proteolytic events.

Expression and cell membrane localization of catenins during mouse preimplantation development.

We have studied transcription, expression, and membrane localization of components of the E-cadherin-catenin complex stage by stage during mouse preimplantation development. Maternal E-cadherin and alpha- and beta-catenin are stored as mRNA and/or protein in unfertilized eggs and are already assembled into a protein complex at this stage. After fertilization, it is likely that they mediate adhesion of early-stage blastomeres. Biosynthesis of plakoglobin is delayed relative to the other components. The temporal mRNA and protein expression patterns of the components of the cadherin-catenin complex correlate with the presence or absence of potential cytoplasmic polyadenylation elements (CPEs) in the 3'-UTRs of the respective cDNAs. Our results suggest that the components of the E-cadherin-catenin complex derived from both maternal and zygotic gene activity are increasingly accumulated and stored in a nonfunctional form during early cleavage stages and are ready to be used for compaction and the formation of the trophectodermal cell layer.

Adhesiveness of the apical surface of uterine epithelial cells: the role of junctional complex integrity.

Embryo implantation necessitates that the apical plasma membrane of uterine epithelial cells acquires adhesiveness. Recent studies have indicated that modulation of a major element of the epithelial phenotype, i.e. apical-basal cell polarity, might be critical in this respect. Here, we analyze polar characteristics of nonadhesive vs. adhesive uterine epithelial cell lines focusing on cytoskeletal-junctional interactions that may play a role in regulating adhesiveness of the apical plasma membrane. HEC-1-A is a human uterine epithelial cell line exhibiting nonadhesive properties of its apical surface for trophoblast, whereas RL95-2 represent another such cell line exhibiting adhesive properties enabling trophoblast attachment. Homotypic intercellular contacts and functionally related proteins, i.e. ZO-1, E-cadherin, alpha-catenin, beta-catenin, plakoglobin, and desmoplakin 1, were examined by transmission electron microscopy, immunocytochemistry, confocal laser scanning microscopy, and immunoprecipitation techniques. In addition, details of actin filament architecture were studied after phalloidin labeling. While nonadhesive HEC-1-A exhibited the well-known pattern of cell-to-cell contacts of polarized epithelial cells, adhesive RL95-2 showed a lack of ZO-1 expression, tracer leakiness of the paracellular pathway, and atypical features in adherens junctions: E-cadherin, alpha-catenin and plakoglobin were colocalized in all plasma membrane domains and beta-catenin was localized in lateral membrane domains. Immunoprecipitations showed in both cell lines the presence of two different E-cadherin-catenin complexes, one composed of E-cadherin, alpha-catenin and beta-catenin, and the other of E-cadherin, alpha-catenin and plakoglobin. Concerning RL95-2 these data indicate that E-cadherin/plakoglobin complexes are randomly distributed, whereas E-cadherin/beta-catenin complexes are laterally localized in these cells. Additionally, the actin-based cytoskeleton of RL95-2 lacked a polar organization. With respect to the intermediate filament-desmosome system, both cell types expressed desmoplakin I, but the vast majority of RL95-2 lacked well-formed desmosomes as demonstrated by electron microscopy. It is concluded that modulation of tight junctions and/or remodelling of adherens junctions, e.g. differential distribution of E-cadherin/plakoglobin complexes and E-cadherin/beta-catenin complexes, are correlated with the development of apical adhesiveness of human uterine epithelial cells. This model system should allow to test experimentally whether this correlation is due to any causal function in the development of epithelial cell polarity.

CASK: a novel dlg/PSD95 homolog with an N-terminal calmodulin-dependent protein kinase domain identified by interaction with neurexins.

Neurexins are neuronal cell surface proteins with hundreds of isoforms. In yeast two-hybrid screens for intracellular molecules interacting with different neurexins, we identified a single interacting protein called CASK. CASK is composed of an N-terminal Ca2+, calmodulin-dependent protein kinase sequence and a C-terminal region that is similar to the intercellular junction proteins dlg-A, PSD95/SAP90, SAP97, Z01, and Z02 and that contains DHR-, SH3-, and guanylate kinase domains. CASK is enriched in brain in synaptic plasma membranes but is also detectable at low levels in all tissues tested. The cytoplasmic domains of all three neurexins bind CASK in a salt-labile interaction. In neurexin I, this interaction is dependent on the C-terminal three residues. Thus, CASK is a membrane-associated protein that combines domains found in Ca2+ - activated protein kinases and in proteins specific for intercellular junctions, suggesting that it may be a signaling molecule operating at the plasma membrane, possibly in conjunction with neurexins.