Breakdown of the interlayer coherence in twisted bilayer graphene

Coherent motion of electrons in Bloch states is one of the fundamental concepts of charge conduction in solid-state physics. In layered materials, however, such a condition often breaks down for the interlayer conduction, when the interlayer coupling is significantly reduced by, e.g., a large interlayer separation. We report that complete suppression of coherent conduction is realized even in an atomic length scale of layer separation in twisted bilayer graphene. The interlayer resistivity of twisted bilayer graphene is much higher than the c-axis resistivity of Bernal-stacked graphite and exhibits strong dependence on temperature as well as on external electric fields. These results suggest that the graphene layers are significantly decoupled by rotation and incoherent conduction is a main transport channel between the layers of twisted bilayer graphene.

Abstract P1-05-03: A requirement for neural precursor cell-expressed developmentally downregulated gene 9 during the initiation of mammary tumorigenesis in MMTV-neu mice

The Neural precursor cell-Expressed Developmentally Downregulated gene 9 (NEDD9; also HEF1, CAS-L) scaffolding protein regulates many signaling pathways associated with mitosis, survival, migration, and ciliary integrity. Within the last few years, elevated NEDD9 expression has been implicated in progression and metastasis of several types of cancer, including those of the lung, skin, and brain. We have investigated the consequences of introducing a Nedd9 genotype into the MMTV-neu mouse mammary tumor model, which in many respects recapitulates features of human HER2+ breast cancer. 80% of wild-type MMTV-Neu; Nedd9+/+ animals developed tumors with an average latency of 339 days, but only 18% of MMTV-Neu;Nedd9−/− animals developed tumors with an average latency of 416 days. This highly significant difference indicates that the Nedd9−/− genotype significantly prevents neu-dependent mammary tumor formation.

HER2-positive human breast tumors and MMTV-neu-induced tumors originate from mammary luminal epithelial progenitor cells. We evaluated mammary progenitor cell populations from non-tumor bearing MMTV-neu;Nedd9−/− versus MMTV-neu;Nedd9+/+ 4-month old mice (2 months prior to appearance of tumors). Flow cytometry analysis indicated a significantly reduced CD24high;CD49flow luminal progenitor subpopulation in MMTV-neu;Nedd9−/− and Nedd9−/− mammary glands, that could be contributed to the tumorigenesis resistance in the MMTV-neu;Nedd9−/− model. The MMTV-neu;Nedd9−/−genotype negatively affected the Matrigel mammosphere colony-forming potential of luminal progenitor cells compared to MMTV-neu; Nedd9+/+cells, causing formation of fewer colonies with aberrant size and morphology. Quantification of mitotic division planes of MMTV-neu;Nedd9−/− mammospheres revealed no contribution to the observed defects. However, MMTV-neu;Nedd9−/− mammospheres had defective expression of signaling proteins governing cell attachment, with reduced levels of FAK and more cytoplasmic localization of SRC.

The results reported above, together with other data, support three main conclusions. First, they revealed a very substantial requirement for Nedd9 during early stages of HER2/neu-dependent tumor formation. Second, these results are the first to demonstrate a role for Nedd9 in supporting the abundance and colony-forming potential of mammary luminal progenitor cells. Third, they indicate that the defects in mammosphere growth likely involve perturbation of crucial cellular attachment signaling pathways involving FAK and SRC. In sum, these data provide a strong justification for future analysis of NEDD9 in the defective signaling of transformed mammary epithelial progenitor cell populations that initiate human breast cancer.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-05-03.

Soft nearest prototype classification

We propose a new method for the construction of nearest prototype classifiers which is based on a Gaussian mixture ansatz and which can be interpreted as an annealed version of learning vector quantization (LVQ). The algorithm performs a gradient descent on a cost-function minimizing the classification error on the training set. We investigate the properties of the algorithm and assess its performance for several toy data sets and for an optical letter classification task. Results show 1) that annealing in the dispersion parameter of the Gaussian kernels improves classification accuracy; 2) that classification results are better than those obtained with standard learning vector quantization (LVQ 2.1, LVQ 3) for equal numbers of prototypes; and 3) that annealing of the width parameter improved the classification capability. Additionally, the principled approach provides an explanation of a number of features of the (heuristic) LVQ methods.

Spatial learning-induced accumulation of agmatine and glutamate at hippocampal CA1 synaptic terminals

Agmatine, the decarboxylated metabolite of l-arginine, is considered to be a novel putative neurotransmitter. Recent studies have demonstrated that endogenous agmatine may directly participate in the processes of spatial learning and memory. Agmatine-immunoreactivity has been observed within synaptic terminals of asymmetric excitatory synapses in the hippocampal CA1 stratum radiatum (SR), suggesting that agmatine may be colocalized with glutamate. In the present study we demonstrate, using immunofluorescence confocal microscopy, that agmatine is colocalized with glutamate within CA1-CA3 hippocampal pyramidal cell bodies, in young Sprague-Dawley rats. Subcellular investigation, using postembedding electron microscopy-immunogold cytochemistry, has also revealed that agmatine is colocalized with glutamate in most synaptic terminals in the SR region of CA1. Ninety-seven percent of all agmatinergic profiles were found to contain glutamate, and 92% of all glutamatergic profiles contained agmatine (n=6; 300 terminals). Alterations in colocalized agmatine and glutamate levels in the SR synaptic terminals, following 4 days Morris water maze training, were also investigated. Compared with swim only control rats, water maze-trained rats had statistically significant increases in both agmatine (78%; P<0.01) and glutamate (41%; P<0.05) levels within SR terminals synapsing onto CA1 dendrites. These findings provide the first evidence that agmatine and glutamate are colocalized in synaptic terminals in the hippocampal CA1 region, and may co-participate in spatial learning and memory processing.

Enhanced reduction of excess sludge and nutrient removal in a pilot-scale A2O-MBR-TAD system

In this study, a pilot scale anaerobic-anoxic-oxic (A2O) process with submerged membrane (MBR) in the oxic tank was coupled with thermophilic aerobic digestion (TAD) reactor and was operated for longer than 600 days to treat real domestic wastewater. Regardless of the varying conditions of the system, the A2O-MBR-TAD process removed MLSS, TCOD, BOD, TN, TP, and E. coli about 99%, 96%, 96%, 70%, 83%, and 99%, respectively. The additional TP removal of the system was due to the precipitating agent directly added in the oxic reactor, without which TP removal was about 56%. In the TAD reactor, receiving MLSS from the oxic tank (MBR), about 25% of TSS and VSS were solubilized during 2 days of retention. The effluent of the TAD reactor was recycled into the anoxic tank of A2O-MBR to provide organic carbon for denitrification and cryptic growth. By controlling the flowrate of wasting stream from the MBR, sludge production decreased to almost zero. From these results, it was concluded that the A2O-MBR-TAD process could be a reliable option for excellent effluent quality and near zero-sludge production.

Genotypes of NK cell KIR receptors, their ligands, and Fcγ receptors in the response of neuroblastoma patients to Hu14.18-IL2 immunotherapy

Response to immunocytokine (IC) therapy is dependent on natural killer cells in murine neuroblastoma (NBL) models. Furthermore, killer immunoglobulin-like receptor (KIR)/KIR-ligand mismatch is associated with improved outcome to autologous stem cell transplant for NBL. Additionally, clinical antitumor response to monoclonal antibodies has been associated with specific polymorphic-FcγR alleles. Relapsed/refractory NBL patients received the hu14.18-IL2 IC (humanized anti-GD2 monoclonal antibody linked to human IL2) in a Children's Oncology Group phase II trial. In this report, these patients were genotyped for KIR, HLA, and FcR alleles to determine whether KIR receptor-ligand mismatch or specific FcγR alleles were associated with antitumor response. DNA samples were available for 38 of 39 patients enrolled: 24 were found to have autologous KIR/KIR-ligand mismatch; 14 were matched. Of the 24 mismatched patients, 7 experienced either complete response or improvement of their disease after IC therapy. There was no response or comparable improvement of disease in patients who were matched. Thus KIR/KIR-ligand mismatch was associated with response/improvement to IC (P = 0.03). There was a trend toward patients with the FcγR2A 131-H/H genotype showing a higher response rate than other FcγR2A genotypes (P = 0.06). These analyses indicate that response or improvement of relapsed/refractory NBL patients after IC treatment is associated with autologous KIR/KIR-ligand mismatch, consistent with a role for natural killer cells in this clinical response.

Plasma brain natriuretic peptide is associated with hepatic veno-occlusive disease and early mortality after allogeneic hematopoietic stem cell transplantation

Fluid retention is characteristic of veno-occlusive disease (VOD). We hypothesized that plasma brain natriuretic peptide (BNP), a neurohormone secreted in response to volume expansion, may be associated with VOD after hematopoietic stem cell transplantation (HSCT). BNP was measured before and weekly after HSCT in 46 recipients. Sixteen patients developed VOD. BNP concentrations were similar before and on day 0 in patients with and without VOD, but were significantly higher on day 7 and later in those with VOD. Patients with VOD had significantly higher peak BNP concentrations before engraftment than those without VOD (median, 634.4 versus 80.9  pg  ml⁻¹; P=0.01). Multivariate analysis showed that VOD was independently associated with BNP elevation (odds ratio, 50.1; 95% CI: 5.2-478.4; P<0.01). Landmark analysis at day 7 showed that patients with peak BNP concentration of ≥ 180  pg  ml⁻¹ had significantly worse 100-day survival than patients with peak BNP <180  pg  ml⁻¹ (54 versus 91%; P<0.01). In multivariate analysis, BNP elevation before day 7 significantly predicted 100-day survival (hazard ratio 5.3; 95% CI: 1.1-24.3; P=0.03). These findings suggest that plasma BNP may serve as a diagnostic and prognostic marker of VOD.