The Role of Hedgehog Acyltransferase & Heparan Sulphate Proteoglycans in Human Sonic Hedgehog Signalling

Hedgehog proteins (Hh) are morphogens and major mediators in many developmental processes. Hh signalling is significant for many aspects of embryonic development, whereas dysregulation of this pathway is associated with several types of cancers. Hh proteins require dual lipidation and Heparan Sulfate Proteoglycans (HSPGs) for their proper distribution and signalling activity. My first aim was to study the role of HSPGs in human (h) Sonic Hedgehog (Shh) signalling and clarify the biological function of hShh/HSPGs complexes in hShh signalling, by investigating the interaction between human hShh and HSPGs. I used DNA mutagenesis and heparin affinity chromatography to determine key residues in hShh involved in heparin binding (K37/38 and K178). The activity of these mutants was tested by detecting induced Alkaline Phosphatase activity in C3H10T1/2 cells and hShh-inducible gene expression in PANC1 human pancreatic carcinoma cells. I examined the biological function of mutated hShhs (K37/38S, K178S and K37/38/178S) that cannot interact with heparin efficiently and showed that they had reduced signalling activity compared to wild type hShh and a control mutation (K74S). Also, I showed that mutant hShh proteins mediate reduced proliferation and invasion of PANC1 cells following hShh RNAi knockdown (KD), and this correlated with reduced Shh multimeric complex formation. Structurally, Shh proteins are unusual in being dually lipid-modified to be fully active. During the post-translational modifications of Shh, N-terminal palmitoylation is facilitated by the product (Hhat) of the hedgehog acyltransferase gene. I have carried out a thorough analysis of Hhat in PANC1 cells. First, I characterised an antibody prepared in the lab to hHhat. I confirmed the specificity of the antibody by immunoblotting using a self-constructed hHhat-EGFP clone, and a control mGup1-EGFP clone. By subcellular fractionation and Western blotting I found Hhat to be a membrane protein. In addition, I used the hHhat antibody to determine the intracellular localisation of hHhat in PANC1 cells by confocal microscopy and showed that hHhat localised in ER mainly but not in Golgi apparatus. I confirmed this using the hHhat-EGFP clone for fluorescence microscopy in transfected cells. To illuminate the biological function of palmitoylation of hShh in production of active hShh and in the formation of hShh multimeric complex I optimised hHhat RNAi knockdown (KD) in PANC1 cells and confirmed this by a cell-based palmitoylation assay. Using semi-quantitative RT-PCR and immunoblot analyses, I showed that hHhat KD caused decreased signalling through the Shh pathway due to reduced production of active hShh. In addition, I investigated the effect of the addition of palmitate to hShh on its association with cells by comparing hHhat KD cells with control cells. Immunoblotting suggests that palmitoylation of Shh improves its ability to associate to cell membranes. Using hHhat KD, gel filtration of high molecular weight complexes of hShh and immunoblotting of hShh I characterised the role of palmitoylation of hShh in multimeric complex formation. Lastly, I investigated the effect of hHhat KD on PANC1 proliferation and invasion, showing that it represses PANC1 proliferation and invasion. These studies provide a firm basis for understanding the functional roles of hShh palmitoylation and its interactions with HSPGs, and provide proof-of-principle for targeting these aspects of hShh biology in tumour cell therapeutics, specifically in the pancreatic carcinoma context

Three-body Baryonic anti-B -->Lambda anti-p pi Decays and Such

We study decay rates and spectra of anti-B --> Lambda anti-p pi, Sigma0 anti-p pi, Sigma- anti-n pi, Xi0 anti-Sigma+ pi, Xi- anti-Sigma0 pi and Xi- anti-Lambda pi modes under a factorization approach. The baryon pairs are produced through vector, axial vector, scalar and pseudoscalar operators. Previous predictions, including ours, are an order of magnitude too small compared to experiment. By incorporating QCD counting rules and studying the asymptotic behavior, we find an earlier relation between the pseudoscalar and axial vector form factors to be too restrictive. Instead, the pseudoscalar and scalar form factors are related asymptotically. Following this approach, the measured Lambda anti-p pi rate (~4.0x10^{-6}) and spectrum can be understood, and Lambda should be dominantly left-hand polarized, while we expect Br(Sigma0 anti-p pi)~1.6x10^{-6}. These results and other predictions can be checked soon.Comment: 18 pages, 3 figures; use updated Belle results, add Lambda polarization stud

When Does Government Debt Crowd Out Investment?

We investigate the relationship between inequality and education funding in a model of probabilistic voting over public education spending where the private option is available. A change in inequality can have opposite effects at different income levels: higher inequality decreases public spending per student and increases enrollment in public schools in poor economies, while the opposite holds in the rich ones. A change in the tax base can also have non-monotonic effects. We also study the implications of different voting participation across income groups. The predictions of the model are supported by U.S. school district-level data.

CERN: Confidence-Energy Recurrent Network for Group Activity Recognition

This work is about recognizing human activities occurring in videos at distinct semantic levels, including individual actions, interactions, and group activities. The recognition is realized using a two-level hierarchy of Long Short-Term Memory (LSTM) networks, forming a feed-forward deep architecture, which can be trained end-to-end. In comparison with existing architectures of LSTMs, we make two key contributions giving the name to our approach as Confidence-Energy Recurrent Network -- CERN. First, instead of using the common softmax layer for prediction, we specify a novel energy layer (EL) for estimating the energy of our predictions. Second, rather than finding the common minimum-energy class assignment, which may be numerically unstable under uncertainty, we specify that the EL additionally computes the p-values of the solutions, and in this way estimates the most confident energy minimum. The evaluation on the Collective Activity and Volleyball datasets demonstrates: (i) advantages of our two contributions relative to the common softmax and energy-minimization formulations and (ii) a superior performance relative to the state-of-the-art approaches.Comment: Accepted to IEEE Conference on Computer Vision and Pattern Recognition (CVPR), 201

Topological surface states and Fermi arcs of the noncentrosymmetric Weyl semimetals TaAs, TaP, NbAs, and NbP

Very recently the topological Weyl semimetal (WSM) state was predicted in the noncentrosymmetric compounds TaAs, TaP, NbAs, and NbP and soon led to photoemission and transport experiments to verify the presumed topological properties such as Fermi arcs (unclosed Fermi surfaces) and the chiral anomaly. In this work, we have performed fully \textit{ab initio} calculations of the surface band structures of these four WSM materials and revealed the Fermi arcs with spin-momentum-locked spin texture. On the (001) polar surface, the shape of the Fermi surface depends sensitively on the surface terminations (cations or anions), although they exhibit the same topology with arcs. The anion (P or As) terminated surfaces are found to fit recent photoemission measurements well. Such surface potential dependence indicates that the shape of the Fermi surface can be manipulated by depositing guest species (such as K atoms), as we demonstrate. On the polar surface of a WSM without inversion symmetry, Rashba-type spin polarization naturally exists in the surface states and leads to strong spin texture. By tracing the spin polarization of the Fermi surface, we can also distinguish Fermi arcs from trivial Fermi circles. The four compounds NbP, NbAs, TaP, and TaAs present an increasing amplitude of spin-orbit coupling (SOC) in the band structure. By comparing their surface states, we reveal the evolution of topological Fermi arcs from the spin-degenerate Fermi circle to spin-split arcs when the SOC increases from zero to a finite value. Our work will help us understand the complicated surface states of WSMs and allow us to manipulate them, especially for future spin-revolved photoemission and transport experiments.Comment: This manuscript has been submitted to Physical Review B on 22 Jul. 201

Prediction of Near-Room-Temperature Quantum Anomalous Hall Effect on Honeycomb Materials

Recently, this long-sought quantum anomalous Hall effect was realized in the magnetic topological insulator. However, the requirement of an extremely low temperature (approximately 30 mK) hinders realistic applications. Based on \textit{ab-initio} band structure calculations, we propose a quantum anomalous Hall platform with a large energy gap of 0.34 and 0.06 eV on honeycomb lattices comprised of Sn and Ge, respectively. The ferromagnetic order forms in one sublattice of the honeycomb structure by controlling the surface functionalization rather than dilute magnetic doping, which is expected to be visualized by spin polarized STM in experiment. Strong coupling between the inherent QSH state and ferromagnetism results in considerable exchange splitting and consequently an FM insulator with a large energy gap. The estimated mean-field Curie temperature is 243 and 509 K for Sn and Ge lattices, respectively. The large energy gap and high Curie temperature indicate the feasibility of the QAH effect in the near-room-temperature and even room-temperature regions.Comment: 6 pages, 4 figures and 1 tabl

Ab initio study of topological surface states of strained HgTe

The topological surface states of mercury telluride (HgTe) are studied by ab initio calculations assuming different strains and surface terminations. For the Te-terminated surface, a single Dirac cone exists at the $\Gamma$ point. The Dirac point shifts up from the bulk valence bands into the energy gap when the substrate-induced strain increases. At the experimental strain value (0.3%), the Dirac point lies slightly below the bulk valence band maximum. A left-handed spin texture was observed in the upper Dirac cone, similar to that of the Bi$_2$Se$_3$-type topological insulator. For the Hg-terminated surface, three Dirac cones appear at three time-reversal-invariant momenta, excluding the $\Gamma$ point, with nontrivial spin textures.Comment: 4 pages, 3 figure