Identification of an N-terminal glycogen synthase kinase 3 phosphorylation site which regulates the functional localisation of polycystin-2 in vivo and in vitro

PKD2 is mutated in 15% of patients with autosomal dominant polycystic kidney disease (ADPKD). Polycystin-2 (PC2), the PKD2 protein, is a nonselective Ca2 + -permeable cation channel which may function at the cell surface and ER. Nevertheless, the factors that regulate the dynamic translocation of PC2 between the ER and other compartments are not well understood. Constitutive phosphorylation of PC2 at a single C-terminal site (Ser812) has been previously reported. Since we were unable to abolish phospholabelling of PC2 in HEK293 cells by site-directed mutagenesis of Ser812 or all 5 predicted phosphorylation sites in the C-terminus, we hypothesised that PC2 could also be phosphorylated at the N-terminus. In this paper, we report the identification of a new phosphorylation site for PC2 within its N-terminal domain (Ser76) and demonstrate that this residue is phosphorylated by glycogen synthase kinase 3 (GSK-3). The consensus recognition sequence for GSK-3 (Ser76/Ser80) is evolutionarily conserved down to lower vertebrates. In the presence of specific GSK-3 inhibitors, the lateral plasma membrane pool of endogenous PC2 redistributes into an intracellular compartment in MDCK cells without a change in primary cilia localization. Finally, co-injection of wild-type but not a S76A/S80A mutant PKD2 capped mRNA could rescue the cystic phenotype induced by an antisense morpholino oligonucleotide to pkd2 in zebrafish pronephric kidney. We conclude that surface localization of PC2 is regulated by phosphorylation at a unique GSK-3 site in its N-terminal domain in vivo and in vitro. This site is functionally significant for the maintenance of normal glomerular and tubular morphology

Frequency-resolved pump-probe for ultrashort pulse characterization

In recent years, frequency-resolved optical gating (FROG) technique has been widely applied for ultrashort pulse characterization. A number of outstanding qualities such as experimental simplicity, uniqueness of the retrieved amplitude and phase, and independent data checks make FROG an invaluable tool in ultra-fast spectroscopy. In this contribution we introduce a new member of the FROG family: frequency-resolved pump-probe (FRPP). Unlike optically heterodyne detected (OHD) FROG, which requires additional polarizers, FRPP employs unmodified pump-probe geometry widely used in ultrafast spectroscopic experiments. Furthermore, a FRPP trace carries both positive and negative values, which should substantially improve the noise stability of the retrieval procedure

Edge and Bulk of the Fractional Quantum Hall Liquids

An effective Chern-Simons theory for the Abelian quantum Hall states with edges is proposed to study the edge and bulk properties in a unified fashion. We impose a condition that the currents do not flow outside the sample. With this boundary condition, the action remains gauge invariant and the edge modes are naturally derived. We find that the integer coupling matrix $K$ should satisfy the condition $\sum_I(K^{-1})_{IJ} = \nu/m$ ($\nu$: filling of Landau levels, $m$: the number of gauge fields ) for the quantum Hall liquids. Then the Hall conductance is always quantized irrespective of the detailed dynamics or the randomness at the edge.Comment: 13 pages, REVTEX, one figure appended as a postscript fil

Magnetoconductivity of Hubbard bands induced in Silicon MOSFETs

Sodium impurities are diffused electrically to the oxide-semiconductor interface of a silicon MOSFET to create an impurity band. At low temperature and at low electron density, the band is split into an upper and a lower sections under the influence of Coulomb interactions. We used magnetoconductivity measurements to provide evidence for the existence of Hubbard bands and determine the nature of the states in each band.Comment: In press in Physica

Quantum Interference between Impurities: Creating Novel Many-Body States in s-wave Superconductors

We demonstrate that quantum interference of electronic waves that are scattered by multiple magnetic impurities in an s-wave superconductor gives rise to novel bound states. We predict that by varying the inter-impurity distance or the relative angle between the impurity spins, the states' quantum numbers, as well as their distinct frequency and spatial dependencies, can be altered. Finally, we show that the superconductor can be driven through multiple local crossovers in which its spin polarization, $$, changes between $=0, 1/2$ and 1.Comment: 4 pages, 4 figure

Current and charge distributions of the fractional quantum Hall liquids with edges

An effective Chern-Simons theory for the quantum Hall states with edges is studied by treating the edge and bulk properties in a unified fashion. An exact steady-state solution is obtained for a half-plane geometry using the Wiener-Hopf method. For a Hall bar with finite width, it is proved that the charge and current distributions do not have a diverging singularity. It is shown that there exists only a single mode even for the hierarchical states, and the mode is not localized exponentially near the edges. Thus this result differs from the edge picture in which electrons are treated as strictly one dimensional chiral Luttinger liquids.Comment: 21 pages, REV TeX fil

Topological Phase Transition and Electrically Tunable Diamagnetism in Silicene

Silicene is a monolayer of silicon atoms forming a honeycomb lattice. The lattice is actually made of two sublattices with a tiny separation. Silicene is a topological insulator, which is characterized by a full insulating gap in the bulk and helical gapless edges. It undergoes a phase transition from a topological insulator to a band insulator by applying external electric field. Analyzing the spin Chern number based on the effective Dirac theory, we find their origin to be a pseudospin meron in the momentum space. The peudospin degree of freedom arises from the two-sublattice structure. Our analysis makes clear the mechanism how a phase transition occurs from a topological insulator to a band insulator under increasing electric field. We propose a method to determine the critical electric field with the aid of diamagnetism of silicene. Diamagnetism is tunable by the external electric field, and exhibits a singular behaviour at the critical electric field. Our result is important also from the viewpoint of cross correlation between electric field and magnetism. Our finding will be important for future electro-magnetic correlated devices.Comment: 4 pages,5 figure