Impact of Pdx1-associated chromatin modifiers on islet ß-cells.

Diabetes mellitus arises from insufficient insulin secretion from pancreatic islet ß-cells. In type 2 diabetes (T2D), ß-cell dysfunction is associated with inactivation and/or loss of transcription factor (TF) activity, including Pdx1. Notably, this particular TF is viewed as a master regulator of pancreas development and islet ß-cell formation, identity and function. TFs, like Pdx1, recruit coregulators to transduce activating and/or repressing signals to the general transcriptional machinery for controlling gene expression, including modifiers of DNA, histones and nucleosome architecture. These coregulators impart a secondary layer of control that can be exploited to modulate TF activity. In this review, we describe Pdx1-recruited coregulators that impact chromatin structure, consequently influencing normal ß-cell function and likely Pdx1 activity in pathophysiological settings.

Measurement of Cu(II) copper defect dipoles in ferroelectric PbTiO3 using electron-nuclear double resonance.

Point defects associated with Cu(II) in ferroelectric PbTiO3 were determined using pulsed electron-nuclear double resonance (ENDOR). Three centers were observed, and neighbor 207Pb superhyperfine tensors to the third shell of equivalent Pb ions measured. The ENDOR angular dependence showed that Cu(II) is incorporated as an acceptor at the Ti site. One center also showed ENDOR from an axial fluorine ion. The three defects were determined to be the Cu(II)-oxygen-vacancy defect dipole, Cu(II) with a complete oxygen octahedron, and a Cu(II)-F- defect dipole center.

High-field optically detected EPR and ENDOR of semiconductor defects using W-band microwave Fabry-Pérot resonators.

The designs of W-band (approximately 95 GHz) Fabry-Pérot microwave resonators for optically detected EPR and ENDOR using the magnetic circular dichroism of the optical absorption (MCDA) as well as for photo-luminescence-detected EPR are briefly described. We report on the first MCDA-detected high-field EPR/ENDOR investigation of the paramagnetic EL2+ defect in semi-insulating GaAs. The higher-order effects, which prevented the unambiguous analysis of previous MCDA-detected K-band EPR/ENDOR experiments could be suppressed in W-band. The analysis of the ENDOR spectra showed that an extremely precise alignment of the samples is necessary. The paramagnetic El2+ defect turned out to be an As antisite defect, which has four almost equivalent nearest 75As neighbours differing less than 1.5% in the superhyperfine interactions suggestive of an isolated As antisite, while the third 75As shell (fifth neighbour shell) is clearly of lower symmetry than expected for an isolated As antisite. We discuss as a possible solution to this paradoxical situation that EL2+ is an isolated antisite at room temperature, which at low temperature, where all magnetic resonance experiments are performed, associates itself with shallow acceptors such as Zn(Ga)- more than two nearest neighbour distances away. According to recent theoretical calculations, such 'loose' complexes with binding energies between 0.01 eV and 0.05 eV and disturb the equivalence of the nearest neighbour superhyperfine (shf) interactions less than 1.5%. Also, W-band EPR was measured using the photo-luminescence for detection to investigate P dopants in 6H-SiC.

Sensitivity enhancement in ESR/ENDOR spectrometers by use of microwave amplifiers.

The introduction of a low-noise microwave preamplifier in a homodyne ESR spectrometer can increase the signal-to-noise ratio by more than a factor of 10 at low modulation frequencies, and makes it superior to a superheterodyne spectrometer. The performance of this new arrangement has been compared to that of a normal homodyne spectrometer.