The replacement histone H2A.Z in a hyperacetylated form is a feature of active genes in the chicken

The replacement histone H2A.Z is variously reported as being linked to gene expression and preventing the spread of heterochromatin in yeast, or concentrated at heterochromatin in mammals. To resolve this apparent dichotomy, affinity-purified antibodies against the N-terminal region of H2A.Z, in both a triacetylatedandnon- acetylatedstate, areusedin native chromatin immmuno-precipitation experiments with mononucleosomes from three chicken cell types. The hyperacetylated species concentrates at the 50 end of active genes, both tissue specific and housekeeping but is absent from inactive genes, while the unacetylated form is absent from both active and inactive genes. A concentration of H2A.Z is also found at insulators under circumstances implying a link to barrier activity but not to enhancer blocking. Although acetylated H2A.Z is widespread throughout the interphase genome, at mitosis its acetylation is erased, the unmodified form remaining. Thus, although H2A.Z may operate as an epigenetic marker for active genes, its N-terminal acetylation does not

The replacement histone H2A.Z in a hyperacetylated form is a feature of active genes in the chicken

The replacement histone H2A.Z is variously reported as being linked to gene expression and preventing the spread of heterochromatin in yeast, or concentrated at heterochromatin in mammals. To resolve this apparent dichotomy, affinity-purified antibodies against the N-terminal region of H2A.Z, in both a triacetylatedandnon- acetylatedstate, areusedin native chromatin immmuno-precipitation experiments with mononucleosomes from three chicken cell types. The hyperacetylated species concentrates at the 50 end of active genes, both tissue specific and housekeeping but is absent from inactive genes, while the unacetylated form is absent from both active and inactive genes. A concentration of H2A.Z is also found at insulators under circumstances implying a link to barrier activity but not to enhancer blocking. Although acetylated H2A.Z is widespread throughout the interphase genome, at mitosis its acetylation is erased, the unmodified form remaining. Thus, although H2A.Z may operate as an epigenetic marker for active genes, its N-terminal acetylation does not

Quantification routines for full 3D elemental distributions of homogeneous and layered samples obtained with laboratory confocal micro XRF spectrometers

Confocal micro X ray fluorescence spectroscopy can be performed with laboratory spectrometers for elemental imaging with 3D resolution. Due to self absorption inside a specimen and energy effects induced by the used polycapillary optics, interpretation of data can be challenging. Thus, quantification techniques to reconstruct sample composition and geometry are mandatory to widen the applicability of the technique to further fields of analytical chemistry. We present an analytical routine which facilitates the quantitative investigation of 3D data sets obtained with laboratory spectrometers. By fully calibrating the spectrometer parameters the procedure is generalized to be suitable for all spectrometers with known excitation spectra and polycapillary optics. Calibration and validation measurements on homogeneous and stratified samples are presented with a discussion on uncertainties and challenges. Finally, the localization of a goethite needle in a quartz matrix is presented as an example of a possible routine applicatio

Laboratory soft X ray setup for transient absorption experiments in the liquid phase using a laser produced plasma source

With time resolved soft X ray spectroscopy, the element specific dynamics of the electronic structure of disordered systems can be investigated. Measurements of species in dilute liquid solutions are particularly challenging and require high photon flux combined with low experimental noise. This mostly limited these experiments to large scale facilities, especially for energies above the water window 533 eV . Based on a laser produced plasma source, our system enables, to the best of our knowledge, the first static and transient experiments in the liquid phase to be performed in the laboratory for energies up to 1400 eV and with a time resolution of 500 ps. We benchmark the system with static investigations of [Ni CN 4]2 amp; 8722; and transient experiments on the widely used model complex [Fe bpy 3]2 , both in an aqueous solution. The introduced self referencing concept ensures that the measurements are photon noise limited. Our results form the basis for further liquid phase experiments investigating the dynamics in diluted solution

Ultrafast NEXAFS spectroscopy in the lab using laser based sources and advanced X ray optics

Laboratory based laser driven short pulse X ray sources like laser produced plasmas LPP and high harmonic generation HHG exhibit a great potential for spectroscopy in the soft X ray range. These sources are complementary to large scale facilities like synchrotrons or free electron lasers. For applications of LPP or HHG sources for time resolved X ray absorption spectroscopy in the water window or beyond a high photon flux is crucial. The available photon flux strongly depends on energy, pulse duration and repetition rate of the pump laser. Depending on the experimental needs in time resolved experiments pulse durations of the X ray pulse ranging from nanoseconds to sub femtoseconds are required. In our contribution we will present a highly brilliant LPP source emitting soft X rays in the photon energy range between 50 and 1500 eV based on CPA and thin disk laser technology as well as the high average power thin disk laser based OPCPA system for high photon flux HHG. In addition we present a new generation of reflection zone plates on spherical substrates, that promises a remarkable high resolution over a wide spectral range making it an ideal and highly efficient diffractive optic for time resolved NEXAFS experiments in the la

Towards understanding excited state properties of organic molecules using time resolved soft X ray absorption spectroscopy

The extension of the pump probe approach known from UV VIS spectroscopy to very short wavelengths together with advanced simulation techniques allows a detailed analysis of excited state dynamics in organic molecules or biomolecular structures on a nanosecond to femtosecond time level. Optical pump soft X ray probe spectroscopy is a relatively new approach to detect and characterize optically dark states in organic molecules, exciton dynamics or transient ligand to metal charge transfer states. In this paper, we describe two experimental setups for transient soft X ray absorption spectroscopy based on an LPP emitting picosecond and sub nanosecond soft X ray pulses in the photon energy range between 50 and 1500 eV. We apply these setups for near edge X ray absorption fine structure NEXAFS investigations of thin films of a metal free porphyrin, an aggregate forming carbocyanine and a nickel oxide molecule. NEXAFS investigations have been carried out at the carbon, nitrogen and oxygen K edge as well as on the Ni L edge. From time resolved NEXAFS carbon, K edge measurements of the metal free porphyrin first insights into a long lived trap state are gained. Our findings are discussed and compared with density functional theory calculation

Nanocrystal residual strains and density layers enhance failure resistance in the cleithrum bone of evolutionary advanced pike fish

Failure resistant designs are particularly crucial for bones subjected to rapid loading, as is the case for the ambush hunting northern pike Esox lucius . These fish have slim and low density osteocyte lacking bones. As part of the swallowing mechanism, the cleithrum bone opens and closes the jaw. The cleithrum needs sufficient strength and damage tolerance, to withstand years of repetitive rapid gape and suck cycles of feeding. The thin wing shaped bone comprises anisotropic layers of mineralized collagen fibers that exhibit periodic variations in mineral density on the mm and micrometer length scales. Wavy collagen fibrils interconnect these layers yielding a highly anisotropic structure. Hydrated cleithra exhibit Young s moduli spanning 3 9 GPa where the yield stress of amp; 8764;40 MPa increases markedly to exceed amp; 8764;180 MPa upon drying. This 5x observation of increased strength corresponds to a change to brittle fracture patterns. It matches the emergence of compressive residual strains of amp; 8764;0.15 within the mineral crystals due to forces from shrinking collagen layers. Compressive stresses on the nanoscale, combined with the layered anisotropic microstructure on the mm length scale, jointly confer structural stability in the slender and lightweight bones. By employing a range of X ray, electron and optical imaging and mechanical characterization techniques, we reveal the structure and properties that make the cleithra impressively damage resistant composite

Absorption Correction for 3D Elemental Distributions of Dental Composite Materials Using Laboratory Confocal Micro X ray Fluorescence Spectroscopy

Confocal micro X ray fluorescence micro XRF spectroscopy facilitates three dimensional 3D elemental imaging of heterogeneous samples in the micrometer range. Laboratory setups using X ray tube excitation render the method accessible for diverse research fields but interpretation of results and quantification remain challenging. The attenuation of X rays in composites depends on the photon energy as well as on the composition and density of the material. For confocal micro XRF, attenuation severely impacts elemental distribution information, as the signal from deeper layers is distorted by superficial layers. Absorption correction and quantification of fluorescence measurements in heterogeneous composite samples have so far not been reported. Here, an absorption correction approach for confocal micro XRF combining density information from microcomputed tomography micro CT data with laboratory X ray absorption spectroscopy XAS and synchrotron transmission measurements is presented. The energy dependency of the probing volume is considered during the correction. The methodology is demonstrated on a model composite sample consisting of a bovine tooth with a clinically used restoration materia

Scan Free GEXRF in the Soft X ray Range for the Investigation of Structured Nanosamples

Scan free grazing emission X ray fluorescence spectroscopy GEXRF is an established technique for the investigation of the elemental depth profiles of various samples. Recently it has been applied to investigating structured nanosamples in the tender X ray range. However, lighter elements such as oxygen, nitrogen or carbon cannot be efficiently investigated in this energy range, because of the ineffective excitation. Moreover, common CCD detectors are not able to discriminate between fluorescence lines below 1 keV. Oxygen and nitrogen are important components of insulation and passivation layers, for example, in silicon oxide or silicon nitride. In this work, scan free GEXRF is applied in proof of concept measurements for the investigation of lateral ordered 2D nanostructures in the soft X ray range. The sample investigated is a Si3N4 lamellar grating, which represents 2D periodic nanostructures as used in the semiconductor industry. The emerging two dimensional fluorescence patterns are recorded with a CMOS detector. To this end, energy dispersive spectra are obtained via single photon event evaluation. In this way, spatial and therefore angular information is obtained, while discrimination between different photon energies is enabled. The results are compared to calculations of the sample model performed by a Maxwell solver based on the finite elements method. A first measurement is carried out at the UE56 2 PGM 2 beamline at the BESSY II synchrotron radiation facility to demonstrate the feasibility of the method in the soft X ray range. Furthermore, a laser produced plasma source LPP is utilized to investigate the feasibility of this technique in the laboratory. The results from the BESSY II measurements are in good agreement with the simulations and prove the applicability of scan free GEXRF in the soft X ray range for quality control and process engineering of 2D nanostructures. The LPP results illustrate the chances and challenges concerning a transfer of the methodology to the laborator

Prox1 Regulates the Notch1-Mediated Inhibition of Neurogenesis

During development of the spinal cord, Prox1 controls the balance between proliferation and differentiation of neural progenitor cells via suppression of Notch1 gene expression