On optical activity of Er⁺³ ions in Si-rich SiO₂ waveguides

Photoluminescence spectroscopy was used to explore the optical activity of Er³⁺ ions in Si-rich SiO₂waveguides prepared by ion implantation. Measurements were performed for a series of materials characterized by different Si excess levels, Er concentrations, and annealing temperatures. The highest fraction of optically active Er³⁺ ions which can be efficiently activated by nonresonant pumping was found to be 2.6%. This was realized in a waveguide with an Er concentration of [Er]=10¹⁸cm⁻³ and Si excess of 20%, annealed at 900°C. This optical activity level is insufficient to realize optical gain. It is therefore clear that further material improvement is needed before optical amplification in SiO₂:Er matrices sensitized by Si nanocrystals/nanoclusters can be achieved

Long-range surface polaritons in ultra-thin films of silicon

We present an experimental and theoretical study of the optical excitation of long-range surface polaritons supported by thin layers of amorphous silicon (a-Si). The large imaginary part of the dielectric constant of a-Si at visible and ultraviolet (UV) frequencies allows the excitation of surface polariton modes similar to long-range surface plasmon polaritons on metals. Propagation of these modes along considerable distances is possible because the electric field is largely excluded from the absorbing thin film. We show that by decreasing the thickness of the Si layer these excitations can be extended up to UV frequencies, opening the possibility to surface polariton UV optics compatible with standard Si technology

Structural and photoluminescence studies of erbium implanted nanocrystalline silicon thin films

Hydrogenated amorphous and nanocrystalline silicon thin films deposited by Hot Wire (HW) and Radio-Frequency Plasma-Enhanced (RF) Chemical Vapor Deposition were Er-bium-implanted. Their pre-implantation structural properties and post-implantation optical properties were studied and cor-related. After one-hour annealing at 150ºC in nitrogen atmos-phere only amorphous films showed photoluminescence (PL) activity at 1.54 μm, measured at 5 K. After further annealing at 300oC for one hour, all the samples exhibited a sharp PL peak positioned at 1.54 m, with a FWHM of ~5 nm. Amorphous films deposited by HW originated a stronger PL peak than corresponding films deposited by RF, while in na-nocrystalline films PL emission was much stronger in sam-ples deposited by RF than by HW. There was no noticeable difference in Er3+ PL activity be-tween films implanted with 1x1014 atoms/cm2 and 5x1015 at-oms/cm2 Er doses.FCT for a post-doctorate grant (SFRH/BPD/14919/2004

Helicase Lymphoid-specific enzyme contributes to the maintenance of methylation of SST1 pericentromeric repeats that are frequently demethylated in colon cancer and associated with genomic damage

DNA hypomethylation at repetitive elements accounts for the genome-wide DNA hypomethylation common in cancer, including colorectal cancer (CRC). We identified a pericentromeric repeat element called SST1 frequently hypomethylated (>5% demethylation compared with matched normal tissue) in several cancers, including 28 of 128 (22%) CRCs. SST1 somatic demethylation associated with genome damage, especially in tumors with wild-type TP53. Seven percent of the 128 CRCs exhibited a higher ("severe") level of demethylation (≥10%) that co-occurred with TP53 mutations. SST1 demethylation correlated with distinct histone marks in CRC cell lines and primary tumors: demethylated SST1 associated with high levels of the repressive histone 3 lysine 27 trimethylation (H3K27me3) mark and lower levels of histone 3 lysine 9 trimethylation (H3K9me3). Furthermore, induced demethylation of SST1 by 5-aza-dC led to increased H3K27me3 and reduced H3K9me3. Thus, in some CRCs, SST1 demethylation reflects an epigenetic reprogramming associated with changes in chromatin structure that may affect chromosomal integrity. The chromatin remodeler factor, the helicase lymphoid-specific (HELLS) enzyme, called the "epigenetic guardian of repetitive elements", interacted with SST1 as shown by chromatin immunoprecipitation, and down-regulation of HELLS by shRNA resulted in demethylation of SST1 in vitro. Altogether these results suggest that HELLS contributes to SST1 methylation maintenance. Alterations in HELLS recruitment and function could contribute to the somatic demethylation of SST1 repeat elements undergone before and/or during CRC pathogenesis

Potential of adipose-derived stem cells in muscular regenerative therapies

Regenerative capacity of skeletal muscles resides in satellite cells, a self-renewing population of muscle cells. Several studies are investigating epigenetic mechanisms that control myogenic proliferation and differentiation to find new approaches that could boost regeneration of endogenous myogenic progenitor populations. In recent years, a lot of effort has been applied to purify, expand and manipulate adult stem cells from muscle tissue. However, this population of endogenous myogenic progenitors in adults is limited and their access is difficult and invasive. Therefore, other sources of stem cells with potential to regenerate muscles need to be examined. An excellent candidate could be a population of adult stromal cells within fat characterized by mesenchymal properties, which have been termed adipose-derived stem cells (ASCs). These progenitor adult stem cells have been successfully differentiated in vitro to osteogenic, chondrogenic, neurogenic and myogenic lineages. Autologous ASCs are multipotent and can be harvested with low morbidity; thus, they hold promise for a range of therapeutic applications. This review will summarize the use of ASCs in muscle regenerative approaches

myomiR-dependent switching of BAF60 variant incorporation into Brg1 chromatin remodeling complexes during embryo myogenesis

Myogenesis involves the stable commitment of progenitor cells followed by the execution of myogenic differentiation, processes that are coordinated by myogenic regulatory factors, microRNAs and BAF chromatin remodeling complexes. BAF60a, BAF60b and BAF60c are structural subunits of the BAF complex that bind to the core ATPase Brg1 to provide functional specificity. BAF60c is essential for myogenesis; however, the mechanisms regulating the subunit composition of BAF/Brg1 complexes, in particular the incorporation of different BAF60 variants, are not understood. Here we reveal their dynamic expression during embryo myogenesis and uncover the concerted negative regulation of BAF60a and BAF60b by the muscle-specific microRNAs (myomiRs) miR-133 and miR-1/206 during somite differentiation. MicroRNA inhibition in chick embryos leads to increased BAF60a or BAF60b levels, a concomitant switch in BAF/Brg1 subunit composition and delayed myogenesis. The phenotypes are mimicked by sustained BAF60a or BAF60b expression and are rescued by morpholino knockdown of BAF60a or BAF60b. This suggests that myomiRs contribute to select BAF60c for incorporation into the Brg1 complex by specifically targeting the alternative variants BAF60a and BAF60b during embryo myogenesis, and reveals that interactions between tissue-specific non-coding RNAs and chromatin remodeling factors confer robustness to mesodermal lineage determination

Dynamics and dispensability of variant-specific histone H1 Lys-26/Ser-27 and Thr-165 post-translational modifications

Jean-Michel Terme et al.In mammals, the linker histone H1, involved in DNA packaging into chromatin, is represented by a family of variants. H1 tails undergo post-translational modifications (PTMs) that can be detected by mass spectrometry. We developed antibodies to analyze several of these as yet unexplored PTMs including the combination of H1.4 K26 acetylation or trimethylation and S27 phosphorylation. H1.2-T165 phosphorylation was detected at S and G2/M phases of the cell cycle and was dispensable for chromatin binding and cell proliferation; while the H1.4-K26 residue was essential for proper cell cycle progression. We conclude that histone H1 PTMs are dynamic over the cell cycle and that the recognition of modified lysines may be affected by phosphorylation of adjacent residues. © 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.This work was supported by the Spanish Ministry of Science and Innovation (MICINN) and European Regional Development Fund (Grant BFU2011-23057 to A.J., and Grant BFU2008-00460 to P.S.), and by the Regional Government of Catalonia (Generalitat de Catalunya; Grant 2009-SGR-1222 to A.J.). J.-M.T. received a JAE-Doc contract from the Spanish National Research Council (CSIC)-MICINN; R.M. a TA contract from CSIC-MICINN; and L.M.-A. an FPU predoctoral fellowship from MICINNPeer Reviewe