rRNA gene activity and control of expression mediated by methylation and imprinting during embryo development in wheat x rye hybrids

Ribosomal RNA genes originating from one parent are often suppressed in interspecific hybrids. We show that treatments during germination with the cytosine analogue 5-azacytidine stably reactivate the expression of the suppressed rRNA genes of rye origin in the wheat x rye amphiploid, triticale, by preventing methylation of sites in the rye rDNA. When 5-azacytidine is applied to embryos of triticale and wheat x rye F1 hybrids nine, or more, days after fertilization, rye rRNA gene expression is stably reactivated in the resulting seedling. Earlier treatments have no effect on rye rRNA gene expression, indicating that undermethylation of DNA early in embryo development is reversible. After 9 days, the methylation status of rRNA genes in maintained throughout development. Since the change in expression follows a methylation change at particular restriction-enzyme sites, the data establish a clear correlation between gene activity and methylation in plants

The Closest Damped Lyman Alpha System

A difficulty of studying damped Lyman alpha systems is that they are distant, so one knows little about the interstellar medium of the galaxy. Here we report upon a damped Lyman alpha system in the nearby galaxy NGC 4203, which is so close (v_helio = 1117 km/s) and bright (B_o = 11.62) that its HI disk has been mapped. The absorption lines are detected against Ton 1480, which lies only 1.9' (12 h_50 kpc) from the center of NGC 4203. Observations were obtained with the Faint Object Spectrograph on HST (G270H grating) over the 2222-3277 Angstrom region with 200 km/s resolution. Low ionization lines of Fe, Mn, and Mg were detected, leading to metallicities of -2.29, -2.4, which are typical of other damped Lyman alpha systems, but well below the stellar metallicity of this type of galaxy. Most notably, the velocity of the lines is 1160 +- 10 km/s, which is identical to the HI rotational velocity of 1170 km/s at that location in NGC 4203, supporting the view that these absorption line systems can be associated with the rotating disks of galaxies. In addition, the line widths of the Mg lines give an upper limit to the velocity dispersion of 167 km/s, to the 99% confidence level.Comment: 4 pages LaTeX, including 1 figure and 1 table, uses emulateapj.sty. Accepted for publication by Astrophysical Journal Letter

The Keck+Magellan Survey for Lyman Limit Absorption I: The Frequency Distribution of Super Lyman Limit Systems

We present the results of a survey for super Lyman limit systems (SLLS; defined to be absorbers with 19.0 <= log(NHI) <= 20.3 cm^-2) from a large sample of high resolution spectra acquired using the Keck and Magellan telescopes. Specifically, we present 47 new SLLS from 113 QSO sightlines. We focus on the neutral hydrogen frequency distribution f(N,X) of the SLLS and its moments, and compare these results with the Lyman-alpha forest and the damped Lyman alpha systems (DLA; absorbers with log(NHI) >= 20.3 cm^-2). We find that that f(N,X) of the SLLS can be reasonably described with a power-law of index alpha = -1.43^{+0.15}_{-0.16} or alpha = -1.19^{+0.20}_{-0.21} depending on whether we set the lower N(HI) bound for the analysis at 10^{19.0} cm^-2 or 10^{19.3}$ cm^-2, respectively. The results indicate a flattening in the slope of f(N,X) between the SLLS and DLA. We find little evidence for redshift evolution in the shape of f(N,X) for the SLLS over the redshift range of the sample 1.68 < z < 4.47 and only tentative evidence for evolution in the zeroth moment of f(N,X), the line density l_lls(X). We introduce the observable distribution function O(N,X) and its moment, which elucidates comparisons of HI absorbers from the Lyman-alpha through to the DLA. We find that a simple three parameter function can fit O(N,X) over the range 17.0 <= log(NHI) <=22.0. We use these results to predict that f(N,X) must show two additional inflections below the SLLS regime to match the observed f(N,X) distribution of the Lyman-alpha forest. Finally, we demonstrate that SLLS contribute a minor fraction (~15%) of the universe's hydrogen atoms and, therefore, an even small fraction of the mass in predominantly neutral gas.Comment: 15 pages, 10 figures, accepted to the Astrophysical Journal. Revision includes updated reference

The developmental stage of inactivation of rye origin rRNA genes in the embryo and endosperm of wheat x rye F1 hybrids

To identify the developmental stage during which the preferential inactivation of rRNA genes from the rye parent occurs in wheat x rye hybrids, nucleolar activity was evaluated in the embryo and endosperm of developing seeds of the hybrids. The hybrids were obtained from crosses of euploid and aneuploid lines of hexaploid wheat, Triticum aestivum cv. Chinese Spring, with rye, Secale cereale cv. Centeio do Alto. The number of nucleolar organizing regions (NORs) and nucleoli present in the embryo and endosperm cells of wheat, and wheat × rye F1 hybrids, at different times after fertilization was scored by silver staining. The inactivation of rDNA of rye origin in F1 hybrids occurs simultaneously in the embryo and in the endosperm between 4 and 5 days after fertilization, when these have been through six and 10 cell cycles respectively. We conclude that the genomic interactions leading to the inactivation of the rye origin rDNA is a time-dependent process, related to the developmental stage and independent of the number of cell cycles (DNA replication rounds) they have been through

Anemia de Fanconi – Estudo retrospetivo num período 34 anos

Introdução: A Anemia de Fanconi (AF) é uma doença rara, com uma frequência estimada de 1 a 5 per 1.000.000 de nascimentos, podendo este valor aumentar se for considerado um grupo étnico com consanguinidade. É uma doença autossómica recessiva, que poderá ter uma transmissão ligada ao cromossoma X. Doentes com AF podem apresentar malformações congénitas, falência da medula óssea (que se carateriza por pancitopénia), hipersensibilidade a agentes clastogénicos, fragilidade cromossómica e uma maior suscetibilidade para doenças oncológicas. Devido à grande complexidade desta patologia a primeira abordagem de diagnóstico, consiste na deteção de aberrações cromossómicas (quebras, rearranjos estruturais, radiais, anéis) em células de sangue periférico em cultura com um agente clastogénico como o diepoxibutano (DEB) ou mitomicina C (MMC). Objetivo: Neste trabalho pretende-se apresentar os resultados dos estudos de instabilidade cromossómica induzida por DEB e MMC efetuados na nossa instituição. Métodos: Foi realizada a análise de uma série retrospetiva de 34 anos (1980-2014) de 243 amostras enviadas ao laboratório citogenética com suspeita de AF e de 28 amostras de familiares de doentes com AF. No total, foram analisadas 260 amostras de sangue periférico, 6 de biópsia de pele, 3 de líquido amniótico, 1 de sangue do cordão e 1 de sangue medular. As amostras foram processadas segundo o protocolo estabelecido para a análise cromossómica de doenças associadas a fraturas, incluindo cultura celular com estimulação por MMC e/ou DED, para cada produto biológico, seguida de análise microscópica com determinação da instabilidade cromossómica induzida pelo DEB, de acordo com o protocolo estabelecido pelo International Fanconi Anemia Registry (IFAR). Resultados: Nas 243 amostras analisadas, foram identificados 37 casos com AF. Nos estudos citogenéticos dos familiares com AF foram identificados mais 2 casos positivos para AF. Foram ainda observados, em 4 amostras de suspeita de AF, cariotipos anormais. Conclusão: Neste trabalho foram identificados 39 novos casos com AF, oriundos maioritariamente da região de Lisboa e Vale do Tejo e alguns casos pontuais da região autónoma dos Açores, região centro e dos países africanos de língua oficial portuguesa (PALOP). Este estudo evidência que a maioria dos casos apresentados se encontra subdiagnosticado. Estes resultados não permitem estimar uma frequência de doentes com AF em Portugal, uma vez que não engloba indivíduos de todas as regiões portuguesas, por outro lado estão incluídos dois indivíduos de origem PALOP. É necessário estabelecer um registo nacional de doentes com AF, para se poder calcular a frequência desta patologia no nosso país

Assessing estuarine environmental quality using fish-based indices: Performance evaluation under climatic instability

http://www.sciencedirect.com/science/article/B6V6N-4TFDY7X-2/2/c9f9bbc565621cbb798d6d663e74a8f

Ribosomal DNA heterochromatin in plants

The aim of this review is to integrate earlier results and recent findings to present the current state-of-the art vision concerning the dynamic behavior of the ribosomal DNA (rDNA) fraction in plants. The global organization and behavioral features of rDNA make it a most useful system to analyse the relationship between chromatin topology and gene expression patterns. Correlations between several heterochromatin fractions and rDNA arrays demonstrate the heterochromatic nature of the rDNA and reveal the importance of the genomic environment and of developmental controls in modulating its dynamicsFCT - Fundação para a Ciência e Tecnologi

An Imaging and Spectroscopic Study of the z=3.38639 Damped Lyman Alpha System in Q0201+1120: Clues to Star Formation Rate at High Redshift

We present the results of a series of imaging and spectroscopic observations aimed at identifying and studying the galaxy responsible for the z = 3.38639 damped lya system in the z = 3.61 QSO Q0201+1120. We find that the DLA is part of a concentration of matter which includes at least four galaxies (probably many more) over linear comoving dimensions, greater than 5h^-1Mpc. The absorber may be a 0.7 L* galaxy at an impact parameter of 15 h^-1 kpc, but follow-up spectroscopy is still required for positive identification. The gas is turbulent, with many absorption components distributed over approximately 270 km/s and a large spin temperature, T_s greater than 4000K. The metallicity is relatively high for this redshift, Z(DLA) approximately 1/20 Z(solar). From consideration of the relative ratios of elements which have different nucleosynthetic timescales, it would appear that the last major episode of star formation in this DLA occurred at z greater than 4.3, more than approximately 500 Myr prior to the time when we observe it.Comment: Accepted for publication in Ap

Infrared FeII Emission in Narrow-Line Seyfert 1 Galaxies

We obtained 0.8-2.4 micron spectra at a resolution of 320 km/s of four narrow-line Seyfert 1 galaxies in order to study the near-infrared properties of these objects. We focus on the analysis of the FeII emission in that region and the kinematics of the low-ionization broad lines. We found that the 1 micron FeII lines (9997 A, 10501 A, 10863 A and 11126 A) are the strongest FeII lines in the observed interval. For the first time, primary cascade lines of FeII arising from the decay of upper levels pumped by Ly-alpha fluorescence are resolved and identified in active galactic nuclei. Excitation mechanisms leading to the emission of the 1 micron FeII features are discussed. A combination of Ly-alpha fluorescence and collisional excitation are found to be the main contributors. The flux ratio between near-IR FeII lines varies from object to object, in contrast to what is observed in the optical region. A good correlation between the 1 micron and optical FeII emission is found. This suggests that the upper z4Fo and z4Do levels from which the bulk of the optical lines descend are mainly populated by the transitions leading to the 1 micron lines. The width and profile shape of FeII 11127, CaII 8642 and OI 8446 are very similar but significantly narrower than Pa-beta, giving strong observational support to the hypothesis that the region where FeII, CaII and OI are produced are co-spatial, interrelated kinematically and most probably located in the outermost portion of the BLR.Comment: Accepted for publication in ApJ - 35 page