The Transcriptionally Permissive Chromatin State of Embryonic Stem Cells Is Acutely Tuned to Translational Output

A permissive chromatin environment coupled to hypertranscription drives the rapid proliferation of embryonic stem cells (ESCs) and peri-implantation embryos. We carried out a genome-wide screen to systematically dissect the regulation of the euchromatic state of ESCs. The results revealed that cellular growth pathways, most prominently translation, perpetuate the euchromatic state and hypertranscription of ESCs. Acute inhibition of translation rapidly depletes euchromatic marks in mouse ESCs and blastocysts, concurrent with delocalization of RNA polymerase II and reduction in nascent transcription. Translation inhibition promotes rewiring of chromatin accessibility, which decreases at a subset of active developmental enhancers and increases at histone genes and transposable elements. Proteome-scale analyses revealed that several euchromatin regulators are unstable proteins and continuously depend on a high translational output. We propose that this mechanistic interdependence of euchromatin, transcription, and translation sets the pace of proliferation at peri-implantation and may be employed by other stem/progenitor cells

Observational constraints on the progenitor metallicities of core-collapse supernovae

We present constraints on the progenitor metallicities of core-collapse supernovae. To date, nearly all metallicity constraints have been inferred from indirect methods such as metallicity gradients in host galaxies, luminosities of host galaxies, or derived global galaxy metallicities. Here, progenitor metallicities are derived from optical spectra taken at the sites of nearby supernovae, from the ratio of strong emission lines found in their host HII regions.We present results from the spectra of 74 host HII regions and discuss the implications that these have on the nature of core-collapse supernova progenitors. Overall, while we find that the mean metallicity of type Ibc environments is higher than that of type II events, this difference is smaller than observed in previous studies. There is only a 0.06 dex difference in the mean metallicity values, at a statistical significance of ~1.5 sigma, while using a KS-test we find that the two metallicity distributions are marginally consistent with being drawn from the same parent population (probability >10%). This argues that progenitor metallicity is not a dominant parameter in deciding supernovae type, with progenitor mass and/or binarity playing a much more significant role.Comment: ACCEPTED for publication in MNRA

Spectroscopy of High-Redshift Supernovae from the ESSENCE Project: The First Two Years

We present the results of spectroscopic observations of targets discovered during the first two years of the ESSENCE project. The goal of ESSENCE is to use a sample of ~200 Type Ia supernovae (SNe Ia) at moderate redshifts (0.2 < z < 0.8) to place constraints on the equation of state of the Universe. Spectroscopy not only provides the redshifts of the objects, but also confirms that some of the discoveries are indeed SNe Ia. This confirmation is critical to the project, as techniques developed to determine luminosity distances to SNe Ia depend upon the knowledge that the objects at high redshift are the same as the ones at low redshift. We describe the methods of target selection and prioritization, the telescopes and detectors, and the software used to identify objects. The redshifts deduced from spectral matching of high-redshift SNe Ia with low-redshift SNe Ia are consistent with those determined from host-galaxy spectra. We show that the high-redshift SNe Ia match well with low-redshift templates. We include all spectra obtained by the ESSENCE project, including 52 SNe Ia, 5 core-collapse SNe, 12 active galactic nuclei, 19 galaxies, 4 possibly variable stars, and 16 objects with uncertain identifications.Comment: 38 pages, 9 figures (many with multiple parts), submitted to A

Protein content and quality of seeds in central mexican maize (Zea mays) accessions

Mexico is the center of the origin, domestication and diversity of maize. This cereal is the main constituent of the Mexican diet, especially in low-income families. In this research, 10 maize accessions derived from a large landrace collection, with the 'INIFAP-QPM' accession and a 'regional landrace' as controls, were studied to identify the accessions with the best biochemical and physiological characteristics showing good adaptation to 'El Bajío' (regional center in Mexico) conditions. The accessions were statistically superior to the two controls in the germination and accelerated aging tests. In the assessment of variable plumule length, variability was observed among the accessions, but the controls showed the lowest values. Protein contents in different fractions (albumins, globulins, prolamins and glutelins) showed variability as did oil and fiber contents. The 'HRH2015' accession showed high contents of albumins and globulins and low contents of prolamins and glutelins. The 'regional landrace' accession exhibited the highest contents of glutelins and prolamins but the lowests content of globulins and albumins. The total percentage of proteins showed variability among the accessions, but the values were within those reported in the literature. The 'RQ2015' accession presented the highest oil content (5.25%). The electrophoretic patterns of prolamins were obtained, and some differences were observed between them. The 'regional landrace' presented the lowest protein content, which was significantly different from those of the other accessions evaluated. This research demonstrates biochemical, germination and vigor variability among the studied maize accessions. Highlights The protein fraction content showed highly significant differences between the accessions, the accession 'HRH2015' presented the highest total soluble protein content. The 'HRH2015' accession contained high percentages of the albumin, globulin and prolamin fractions, but a lower percentage of the glutelin fraction, which is a suitable material for breeding. The accessions 'A2015', 'POL2015' and 'FVR12015' were superior in seed quality, these accessions could be used in a future breeding program.Mexico is the center of the origin, domestication and diversity of maize. This cereal is the main constituent of the Mexican diet, especially in low-income families. In this research, 10 maize accessions derived from a large landrace collection, with the 'INIFAP-QPM' accession and a 'regional landrace' as controls, were studied to identify the accessions with the best biochemical and physiological characteristics showing good adaptation to 'El Bajío' (regional center in Mexico) conditions. The accessions were statistically superior to the two controls in the germination and accelerated aging tests. In the assessment of variable plumule length, variability was observed among the accessions, but the controls showed the lowest values. Protein contents in different fractions (albumins, globulins, prolamins and glutelins) showed variability as did oil and fiber contents. The 'HRH2015' accession showed high contents of albumins and globulins and low contents of prolamins and glutelins. The 'regional landrace' accession exhibited the highest contents of glutelins and prolamins but the lowests content of globulins and albumins. The total percentage of proteins showed variability among the accessions, but the values were within those reported in the literature. The 'RQ2015' accession presented the highest oil content (5.25%). The electrophoretic patterns of prolamins were obtained, and some differences were observed between them. The 'regional landrace' presented the lowest protein content, which was significantly different from those of the other accessions evaluated. This research demonstrates biochemical, germination and vigor variability among the studied maize accessions. Highlights The protein fraction content showed highly significant differences between the accessions, the accession 'HRH2015' presented the highest total soluble protein content. The 'HRH2015' accession contained high percentages of the albumin, globulin and prolamin fractions, but a lower percentage of the glutelin fraction, which is a suitable material for breeding. The accessions 'A2015', 'POL2015' and 'FVR12015' were superior in seed quality, these accessions could be used in a future breeding program

The SuperMACHO Microlensing Survey

We present the first results from our next-generation microlensing survey, the SuperMACHO project. We are using the CTIO 4m Blanco telescope and the MOSAIC imager to carry out a search for microlensing toward the Large Magellanic Cloud (LMC). We plan to ascertain the nature of the population responsible for the excess microlensing rate seen by the MACHO project. Our observing strategy is optimized to measure the differential microlensing rate across the face of the LMC. We find this derivative to be relatively insensitive to the details of the LMC's internal structure but a strong discriminant between Galactic halo and LMC self lensing. In December 2003 we completed our third year of survey operations. 2003 also marked the first year of real-time microlensing alerts and photometric and spectroscopic followup. We have extracted several dozen microlensing candidates, and we present some preliminary light curves and related information. Similar to the MACHO project, we find SNe behind the LMC to be a significant contaminant - this background has not been completely removed from our current single-color candidate sample. Our follow-up strategy is optimized to discriminate between SNe and true microlensing.Comment: To appear in Proceedings of IAU Symposium 225: Impact of Gravitational Lensing on Cosmology, 6 page

Spectral Identification of an Ancient Supernova using Light Echoes in the LMC

We report the successful identification of the type of the supernova responsible for the supernova remnant SNR 0509-675 in the Large Magellanic Cloud (LMC) using Gemini spectra of surrounding light echoes. The ability to classify outbursts associated with centuries-old remnants provides a new window into several aspects of supernova research and is likely to be successful in providing new constraints on additional LMC supernovae as well as their historical counterparts in the Milky Way Galaxy (MWG). The combined spectrum of echo light from SNR 0509-675 shows broad emission and absorption lines consistent with a supernova (SN) spectrum. We create a spectral library consisting of 26 SNe Ia and 6 SN Ib/c that are time-integrated, dust-scattered by LMC dust, and reddened by the LMC and MWG. We fit these SN templates to the observed light echo spectrum using $\chi^2$ minimization as well as correlation techniques, and we find that overluminous 91T-like SNe Ia with \dm15<0.9 match the observed spectrum best.Comment: 12 pages, 18 Figures, to be published in Ap

Hubble Space Telescope Observations of Nine High-Redshift ESSENCE Supernovae

We present broad-band light curves of nine supernovae ranging in redshift from 0.5 to 0.8. The supernovae were discovered as part of the ESSENCE project, and the light curves are a combination of Cerro Tololo 4-m and Hubble Space Telescope (HST) photometry. On the basis of spectra and/or light-curve fitting, eight of these objects are definitely Type Ia supernovae, while the classification of one is problematic. The ESSENCE project is a five-year endeavor to discover about 200 high-redshift Type Ia supernovae, with the goal of tightly constraining the time average of the equation-of-state parameter [w = p/(rho c^2)] of the "dark energy." To help minimize our systematic errors, all of our ground-based photometry is obtained with the same telescope and instrument. In 2003 the highest-redshift subset of ESSENCE supernovae was selected for detailed study with HST. Here we present the first photometric results of the survey. We find that all but one of the ESSENCE SNe have slowly declining light curves, and the sample is not representative of the low-redshift set of ESSENCE Type Ia supernovae. This is unlikely to be a sign of evolution in the population. We attribute the decline-rate distribution of HST events to a selection bias at the high-redshift edge of our sample and find that such a bias will infect other magnitude-limited SN Ia searches unless appropriate precautions are taken.Comment: 62 pages, 18 numbered figures, accepted for publication in the Astronomical Journa

The ESSENCE Supernova Survey: Survey Optimization, Observations, and Supernova Photometry

We describe the implementation and optimization of the ESSENCE supernova survey, which we have undertaken to measure the equation of state parameter of the dark energy. We present a method for optimizing the survey exposure times and cadence to maximize our sensitivity to the dark energy equation of state parameter w=P/rho c^2 for a given fixed amount of telescope time. For our survey on the CTIO 4m telescope, measuring the luminosity distances and redshifts for supernovae at modest redshifts (z~0.5 +- 0.2) is optimal for determining w. We describe the data analysis pipeline based on using reliable and robust image subtraction to find supernovae automatically and in near real-time. Since making cosmological inferences with supernovae relies crucially on accurate measurement of their brightnesses, we describe our efforts to establish a thorough calibration of the CTIO 4m natural photometric system. In its first four years, ESSENCE has discovered and spectroscopically confirmed 102 type Ia SNe, at redshifts from 0.10 to 0.78, identified through an impartial, effective methodology for spectroscopic classification and redshift determination. We present the resulting light curves for the all type Ia supernovae found by ESSENCE and used in our measurement of w, presented in Wood-Vasey et al, 2007.Comment: Submitted to ApJ. Companion paper to Wood-Vasey et al (2007). Electronic tables available at http://www.ctio.noao.edu/essence/wresult

Identification of superior doubled haploid maize (Zea mays) inbred lines derived from high oil content subtropical populations

High oil maize (HOM) hybrids, adapted to subtropical regions are needed to meet existing requirements forindustrial and livestock purposes. Recently, the doubled haploid (DH) breeding technology is applied to reduceconsiderably the time to generate homozygous maize lines, however, information of heterotic response, per seproductivity, stress, disease reaction, and adaptation to different environments are not known. In this work, fieldevaluations of per se and testcross high oil content DH lines adapted for subtropical environments were studiedto identify superior DH lines with good heterotic response and agronomic characteristics. White and yellow kerneltest crosses were formed using the different heterotic population as testers from which DH lines were derived.Test crosses were evaluated at three locations in Mexico. Superior DH lines from each tester presented highGCA effects through test crosses, with a range of grain yield across locations of 12.8 to 10.4 Mg ha-1 and 11.1to 9.1 Mg ha-1 respectively. Per se DH lines were observed and screened for adaptation, productivity, diseasereaction and other agronomic traits in five locations/year environments. Per se DH lines screening process acrossenvironments was able to obtain information for adaptation, productivity, and healthiness. Also of DH lines withhigh response of GCA, information regarding heterotic groups, and DH lines oil content determination was usedto identify outstanding DH lines for developing HOM high-yielding hybrids adapted for subtropical regions, withfewer costs and time. This research demonstrated that it was feasible to identify subtropical elite DH lines withhigh oil content

Hubble Space Telescope and Ground-Based Observations of Type Ia Supernovae at Redshift 0.5: Cosmological Implications

We present observations of the Type Ia supernovae (SNe) 1999M, 1999N, 1999Q, 1999S, and 1999U, at redshift z~0.5. They were discovered in early 1999 with the 4.0~m Blanco telescope at Cerro Tololo Inter-American Observatory by the High-z Supernova Search Team (HZT) and subsequently followed with many ground-based telescopes. SNe 1999Q and 1999U were also observed with the Hubble Space Telescope. We computed luminosity distances to the new SNe using two methods, and added them to the high-z Hubble diagram that the HZT has been constructing since 1995. The new distance moduli confirm the results of previous work. At z~0.5, luminosity distances are larger than those expected for an empty universe, implying that a ``Cosmological Constant,'' or another form of ``dark energy,'' has been increasing the expansion rate of the Universe during the last few billion years.Comment: 68 pages, 22 figures. Scheduled for the 01 February 2006 issue of Ap.J. (v637