Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy

We review HB stars in a broad astrophysical context, including both variable and non-variable stars. A reassessment of the Oosterhoff dichotomy is presented, which provides unprecedented detail regarding its origin and systematics. We show that the Oosterhoff dichotomy and the distribution of globular clusters (GCs) in the HB morphology-metallicity plane both exclude, with high statistical significance, the possibility that the Galactic halo may have formed from the accretion of dwarf galaxies resembling present-day Milky Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the second-parameter problem is presented. A technique is proposed to estimate the HB types of extragalactic GCs on the basis of integrated far-UV photometry. The relationship between the absolute V magnitude of the HB at the RR Lyrae level and metallicity, as obtained on the basis of trigonometric parallax measurements for the star RR Lyrae, is also revisited, giving a distance modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are studied. Finally, the conductive opacities used in evolutionary calculations of low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and Space Scienc

Induction of epigenetic variation in Arabidopsis by over-expression of DNA METHYLTRANSFERASE1 (MET1)

Epigenetic marks such as DNA methylation and histone modification can vary among plant accessions creating epi-alleles with different levels of expression competence. Mutations in epigenetic pathway functions are powerful tools to induce epigenetic variation. As an alternative approach, we investigated the potential of over-expressing an epigenetic function, using DNA METHYLTRANSFERASE1 (MET1) for proof-of-concept. In Arabidopsis thaliana, MET1 controls maintenance of cytosine methylation at symmetrical CG positions. At some loci, which contain dense DNA methylation in CG- and non-CG context, loss of MET1 causes joint loss of all cytosines methylation marks. We find that over-expression of both catalytically active and inactive versions of MET1 stochastically generates new epi-alleles at loci encoding transposable elements, non-coding RNAs and proteins, which results for most loci in an increase in expression. Individual transformants share some common phenotypes and genes with altered gene expression. Altered expression states can be transmitted to the next generation, which does not require the continuous presence of the MET1 transgene. Long-term stability and epigenetic features differ for individual loci. Our data show that over-expression of MET1, and potentially of other genes encoding epigenetic factors, offers an alternative strategy to identify epigenetic target genes and to create novel epi-alleles

The role of released ATP in killing Candida albicans and other extracellular microbial pathogens by cationic peptides

A unifying theme common to the action of many cationic peptides that display lethal activities against microbial pathogens is their specific action at microbial membranes that results in selective loss of ions and small nucleotides chiefly ATP. One model cationic peptide that induces non-lytic release of ATP from the fungal pathogen Candida albicans is salivary histatin 5 (Hst 5). The major characteristic of Hst 5-induced ATP release is that it occurs rapidly while cells are still metabolically active and have polarized membranes, thus precluding cell lysis as the means of release of ATP. Other cationic peptides that induce selective release of ATP from target microbes are lactoferricin, human neutrophil defensins, bactenecin, and cathelicidin peptides. The role of released extracellular ATP induced by cationic peptides is not known, but localized increases in extracellular ATP concentration may serve to potentiate cell killing, facilitate further peptide uptake, or function as an additional signal to activate the host innate immune system at the site of infection

Relating gene expression data on two-component systems to functional annotations in Escherichia coli

<p>Abstract</p> <p>Background</p> <p>Obtaining physiological insights from microarray experiments requires computational techniques that relate gene expression data to functional information. Traditionally, this has been done in two consecutive steps. The first step identifies important genes through clustering or statistical techniques, while the second step assigns biological functions to the identified groups. Recently, techniques have been developed that identify such relationships in a single step.</p> <p>Results</p> <p>We have developed an algorithm that relates patterns of gene expression in a set of microarray experiments to functional groups in one step. Our only assumption is that patterns co-occur frequently. The effectiveness of the algorithm is demonstrated as part of a study of regulation by two-component systems in <it>Escherichia coli</it>. The significance of the relationships between expression data and functional annotations is evaluated based on density histograms that are constructed using product similarity among expression vectors. We present a biological analysis of three of the resulting functional groups of proteins, develop hypotheses for further biological studies, and test one of these hypotheses experimentally. A comparison with other algorithms and a different data set is presented.</p> <p>Conclusion</p> <p>Our new algorithm is able to find interesting and biologically meaningful relationships, not found by other algorithms, in previously analyzed data sets. Scaling of the algorithm to large data sets can be achieved based on a theoretical model.</p

Genome-wide comparative analysis of microRNAs in three non-human primates

Abstract Background MicroRNAs (miRNAs) are negative regulators of gene expression in multicellular eukaryotes. With the recently completed sequencing of three primate genomes, the study of miRNA evolution within the primate lineage has only begun and may be expected to provide the genetic and molecular explanations for many phenotypic differences between human and non-human primates. Findings We scanned all three genomes of non-human primates, including chimpanzee (Pan troglodytes), orangutan (Pongo pygmaeus), and rhesus monkey (Macaca mulatta), for homologs of human miRNA genes. Besides sequence homology analysis, our comparative method relies on various postprocessing filters to verify other features of miRNAs, including, in particular, their precursor structure or their occurrence (prediction) in other primate genomes. Our study allows direct comparisons between the different species in terms of their miRNA repertoire, their evolutionary distance to human, the effects of filters, as well as the identification of common and species-specific miRNAs in the primate lineage. More than 500 novel putative miRNA genes have been discovered in orangutan that show at least 85 percent identity in precursor sequence. Only about 40 percent are found to be 100 percent identical with their human ortholog. Conclusion Homologs of human precursor miRNAs with perfect or near-perfect sequence identity may be considered to be likely functional in other primates. The computational identification of homologs with less similar sequence, instead, requires further evidence to be provided.</p

Auger electron wave packet interferometry on extreme timescales with coherent soft x rays

Wave packet interferometry provides benchmark information on light-induced electronic quantum states by monitoring their relative amplitudes and phases during coherent excitation, propagation,and decay. The relative phase control of soft x-ray pulse replicas on the single-digit attosecond timescale achieved in our experiments makes this method a powerful tool to probe ultrafast quantum phenomena such as the excitation of Auger shake-up states with sub-cycle precision. In this contribution we present first results obtained for different Auger decay channels upon generating L-shell vacancies in argon atoms using Michelson-type all-reflective interferometric autocorrelation at a central free-electron laser photon energy of 274.7 eV

Electronic quantum coherence in glycine molecules probed with ultrashort x ray pulses in real time

Here, we use x rays to create and probe quantum coherence in the photoionized amino acid glycine. The outgoing photoelectron leaves behind the cation in a coherent superposition of quantum mechanical eigenstates. Delayed x ray pulses track the induced coherence through resonant x ray absorption that induces Auger decay and by photoelectron emission from sequential double photoionization. Sinusoidal temporal modulation of the detected signal at early times 0 to 25 fs is observed in both measurements. Advanced ab initio many electron simulations allow us to explain the first 25 fs of the detected coherent quantum evolution in terms of the electronic coherence. In the kinematically complete x ray absorption measurement, we monitor its dynamics for a period of 175 fs and observe an evolving modulation that may implicate the coupling of electronic to vibronic coherence at longer time scales. Our experiment provides a direct support for the existence of long lived electronic coherence in photoionized biomolecule

Destination development in Western Siberia:Tourism governance and evolutionary economic geography

Tourism development has often been identified as a tool for balancing negative effects of economic restructuring, especially in peripheral regions. Tourism-based activities often utilize the availability of abundant nature, but although most English language studies of destination development are presented from western contexts, examples from post-Soviet Russia are rare. Western Siberia is a periphery with access to natural resources and heavy industrialization but remotely located from domestic (Russian) and international markets, where tourism is often considered a saviour, especially for the regional economies. Stakeholders in this Russian resource periphery face challenges in managing governance and cooperation in destinations development due to frequent institutional, economic and social changes. Using evolutionary economic geography and based on primary sources and interview data, tourism development and stakeholder relations are assessed in three Western Siberia regions: Tomsk, Kemerovo and Altai Krai. Findings show that for tourism to make a significant contribution, it must be more central to the economic development agenda in all three regions. However, it is currently only achieving a permanent high-profile in one of them, being crowded out by other (mostly primary) industries in the other two. Although the specific tourism governance set-up varies between the three regions, it is clear that public tourism governance still sits somewhat uneasily between state control and the market economy. Tourism receives substantial public subsidies, especially in large-scale investment projects, which depend on federal support within a governance system where decentralization seems to be somewhat limited and unstable. As a result, the tourism path development in the Siberian periphery is highly dependent on state intervention and success in other sectors.</p