Acoel and Platyhelminth Models for Stem-cell Research

Acoel and platyhelminth worms are particularly attractive invertebrate models for stem-cell research because their bodies are continually renewed from large pools of somatic stem cells. Several recent studies, including one in BMC Developmental Biology, are beginning to reveal the cellular dynamics and molecular basis of stem-cell function in these animals. See research article http://www.biomedcentral.com/1471-213X/9/69. Adult somatic stem cells can play critical roles in postembryonic developmental processes such as tissue renewal, growth, repair, and regeneration [1]. Understanding how such cells are maintained and produce differentiated progeny is thus of general interest in developmental biology, in addition to being of clear biomedical relevance. Invertebrate models have great potential for elucidating the cellular and molecular basis of stem-cell function. However, in the main invertebrate models used for dissecting the details of animal development, including Drosophila and Caenorhabditis, adult somatic tissues are primarily post-mitotic and are largely or entirely devoid of adult stem cells, which limits the use of these established models for stem-cell research. Representatives of two groups of soft-bodied worms, the Acoela and the Platyhelminthes, possess large pools of adult somatic stem cells, making them useful invertebrate models for stem-cell biology. These organisms are now beginning to provide new insights into the cellular and molecular basis of adult stem-cell function

Stochastic WNT signaling between nonequivalent cells regulates adhesion but not fate in the two-cell leech embryo

AbstractBackground: In the leech Helobdella robusta, an annelid worm, the early pattern of cell divisions is stereotyped. The unequal first cleavage yields cells AB and CD, which differ in size, cytoplasmic inheritance, normal fate, and developmental potential.Results: Here we report a dynamic and transcription-independent pattern of WNT signaling in the two-cell stage of H. robusta. Surprisingly, HRO-WNT-A is first expressed in a stochastic manner, such that either AB or CD secretes the protein in each embryo. This stochastic phase is followed by a deterministic phase during which first AB, then CD expresses HRO-WNT-A. When contact between the cells is reduced or eliminated, both AB and CD express HRO-WNT-A simultaneously. Finally, bathing embryos in anti-HRO-WNT-A antibody during first cleavage reduces the adhesion between cells AB and CD.Conclusions: Our findings show that the stochastic phase of HRO-WNT-A signaling in the two-cell stage of Helobdella is negatively regulated by cell-cell contact and that this early signaling affects cell adhesion without affecting cell fate. We speculate that the primordial function of wnt class genes may have been to regulate cell-cell adhesion and that the nuclear signaling components of the wnt pathway arose later in association with the evolution of diverse cell types

Excitation of the 3.071mm Hyperfine Line in Li-Like 57-Fe in Astrophysical Plasmas

As noted first by Sunyaev & Churazov (1984), the 3.071 mm hyperfine line from $^{57}Fe^{+23}$ might be observable in astrophysical plasmas. We assess the atomic processes which might contribute to the excitation of this line. We determine the intensity of the hyperfine line from an isothermal, coronal plasma in collisional ionization equilibrium and for a coronal plasma cooling isobarically due to its own radiation. Comparisons of the hyperfine line to other lines emitted by the same ion, Fe$^{+23}$, are shown to be useful for deriving the isotopic fraction of $^{57}$Fe. We calculate the ratios of the hyperfine line to the 2s--2p EUV lines at 192 \AA and 255 \AA, and the 2s--3p X-ray doublet at 10.6 \AA.Comment: 28 pages text+figures, Accepted to ApJ in Jan 98, also at http://www.astro.virginia.edu/~nld2n/research.htm

K-shell dielectronic resonances in photoabsorption: differential oscillator strengths for Li-like C IV, O VI, and Fe XXIV

Recently X-ray photoabsorption in KLL resonances of O VI was predicted [Pradhan, Astrophys.J. Lett. 545, L165 (2000)], and detected by the Chandra X-ray Observatory [Lee et al, Astrophys. J. {\it Lett.}, submitted]. The required resonance oscillator strengths f_r, are evaluated in terms of the differential oscillator strength df/de that relates bound and continuum absorption. We present the f_r values from radiatively damped and undamped photoionization cross sections for Li-like C,O, and Fe calculated using relativistic close coupling Breit-Pauli R-matrix method. The KLL resonances of interest here are: 1s2p (^3P^o) 2s [^4P^o_{1/2,3/2}, ^2P^o_{1/2,3/2}] and 1s2p (^1P^o) 2s [^2P^o_{1/2,3/2}]. The KLL photoabsorption resonances in Fe XXIV are fully resolved up to natural autoionization profiles for the first time. It is demonstrated that the undamped f_r independently yield the resonance radiative decay rates, and thereby provide a precise check on the resolution of photoionization calculations in general. The predicted photoabsorption features should be detectable by the X-ray space observatories and enable column densities in highly ionized astrophysical plasmas to be determined from the calculated f_r. The dielectronic satellites may appear as redward broadening of resonances lines in emission and absorption.Comment: 9 pages, 2 figurs, Phys. Rev. A, Rapid Communication (submitted

Transcriptome characterization via 454 pyrosequencing of the annelid Pristina leidyi, an emerging model for studying the evolution of regeneration

Background: The naid annelids contain a number of species that vary in their ability to regenerate lost body parts, making them excellent candidates for evolution of regeneration studies. However, scant sequence data exists to facilitate such studies. We constructed a cDNA library from the naid Pristina leidyi, a species that is highly regenerative and also reproduces asexually by fission, using material from a range of regeneration and fission stages for our library. We then sequenced the transcriptome of P. leidyi using 454 technology. Results: 454 sequencing produced 1,550,174 reads with an average read length of 376 nucleotides. Assembly of 454 sequence reads resulted in 64,522 isogroups and 46,679 singletons for a total of 111,201 unigenes in this transcriptome. We estimate that over 95% of the transcripts in our library are present in our transcriptome. 17.7% of isogroups had significant BLAST hits to the UniProt database and these include putative homologs of a number of genes relevant to regeneration research. Although many sequences are incomplete, the mean sequence length of transcripts (isotigs) is 707 nucleotides. Thus, many sequences are large enough to be immediately useful for downstream applications such as gene expression analyses. Using in situ hybridization, we show that two Wnt/β-catenin pathway genes (homologs of frizzled and β-catenin) present in our transcriptome are expressed in the regeneration blastema of P. leidyi, demonstrating the usefulness of this resource for regeneration research. Conclusions: 454 sequencing is a rapid and efficient approach for identifying large numbers of genes in an organism that lacks a sequenced genome. This transcriptome dataset will be a valuable resource for molecular analyses of regeneration in P. leidyi and will serve as a starting point for comparisons to non-regenerating naids. It also contributes significantly to the still limited genomic resources available for annelids and lophotrochozoans more generally.https://doi.org/10.1186/1471-2164-13-28

CHIANTI - an Atomic Database for Emission Lines. Paper VI: Proton Rates and Other Improvements

The CHIANTI atomic database contains atomic energy levels, wavelengths, radiative transition probabilities and electron excitation data for a large number of ions of astrophysical interest. Version 4 has been released, and proton excitation data is now included, principally for ground configuration levels that are close in energy. The fitting procedure for excitation data, both electrons and protons, has been extended to allow 9 point spline fits in addition to the previous 5 point spline fits. This allows higher quality fits to data from close-coupling calculations where resonances can lead to significant structure in the Maxwellian-averaged collision strengths. The effects of photoexcitation and stimulated emission by a blackbody radiation field in a spherical geometry on the level balance equations of the CHIANTI ions can now be studied following modifications to the CHIANTI software. With the addition of H I, He I and N I, the first neutral species have been added to CHIANTI. Many updates to existing ion data-sets are described, while several new ions have been added to the database, including Ar IV, Fe VI and Ni XXI. The two-photon continuum is now included in the spectral synthesis routines, and a new code for calculating the relativistic free-free continuum has been added. The treatment of the free-bound continuum has also been updated.Comment: CHIANTI is available at http://wwwsolar.nrl.navy.mil/chianti.htm

Возобновляемая энергетика - эффективное направление повышения энергетической и экологической безопасности Республики Беларусь

The structure of the world electricity production is reviewed. It provides an assessment of actual use of the most promising renewable energy sources in Belarus; an environmental impact assessment of different power sources and fuels; an evaluation of economic efficiency of renewable energy considering environmental factors. It also presents an analysis of the reasons impeding the development of renewable energy in Belarus, and possible solutions.Рассмотрена структура мирового производства электроэнергии. Приведена оценка состояния использования наиболее перспективных для Беларуси возобновляемых источников энергии (ВИЭ). Дана оценка воздействия различных источников энергии и видов топлива на окружающую среду, оценка экономической эффективности использования ВИЭ с учетом экологических факторов. Представлен анализ причин, сдерживающих развитие ВИЭ в Беларуси, и меры для их устранения

Dural arteriovenous fistulas: two case reports and review

The paper discusses the etiology, pathogenesis, classification, principles of diagnosis and tactics of surgical treatment of dural arteriovenous fistulas. The study presents two case reports of successful treatment of patients with symptomatic dural arteriovenous fistulas

НОВЫЕ ДАННЫЕ О ЛИШАЙНИКАХ РОДА CETRELIA (LECANORALES, ASCOMYCOTA) В БЕЛАРУСИ

Two hundred and ten lichen specimens of Cetrelia collected in Belarus during 1954–2012 were examined based on morphological and chemical characters. Three species of Cetrelia (C. cetrarioides, C. monachorum, and C. olivetorum) have been identified in this study. The occurrence of detected species in Belarus is reviewed and distribution maps are provided.Ревизия гербарного материала по роду Cetrelia в Беларуси выявила неполноту опубликованных флористических данных по рассматриваемому роду. Установлено, что большинство гербарных образцов, определенных ранее как C. cetrarioides, относится к другому виду – C. monachorum. Таким образом, в настоящее время в состав рода Cetrelia на территории Беларуси входит три вида: C. cetrarioides, C. monachorum и C. olivetorum. Полученные в ходе исследования данные уточняют представления о таксономических особенностях и ареалах лишайников рода Cetrelia в Европе и, кроме того, могут быть использованы при составлении Красной книги Республики Беларусь, а также фундаментального многотомного издания "Флора БеларусиЙ"