The holocentric species Luzula elegans shows interplay between centromere and large‐scale genome organization

In higher plants, the large‐scale structure of monocentric chromosomes consists of distinguishable eu‐ and heterochromatic regions, the proportions and organization of which depend on a species' genome size. To determine whether the same interplay is maintained for holocentric chromosomes, we investigated the distribution of repetitive sequences and epigenetic marks in the woodrush Luzula elegans (3.81 Gbp/1C). Sixty‐one per cent of the L. elegans genome is characterized by highly repetitive DNA, with over 30 distinct sequence families encoding an exceptionally high diversity of satellite repeats. Over 33% of the genome is composed of the Angela clade of Ty1/copia LTR retrotransposons, which are uniformly dispersed along the chromosomes, while the satellite repeats occur as bands whose distribution appears to be biased towards the chromosome termini. No satellite showed an almost chromosome‐wide distribution pattern as expected for a holocentric chromosome and no typical centromere‐associated LTR retrotransposons were found either. No distinguishable large‐scale patterns of eu‐ and heterochromatin‐typical epigenetic marks or early/late DNA replicating domains were found along mitotic chromosomes, although super‐high‐resolution light microscopy revealed distinguishable interspersed units of various chromatin types. Our data suggest a correlation between the centromere and overall genome organization in species with holocentric chromosomes.     

Experimentelle Untersuchungen anEuplotes crassus

Ohne ZusammenfassungMit 2 TextabbildungenDer Deutschen Forschungsgemeinschaft danke ich für die großzügige Unterstützung der Untersuchungen. Dank schulde ich auch Frl.B. Jaumann für sorgfältige Mitarbeit und HerrnH. Bauschert für das Zeichnen der Abbildungsvorlagen.     

Osteoblast autophagy in glucocorticoid-induced osteoporosis

Administration of glucocorticoids is an effective strategy for treating many inflammatory and autoimmune diseases. However, glucocorticoid treatment can have adverse effects on bone, leading to glucocorticoid-induced osteoporosis (GIO), the most common form of secondary osteoporosis. Although the pathogenesis of GIO has been studied for decades, over the past ten years the autophagy machinery has been implicated as a novel mechanism. Autophagy in osteoblasts, osteocytes, and osteoclasts plays a critical role in the maintenance of bone homeostasis. Herein, we specifically discuss how osteoblast autophagy responds to glucocorticoids and its role in the development of GIO.     

Current-Voltage Curves of Porous Membranes in the Presence of Pore-Blocking Ions: I. Narrow Pores Containing No More Than One Moving Ion

We propose a physical model for voltage-dependent conductance changes of excitable cell membranes. It is based on competition of uni- and bivalent ions for chains of stable sites extending through the membrane. These one-dimensional pathways (pores) have different profiles of chemical potential for the two ionic species so that bivalent ions can block the passage of univalent ions at large membrane potentials. We treat the special case that each pore is either empty or, because of electrostatic repulsion, contains no more than one uni- or bivalent ion at a time. A system of linear differential equations describes the time-dependent probabilities of the various possible pore states. The states are limited by transition rate constants involving the profile of the chemical potential, the membrane voltage, the ionic concentrations in the adjacent baths, and electrostatic interactions between the ions. The steady-state solutions (Kirchhoff-Hill theorem) yield expressions for the relationship between the small signal conductance of univalent ions and the concentration of these ions in the external bathing medium (a saturation curve) and for the ionic currents and the steady-state current-voltage curve (N-shaped). From the latter curve we compute the shift of theshold potential caused by concentration changes of the external bathing medium. The model yields a number of predictions which can be tested experimentally.     

Attenuation of pattern recognition receptor signaling is mediated by a MAP kinase kinase kinase

Pattern recognition receptors (PRRs) play a key role in plant and animal innate immunity. PRR binding of their cognate ligand triggers a signaling network and activates an immune response. Activation of PRR signaling must be controlled prior to ligand binding to prevent spurious signaling and immune activation. Flagellin perception in Arabidopsis through FLAGELLIN‐SENSITIVE 2 (FLS2) induces the activation of mitogen‐activated protein kinases (MAPKs) and immunity. However, the precise molecular mechanism that connects activated FLS2 to downstream MAPK cascades remains unknown. Here, we report the identification of a differentially phosphorylated MAP kinase kinase kinase that also interacts with FLS2. Using targeted proteomics and functional analysis, we show that MKKK7 negatively regulates flagellin‐triggered signaling and basal immunity and this requires phosphorylation of MKKK7 on specific serine residues. MKKK7 attenuates MPK6 activity and defense gene expression. Moreover, MKKK7 suppresses the reactive oxygen species burst downstream of FLS2, suggesting that MKKK7‐mediated attenuation of FLS2 signaling occurs through direct modulation of the FLS2 complex.     

Varietal effects of eight paired lines of transgenic Bt maize and near-isogenic non-Bt maize on soil microbial and nematode community structure

A glasshouse experiment was undertaken to provide baseline data on the variation between conventional maize (Zea mays L.) varieties and genetically modified maize plants expressing the insecticidal Bacillus thuringiensis protein (Bt, Cry1Ab). The objective was to determine whether the variation in soil parameters under a range of conventional maize cultivars exceeded the differences between Bt and non-Bt maize cultivars. Variations in plant growth parameters (shoot and root biomass, percentage carbon, percentage nitrogen), Bt protein concentration in shoots, roots and soil, soil nematode abundance and soil microbial community structure were determined. Eight paired varieties (i.e. varieties genetically modified to express Bt protein and their near-isogenic control varieties) were investigated, together with a Bt variety for which no near-isogenic control was available (NX3622, a combined transformant expressing both Bt and herbicide tolerance) and a conventional barley (Hordeum vulgare L.) variety which was included as a positive control. The only plant parameter which showed a difference between Bt varieties and near-isogenic counterparts was the shoot carbon to nitrogen ratio; this was observed for only two of the eight varieties, and so was not attributable to the Bt trait. There were no detectable differences in the concentration of Bt protein in plant or soil with any of the Bt-expressing varieties. There were significant differences in the abundance of soil nematodes, but this was not related to the Bt trait. Differences in previously published soil nematode studies under Bt maize were smaller than these varietal effects. Soil microbial community structure, as determined by phospholipid fatty acid (PLFA) analysis, was strongly affected by plant growth stage but not by the Bt trait. The experimental addition of purified Cry1Ab protein to soil confirmed that, at ecologically relevant concentrations, there were no measurable effects on microbial community structure.     

New and already known acanthocephalans mostly from mammals in Vietnam, with descriptions of two new genera and species in Archiacanthocephala

Adults of 2 new species and 2 new genera of acanthocephalans in class Archiacanthocephala, collected between 1998 and 2004 in Vietnam from the intestines of mammals, are described, i.e., Cucullanorhynchus constrictruncatus n. gen., n. sp. (Oligacanthorhynchidae) from a leopard Panthera pardus (Linnaeus) (Mammalia: Felidae) and Paraprosthenorchis ornatus n. gen. n. sp. (Oligacanthorhynchidae) from the Chinese pangolin Manis pentadactyla (Linnaeus) (Mammalia: Manidae). Adult Sphaerechinorhynchus macropisthospinus Amin, Wongsawad, Marayong, Saehoong, Suwattanacoupt, and Sey, 1998 (Plagiorhynchidae) are described for the first time from 2 females collected from a tiger Panthera tigris (Linnaeus) (Mammalia: Felidae) and from 1 male from a water monitor Varanus salvator Laurenti (Reptilia: Varanidae). Characteristic features distinguishing the new species or genera from related taxa are as follows. The trunk of C. constrictruncatus has an anterior hood in both sexes and a posterior constriction in females. The anterior trunk of P. ornatus has many small festoons and proboscis hooks are inserted in elevated papillae separated by beady, near hexagonal, ornate grids.