1-D coordination chains of Cu(hfac)2 and Mn(hfac)2 bridged by phenyl-nitronylnitroxide derivatives

Two alternating 1-D metal-radical linear [L:Cu(hfac)₂]_n and zig-zag [L:Mn(hfac)₂]_n chains (where L = 4-trimethylsilylethynyl-1-(4,4,5,5-tetramethyl-3-oxylimidazoline-1-oxide)benzene) and hfac = hexafluoroacetylacetonate) are described and characterized by X-ray diffraction of their crystals. Bulk magnetic measurements of L:Cu(hfac)₂ indicated a ferromagnetic interaction with J = 6 cm⁻¹ and L:Mn(hfac)₂ yielded ferrimagnetic interactions with J = −95 cm⁻¹. For the latter, a strong increase of their magnetic moment at lowest temperatures was observed only at very low static magnetic field, while for H_dc > 0.05 T saturation effect led to a downward slope after reaching a maximum.     

Predation effects on the evolution of life-history traits in a clonal oligochaete

Although size at maturity and size and number of offspring are life-history traits widely studied in sexual and parthenogenetic reproduction, there is no such research on animals reproducing asexually without the involvement of gametes. Here we present an individual-based model in combination with experiments to study the clonal growth of Stylaria lacustris, an oligochaete reproducing through fission. We studied the effect of individual size at fission and fission ratio on clone fitness. Our results show that in benign environments without predators, fitness is higher when small worms produce small offspring. Then we included size-specific sublethal predation and found that the fitness of the clone is maximized when parental worms start fission at a large size and produce large descendants intercalated in the middle of the parental worm's body. These results agree with empirical findings. Furthermore, the results of our own laboratory experiment revealed that when S. lacustris is exposed to chemical alarm signals from injured conspecifics, it alters its life history in the same direction as predicted by the model. Our findings suggest that the effect of size-specific sublethal predation is similar to the effect of size-specific lethal predation because both modes of predation result in size-dependent prey mortality.     

Endotoxin elicits nitric oxide release in rat but prostacyclin synthesis in human and bovine vascular smooth muscle cells

Lipopolysaccharide (LPS) exposure to cells and tissues can mimic the biochemical events leading to septic shock. Previous data demonstrated a massive upregulation of prostaglandin endoperoxide H2 synthase (PGHS-2), but not NO synthase-2 (NOS-2) in bovine smooth muscle cells (SMC) between 2 and 12 h of LPS exposure. This caused an abundant release of prostacyclin (PGI2) by constitutive PGI2-synthase as a counterregulation to a dysfunctional endothelium. We here report that human as well as bovine SMC mainly respond by the induction of PGHS-2 and the subsequent release of PGI2, whereas rat SMC exhibited a distinct induction of NOS-2 and released significantly higher amounts of *NO compared with cattle and human. The induction of either PGHS-2 or NOS-2 in the three different species investigated seems to be mutually exclusive in the time window of 2-24 h. This finding should be considered in the setup of experimental models for the investigation of septic shock.     

Embolized conduits of rice (Oryza sativa, Poaceae) refill despite negative xylem pressure

Embolism reversal in rice plants was studied by testing the plant's ability to refill embolized conduits while xylem pressures were substantially negative. Intact, potted plants were water-stressed to a xylem pressure of -1.88 ± 0.1 MPa and a 66.3 ± 3.8% loss of xylem conductivity (PLC) by cavitation. Stressed plants were carefully rewatered, allowing xylem pressure to rise, but not above the theoretical threshold of c. -0.15 MPa for embolism collapse. Despite xylem pressures being more negative than this threshold, the PLC fell significantly (28.5 ± 5.6%), indicating the refilling of vessels. Above c. -1.0 MPa, almost all plants regained their maximum hydraulic conductivity. Dye uptake experiments showed the same pattern of embolism refilling despite negative pressure. Refilling was prevented in plants that were light-starved for 5 d, suggesting the unknown mechanism is dependent on metabolic energy. Results are among the first showing that herbaceous plants can reverse embolism without bulk xylem pressures rising near or above atmospheric.     

Hepatitis C virus NS2/3 processing is required for NS3 stability and viral RNA replication

The hepatitis C virus NS2/3 protease is responsible for cleavage of the viral polyprotein between nonstructural proteins NS2 and NS3. We show here that mutation of three highly conserved residues in NS2 (His(952), Glu(972), and Cys(993)) abrogates NS2/3 protease activity and that introduction of any of these mutations into subgenomic NS2-5B replicons results in complete inactivation of NS2/3 processing and RNA replication in both stable and transient replication assays. The effect of uncleaved NS2 on the various activities of NS3 was therefore explored. Unprocessed NS2 had no significant effect on the in vitro ATPase and helicase activities of NS3, whereas immunoprecipitation experiments demonstrated a decreased affinity of NS4A for uncleaved NS2/3 as compared with NS3. This subsequently resulted in reduced kinetics in an in vitro NS3 protease assay with the unprocessed NS2/3 protein. Interestingly, NS3 was still capable of efficient processing of the polyprotein expressed from a subgenomic replicon in Huh-7 cells in the presence of uncleaved NS2. Notably, we show that fusion with NS2 leads to the rapid degradation of NS3, whose activity is essential for RNA replication. Finally, we demonstrate that uncleaved NS2/3 degradation can be prevented by the addition of a proteasome inhibitor. We therefore propose that NS2/3 processing is a critical step in the viral life cycle and is required to permit the accumulation of sufficient NS3 for RNA replication to occur. The regulation of NS2/3 cleavage could constitute a novel mechanism of switching between viral RNA replication and other processes of the hepatitis C virus life cycle.     

A general model for preferential hetero-oligomerization of LIN-2/7 domains: mechanism underlying directed assembly of supramolecular signaling complexes

LIN-2/7 (L27) domains are protein interaction modules that preferentially hetero-oligomerize, a property critical for their function in directing specific assembly of supramolecular signaling complexes at synapses and other polarized cell-cell junctions. We have solved the solution structure of the heterodimer composed of the L27 domains from LIN-2 and LIN-7. Comparison of this structure with other L27 domain structures has allowed us to formulate a general model for why most L27 domains form an obligate heterodimer complex. L27 domains can be divided in two types (A and B), with each heterodimer comprising an A/B pair. We have identified two keystone positions that play a central role in discrimination. The residues at these positions are energetically acceptable in the context of an A/B heterodimer, but would lead to packing defects or electrostatic repulsion in the context of A/A and B/B homodimers. As predicted by the model, mutations of keystone residues stabilize normally strongly disfavored homodimers. Thus, L27 domains are specifically optimized to avoid homodimeric interactions.     

Internal Pipping (IP): obligat oder fakultativ für erfolgreichen Schlupf?

Zusammenfassung Beim Internal Pipping (IP=inneres Schlüpfen) durchstößt der Embryo mit dem Schnabel die Schalenmembran zur Luftkammer und kann somit direkt Luft aus dem Eiinnenraum atmen (die allerdings durch die Austauschvorgänge der Chorioallantois und der Lunge sowie durch die Diffusionsbarriere der Poren der Kalkschale eine wesentlich andere Partialdruckzusammensetzung als die umgebende atmosphärische Luft besitzt). Dieses Verhalten tritt normalerweise nach Ablauf von ca. 90 % der Bebrütungszeit vor dem eigentlichen An- bzw. Aufbrechen der Eischale (EP=External Pipping) auf. Bei einigen Vogelarten (Sturmtaucher, Möwen, Tauben, Sturmvögel und Seeschwalben) soll das EP auch vor oder mit dem IP stattfinden. Für die Felsentaube (Columba livia) und das Diamanttäubchen (Geopelia cuneata) konnten wir dies aber nicht bestätigen.IP wird in der Literatur i. d. R. in einem kausalen Zusammenhang mit einer Stagnation im sonst kontinuierlichen Anstieg des Sauerstoffverbrauchs (Plateauphase) des sich entwikkelnden Embryos beschrieben: Die Atmung soll in dieser Phase von der Chorioallantois auf die Lunge umgestellt werden und ermöglicht so deren Füllung mit Luft, was für ihre funktionale Entwicklung unerläßlich ist. Über 50 Veröffentlichungen beschäftigen sich mit diesem Phänomen, ohne daß es dazu aber detaillierte Beobachtungen oder gar systematische Untersuchungen (Experimente) gäbe.Um diesen Mangel zu beseitigen, führten wir entsprechende Untersuchungen durch:(1) Im Rahmen von Experimenten zum Energieumsatz in der Vogelembryogenese beobachteten wir bei einer großen Anzahl von Schlüpflingen von 17 verschiedenen Vogelarten einen erfolgreichen Schlupf ohne jegliche Anzeichen von IP. Die innere Eimembran zur Luftkammer war intakt, also nicht mit dem Schnabel durchstoßen worden (Tab. 1). (2) Systematische Beobachtungen an 1040 Eiern von Hühnern (Gallus gallus domesticus) in einer professionellen Bebrütungsanstalt zeigten, daß zwischen 7–13,5 % ohne IP schlüpften (Tab. 2). (3) Mit experimentellen Untersuchungen an Haushuhn, Felsentaube, Wachtel (Coturnix coturnix) und (Nordinsel-)Streifenkiwi (Apteryx mantelli) konnten wir in 7–65 % (Mittelwert: 35,7 %) aller Fälle zeigen, daß Vogelembryonen ohne IP erfolgreich und ohne negative Folgen für ihre nachfolgende Entwicklung schlüpfen können.Diese Ergebnisse zeigen, daß IP also allem Anschein nach keine obligate, sondern höchstens eine fakultative Verhaltensweise ist. Die Lunge kann über den luftgefüllten Raum innerhalb der Chorioallantois belüftet werden.

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Internal Pipping (IP): obligatory or facultative behaviour for successful hatching?

Summary The (invisible) behaviour called Internal Pipping (IP, the puncturing of the inner egg membrane to bring the bill tip inside the air-cell to breathe air) is considered as a regular and obligatory element in the normal hatching process of a bird. It does, indeed, frequently occur when about 90 % of the incubation period has elapsed, shortly before the embryo cracks the eggshell with its bill (External Pipping, EP). In some bird species (e. g. pigeons, shearwaters, petrels, gulls and terns) EP is reported to precede IP. However, in the Rock Dove (Columba livia) and the Diamond Dove (Geopelia cuneata) we could not confirm this observation.In many papers IP is said normally to be especially correlated with a change in embryonic oxygen consumption, namely a transition to a plateau phase. At this time respiration changes from chorioallantoic membrane to lungs; the lungs are filled with air which is thought to be provided exclusively from the air-cell. Many authors describe this behaviour accordingly. Nevertheless, there exist no direct observations or even experimental data to substantiate this claim. Our paper deals with this problem:During our long-term experiments on embryonic metabolic rate we first observed that embryos of at least 17 different bird species frequently hatched and developed successfully without any signs of a general IP. The membrane of the air-cell was not pipped (see Table 1).Additional and systematic observations in a professional breeding station on 1040 eggs ofGallus gallus domesticus showed that in 7–13,5 % of cases embryos hatched without any signs of IP (see Table 2).To determine whether this phenomenon is a common event we performed special experiments in four different bird species (Domestic FowlGallus gallus domesticus, Rock Dove, Common QuailCoturnix coturnix, Brown KiwiApteryx mantelli). These tests showed that hatching without IP occurs in 7 to 65 % (mean value 35.7 %) of cases in all four species without any negative effects on subsequent ontogenetic development.Evidently, IP is not an obligatory but a facultative behaviour in these cases, and probably in general. The aeration of the lungs can be done a different way within the space of the chorioallantoic membrane; for this reason no air-cell is needed.