Influence of the virus LbFV and of Wolbachia in a host-parasitoid interaction

Symbionts are widespread and might have a substantial effect on the outcome of interactions between species, such as in host-parasitoid systems. Here, we studied the effects of symbionts on the outcome of host-parasitoid interactions in a four-partner system, consisting of the parasitoid wasp Leptopilina boulardi, its two hosts Drosophila melanogaster and D. simulans, the wasp virus LbFV, and the endosymbiotic bacterium Wolbachia. The virus is known to manipulate the superparasitism behavior of the parasitoid whereas some Wolbachia strains can reproductively manipulate and/or confer pathogen protection to Drosophila hosts. We used two nuclear backgrounds for both Drosophila species, infected with or cured of their respective Wolbachia strains, and offered them to L. boulardi of one nuclear background, either infected or uninfected by the virus. The main defence mechanism against parasitoids, i.e. encapsulation, and other important traits of the interaction were measured. The results showed that virus-infected parasitoids are less frequently encapsulated than uninfected ones. Further experiments showed that this viral effect involved both a direct protective effect against encapsulation and an indirect effect of superparasitism. Additionally, the Wolbachia strain wAu affected the encapsulation ability of its Drosophila host but the direction of this effect was strongly dependent on the presence/absence of LbFV. Our results confirmed the importance of heritable symbionts in the outcome of antagonistic interactions.     

Both Hepatic and Body Iron Stores Are Increased in Dysmetabolic Iron Overload Syndrome. A Case-Control Study

Background & Aims

Hepatic iron is increased in dysmetabolic iron overload syndrome (DIOS). Whether this reflects elevated body iron stores is still debated. The study was aimed at assessing body iron stores in DIOS patients by calculating the amount of mobilized iron (AMI).

Methods

We conducted a prospective case-control study comparing AMI in 12 DIOS patients and 12 overweight normoferritinemic subjects matched on BMI and age. All participants were phlebotomized until serum ferritin dropped ≤ 50μg/L.

Results

The two groups were comparable with respect to metabolic abnormalities and differed according to serum ferritin levels only. AMI was significantly (p<0.0001) higher in DIOS (2.5g±0.7) than in controls (0.8g±0.3). No side effects were related to phlebotomies.     

Radical-induced oxidation of trans-resveratrol

trans-Resveratrol (RVT) (3,5,4'-trihydroxystilbene), a polyphenolic constituent of red wine, is thought to be beneficial in reducing the incidence of cardiovascular diseases, partly via its antioxidant properties. However, the mechanism of action by which trans-resveratrol displays its antioxidant effect has not been totally unravelled. This study aimed at establishing a comprehensive scheme of the reaction mechanisms of the direct scavenging of HO(*) and O(2)(*-) radicals generated by water gamma radiolysis. Aerated aqueous solutions of trans-RVT (from 10 to 100μmolL(-1)) were irradiated with increasing radiation doses (from 25 to 400Gy) and further analyzed by UV-visible absorption spectrophotometry for detection of trans-RVT oxidation products. Separation and quantification of RVT and its four oxidation products previously identified by mass spectrometry, i.e., piceatannol (PCT), 3,5-dihydroxybenzoic acid (3,5-DHBA), 3,5-dihydroxybenzaldehyde (3,5-DHB) and para-hydroxybenzaldehyde (PHB), were performed by HPLC/UV-visible spectrophotometry. Determination of the radiolytic yields of trans-RVT consumption and oxidation product formation has allowed us to establish balance between trans-RVT disappearance and the sum of oxidation products formation. Under our conditions, O(2)(-) radicals seemed to poorly initiate oxidation of trans-RVT, whereas the latter, whatever its initial concentration, quantitatively reacted with HO() radicals, via a dismutation mechanism. Two reaction pathways involving HO()-induced trans-RVT primary radicals have been proposed to explain the formation of the oxidation end-products of trans-RVT.     

Amphioxus postembryonic development reveals the homology of chordate metamorphosis

Most studies in evolution are centered on how homologous genes, structures, and/or processes appeared and diverged. Although historical homology is well defined as a concept, in practice its establishment can be problematic, especially for some morphological traits or developmental processes. Metamorphosis in chordates is such an enigmatic character. Defined as a spectacular postembryonic larva-to-adult transition, it shows a wide morphological diversity between the different chordate lineages, suggesting that it might have appeared several times independently. In vertebrates, metamorphosis is triggered by binding of the thyroid hormones (THs) T(4) and T(3) to thyroid-hormone receptors (TRs). Here we show that a TH derivative, triiodothyroacetic acid (TRIAC), induces metamorphosis in the cephalochordate amphioxus. The amphioxus TR (amphiTR) mediates spontaneous and TRIAC-induced metamorphosis because it strongly binds to TRIAC, and a specific TR antagonist, NH3, inhibits both spontaneous and TRIAC-induced metamorphosis. Moreover, as in amphibians, amphiTR expression levels increase around metamorphosis and are enhanced by THs. Therefore, TH-regulated metamorphosis, mediated by TR, is an ancestral feature of all chordates. This conservation of a regulatory network supports the homology of metamorphosis in the chordate lineage.     

Biosynthetic exchange of bromide for chloride and strontium for calcium in the photosystem II oxygen-evolving enzymes

The active site for water oxidation in photosystem II goes through five sequential oxidation states (S(0) to S(4)) before O(2) is evolved. It consists of a Mn(4)Ca cluster close to a redox-active tyrosine residue (Tyr(Z)). Cl(-) is also required for enzyme activity. To study the role of Ca(2+) and Cl(-) in PSII, these ions were biosynthetically substituted by Sr(2+) and Br(-), respectively, in the thermophilic cyanobacterium Thermosynechococcus elongatus. Irrespective of the combination of the non-native ions used (Ca/Br, Sr/Cl, Sr/Br), the enzyme could be isolated in a state that was fully intact but kinetically limited. The electron transfer steps affected by the exchanges were identified and then investigated by using time-resolved UV-visible absorption spectroscopy, time-resolved O(2) polarography, and thermoluminescence spectroscopy. The effect of the Ca(2+)/Sr(2+) and Cl(-)/Br(-) exchanges was additive, and the magnitude of the effect varied in the following order: Ca/Cl < Ca/Br < Sr/Cl < Sr/Br. In all cases, the rate of O(2) release was similar to that of the S(3)Tyr(Z)(.) to S(0)Tyr(Z) transition, with the slowest kinetics (i.e. the Sr/Br enzyme) being approximately 6-7 slower than in the native Ca/Cl enzyme. This slowdown in the kinetics was reflected in a decrease in the free energy level of the S(3) state as manifest by thermoluminescence. These observations indicate that Cl(-) is involved in the water oxidation mechanism. The possibility that Cl(-) is close to the active site is discussed in terms of recent structural models.     

Automatic particle selection: results of a comparative study

Manual selection of single particles in images acquired using cryo-electron microscopy (cryoEM) will become a significant bottleneck when datasets of a hundred thousand or even a million particles are required for structure determination at near atomic resolution. Algorithm development of fully automated particle selection is thus an important research objective in the cryoEM field. A number of research groups are making promising new advances in this area. Evaluation of algorithms using a standard set of cryoEM images is an essential aspect of this algorithm development. With this goal in mind, a particle selection "bakeoff" was included in the program of the Multidisciplinary Workshop on Automatic Particle Selection for cryoEM. Twelve groups participated by submitting the results of testing their own algorithms on a common dataset. The dataset consisted of 82 defocus pairs of high-magnification micrographs, containing keyhole limpet hemocyanin particles, acquired using cryoEM. The results of the bakeoff are presented in this paper along with a summary of the discussion from the workshop. It was agreed that establishing benchmark particles and using bakeoffs to evaluate algorithms are useful in promoting algorithm development for fully automated particle selection, and that the infrastructure set up to support the bakeoff should be maintained and extended to include larger and more varied datasets, and more criteria for future evaluations.     

Cellular and Behavioral Effects of Cranial Irradiation of the Subventricular Zone in Adult Mice

Background

In mammals, new neurons are added to the olfactory bulb (OB) throughout life. Most of these new neurons, granule and periglomerular cells originate from the subventricular zone (SVZ) lining the lateral ventricles and migrate via the rostral migratory stream toward the OB. Thousands of new neurons appear each day, but the function of this ongoing neurogenesis remains unclear.

Methodology/Principal Findings

In this study, we irradiated adult mice to impair constitutive OB neurogenesis, and explored the functional impacts of this irradiation on the sense of smell. We found that focal irradiation of the SVZ greatly decreased the rate of production of new OB neurons, leaving other brain areas intact. This effect persisted for up to seven months after exposure to 15 Gray. Despite this robust impairment, the thresholds for detecting pure odorant molecules and short-term olfactory memory were not affected by irradiation. Similarly, the ability to distinguish between odorant molecules and the odorant-guided social behavior of irradiated mice were not affected by the decrease in the number of new neurons. Only long-term olfactory memory was found to be sensitive to SVZ irradiation.

Conclusion/Significance

These findings suggest that the continuous production of adult-generated neurons is involved in consolidating or restituting long-lasting olfactory traces.     

Evidence for a direct but sequential binding of titin to tropomyosin and actin filaments

Titin is a giant molecule that spans half a sarcomere, establishing several specific bindings with both structural and contractile myofibrillar elements. It has been demonstrated that this giant protein plays a major role in striated muscle cell passive tension and contractile filament alignment. The in vitro interaction of titin with a new partner (tropomyosin) reported here is reinforced by our recent in vitro motility study using reconstituted Ca-regulated thin filaments, myosin and a native 800-kDa titin fragment. In the presence of the tropomyosin-troponin complex, the actin filament movement onto coated S1 is improved by the titin fragment. Here, we found that two purified native titin fragments of 150 and 800 kDa, covering respectively the N1-line and the N2-line/PEVK region in the I-band and known to contain actin-binding sites, directly bind tropomyosin in the absence of actin. We have also shown that binding of the 800-kDa fragment with filamentous actin inhibited the subsequent interaction of tropomyosin with actin, as judged by cosedimentation. However, this was not the case if the complex of actin and tropomyosin was formed before the addition of the 800-kDa fragment. We thus conclude that a sequential arrangement of contacts exists between parts of the titin I-band region, tropomyosin and actin in the thin filament.     

Auxin at the Shoot Apical Meristem

Plants continuously generate new tissues and organs through the activity of populations of undifferentiated stem cells, called meristems. Here, we discuss the so-called shoot apical meristem (SAM), which generates all the aerial parts of the plant. It has been known for many years that auxin plays a central role in the functioning of this meristem. Auxin is not homogeneously distributed at the SAM and it is thought that this distribution is interpreted in terms of differential gene expression and patterned growth. In this context, auxin transporters of the PIN and AUX families, creating auxin maxima and minima, are crucial regulators. However, auxin transport is not the only factor involved. Auxin biosynthesis genes also show specific, patterned activities, and local auxin synthesis appears to be essential for meristem function as well. In addition, auxin perception and signal transduction defining the competence of cells to react to auxin, add further complexity to the issue. To unravel this intricate signaling network at the SAM, systems biology approaches, involving not only molecular genetics but also live imaging and computational modeling, have become increasingly important.Plants continuously generate new tissues and organs through the activity of populations of undifferentiated stem cells, called meristems. Because meristems can modulate their activity, they provide the developmental flexibility that allows plants to adapt their development in reaction to the environment (reviews: Lyndon 1998; Traas and Doonan 2001; Aida and Tasaka 2006; Sablowski 2007).Distinct meristems exist. Apical meristems, positioned at the tip of the shoots and roots, initiate aerial and underground organs, respectively. Along the stems and roots, more diffuse secondary meristems are responsible for secondary thickening of these structures.The plant hormone auxin plays an instrumental role in meristem biology and we discuss here its role in a particular meristem, the shoot apical meristem (SAM) that generates all the aerial organs including the floral meristems (Fig. 1A–C). In this context, we limit ourselves to the meristems in angiosperm that have been studied in most detail.Open in a separate windowFigure 1.The shoot apical meristem of Arabidopsis thaliana. (A) Aerial part of a wild-type plant of the Columbia ecotype (Col-0). The SAM is responsible for the production of rosette leaves and, after floral transition, for the production of the stem, cauline leaves, lateral meristems, and flowers of the inflorescence. (B) Details of the tip of the inflorescence, showing the highly organized positioning of flowers around the main axis (a spiral). (C) A dissected inflorescence meristem. Older flowers have been removed to expose the meristem surrounded by young floral buds. (D) Longitudinal section of an inflorescence meristem showing the layered organization (L1, L2, and L3 cell layers). L1 and L2 are also called the tunica and L3 to the corpus. The functional zones are also represented. At the meristem summit the central zone (CZ) contains the stem cells, whereas primordia are initiated in the peripheral zone (PZ). The rib zone (RZ) produces the internal part of the stem.     

Nanoarchaea: representatives of a novel archaeal phylum or a fast-evolving euryarchaeal lineage related to Thermococcales?

Background  

Cultivable archaeal species are assigned to two phyla - the Crenarchaeota and the Euryarchaeota - by a number of important genetic differences, and this ancient split is strongly supported by phylogenetic analysis. The recently described hyperthermophile Nanoarchaeum equitans, harboring the smallest cellular genome ever sequenced (480 kb), has been suggested as the representative of a new phylum - the Nanoarchaeota - that would have diverged before the Crenarchaeota/Euryarchaeota split. Confirming the phylogenetic position of N. equitans is thus crucial for deciphering the history of the archaeal domain.