Ant-based swarming with positionless micro air vehicles for communication relay

Swarming without positioning information is interesting in application-oriented systems because it alleviates the need for sensors which are dependent on the environment, expensive in terms of energy, cost, size and weight, or unusable at useful ranges for real-life scenarios. This principle is applied to the development of a swarm of micro air vehicles (SMAVs) for the deployment of ad hoc wireless communication networks (SMAVNETs) between ground users in disaster areas. Rather than relying on positioning information, MAVs rely on local communication with immediate neighbors and proprioceptive sensors which provide heading, speed and altitude. To solve the challenging task of designing agent controllers to achieve the swarm behavior of the SMAVNET, inspiration is taken from army ants which are capable of laying and maintaining pheromone paths leading from their nest to food sources in nature. This is analogous to the deployment of communication pathways between multiple ground users. However, instead of being physically deposited in the air or on a map, pheromone is virtually deposited on the MAVs using local communication. This approach is investigated in 3D simulation in a simplified scenario with two ground users.     

Direct interaction enables cross-talk between ionotropic and group I metabotropic glutamate receptors

Functional interplay between ionotropic and metabotropic receptors frequently involves complex intracellular signaling cascades. The group I metabotropic glutamate receptor mGlu5a co-clusters with the ionotropic N-methyl-d-aspartate (NMDA) receptor in hippocampal neurons. In this study, we report that a more direct cross-talk can exist between these types of receptors. Using bioluminescence resonance energy transfer in living HEK293 cells, we demonstrate that mGlu5a and NMDA receptor clustering reflects the existence of direct physical interactions. Consequently, the mGlu5a receptor decreased NMDA receptor current, and reciprocally, the NMDA receptor strongly reduced the ability of the mGlu5a receptor to release intracellular calcium. We show that deletion of the C terminus of the mGlu5a receptor abolished both its interaction with the NMDA receptor and reciprocal inhibition of the receptors. This direct functional interaction implies a higher degree of target-effector specificity, timing, and subcellular localization of signaling than could ever be predicted with complex signaling pathways.     

The HIV-1 envelope glycoprotein gp120 features four heparan sulfate binding domains, including the co-receptor binding site

It is well established that the human immunodeficiency virus-1 envelope glycoprotein surface unit, gp120, binds to cell-associated heparan sulfate (HS). Virus infectivity is increased by such interaction, and a variety of soluble polyanions efficiently neutralize immunodeficiency virus-1 in vitro. This interaction has been mainly attributed to the gp120 V3 loop. However, although evidence suggested that this particular domain does not fully recapitulate the binding activity of the protein, the ability of HS to bind to other regions of gp120 has not been completely addressed, and the exact localizations of the polysaccharide binding sites are not known. To investigate in more detail the structural basis of the HS-gp120 interaction, we used a mapping strategy and compared the heparin binding activity of wild type and mutant gp120 using surface plasmon resonance-based binding assays. Four heparin binding domains (1-4) were identified in the V2 and V3 loops, in the C-terminal domain, and within the CD4-induced bridging sheet. Interestingly, three of them were found in domains of the protein that undergo structural changes upon binding to CD4 and are involved in co-receptor recognition. In particular, Arg(419), Lys(421), and Lys(432), which directly interact with the co-receptor, are targeted by heparin. This study provides a complete account of the gp120 residues involved in heparin binding and identified several binding surfaces that constitute potential target for viral entry inhibition.     

Flavonoids redirect PIN-mediated polar auxin fluxes during root gravitropic responses

The rate, polarity, and symmetry of the flow of the plant hormone auxin are determined by the polar cellular localization of PIN-FORMED (PIN) auxin efflux carriers. Flavonoids, a class of secondary plant metabolites, have been suspected to modulate auxin transport and tropic responses. Nevertheless, the identity of specific flavonoid compounds involved and their molecular function and targets in vivo are essentially unknown. Here we show that the root elongation zone of agravitropic pin2/eir1/wav6/agr1 has an altered pattern and amount of flavonol glycosides. Application of nanomolar concentrations of flavonols to pin2 roots is sufficient to partially restore root gravitropism. By employing a quantitative cell biological approach, we demonstrate that flavonoids partially restore the formation of lateral auxin gradients in the absence of PIN2. Chemical complementation by flavonoids correlates with an asymmetric distribution of the PIN1 protein. pin2 complementation probably does not result from inhibition of auxin efflux, as supply of the auxin transport inhibitor N-1-naphthylphthalamic acid failed to restore pin2 gravitropism. We propose that flavonoids promote asymmetric PIN shifts during gravity stimulation, thus redirecting basipetal auxin streams necessary for root bending.     

Denitration of 2,4,6-trinitrotoluene by <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> ESA-5 in the presence of ferrihydrite

Denitration of 2,4,6-trinitrotoluene (TNT) was evaluated in oxygen-depleted enrichment cultures. These cultures were established starting with an uncontaminated or a TNT-contaminated soil inoculum and contained TNT as sole nitrogen source. Incubations were carried out in the presence or absence of ferrihydrite. A significant release of nitrite was observed in the liquid culture containing TNT, ferrihydrite, and inoculum from a TNT-contaminated soil. Under these conditions, Pseudomonas aeruginosa was the predominant bacterium in the enrichment, leading to the isolation of P. aeruginosa ESA-5 as a pure strain. The isolate had TNT denitration capabilities as confirmed by nitrite release in oxygen-depleted cultures containing TNT and ferrihydrite. In addition to reduced derivatives of TNT, several unidentified metabolites were detected. Concomitant to a decrease of TNT concentration, a release of nitrite was observed. The concentration of nitrite peaked and then it slowly decreased. In the absence of TNT, the drop in the concentration of nitrite in oxygen-depleted cultures was lower when ferrihydrite was provided, suggesting that ferrihydrite inhibited the utilization of nitrite by P. aeruginosa ESA-5.     

Long-term drought modifies the fundamental relationships between light exposure, leaf nitrogen content and photosynthetic capacity in leaves of the lychee tree (Litchi chinensis)

Drought has dramatic negative effects on plants' growth and crop productivity. Although some of the responses and underlying mechanisms are still poorly understood, there is increasing evidence that drought may have a negative effect on photosynthetic capacity. Biochemical models of leaf photosynthesis coupled with models of radiation transfer have been widely used in ecophysiological studies, and, more recently, in global change modeling. They are based on two fundamental relationships at the scale of the leaf: (i) nitrogen content-light exposure and (ii) photosynthetic capacity-nitrogen content. Although drought is expected to increase in many places across the world, such models are not adapted to drought conditions. More specifically, the effects of drought on the two fundamental relationships are not well documented. The objective of our study was to investigate the effects of a long-term drought imposed slowly on the nitrogen content and photosynthetic capacity of leaves similarly exposed to light, from 3-year-old lychee trees cv. Kwa? Mi. Leaf nitrogen and non-structural carbohydrate concentrations were measured along with gas exchanges and the light-saturated rate of photosynthetic electron transport (J(max)) after a 5.5-month-long period of drought. Leaf nitrogen content on a mass basis remained stable, while the leaf mass-to-area ratio (LMA) increased with increasing water stress. Consequently, the leaf nitrogen content on an area basis (N(a)) increased in a non-linear fashion. The starch content decreased, while the soluble sugar content increased. Stomata closed and net assimilation decreased to zero, while J(max) and the ratio J(max)/N(a) decreased with increasing water stress. The drought-associated decrease in photosynthetic capacity can be attributed to downregulation of photosynthetic electron transport and to reallocation of leaf nitrogen content. It is concluded that modeling photosynthesis in drought conditions will require, first, the modeling of the effect of drought on LMA and J(max).     

Pleiotropy in the melanocortin system, coloration and behavioural syndromes

In vertebrates, melanin-based coloration is often associated with variation in physiological and behavioural traits. We propose that this association stems from pleiotropic effects of the genes regulating the synthesis of brown to black eumelanin. The most important regulators are the melanocortin 1 receptor and its ligands, the melanocortin agonists and the agouti-signalling protein antagonist. On the basis of the physiological and behavioural functions of the melanocortins, we predict five categories of traits correlated with melanin-based coloration. A review of the literature indeed reveals that, as predicted, darker wild vertebrates are more aggressive, sexually active and resistant to stress than lighter individuals. Pleiotropic effects of the melanocortins might thus account for the widespread covariance between melanin-based coloration and other phenotypic traits in vertebrates.     

Relaxivities of paramagnetic liposomes: on the importance of the chain type and the length of the amphiphilic complex

Nuclear magnetic relaxation dispersion (NMRD) profiles of unilamellar DPPC liposomes incorporating Gd-DTPA-bisamides with alkyl chains of 12 to 18 C atoms in their external and internal layers were recorded in order to study the influence that the chain length and structure of Gd-bisamides incorporated in the liposomal membrane have on their proton relaxivity. The NMRD profiles recorded at 310 K show that the relaxivity reaches a minimum value when the carbon chain lengths of the phospholipid and of the Gd complex match and is at a maximum in the presence of a carbon-carbon double bond. For these DPPC paramagnetic liposomes, the longer the aliphatic chains of the complex, the larger will be its immobilization in the membrane. In addition, the presence of an unsaturated carbon-carbon bond in the alkyl chain of the Gd complex induces an increase of its mobility and of its water exchange rate with, as a result, a much greater efficiency as an MRI contrast agent.     

Drosophila retinal pigment cell death is regulated in a position-dependent manner by a cell memory gene

The stereotyped organization of the Drosophila compound eye depends on the elimination by apoptosis of about 25% of the inter-ommatidial pigment cell precursors (IOCs) during metamorphosis. This program of cell death is under antagonistic effects of the Notch and the EGFR pathways. In addition, uncharacterized positional cues may underlie death versus survival choices among IOCs. Our results provide new genetic evidences that cell death is regulated in a position- dependent manner in the eye. We show that mutations in Trithorax-like (Trl) and lola-like/batman specifically block IOC death during eye morphogenesis. These genes share characteristics of both Polycomb-Group and trithorax-Group genes, in that they are required for chromatin-mediated repression and activation of Hox genes. However, Trl function in triggering IOC death is independent from a function in repressing Hox gene expression during eye development. Analysis of mosaic ommatidiae containing Trl mutant cells revealed that Trl function for IOC death is required in cone cells. Strikingly, cell death suppression in Trl mutants depends on the position of IOCs. Our results further support a model whereby death of IOCs on the oblique sides of ommatidiae requires Trl-dependent reduction of a survival signal, or an increase of a death signal, emanating from cone cells. Trl does not have the same effect on horizontal IOCs whose survival seems to involve additional topological constraints.