Cellular and molecular basis of decision‐making

People think they are in control of their own decisions: what to eat or drink, whom to marry or pick a fight with, where to live, what to buy. Behavioural economists and neurophysiologists have long studied decision‐making behaviours. However, these behaviours have only recently been studied through the light of molecular genetics. Here, we review recent research in mice, Drosophila melanogaster and Caenorhabditis elegans, that analyses the molecular and cellular mechanisms underlying decision‐making. These studies interrogate decision‐making about food, sexual behaviour, aggression or foraging strategies, and add molecular and cell biology understanding onto the consilience of brain and decision.     

Three‐dimensional structure of a sugar N‐formyltransferase from Francisella tularensis

N‐formylated sugars have been observed on the O‐antigens of such pathogenic Gram‐negative bacteria as Campylobacter jejuni and Francisella tularensis. Until recently, however, little was known regarding the overall molecular architectures of the N‐formyltransferases that are required for the biosynthesis of these unusual sugars. Here we demonstrate that the protein encoded by the wbtj gene from F. tularensis is an N‐formyltransferase that functions on dTDP‐4‐amino‐4,6‐dideoxy‐d ‐glucose as its substrate. The enzyme, hereafter referred to as WbtJ, demonstrates a strict requirement for N¹⁰‐formyltetrahydrofolate as its carbon source. In addition to the kinetic analysis, the three‐dimensional structure of the enzyme was solved in the presence of dTDP‐sugar ligands to a nominal resolution of 2.1 Å. Each subunit of the dimeric enzyme is dominated by a “core” domain defined by Met 1 to Ser 185. This core motif harbors the active site residues. Following the core domain, the last 56 residues fold into two α‐helices and a β‐hairpin motif. The hairpin motif is responsible primarily for the subunit:subunit interface, which is characterized by a rather hydrophobic pocket. From the study presented here, it is now known that WbtJ functions on C‐4′ amino sugars. Another enzyme recently investigated in the laboratory, WlaRD, formylates only C‐3′ amino sugars. Strikingly, the quaternary structures of WbtJ and WlaRD are remarkably different. In addition, there are several significant variations in the side chains that line their active site pockets, which may be important for substrate specificity. Details concerning the kinetic and structural properties of WbtJ are presented.     

Spatiotemporal analysis of mycolactone distribution in vivo reveals partial diffusion in the central nervous system

Mycobacterium ulcerans, the causative agent of Buruli ulcer (BU) disease, is unique amongst human pathogens in its capacity to produce a lipid toxin called mycolactone. While previous studies have demonstrated that bacterially-released mycolactone diffuses beyond infection foci, the spatiotemporal distribution of mycolactone remained largely unknown. Here, we used the zebrafish model to provide the first global kinetic analysis of mycolactone’s diffusion in vivo, and multicellular co-culture systems to address the critical question of the toxin’s access to the brain.Zebrafish larvae were injected with a fluorescent-derivative of mycolactone to visualize the in vivo diffusion of the toxin from the peripheral circulation. A rapid, body-wide distribution of mycolactone was observed, with selective accumulation in tissues near the injection site and brain, together with an important excretion through the gastro-intestinal tract. Our conclusion that mycolactone reached the central nervous system was reinforced by an in cellulo model of human blood brain barrier and a mouse model of M. ulcerans-infection.Here we show that mycolactone has a broad but heterogenous profile of distribution in vivo. Our investigations in vitro and in vivo support the view that a fraction of bacterially-produced mycolactone gains access to the central nervous system. The relative persistence of mycolactone in the bloodstream suggests that assays of circulating mycolactone are relevant for BU disease monitoring and treatment optimization.     

Chromosome Partitioning in Escherichia coli in the Absence of Dam-Directed Methylation

Escherichia coli dam mutants, lacking the GATC DNA methylase, do not produce anucleate cells at high frequencies, suggesting that hemimethylation of the chromosome origin of replication, oriC, is not essential for correct chromosome partitioning.     

Regulation of Toll-like receptor 4-mediated immune responses through Pasteurella multocida toxin-induced G protein signalling

Background

Lipopolysaccharide (LPS)-triggered Toll-like receptor (TLR) 4-signalling belongs to the key innate defence mechanisms upon infection with Gram-negative bacteria and triggers the subsequent activation of adaptive immunity. There is an active crosstalk between TLR4-mediated and other signalling cascades to secure an effective immune response, but also to prevent excessive inflammation. Many pathogens induce signalling cascades via secreted factors that interfere with TLR signalling to modify and presumably escape the host response. In this context heterotrimeric G proteins and their coupled receptors have been recognized as major cellular targets. Toxigenic strains of Gram-negative Pasteurella multocida produce a toxin (PMT) that constitutively activates the heterotrimeric G proteins G??_q, G??₁₃ and G??_i independently of G protein-coupled receptors through deamidation. PMT is known to induce signalling events involved in cell proliferation, cell survival and cytoskeleton rearrangement.

Results

Here we show that the activation of heterotrimeric G proteins through PMT suppresses LPS-stimulated IL-12p40 production and eventually impairs the T cell-activating ability of LPS-treated monocytes. This inhibition of TLR4-induced IL-12p40 expression is mediated by G??_i-triggered signalling as well as by G?|?-dependent activation of PI3kinase and JNK. Taken together we propose the following model: LPS stimulates TLR4-mediated activation of the NF?B-pathway and thereby the production of TNF-??, IL-6 and IL-12p40. PMT inhibits the production of IL-12p40 by G??_i-mediated inhibition of adenylate cyclase and cAMP accumulation and by G?|?-mediated activation of PI3kinase and JNK activation.

Conclusions

On the basis of the experiments with PMT this study gives an example of a pathogen-induced interaction between G protein-mediated and TLR4-triggered signalling and illustrates how a bacterial toxin is able to interfere with the host??s immune response.     

Branchial and extra-branchial ammonia excretion in goldfish (Carassius auratus) following thermally induced gill remodeling

Under cold acclimated conditions, goldfish (Carassius auratus) express an interlamellar cell mass (ILCM) which limits diffusive ion loss but may also impede branchial ammonia excretion (J(amm)). In the present study, goldfish were subjected to a 2-week 5 or 25 °C acclimation in order to modulate the degree of ILCM gill coverage and determine potential effects on J(amm). 25 °C-fish displayed gill coverage which was significantly lower than the 5 °C-fish, though the ILCM was not completely absent in these fish. 5 °C-fish demonstrated J(amm) values approximately 60% lower than those of 25 °C-fish. The magnitude of anterior (branchial) J(amm) strongly correlated with gill coverage (r(2)=0.83), suggesting that the ILCM may impede branchial J(amm). Divided chamber experiments demonstrated that relative to the 25 °C-fish, 5 °C-fish relied more upon posterior routes of excretion. In response to high external ammonia (HEA; 1.5mM NH(4)HCO(3)) exposures, 25 °C-fish displayed ammonia uptake while 5 °C-fish maintained excretion against HEA, suggesting that the ILCM may act as a barrier preventing ammonia uptake. In summary, the ILCM appears to impede branchial J(amm), such that 5 °C-rely more on extra-branchial routes of excretion. We hypothesize that gill remodeling in these fish may be intimately tied to physiological adjustments on the whole-body scale.     

Walteriella n. g. (Monogenoidea: Dactylogyridae) from the gills of pimelodid catfishes (Siluriformes: Pimelodidae) from the Peruvian Amazonia based on morphological and molecular data

Systematic Parasitology - On the basis of morphological and molecular data, Walteriella n. g. is proposed to accommodate the dactylogyrid parasites Walteriella conica n. sp. (type-species) from the...     

Damming reduced the functional richness and caused the shift to a new functional state of the phytoplankton in a subtropical region

Hydrobiologia - We analyzed the effect of damming on the temporal patterns of the composition and richness of phytoplankton Reynolds functional groups (RFG) from a subtropical floodplain, together...