A caterpillar (Callopistria floridensis G. (Lepidoptera: Noctuidae)) accumulates arsenic from an arsenic‐hyperaccumulating fern (Pteris vittata L.).

1. The consumption of arsenic is toxic to most biota. However, a noctuid caterpillar was recently reported feeding on a plant known to hyperaccumulate arsenic. 2. The aim of this study was to investigate the effects of arsenic‐rich Pteris vittata L. consumption by Callopistria floridensis G., and measure differences in arsenic concentrations at various stages of development (larval and adult), and associated with exuviae and frass. 3. Callopistria floridensis accumulated extraordinary concentrations of arsenic. The relative accumulation of arsenic was highest in exuviae and larvae. Larvae invariably preferred P. vittata grown on low arsenic soil to P. vittata grown on higher soil arsenic concentrations, and appeared able to selectively forage on lower arsenic concentrations within each treatment. 4. These findings show that C. floridensis is tolerant of arsenic, and successfully develops to adulthood containing elevated concentrations of arsenic. Callopistria floridensis represents the only known terrestrial animal capable of accumulating arsenic, and may have developed novel physiological and behavioural adaptations to regulate the negative effects of arsenic.     

Phytosphingosine-phosphate is a signal for AtMPK6 activation and Arabidopsis response to chilling

? Long-chain bases (LCBs) are pleiotropic sphingolipidic signals in eukaryotes. We investigated the source and function of phytosphingosine-1-phosphate (PHS-P), a phospho-LCB rapidly and transiently formed in Arabidopsis thaliana on chilling. ? PHS-P was analysed by thin-layer chromatography following in?vivo metabolic radiolabelling. Pharmacological and genetic approaches were used to identify the sphingosine kinase isoforms involved in cold-responsive PHS-P synthesis. Gene expression, mitogen-activated protein kinase activation and growth phenotypes of three LCB kinase mutants (lcbk1, sphk1 and lcbk2) were studied following cold exposure. ? Chilling provoked the rapid and transient formation of PHS-P in Arabidopsis cultured cells and plantlets. Cold-evoked PHS-P synthesis was reduced by LCB kinase inhibitors and abolished in the LCB kinase lcbk2 mutant, but not in lcbk1 and sphk1 mutants. lcbk2 presented a constitutive AtMPK6 activation at 22°C. AtMPK6 activation was also triggered by PHS-P treatment independently of PHS/PHS-P balance. lcbk2 mutants grew comparably with wild-type plants at 22 and 4°C, but exhibited a higher root growth at 12°C, correlated with an altered expression of the cold-responsive DELLA gene RGL3. ? Together, our data indicate a function for LCBK2 in planta. Furthermore, they connect PHS-P formation with plant response to cold, expanding the field of LCB signalling in plants.     

Epithelial morphogenesis in embryos: asymmetries, motors and brakes

Epithelial cells play a central role in many embryonic morphogenetic processes, during which they undergo highly coordinated cell shape changes. Here, we review some common principles that have recently emerged through genetic and cellular analyses performed mainly with invertebrate genetic models, focusing on morphogenetic processes involving epithelial sheets. All available data argue that myosin II is the main motor that induces cell shape changes during morphogenesis. We discuss the control of myosin II activity during epithelial morphogenesis, as well as the recently described involvement of microtubules in this process. Finally, we examine how forces unleashed by myosin II can be measured, how embryos use specific brakes to control molecular motors and the potential input of mechano-sensation in morphogenesis.     

Preliminary dielectric measurement and analysis protocol for determining the melting temperature and binding energy of short sequences of DNA in solution

Measurement of the real dielectric constant of bulk buffer solutions containing short sequences of DNA as a function of temperature through the DNA melting or denaturiztion transition can be used to determine melting temperatures, T(m), and to estimate the binding energy of the complimentary strands. We describe a preliminary dielectric measurement and analysis protocol to determine these parameters and its application to two known short sequences. The relative real dielectric constant for the bulk solutions was determined over the frequency range of 50 Hz-20 kHz and temperature range of <40-65 degrees C. The measurements were performed on dilute solutions and utilized low electric field strengths. Based on fits to the data by modified sigmoid functions, the melting temperatures, width of transition, and binding energy for the two sequences in solution were estimated. It was observed that the order of the transition appeared to be second order. The results were then compared against predictions of a number of models from the literature that provide theoretical estimates for the melting temperatures of known short sequences of DNA.     

Cooperative Anti-Invasive Effect of Cdc42/Rac1 Activation and ROCK Inhibition in SW620 Colorectal Cancer Cells with Elevated Blebbing Activity

Rho GTPases are key regulators of tumour cell invasion and therefore constitute attractive targets for the design of anticancer agents. Several strategies have been developed to modulate their increased activities during cancer progression. Interestingly, none of these approaches took into account the existence of the well-known antagonistic relationship between RhoA and Rac1. In this study, we first compared the invasiveness of a collection of colorectal cancer cell lines with their RhoA, Rac1 and Cdc42 activities. A marked decrease of active Cdc42 and Rac1 correlated with the high invasive potential of the cell lines established from metastatic sites of colorectal adenocarcinoma (LoVo, SKCo1, SW620 and CoLo205). Conversely, no correlation between RhoA activity and invasiveness was detected, whereas the activity of its kinase effector ROCK was higher in cancer cell lines with a more invasive phenotype. In addition, invasiveness in these colon cancer cell lines was correlated with a typical round and blebbing morphology. We then tested whether treatment with PDGF to restore Cdc42 and Rac1 activities and/or with Y27632, a chemical inhibitor of ROCK, could decrease the invasiveness of SW620 cells. The association of both treatments substantially decreased the invasive potential of SW620 cells and this effect was accompanied by loss of membrane blebbing, restoration of a more elongated cell morphology and re-establishment of E-cadherin-dependent adherens junctions. This study paves the road to the development of therapeutic strategies in which different Rho GTPase modulators are combined to modulate the cross-talk between Rho GTPases and their specific input in metastatic progression.     

N-3 long chain polyunsaturated fatty acids: a nutritional tool to prevent insulin resistance associated to type 2 diabetes and obesity?

n-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA), mainly eicosapentaenoic acid (EPA, 20:5 n-3) and docosahexaenoic acid (DHA, 22:6 n-3), are present in mammal tissues both from endogenous synthesis from desaturation and elongation of 18:3 n-3 and/or from dietary origin (marine products and fish oils). In rodents in vivo, n-3 LC-PUFA have a protective effect against high fat diet induced insulin resistance. Such an effect is explained at the molecular level by the prevention of many alterations of insulin signaling induced by a high fat diet. Indeed, the protective effect of n-3 LC-PUFA results from the following: (a) the prevention of the decrease of phosphatidyl inositol 3' kinase (PI3 kinase) activity and of the depletion of the glucose transporter protein GLUT4 in the muscle; (b) the prevention of the decreased expression of GLUT4 in adipose tissue. In addition, n-3 LC-PUFA inhibit both the activity and expression of liver glucose-6-phosphatase which could explain the protective effect with respect to the excessive hepatic glucose output induced by a high fat diet. n-3 LC-PUFA also decrease muscle intramyofibrillar triglycerides and liver steatosis. This last effect results on the one hand, from a decreased expression of lipogenesis enzymes and of delta 9 desaturase (via a depleting effect on sterol response element binding protein 1c (SREBP-1c). On the other hand, n-3 LC-PUFA stimulate fatty acid oxidation in the liver (via the activation of peroxisome proliferator activated receptor alpha (PPAR-alpha)). In patients with type 2 diabetes, fish oil dietary supplementation fails to reverse insulin resistance for unclear reasons, but systematically decreases plasma triglycerides. Conversely, in healthy humans, fish oil has many physiological effects. Indeed, fish oil reduces insulin response to oral glucose without altering the glycaemic response, abolishes extraggression at times of mental stress, decreases the activation of sympathetic activity during mental stress and also decreases plasma triglycerides. These effects are encouraging in the perspective of prevention of insulin resistance but further clinical and basic studies must be designed to confirm and complete our knowledge in this field.     

Geranylgeranyl switching regulates GDI-Rab GTPase recycling

Rab GTPases, key regulators of membrane targeting and fusion, require the covalent attachment of geranylgeranyl lipids to their C terminus for function. To elucidate the role of lipid in Rab recycling, we have determined the crystal structure of Rab guanine nucleotide dissociation inhibitor (alphaGDI) in complex with a geranylgeranyl (GG) ligand (H(2)N-Cys-(S-GG)-OMe). The lipid is bound beneath the Rab binding platform in a shallow hydrophobic groove. Mutation of the binding pocket in the brain-specific alphaGDI leads to mental retardation. Strikingly, lipid binding acts through a conserved allosteric switching mechanism to promote release of the GDI-Rab[GDP] complex from the membrane.