Association of specific expansins with growth in maize leaves is maintained under environmental, genetic, and developmental sources of variation

We aimed to evaluate whether changes in maize (Zea mays) leaf expansion rate in response to environmental stimuli or developmental gradients are mediated by common or specific expansins, a class of proteins known to enhance cell wall extensibility. Among the 33 maize expansin or putative expansin genes analyzed, 19 were preferentially expressed at some point of the leaf elongation zone and these expansins could be organized into three clusters related to cell division, maximal leaf expansion, and cell wall differentiation. Further analysis of the spatial distribution of expression was carried out for three expansins in leaves displaying a large range of expansion rates due to water deficit, genotype, and leaf developmental stage. With most sources of variation, the three genes showed similar changes in expression and consistent association with changes in leaf expansion. Moreover, our analysis also suggested preferential association of each expansin with elongation, widening, or both of these processes. Finally, using in situ hybridization, expression of two of these genes was increased in load-bearing tissues such as the epidermis and differentiating xylem. Together, these results suggest that some expansins may be preferentially related to elongation and widening after integrating several spatial, environmental, genetic, and developmental cues.     

Dual Effect of Phosphatidyl (4,5)-Bisphosphate PIP2 on Shaker K+ Channels

Phosphatidylinositol (4,5)-bisphosphate (PIP₂) is a phospholipid of the plasma membrane that has been shown to be a key regulator of several ion channels. Functional studies and more recently structural studies of Kir channels have revealed the major impact of PIP₂ on the open state stabilization. A similar effect of PIP₂ on the delayed rectifiers Kv7.1 and Kv11.1, two voltage-gated K⁺ channels, has been suggested, but the molecular mechanism remains elusive and nothing is known on PIP₂ effect on other Kv such as those of the Shaker family. By combining giant-patch ionic and gating current recordings in COS-7 cells, and voltage-clamp fluorimetry in Xenopus oocytes, both heterologously expressing the voltage-dependent Shaker channel, we show that PIP₂ exerts 1) a gain-of-function effect on the maximal current amplitude, consistent with a stabilization of the open state and 2) a loss-of-function effect by positive-shifting the activation voltage dependence, most likely through a direct effect on the voltage sensor movement, as illustrated by molecular dynamics simulations.     

STD and TRNOESY NMR studies for the epitope mapping of the phosphorylation motif of the oncogenic protein beta-catenin recognized by a selective monoclonal antibody

The interaction of the P-beta-Cat(19-44) peptide, a 26 amino acid peptide (K(19)AAVSHWQQQSYLDpSGIHpSGATTTAP(44)) that mimics the phosphorylated beta-Catenin antigen, has been studied with its monoclonal antibody BC-22, by transferred nuclear Overhauser effect NMR spectroscopy (TRNOESY) and saturation transfer difference NMR (STD NMR) spectroscopy. This antibody is specific to diphosphorylated beta-Catenin and does not react with the non-phosphorylated protein. Phosphorylation of beta-Catenin at sites Ser33 and Ser37 on the DSGXXS motif is required for the interaction of beta-Catenin with the ubiquitin ligase SCF(beta-TrCP). beta-TrCP is involved in the ubiquitination and proteasome targeting of the oncogenic protein beta-Catenin, the accumulation of which has been implicated in various human cancers. The three-dimensional structure of the P-beta-Cat(19-44) in the bound conformation was determined by TRNOESY NMR experiments; the peptide adopts a compact structure in the presence of mAb with formation of turns around Trp25 and Gln26, with a tight bend created by the DpS(33)GIHpS(37) motif; the peptide residues (D32-pS37) forming this bend are recognized by the antibody as demonstrated by STD NMR experiments. STD NMR studies provide evidence for the existence of a conformational epitope containing tandem repeats of phosphoserine motifs. The peptide's epitope is predominantly located in the large bend and in the N-terminal segment, implicating bidentate association. These findings are in excellent agreement with a recently published NMR structure required for the interaction of beta-Catenin with the SCF(beta-TrCP) protein.     

Distribution and ecology of the generalist lactic acid bacterium Carnobacterium maltaromaticum in different freshwater habitats: Metabolic and antagonistic abilities

We explored the distribution, metabolic and antagonistic activities of Carnobacterium maltaromaticum, isolated from freshwater locations in Denmark during winter or early spring. This species was widely distributed in such habitats although it was relatively rare in low pH locations. Isolates possessed a diverse metabolism, potentially enabling functional capacities independent of habitat. The intraspecies competition showed a relatively high degree of mostly low-intensity interactions, which overall were not correlated with phylogeny or location. Only a few isolates exhibited broad-spectrum inhibition activity, targeting species from other genera and families, including one isolate that exhibited a broad inhibitory activity due to H₂O₂ production. Bioinformatic analyses revealed that the frequency of bacteriocinogenic systems was low, and only one unmodified bacteriocin, piscicolin 126, correlated with phenotypic antagonistic activity. Furthermore, most potential bacteriocin gene complexes were not complete. Overall, this study showed C. maltaromaticum to be a generalist (nomadic) species with a constant presence in freshwater habitats, especially those with pH values >5. General metabolic properties did not suggest a strong degree of adaptation to the freshwater environment, and bacteriocin-mediated antagonistic activities appeared to play a minimal ecological role.     

Phosphatidylinositol-4,5-Bisphosphate (PIP2) Stabilizes the Open Pore Conformation of the Kv11.1 (hERG) Channel

Phosphatidylinositol-4,5-bisphosphate (PIP₂) is a phospholipid that has been shown to modulate several ion channels, including some voltage-gated channels like Kv11.1 (hERG). From a biophysical perspective, the mechanisms underlying this regulation are not well characterized. From a physiological perspective, it is critical to establish whether the PIP₂ effect is within the physiological concentration range. Using the giant-patch configuration of the patch-clamp technique on COS-7 cells expressing hERG, we confirmed the activating effect of PIP₂. PIP₂ increased the hERG maximal current and concomitantly slowed deactivation. Regarding the molecular mechanism, these increased amplitude and slowed deactivation suggest that PIP₂ stabilizes the channel open state, as it does in KCNE1-KCNQ1. We used kinetic models of hERG to simulate the effects of the phosphoinositide. Simulations strengthened the hypothesis that PIP₂ is more likely stabilizing the channel open state than affecting the voltage sensors. From the physiological aspect, we established that the sensitivity of hERG to PIP₂ comes close to that of KCNE1-KCNQ1 channels, which lies in the range of physiological PIP₂ variations.     

Dental microwear textural analyses to track feeding ecology of reindeer: a comparison of two contrasting populations in Norway

Using dental microwear textural analysis, we aim to explore variations in feeding habits within and between wild reindeer populations (Rangifer tarandus) in Norway. Specimens from the two wild reindeer areas of Knutshø and Hardangervidda were hunted between late August and the end of September 2014, and found to share very similar topological and ecological characteristics (continental alpine tundra). Despite the homogenisation of plant resources at the end of the snow-free period, dental microwear textural analysis on cheek teeth indicates differences in feeding behaviors between the two populations, in that reindeer from Knutshø might display a more “grazing” signal than the ones from Hardangervidda. Such differences in dental microwear textures reflect the differences in feeding habits that could be linked with differences in population density of reindeer. The Knutshø reindeer density is lower than at Hardangervidda, where primary food resources like grasses, sedges, and lichens are less abundant. Analyses also show the differences in gender for the population of Knutshø, but more studies are necessary for the clearest interpretation of data. Our results emphasize the need to explore local variations at a monthly time frame in order to better assess the versatility of dental microwear textures before applying this kind of analysis to either extant or extinct multi-population scales.     

Spatial and temporal ecological diversity amongst Eocene primates of France: evidence from teeth

Diet is of paramount importance in the life of a primate. It is also highly variable, as potential food sources vary in spatial distribution and availability over time. The fossil record, due to its fragmentary nature, offers few possibilities to assess the dietary range of a given primate across its spatial and temporal distribution. Here we focus on three taxa, Leptadapis magnus (Adapidae, Adapiformes), Necrolemur cf. antiquus (Microchoeridae, Omomyiformes), and Pseudoloris parvulus (Microchoeridae, Omomyiformes). These taxa occur at different localities of the Late Eocene in the south of France ranging from MP16 (Robiac, Lavergne; 39 Ma), MP17a (La Bouffie, Euzet, Fons 4; 38 Ma) to MP17b (Perrière; 37 Ma). Diets of fossil taxa are assessed here by dental microwear analysis using a comparative database of 11 species of living strepsirhines. On the whole, leaves were a preferred food for the large-bodied Leptadapis (4-5 kg). However, the diet of this taxon varied from a mix of leaves and fruit at La Bouffie, a closed tropical rain forest environment, to a strictly leaf-eating one in the more open environment of Perrière. Based on body mass (200-350 g) and dental microwear patterns, Necrolemur had a mainly fruit-based diet, perhaps supplemented by insects. However, the comparison of the different localities reveals the dietary range of this small-bodied omomyiform which seems to vary between insects and a much softer diet. Pseudoloris had a diet strictly based on insects. Contrary to Leptadapis or Necrolemur, its diet seems to have been confined to insects whatever the locality considered.