Toxin-based in-vitro selection and its potential application to date palm for resistance to the bayoud Fusarium wilt

Date palm (Phoenix dactylifera L.) is qualified as a 'tree' of great ecological and socio-economical importance in desert oases. Unfortunately, it is being decimated, especially in Morocco and Algeria, by a fusariosis wilt called bayoud and caused by Fusarium oxysporum f. sp. albedinis (Fao). Controlling this disease requires the implementation of an integrated management program. Breeding for resistance is one of the most promising component strategies of this program. Few naturally resistant cultivars with a mediocre fruit quality (dates) are known. Conventional and non-conventional methods are under development and have to use the simplest and easiest methods to screen for resistant individuals. The use of pathogen toxins as selective agents at the tissue culture step might be a source of variability that can lead to the selection of individuals with suitable levels of resistance to the toxin and/or to the pathogen among the genetic material available. Foa produces toxins such as fusaric, succinic, 3-phenyl lactic acids and their derivatives, marasmins and peptidic toxins. These toxins can be used bulked or separately as selective agents. The aim of this contribution was to give a brief overview on toxins and their use as a mean to select resistant lines and to initiate a discussion about the potential use of this approach for the date palm-Foa pathosystem. This review does not pretend to be comprehensive or exhaustive and was prepared mainly to highlight the potential use of Foa toxins for selecting date palm individuals with a suitable resistance level to bayoud using toxin-based selective media.     

TRIM family proteins: retroviral restriction and antiviral defence

Members of the tripartite motif (TRIM) protein family are involved in various cellular processes, including cell proliferation, differentiation, development, oncogenesis and apoptosis. Some TRIM proteins display antiviral properties, targeting retroviruses in particular. The potential activity of TRIM19, better known as promyelocytic leukaemia protein, against several viruses has been well documented and, recently, TRIM5alpha has been identified as the factor responsible for the previously described Lv1 and Ref1 antiretroviral activities. There is also evidence indicating that other TRIM proteins can influence viral replication. These findings are reviewed here, and the possibility that TRIMs represent a new and widespread class of antiviral proteins involved in innate immunity is also considered.     

Parkinson's disease: from causes to mechanisms

Parkinson's disease (PD) is a common age-related, progressive neurodegenerative disease of unknown etiology. Environmental factors have long been suspected to participate in the pathogenesis of PD due to the existence of neurotoxins that preferentially damage the dopaminergic nigrostriatal pathway. In the past few years, novel insights into the degenerative process have been provided by the discovery of genes responsible for rare monogenic parkinsonian syndromes. Compelling evidence is accumulating, suggesting that the products of several of these genes can interact with environmental toxins and intervene in molecular pathways controlling the functional integrity of mitochondria.     

Polarized distribution of inducible nitric oxide synthase regulates activity in intestinal epithelial cells

Inducible nitric oxide synthase (iNOS) functions as a homodimer. In cell extracts, iNOS molecules partition both in cytosolic and particulate fractions, indicating that iNOS exists as soluble and membrane associated forms. In this study, iNOS features were investigated in human intestinal epithelial cells stimulated with cytokines and in duodenum from mice exposed to flagellin. Our experiments indicate that iNOS is mainly associated with the particulate fraction of cell extracts. Confocal microscopy showed a preferential localization of iNOS at the apical pole of intestinal epithelial cells. In particulate fractions, iNOS dimers were more abundant than in the cytosolic fraction. Similar observations were seen in mouse duodenum samples. These results suggest that, in epithelial cells, iNOS activity is regulated by localization-dependent processes.     

The RNA recognition motif, a plastic RNA-binding platform to regulate post-transcriptional gene expression

The RNA recognition motif (RRM), also known as RNA-binding domain (RBD) or ribonucleoprotein domain (RNP) is one of the most abundant protein domains in eukaryotes. Based on the comparison of more than 40 structures including 15 complexes (RRM-RNA or RRM-protein), we reviewed the structure-function relationships of this domain. We identified and classified the different structural elements of the RRM that are important for binding a multitude of RNA sequences and proteins. Common structural aspects were extracted that allowed us to define a structural leitmotif of the RRM-nucleic acid interface with its variations. Outside of the two conserved RNP motifs that lie in the center of the RRM beta-sheet, the two external beta-strands, the loops, the C- and N-termini, or even a second RRM domain allow high RNA-binding affinity and specific recognition. Protein-RRM interactions that have been found in several structures reinforce the notion of an extreme structural versatility of this domain supporting the numerous biological functions of the RRM-containing proteins.     

Differential trafficking of GluR7 kainate receptor subunit splice variants

Kainate receptors (KARs) are heteromeric ionotropic glutamate receptors that play a variety of roles in the regulation of synaptic network activity. The function of glutamate receptors (GluRs) is highly dependent on their surface density in specific neuronal domains. Alternative splicing is known to regulate surface expression of GluR5 and GluR6 subunits. The KAR subunit GluR7 exists under different splice variant isoforms in the C-terminal domain (GluR7a and GluR7b). Here we have studied the trafficking of GluR7 splice variants in cultured hippocampal neurons from wild-type and KAR mutant mice. We have found that alternative splicing regulates surface expression of GluR7-containing KARs. GluR7a and GluR7b differentially traffic from the ER to the plasma membrane. GluR7a is highly expressed at the plasma membrane, and its trafficking is dependent on a stretch of positively charged amino acids also found in GluR6a. In contrast, GluR7b is detected at the plasma membrane at a low level and retained mostly in the endoplasmic reticulum (ER). The RXR motif of GluR7b does not act as an ER retention motif, at variance with other receptors and ion channels, but might be involved during the assembly process. Like GluR6a, GluR7a promotes surface expression of ER-retained subunit splice variants when assembled in heteromeric KARs. However, our results also suggest that this positive regulation of KAR trafficking is limited by the ability of different combinations of subunits to form heteromeric receptor assemblies. These data further define the complex rules that govern membrane delivery and subcellular distribution of KARs.     

PRAM-1 potentiates arsenic trioxide-induced JNK activation

The promyelocytic leukemia RARalpha target gene encoding an adaptor molecule-1 (PRAM-1) is involved in a signaling pathway induced by retinoic acid in acute promyelocytic leukemia (APL) cells. To better understand the function of PRAM-1, we have undertaken the identification of its partners through a yeast two-hybrid screen. Here, we show that the proline-rich domain of PRAM-1 interacted with the Src homology 3 (SH3) domain of hematopoietic progenitor kinase 1 (HPK-1)-interacting protein of 55 kDa (HIP-55, also called SH3P7 and Abp1) known to stimulate the activity of HPK-1 and c-Jun N-terminal kinase (JNK). Overexpression of PRAM-1 in the NB4 APL cell line increased arsenic trioxide-induced JNK activation through a caspase 3-like-dependent activity. Dissociation of the SH3 domain from the rest of the HIP-55 protein was observed in the NB4 APL cell line treated with arsenic trioxide due to specific cleavage by caspase 3-like enzymes. The cleavage of HIP-55 correlated with the induction of PRAM-1 mRNA and protein expression. Taken together, our results suggest that the caspase 3-cleaved SH3 domain of HIP-55 is likely involved in PRAM-1-mediated JNK activation upon arsenic trioxide-induced differentiation of NB4 cells.     

Role of the lid hydrophobicity pattern in pancreatic lipase activity

Pancreatic lipase is a soluble globular protein that must undergo structural modifications before it can hydrolyze oil droplets coated with bile salts. The binding of colipase and movement of the lipase lid open access to the active site. Mechanisms triggering lid mobility are unclear. The *KNILSQIVDIDGI* fragment of the lid of the human pancreatic lipase is predicted by molecular modeling to be a tilted peptide. Tilted peptides are hydrophobicity motifs involved in membrane fusion and more globally in perturbations of hydrophobic/hydrophilic interfaces. Analysis of this lid fragment predicts no clear consensus of secondary structure that suggests that its structure is not strongly sequence determined and could vary with environment. Point mutations were designed to modify the hydrophobicity profile of the [240-252] fragment and their consequences on the lipase-mediated catalysis were tested. Two mutants, in which the tilted peptide motif was lost, also have poor activity on bile salt-coated oil droplets and cannot be reactivated by colipase. Conversely, one mutant in which a different tilted peptide is created retains colipase dependence. These results suggest that the tilted hydrophobicity pattern of the [240-252] fragment is neither important for colipase binding to lipase, nor for interfacial binding but is important to trigger the maximal catalytic efficiency of lipase in the presence of bile salt.     

A high-frequency lung injury mechanism in blunt thoracic impact

When a mechanical load is applied very rapidly to the thoracic wall, part of the internal damage is suspected to be due to a "high-frequency" injury mechanism, that is, a phenomenon in which waves are involved. This paper addresses a specific high-frequency mechanism for lung injury in which a stress wave is generated through rapid acceleration of the body wall. Displacement-related injuries, which are rather "low-frequency" phenomena, are not considered. The present work was done in the context of assessing behind armor blunt trauma (injury to thoracic organs occurring when a bullet is stopped by a body armor) through mathematical modeling. One aspect of the thorax response to high-speed blunt impact and an associated injury mechanism are investigated based on an idealized model of thorax and a set of computations presented in previous papers. The injury mechanism considered elucidates a possible mathematical relationship between the acceleration at the surface of the thoracic wall and the occurrence of lung injury.