Green Tea Polyphenols Rescue of Brain Defects Induced by Overexpression of DYRK1A

Individuals with partial HSA21 trisomies and mice with partial MMU16 trisomies containing an extra copy of the DYRK1A gene present various alterations in brain morphogenesis. They present also learning impairments modeling those encountered in Down syndrome. Previous MRI and histological analyses of a transgenic mice generated using a human YAC construct that contains five genes including DYRK1A reveal that DYRK1A is involved, during development, in the control of brain volume and cell density of specific brain regions. Gene dosage correction induces a rescue of the brain volume alterations. DYRK1A is also involved in the control of synaptic plasticity and memory consolidation. Increased gene dosage results in brain morphogenesis defects, low BDNF levels and mnemonic deficits in these mice. Epigallocatechin gallate (EGCG) — a member of a natural polyphenols family, found in great amount in green tea leaves — is a specific and safe DYRK1A inhibitor. We maintained control and transgenic mice overexpressing DYRK1A on two different polyphenol-based diets, from gestation to adulthood. The major features of the transgenic phenotype were rescued in these mice.     

Changes in soil diversity and global activities following invasions of the exotic invasive plant, Amaranthus viridis L., decrease the growth of native sahelian Acacia species

The objectives of this study were to determine whether the invasive plant Amaranthus viridis influenced soil microbial and chemical properties and to assess the consequences of these modifications on native plant growth. The experiment was conducted in Senegal at two sites: one invaded by A. viridis and the other covered by other plant species. Soil nutrient contents as well as microbial community density, diversity and functions were measured. Additionally, five sahelian Acacia species were grown in (1) soil disinfected or not collected from both sites, (2) uninvaded soil exposed to an A. viridis plant aqueous extract and (3) soil collected from invaded and uninvaded sites and inoculated or not with the arbuscular mycorrhizal (AM) fungus Glomus intraradices . The results showed that the invasion of A. viridis increased soil nutrient availability, bacterial abundance and microbial activities. In contrast, AM fungi and rhizobial development and the growth of Acacia species were severely reduced in A. viridis -invaded soil. Amaranthus viridis aqueous extract also exhibited an inhibitory effect on rhizobial growth, indicating an antibacterial activity of this plant extract. However, the inoculation of G. intraradices was highly beneficial to the growth and nodulation of Acacia species. These results highlight the role of AM symbiosis in the processes involved in plant coexistence and in ecosystem management programs that target preservation of native plant diversity.     

Determining the antibiotic resistance potential of the indigenous oral microbiota of humans using a metagenomic approach

Studies of the prevalence and identity of genes encoding resistance to antibiotics in a microbial community are usually carried out on only the cultivable members of the community. However, it is possible to include the as-yet-uncultivable organisms present by adopting a metagenomic approach to such studies. In this investigation, four metagenomic libraries of the oral microbiota were prepared from three groups of 20 adult humans and screened for antibiotic-resistant clones. Clones resistant to tetracycline and amoxycillin were present in all four libraries while gentamicin-resistant clones were found in three of the libraries. The genes encoding tetracycline resistance in the clones were identified and found to be tet(M), tet(O), tet(Q), tet(W), tet37 and tet(A). However, only the first three of these were detected in all three groups of individuals investigated.     

Dissecting the role of the Tir:Nck and Tir:IRTKS/IRSp53 signalling pathways in vivo

Attaching and effacing (A/E) lesions and actin polymerization, the hallmark of enteropathogenic Escherichia coli (EPEC), enterohemorrhagic E. coli (EHEC) and Citrobacter rodentium (CR) infections, are dependent on the effector Tir. Phosphorylation of Tir_EPEC/CR Y474/1 leads to recruitment of Nck and neural Wiskott–Aldrich syndrome protein (N‐WASP) and strong actin polymerization in cultured cells. Tir_EPEC/CR also contains an Asn‐Pro‐Tyr (NPY_454/1) motif, which triggers weak actin polymerization. In EHEC the NPY₄₅₈ actin polymerization pathway is amplified by TccP/EspF_U, which is recruited to Tir via IRSp53 and/or insulin receptor tyrosine kinase substrate (IRTKS). Here we used C. rodentium to investigate the different Tir signalling pathways in vivo. Following infection with wild‐type C. rodentium IRTKS, but not IRSp53, was recruited to the bacterial attachment sites. Similar results were seen after infection of human ileal explants with EHEC. Mutating Y471 or Y451 in Tir_CR abolished recruitment of Nck and IRTKS respectively, but did not affect recruitment of N‐WASP or A/E lesion formation. This suggests that despite their crucial role in actin polymerization in cultured cells the Tir:Nck and Tir:IRTKS pathways are not essential for N‐WASP recruitment or A/E lesion formation in vivo. Importantly, wild‐type C. rodentium out‐competed the tir tyrosine mutants during mixed infections. These results uncouple the Tir:Nck and Tir:IRTKS pathways from A/E lesion formation in vivo but assign them an important in vivo role.     

Mechanism of Phosphorylation-induced Activation of Phospholipase C-γ Isozymes

The lipase activity of most phospholipases C (PLCs) is basally repressed by a highly degenerate and mostly disordered X/Y linker inserted within the catalytic domain. Release of this auto-inhibition is driven by electrostatic repulsion between the plasma membrane and the electronegative X/Y linker. In contrast, PLC-γ isozymes (PLC-γ1 and -γ2) are structurally distinct from other PLCs because multiple domains are present in their X/Y linker. Moreover, although many tyrosine kinases directly phosphorylate PLC-γ isozymes to enhance their lipase activity, the underlying molecular mechanism of this activation remains unclear. Here we define the mechanism for the unique regulation of PLC-γ isozymes by their X/Y linker. Specifically, we identify the C-terminal SH2 domain within the X/Y linker as the critical determinant for auto-inhibition. Tyrosine phosphorylation of the X/Y linker mediates high affinity intramolecular interaction with the C-terminal SH2 domain that is coupled to a large conformational rearrangement and release of auto-inhibition. Consequently, PLC-γ isozymes link phosphorylation to phospholipase activation by elaborating upon primordial regulatory mechanisms found in other PLCs.     

Screening of In Vivo Activated Genes in Enterococcus faecalis during Insect and Mouse Infections and Growth in Urine

Enterococcus faecalis is part of the commensal microbiota of humans and its main habitat is the gastrointestinal tract. Although harmless in healthy individuals, E. faecalis has emerged as a major cause of nosocomial infections. In order to better understand the transformation of a harmless commensal into a life-threatening pathogen, we developed a Recombination-based In Vivo Expression Technology for E. faecalis. Two R-IVET systems with different levels of sensitivity have been constructed in a E. faecalis V583 derivative strain and tested in the insect model Galleria mellonella, during growth in urine, in a mouse bacteremia and in a mouse peritonitis model. Our combined results led to the identification of 81 in vivo activated genes. Among them, the ef_3196/7 operon was shown to be strongly induced in the insect host model. Deletion of this operonic structure demonstrated that this two-component system was essential to the E. faecalis pathogenic potential in Galleria. Gene ef_0377, induced in insect and mammalian models, has also been further analyzed and it has been demonstrated that this ankyrin-encoding gene was also involved in E. faecalis virulence. Thus these R-IVET screenings led to the identification of new E. faecalis factors implied in in vivo persistence and pathogenic potential of this opportunistic pathogen.     

Are Hematopoietic Stem Cells Generated in the Placenta?

In this issue of Cell Stem Cell, the origin of multipotent hematopoietic cells present in the placenta has been assessed in Ncx1(-/-) embryos lacking a functional heart and circulation. Rhodes and colleagues (Rhodes et al., 2008) found lymphoid progenitors in the placenta, as well as in dorsal aorta and yolk sac and vitelline vessels, indicating that they arose in situ.