EARLY RESPONSIVE TO DEHYDRATION 15, a negative regulator of abscisic acid responses in Arabidopsis

EARLY RESPONSIVE TO DEHYDRATION 15 (ERD15) is rapidly induced in response to various abiotic and biotic stress stimuli in Arabidopsis (Arabidopsis thaliana). Modulation of ERD15 levels by overexpression or RNAi silencing altered the responsiveness of the transgenic plants to the phytohormone abscisic acid (ABA). Overexpression of ERD15 reduced the ABA sensitivity of Arabidopsis manifested in decreased drought tolerance and in impaired ability of the plants to increase their freezing tolerance in response to this hormone. In contrast, RNAi silencing of ERD15 resulted in plants that were hypersensitive to ABA and showed improved tolerance to both drought and freezing, as well as impaired seed germination in the presence of ABA. The modulation of ERD15 levels not only affected abiotic stress tolerance but also disease resistance: ERD15 overexpression plants showed improved resistance to the bacterial necrotroph Erwinia carotovora subsp. carotovora accompanied with enhanced induction of marker genes for systemic acquired resistance. We propose that ERD15 is a novel mediator of stress-related ABA signaling in Arabidopsis.     

Population genetic structure of the dengue mosquito Aedes aegypti in Venezuela

The mosquito Aedes aegypti is the main vector of dengue in Venezuela. The genetic structure of this vector was investigated in 24 samples collected from eight geographic regions separated by up to 1160 km. We examined the distribution of a 359-basepair region of the NADH dehydrogenase subunit 4 mitochondrial gene among 1144 Ae. aegypti from eight collections. This gene was amplified by the polymerase chain reaction and tested for variation using single strand conformation polymorphism analysis. Seven haplotypes were detected throughout Venezuela and these were sorted into two clades. Significant differentiation was detected among collections and these were genetically isolated by distance.     

Phenotypic characterization of transgenic mice harboring Nf1+/- or Nf1-/- osteoclasts in otherwise Nf1+/+ background

Skeletal abnormalities in neurofibromatosis type 1 syndrome (NF1) are observed in ～50% of patients. Here, we describe the phenotype of Nf1_Ocl mouse model with Nf1‐deficient osteoclasts. Nf1_Ocl mice with Nf1^+/? or Nf1^?/? osteoclasts in otherwise Nf1^+/+ background were successfully generated by mating parental Nf1flox/flox and TRAP‐Cre mice. Contrary to our original hypothesis, osteoporotic or fragile bone phenotype was not observed. The µCT analysis revealed that tibial bone marrow cavity, trabecular tissue volume, and the perimeter of cortical bone were smaller in Nf1 mice compared to Nf1 control mice. Nf1 mice also a displayed narrowed growth plate in the proximal tibia. In vitro analysis showed increased bone resorption capacity and cytoskeletal changes including irregular cell shape and abnormal actin ring formation in Nf1^?/? osteoclasts. Surprisingly, the size of spleen in Nf1 mice was two times larger than in controls and histomorphometric analysis showed splenic megakaryocytosis. In summary, Nf1Ocl mouse model presented with a mild but specific bone phenotype. This study shows that NF1‐deficiency in osteoclasts may have a role in the development of NF1‐related skeletal abnormalities, but Nf1‐deficiency in osteoclasts in Nf1^+/+ background is not sufficient to induce skeletal abnormalities analogous to those observed in patients with NF1. J. Cell. Biochem. 113: 2136–2146, 2012. © 2012 Wiley Periodicals, Inc.     

Abnormal actin binding of aberrant β-tropomyosins is a molecular cause of muscle weakness in TPM2-related nemaline and cap myopathy

NM (nemaline myopathy) is a rare genetic muscle disorder defined on the basis of muscle weakness and the presence of structural abnormalities in the muscle fibres, i.e. nemaline bodies. The related disorder cap myopathy is defined by cap-like structures located peripherally in the muscle fibres. Both disorders may be caused by mutations in the TPM2 gene encoding β-Tm (tropomyosin). Tm controls muscle contraction by inhibiting actin-myosin interaction in a calcium-sensitive manner. In the present study, we have investigated the pathogenetic mechanisms underlying five disease-causing mutations in Tm. We show that four of the mutations cause changes in affinity for actin, which may cause muscle weakness in these patients, whereas two show defective Ca2+ activation of contractility. We have also mapped the amino acids altered by the mutation to regions important for actin binding and note that two of the mutations cause altered protein conformation, which could account for impaired actin affinity.     

Diversity in prokaryotic glycosylation: an archaeal-derived N-linked glycan contains legionaminic acid

VP4, the major structural protein of the haloarchaeal pleomorphic virus, HRPV‐1, is glycosylated. To define the glycan structure attached to this protein, oligosaccharides released by β‐elimination were analysed by mass spectrometry and nuclear magnetic resonance spectroscopy. Such analyses showed that the major VP4‐derived glycan is a pentasaccharide comprising glucose, glucuronic acid, mannose, sulphated glucuronic acid and a terminal 5‐N‐formyl‐legionaminic acid residue. This is the first observation of legionaminic acid, a sialic acid‐like sugar, in an archaeal‐derived glycan structure. The importance of this residue for viral infection was demonstrated upon incubation with N‐acetylneuraminic acid, a similar monosaccharide. Such treatment reduced progeny virus production by half 4 h post infection. LC‐ESI/MS analysis confirmed the presence of pentasaccharide precursors on two different VP4‐derived peptides bearing the N‐glycosylation signal, NTT. The same sites modified by the native host, Halorubrum sp. strain PV6, were also recognized by the Haloferax volcanii N‐glycosylation apparatus, as determined by LC‐ESI/MS of heterologously expressed VP4. Here, however, the N‐linked pentasaccharide was the same as shown to decorate the S‐layer glycoprotein in this species. Hence, N‐glycosylation of the haloarchaeal viral protein, VP4, is host‐specific. These results thus present additional examples of archaeal N‐glycosylation diversity and show the ability of Archaea to modify heterologously expressed proteins.     

CD200 positive human mesenchymal stem cells suppress TNF-alpha secretion from CD200 receptor positive macrophage-like cells

Human mesenchymal stem cells (hMSCs) display immunosuppressive properties in vitro and the potential has also been transferred successfully to clinical trials for treatment of autoimmune diseases. OX-2 (CD200), a member of the immunoglobulin superfamily, is widely expressed in several tissues and has recently been found from hMSCs. The CD200 receptor (CD200R) occurs only in myeloid-lineage cells. The CD200-CD200R is involved in down-regulation of several immune cells, especially macrophages. The present study on 20 hMSC lines shows that the CD200 expression pattern varied from high (CD200Hi) to medium (CD200Me) and low (CD200Lo) in bone marrow-derived mesenchymal stem cell (BMMSC) lines, whereas umbilical cord blood derived mesenchymal stem cells (UCBMSCs) were constantly negative for CD200. The role of the CD200-CD200R axis in BMMSCs mediated immunosuppression was studied using THP-1 human macrophages. Interestingly, hMSCs showed greater inhibition of TNF-α secretion in co-cultures with IFN-γ primed THP-1 macrophages when compared to LPS activated cells. The ability of CD200Hi BMMSCs to suppress TNF-α secretion from IFN-γ stimulated THP-1 macrophages was significantly greater when compared to CD200Lo whereas UCBMSCs did not significantly reduce TNF-α secretion. The interference of CD200 binding to the CD200R by anti-CD200 antibody weakened the capability of BMMSCs to inhibit TNF-α secretion from IFN-γ activated THP-1 macrophages. This study clearly demonstrated that the efficiency of BMMSCs to suppress TNF-α secretion of THP-1 macrophages was dependent on the type of stimulus. Moreover, the CD200-CD200r axis could have a previously unidentified role in the BMMSC mediated immunosuppression.     

Toll-like receptor 7 is required for effective adaptive immune responses that prevent persistent virus infection

TLR7 is an innate signaling receptor that recognizes single-stranded viral RNA and is activated by viruses that cause persistent infections. We show that TLR7 signaling dictates either clearance or establishment of life-long chronic infection by lymphocytic choriomeningitis virus (LCMV) Cl 13 but does not affect clearance of the acute LCMV Armstrong 53b strain. TLR7(-/-) mice infected with LCMV Cl 13 remained viremic throughout life from defects in the adaptive antiviral immune response-notably, diminished T?cell function, exacerbated T?cell exhaustion, decreased plasma cell maturation, and negligible antiviral antibody production. Adoptive transfer of TLR7(+/+) LCMV immune memory cells that enhanced clearance of persistent LCMV Cl 13 infection in TLR7(+/+) mice failed to purge LCMV Cl 13 infection in TLR7(-/-) mice, demonstrating that a TLR7-deficient environment renders antiviral responses ineffective. Therefore, methods that promote TLR7 signaling are promising treatment strategies for chronic viral infections.