Experimental evolution of nodule intracellular infection in legume symbionts

Soil bacteria known as rhizobia are able to establish an endosymbiosis with legumes that takes place in neoformed nodules in which intracellularly hosted bacteria fix nitrogen. Intracellular accommodation that facilitates nutrient exchange between the two partners and protects bacteria from plant defense reactions has been a major evolutionary step towards mutualism. Yet the forces that drove the selection of the late event of intracellular infection during rhizobium evolution are unknown. To address this question, we took advantage of the previous conversion of the plant pathogen Ralstonia solanacearum into a legume-nodulating bacterium that infected nodules only extracellularly. We experimentally evolved this draft rhizobium into intracellular endosymbionts using serial cycles of legume-bacterium cocultures. The three derived lineages rapidly gained intracellular infection capacity, revealing that the legume is a highly selective environment for the evolution of this trait. From genome resequencing, we identified in each lineage a mutation responsible for the extracellular–intracellular transition. All three mutations target virulence regulators, strongly suggesting that several virulence-associated functions interfere with intracellular infection. We provide evidence that the adaptive mutations were selected for their positive effect on nodulation. Moreover, we showed that inactivation of the type three secretion system of R. solanacearum that initially allowed the ancestral draft rhizobium to nodulate, was also required to permit intracellular infection, suggesting a similar checkpoint for bacterial invasion at the early nodulation/root infection and late nodule cell entry levels. We discuss our findings with respect to the spread and maintenance of intracellular infection in rhizobial lineages during evolutionary times.     

Identification of CANT1 Mutations in Desbuquois Dysplasia

Desbuquois dysplasia is a severe condition characterized by short stature, joint laxity, scoliosis, and advanced carpal ossification with a delta phalanx. Studying nine Desbuquois families, we identified seven distinct mutations in the Calcium-Activated Nucleotidase 1 gene (CANT1), which encodes a soluble UDP-preferring nucleotidase belonging to the apyrase family. Among the seven mutations, four were nonsense mutations (Del 5′ UTR and exon 1, p.P245RfsX3, p.S303AfsX20, and p.W125X), and three were missense mutations (p.R300C, p.R300H, and p.P299L) responsible for the change of conserved amino acids located in the seventh nucleotidase conserved region (NRC). The arginine substitution at position 300 was identified in five out of nine families. The specific function of CANT1 is as yet unknown, but its substrates are involved in several major signaling functions, including Ca²⁺ release, through activation of pyrimidinergic signaling. Importantly, using RT-PCR analysis, we observed a specific expression in chondrocytes. We also found electron-dense material within distended rough endoplasmic reticulum in the fibroblasts of Desbuquois patients. Our findings demonstrate the specific involvement of a nucleotidase in the endochondral ossification process.     

Pivotal Role of Translokin/CEP57 in the Unconventional Secretion Versus Nuclear Translocation of FGF2

Intracellular trafficking of fibroblast growth factor 2 (FGF2) exhibits two unusual features: (i) it is secreted despite the lack of signal peptide and (ii) it can translocate to the nucleus after interaction with high- and low-affinity receptors on the cell surface, although it does not possess any classical nuclear localization signal. This nuclear translocation constitutes an important part of the response to the growth factor. Previously, we identified Translokin/CEP57, an FGF2 binding partner, as an intracellular mediator of FGF2 trafficking, which is essential for the nuclear translocation of the growth factor. Here, we report the identification of four Translokin partners: sorting nexin 6, Ran-binding protein M and the kinesins KIF3A and KIF3B. These proteins, through their interaction with Translokin, are involved in two exclusive complexes allowing the bidirectional trafficking of FGF2. Thus, Translokin plays a pivotal role in this original mechanism. In addition, we show that FGF2 secretion is regulated by a negative loop, retro-controlled by FGF receptor and involving FGF2 itself.     

Bacillus subtilis Bacteria Generate an Internal Mechanical Force within a Biofilm

A key issue in understanding why biofilms are the most prevalent mode of bacterial life is the origin of the degree of resistance and protection that bacteria gain from self-organizing into biofilm communities. Our experiments suggest that their mechanical properties are a key factor. Experiments on pellicles, or floating biofilms, of Bacillus subtilis showed that while they are multiplying and secreting extracellular substances, bacteria create an internal force (associated with a −80 ± 25 Pa stress) within the biofilms, similar to the forces that self-equilibrate and strengthen plants, organs, and some engineered buildings. Here, we found that this force, or stress, is associated with growth-induced pressure. Our observations indicate that due to such forces, biofilms spread after any cut or ablation by up to 15–20% of their initial size. The force relaxes over very short timescales (tens of milliseconds). We conclude that this force helps bacteria to shape the biofilm, improve its mechanical resistance, and facilitate its invasion and self-repair.     

Complexity,polymorphism, and recombination of mouse T-cell receptor α gene families

Genomic DNA from a large panel of inbred strains of mice were hybridized sequentially with 15 V_α, 2 V_δ, 1 C_α, and 1 C_δ probes. Most of the V_α probes detected a high degree of plymorphism and have allowed the definition of five mouse T-cell receptor α (Tcr _α) haplotypes. One of these haplotypes (Tcr _α ^e ) appears to arise from a recombination between theTcr _α ^b andTcr _α ^a haplotypes, the latter being the most frequently found in the conventional inbred strains. This recombination event clearly indicates that the members of at least 11 V_α subfamilies are not closely linked but highly interspersed with one another on chromosome 14.     

The use of tucumã oil (<Emphasis Type="Italic">Astrocaryum vulgare</Emphasis>) in alloxan-induced diabetic mice: effects on behavior,oxidant/antioxidant status,and enzymes involved in brain neurotransmission

Diabetes increases the risk of vascular events and mortality. While earlier type 2 diabetes trials demonstrated that intensive glucose lowering reduces microvascular complications, it is only recently that treatment with some of the newer antihyperglycemic agents has been associated with macrovascular benefits. We report herein that db/db mice concomitantly fed the Western diet and treated with the anti-inflammatory agent methotrexate display a less aggressive inflammatory (lower serum IL-1β, IL-6, SDF-1, and TNFα levels; higher circulating adiponectin, IL-12p70 and IL-10 concentrations; lower aortic VCAM-1 levels) profile than their saline-treated counterpart. Furthermore, acetylcholine-elicited endothelium-dependent vasodilatation was significantly greater in thoracic aortic segments from the former group. Collectively, the data lend support to the notion that alterations in the inflammatory system may be involved in the macrovascular benefits observed in type 2 diabetes trials and provide credence for the development of anti-inflammatory tools to lower CV risk and CV events in diabetes.