Responsiveness of cortical neurons to serotonin after 5,7-DHT denervation or PCPA depletion

1. In adult rats under urethane anesthesia, a vast majority of spontaneously active neurons in the frontoparietal cortex undergo a prolonged depression of their firing rate upon microiontophoretic application of 5-HT. 2. In 5,7-DHT-deafferented cortex, this effect is of a longer duration (mean 14 min) than in controls (mean 5 min). Moreover, small ejection currents of 5-HT are sufficient to induce a prolonged depression of the firing rate. 3. In PCPA-pretreated rats, there are no changes in the responsiveness to 5-HT. 4. In control and PCPA-pretreated rats, blocking of the 5-HT reuptake with fluoxetine increases the duration of responses to 5-HT (mean 15 min), whereas small ejection currents remain without effect. 5. These data indicate that, in the cerebral cortex, denervation supersensitivity to 5-HT results primarily from the removal of 5-HT afferents, and not from depletion of their 5-HT content. The enhanced responsiveness to microiontophoresed 5-HT appears to be due to a suppression of reuptake mechanisms, mainly responsible for the prolongation of 5-HT effects, and to a modification of receptors on target cells, which accounts for their greater sensitivity to 5-HT.     

Endocrine regulation of energy metabolism by the skeleton

The regulation of bone remodeling by an adipocyte-derived hormone implies that bone may exert a feedback control of energy homeostasis. To test this hypothesis we looked for genes expressed in osteoblasts, encoding signaling molecules and affecting energy metabolism. We show here that mice lacking the protein tyrosine phosphatase OST-PTP are hypoglycemic and are protected from obesity and glucose intolerance because of an increase in beta-cell proliferation, insulin secretion, and insulin sensitivity. In contrast, mice lacking the osteoblast-secreted molecule osteocalcin display decreased beta-cell proliferation, glucose intolerance, and insulin resistance. Removing one Osteocalcin allele from OST-PTP-deficient mice corrects their metabolic phenotype. Ex vivo, osteocalcin can stimulate CyclinD1 and Insulin expression in beta-cells and Adiponectin, an insulin-sensitizing adipokine, in adipocytes; in vivo osteocalcin can improve glucose tolerance. By revealing that the skeleton exerts an endocrine regulation of sugar homeostasis this study expands the biological importance of this organ and our understanding of energy metabolism.     

Structural basis for the actin-binding function of missing-in-metastasis

The adaptor protein missing-in-metastasis (MIM) contains independent F- and G-actin binding domains, consisting, respectively, of an N-terminal 250 aa IRSp53/MIM homology domain (IMD) and a C-terminal WASP-homology domain 2 (WH2). We determined the crystal structures of MIM's IMD and that of its WH2 bound to actin. The IMD forms a dimer, with each subunit folded as an antiparallel three-helix bundle. This fold is related to that of the BAR domain. Like the BAR domain, the IMD has been implicated in membrane binding. Yet, comparison of the structures reveals that the membrane binding surfaces of the two domains have opposite curvatures, which may determine the type of curvature of the interacting membrane. The WH2 of MIM is longer than the prototypical WH2, interacting with all four subdomains of actin. We characterize a similar WH2 at the C terminus of IRSp53 and propose that in these two proteins WH2 performs a scaffolding function.     

Inositol polyphosphate 4-phosphatase B as a regulator of bone mass in mice and humans

Osteoporosis is a multifactorial genetic disease characterized by reduction of bone mass due to dysregulation of osteoclast differentiation or maturation. Herein, we identified a regulator of osteoclastogenesis, the murine homolog of inositol polyphosphate 4-phosphatase type IIα (Inpp4bα). Expression of Inpp4bα is detected from early osteoclast differentiation to activation stage. Targeted expression of native Inpp4bα ex?vivo repressed whereas phosphatase-inactive Inpp4bα stimulated osteoclast differentiation. Inpp4bα acts on intracellular calcium level that modulates NFATc1 nuclear translocation and activation. In?vivo mice deficient in Inpp4b displayed increased osteoclast differentiation rate and potential resulting in decreased bone mass and osteoporosis. Importantly, INPP4B in human was identified as a susceptibility locus for osteoporosis. This study defined Inpp4b as a major modulator of the osteoclast differentiation and as a gene linked to variability of bone mineral density in mice and humans.     

Essential amino acids of the hantaan virus N protein in its interaction with RNA

The nucleocapsid (N) protein of hantavirus encapsidates viral genomic and antigenomic RNAs. Previously, deletion mapping identified a central, conserved region (amino acids 175 to 217) within the Hantaan virus (HTNV) N protein that interacts with a high affinity with these viral RNAs (vRNAs). To further define the boundaries of the RNA binding domain (RBD), several peptides were synthesized and examined for the ability to bind full-length S-segment vRNA. Peptide 195-217 retained 94% of the vRNA bound by the HTNV N protein, while peptides 175-186 and 205-217 bound only 1% of the vRNA. To further explore which residues were essential for binding vRNA, we performed a comprehensive mutational analysis of the amino acids in the RBD. Single and double Ala substitutions were constructed for 18 amino acids from amino acids 175 to 217 in the full-length N protein. In addition, Ala substitutions were made for the three R residues in peptide 185-217. An analysis of protein-RNA interactions by electrophoretic mobility shift assays implicated E192, Y206, and S217 as important for binding. Chemical modification experiments showed that lysine residues, but not arginine or cysteine residues, contribute to RNA binding, which agreed with bioinformatic predictions. Overall, these data implicate lysine residues dispersed from amino acids 175 to 429 of the protein and three amino acids located in the RBD as essential for RNA binding.     

Digestive plasticity as a response to woodland fragmentation in roe deer

Digestive plasticity, which refers to changes in digestive features due to changes in both internal and external environmental conditions, is a crucial factor for understanding the ability of species to cope with environmental changes. In Europe, agricultural intensification and the loss of forests have been major challenges for original forest dwellers, however some species, such as the European roe deer (Capreolus capreolus), have been able to successfully colonize these new habitats. In this work, we investigated the adaptation of some digestive features of roe deer to the agricultural landscapes. We assessed whether changes in local landscape structure influenced the mass of both reticulorumen (RR) and distal fermentation chamber (DFC) of 47 juvenile and adult roe deer inhabiting an agro-ecosystem in southwest France. Woodland cover had a clear effect on diet quality (estimated by the rate of gas production of digestive contents) and DFC weight of animals. In fact, deer from the most forested landscapes showed heavier DFCs and fed on poorer quality diet (lower gas production) than their counterparts from the most open landscapes. RR mass was less influenced by the landscape openness, being the age of animals the main factor for understanding the variations of this digestive feature in our study area. We can conclude that colonizing agricultural landscapes increases the access to highly energetic and digestive resources.     

Metagenomes of the picoalga Bathycoccus from the Chile coastal upwelling

Among small photosynthetic eukaryotes that play a key role in oceanic food webs, picoplanktonic Mamiellophyceae such as Bathycoccus, Micromonas, and Ostreococcus are particularly important in coastal regions. By using a combination of cell sorting by flow cytometry, whole genome amplification (WGA), and 454 pyrosequencing, we obtained metagenomic data for two natural picophytoplankton populations from the coastal upwelling waters off central Chile. About 60% of the reads of each sample could be mapped to the genome of Bathycoccus strain from the Mediterranean Sea (RCC1105), representing a total of 9 Mbp (sample T142) and 13 Mbp (sample T149) of non-redundant Bathycoccus genome sequences. WGA did not amplify all regions uniformly, resulting in unequal coverage along a given chromosome and between chromosomes. The identity at the DNA level between the metagenomes and the cultured genome was very high (96.3% identical bases for the three larger chromosomes over a 360 kbp alignment). At least two to three different genotypes seemed to be present in each natural sample based on read mapping to Bathycoccus RCC1105 genome.