MeCP2 Affects Skeletal Muscle Growth and Morphology through Non Cell-Autonomous Mechanisms

Rett syndrome (RTT) is an autism spectrum disorder mainly caused by mutations in the X-linked MECP2 gene and affecting roughly 1 out of 10.000 born girls. Symptoms range in severity and include stereotypical movement, lack of spoken language, seizures, ataxia and severe intellectual disability. Notably, muscle tone is generally abnormal in RTT girls and women and the Mecp2-null mouse model constitutively reflects this disease feature. We hypothesized that MeCP2 in muscle might physiologically contribute to its development and/or homeostasis, and conversely its defects in RTT might alter the tissue integrity or function. We show here that a disorganized architecture, with hypotrophic fibres and tissue fibrosis, characterizes skeletal muscles retrieved from Mecp2-null mice. Alterations of the IGF-1/Akt/mTOR pathway accompany the muscle phenotype. A conditional mouse model selectively depleted of Mecp2 in skeletal muscles is characterized by healthy muscles that are morphologically and molecularly indistinguishable from those of wild-type mice raising the possibility that hypotonia in RTT is mainly, if not exclusively, mediated by non-cell autonomous effects. Our results suggest that defects in paracrine/endocrine signaling and, in particular, in the GH/IGF axis appear as the major cause of the observed muscular defects. Remarkably, this is the first study describing the selective deletion of Mecp2 outside the brain. Similar future studies will permit to unambiguously define the direct impact of MeCP2 on tissue dysfunctions.     

Subcellular Distribution of Two Spin Trapping Agents in Rat Heart: Possible Explanation for Their Different Protective Effects Against Doxorubicin-Induced Cardiotoxicity

Previous investigations, performed on isolated rat atria, showed that the lipophylic spin-trapping agent N-tert-butyl-alpha-phenylnitrone (PBN) is able to prevent the acute cardiotoxic effects produced by doxorubicin (DXR), whereas the hydrophylic compound 5,5-dimethyl-pyrroline-N-oxide (DMPO) is inactive. The present study was designed to ascertain whether differences in the pharmacological effects of the two spin traps are related to their different subcellular distribution. Langendorff rat hearts were perfused for 60 minutes with [^I4C]-DXR and either PBN or DMPO. The subcellular mapping of the three compounds was performed by measuring DXR by liquid scintillation counting, PBN by GC/MS, and DMPO by HPLC in the following isolated fractions: nuclei, mitochondria, sarcoplasmic reticulum, sarcolemma, cytosol. DMPO was shown to accumulate in the cytosolic compartment; both PBM and DXR are taken up by nuclei and mitochondria, while only trace amounts of DXR were detected in the sarcoplasmic reticulum. These results suggest that mitochondrial (and not sarcoplasmic) enzymes are mainly involved in DXR-induced free radical production, which is thought to cause the acute cardiotoxic effects of DXR. An involvement of DXR-induced free radical generation in the nuclear compartment seems unlikely in the short-term “in vitro” effects observed with the experimental model adopted for these studies, although it may play a role in the delayed pathology.     

Phenotypic Changes Across a Geographic Gradient: The Case of Three Sympatric Dolphin Species

Phenotypic changes in the mammalian mandible can occur at different spatial and temporal scales. We investigated mandibular size and shape variation in three extant closely related dolphins (Cetacea, Odontoceti): Tursiops truncatus, Stenella coeruleoalba and Delphinus delphis in order to test the hypothesis that similar phenotypic changes occur across the same geographical gradient. Our data included 219 specimens representative of the following geographic locations: the Mediterranean Sea, the eastern north Atlantic and the North Sea. Each mandibula was photographed laterally and spatial positioning of eight homologous 2D landmarks was recorded. After applying generalised Procrustes analysis (GPA), intraspecific variation was first investigated between sexes and among populations to allow further pooling of samples. Size and shape differences among populations and species were investigated through multivariate ordination techniques (PCA), Procrustes ANOVA and allometric analyses. In all three species, Mediterranean populations clearly differed in mandible shape from the extra-Mediterranean ones. Among the three, the direction of geographic phenotypic changes was significantly similar in the striped and common dolphin, while the bottlenose dolphin was the most divergent species, differing both in size and allometric trajectory. Shape variation of the two former species highlighted a morphological convergence in the Atlantic, and a phenotypic divergence in the Mediterranean. Shape differences among the three dolphin species were interpreted in the light of different prey preferences, feeding strategies and habitat partitioning to avoid direct competition.     

Plant traits shape the effects of tidal flooding on soil and plant communities in saltmarshes

Saltmarshes are recognised worldwide to be among the most complex ecosystems, where several environmental factors concur to sustain their fragile functioning. Among them, soil–plant interactions are pivotal but often overlooked. The aim of this work was to use a structural equation modelling (SEM) approach to get new insight into soil–plant interactions, focusing on the effect of plant traits and abundance on soil, and test the effect of soil and/or plants on the entire community, monitoring changes in plant richness. The target halophytes Limonium narbonense and Sarcocornia fruticosa were sampled in the Marano and Grado lagoon (northern Adriatic Sea). Basal leaves of L. narbonense and green shoots of S. fruticosa were used to estimate plant growth, while the abundance of both species was used as a proxy of species competition. SEM was applied to test relationships between predictors and response variables in a single causal network. The flooding period (hydroperiod) negatively affected plant growth and soil properties, whereas plants decreased the intensity of soil reduction. Flooding did not directly affect species abundance or diversity, whose changes were instead driven by plant traits. The direct relationships between plant traits and species richness highlighted that species competition could be even more important than environmental stresses in defining plant diversity and zonation.     

Prosystemin,a prohormone that modulates plant defense barriers,is an intrinsically disordered protein

Prosystemin, originally isolated from Lycopersicon esculentum, is a tomato pro‐hormone of 200 aminoacid residues which releases a bioactive peptide of 18 aminoacids called Systemin. This signaling peptide is involved in the activation of defense genes in solanaceous plants in response to herbivore feeding damage. Using biochemical, biophysical and bioinformatics approaches we characterized Prosystemin, showing that it is an intrinsically disordered protein possessing a few secondary structure elements within the sequence. Plant treatment with recombinant Prosystemin promotes early and late plant defense genes, which limit the development and survival of Spodoptera littoralis larvae fed with treated plants.     

First evidence of DAAM1 localization in mouse seminal vesicles and its possible involvement during regulated exocytosis

Dishevelled-associated activator of morphogenesis 1 (DAAM1) is a protein belonging to the formin family, which regulates, together with the small GTPase RhoA, the nucleation and the assembly of actin fibres through Wnt-Dishevelled PCP pathway. Its role has been investigated in essential biological processes, such as cell polarity, movement and adhesion during morphogenesis and organogenesis. In this work, we studied the expression of DAAM1 mRNA and protein by PCR and Western blot analyses and its co-localization with actin in adult mouse seminal vesicles by immunofluorescence. We show that both proteins are cytoplasmic: actin is evident at cell–cell junctions and at cell cortex; DAAM1 had a more diffused localization, but is also prominent at the apical plasmatic membrane of epithelial cells. These findings support our hypothesis of a role of DAAM1 in cytoskeletal rearrangement that occurs during the exocytosis of secretory vesicles, and in particular concerning actin filaments. We were also able to detect DAAM1 and actin association in the smooth muscle cells that surround the epithelium too. In this case, we could only speculate the possible involvement of this formin in muscular cells in the maintenance and the regulation of the contractile structures. The present results strongly suggest that DAAM1 could have a pivotal role in vesicle exocytosis and in the physiology of mouse seminal vesicles.     

Structures,intermolecular interactions,and chemical hardness of binary water–organic solvents: a molecular dynamics study

The evolution of structural properties, thermodynamics and averaged (dynamic) total hardness values as a function of the composition of binary water–organic solvents, was rationalized in view of the intermolecular interactions. The organic solvents considered were ethanol, acetonitrile, and isopropanol at 0.25, 0.5, 0.75, and 1 mass fractions, and the results were obtained using molecular dynamics simulations. The site-to-site radial distribution functions reveal a well-defined peak for the first coordination shell in all solvents. A characteristic peak of the second coordination shell exists in aqueous mixtures of acetonitrile, whereas in the water–alcohol solvents, a second peak develops with the increase in alcohol content. From the computed coordination numbers, averaged hydrogen bonds and their lifetimes, we found that water mixed with acetonitrile largely preserves its structural features and promotes the acetonitrile structuring. Both the water and alcohol structures in their mixtures are disturbed and form hydrogen bonds between molecules of different kinds. The dynamic hardness values are obtained as the average over the total hardness values of 1200 snapshots per solvent type, extracted from the equilibrium dynamics. The dynamic hardness profile has a non-linear evolution with the liquid compositions, similarly to the thermodynamic properties of these non-ideal solvents.

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Graphical abstract Computed dynamic total hardness, as a function of the cosolvent mass fraction for water–ethanol (EtOH), water–isopropanol (2PrOH) and water–acetonitrile (AN)

     

Mitochondrial Complex I defects in aging

According to the 'mitochondrial theory of aging' it is expected that the activity of NADH Coenzyme Q reductase (Complex I) would be most severely affected among mitochondrial enzymes, since mitochondrial DNA encodes for 7 subunits of this enzyme. Being these subunits the site of binding of the acceptor substrate (Coenzyme Q) and of most inhibitors of the enzyme, it is also expected that subtle kinetic changes of quinone affinity and enzyme inhibition could develop in aging before an overall loss of activity would be observed.The overall activity of Complex I was decreased in several tissues from aged rats, nevertheless it was found that direct assay of Complex I using artificial quinone acceptors may underevaluate the enzyme activity. The most acceptable results could be obtained by applying the 'pool equation' to calculate Complex I activity from aerobic NADH oxidation; using this method it was found that the decrease in Complex I activity in mitochondria from old animals was greater than the activity calculated by direct assay of NADH Coenzyme Q reductase.A decrease of NADH oxidation and its rotenone sensitivity was observed in nonsynaptic mitochondria, but not in synaptic 'light' and 'heavy' mitochondria of brain cortex from aged rats.In a study of Complex I activity in human platelet membranes we found that the enzyme activity was unchanged but the titre for half-inhibition by rotenone was significantly increased in aged individuals and proposed this change as a suitable biomarker of aging and age-related diseases. (Mol Cell Biochem 174: 329–333, 1997)