Involvement of NMDAR2A tyrosine phosphorylation in depression‐related behaviour

Major depressive and bipolar disorders are serious illnesses that affect millions of people. Growing evidence implicates glutamate signalling in depression, though the molecular mechanism by which glutamate signalling regulates depression‐related behaviour remains unknown. In this study, we provide evidence suggesting that tyrosine phosphorylation of the NMDA receptor, an ionotropic glutamate receptor, contributes to depression‐related behaviour. The NR2A subunit of the NMDA receptor is tyrosine‐phosphorylated, with Tyr 1325 as its one of the major phosphorylation site. We have generated mice expressing mutant NR2A with a Tyr‐1325‐Phe mutation to prevent the phosphorylation of this site in vivo. The homozygous knock‐in mice show antidepressant‐like behaviour in the tail suspension test and in the forced swim test. In the striatum of the knock‐in mice, DARPP‐32 phosphorylation at Thr 34, which is important for the regulation of depression‐related behaviour, is increased. We also show that the Tyr 1325 phosphorylation site is required for Src‐induced potentiation of the NMDA receptor channel in the striatum. These data argue that Tyr 1325 phosphorylation regulates NMDA receptor channel properties and the NMDA receptor‐mediated downstream signalling to modulate depression‐related behaviour.     

Methane emissions from soils: synthesis and analysis of a large UK data set

Nearly 5000 chamber measurements of CH₄ flux were collated from 21 sites across the United Kingdom, covering a range of soil and vegetation types, to derive a parsimonious model that explains as much of the variability as possible, with the least input requirements. Mean fluxes ranged from ?0.3 to 27.4 nmol CH₄ m^?2 s^?1, with small emissions or low rates of net uptake in mineral soils (site means of ?0.3 to 0.7 nmol m^?2 s^?1) and much larger emissions from organic soils (site means of ?0.3 to 27.4 nmol m^?2 s^?1). Less than half of the observed variability in instantaneous fluxes could be explained by independent variables measured. The reasons for this include measurement error, stochastic processes and, probably most importantly, poor correspondence between the independent variables measured and the actual variables influencing the processes underlying methane production, transport and oxidation. When temporal variation was accounted for, and the fluxes averaged at larger spatial scales, simple models explained up to ca. 75% of the variance in CH₄ fluxes. Soil carbon, peat depth, soil moisture and pH together provided the best sub‐set of explanatory variables. However, where plant species composition data were available, this provided the highest explanatory power. Linear and nonlinear models generally fitted the data equally well, with the exception that soil moisture required a power transformation. To estimate the impact of changes in peatland water table on CH₄ emissions in the United Kingdom, an emission factor of +0.4 g CH₄ m^?2 yr^?1 per cm increase in water table height was derived from the data.     

Genome-wide patterns of intrahuman dengue virus diversity reveal associations with viral phylogenetic clade and interhost diversity

Analogous to observations in RNA viruses such as human immunodeficiency virus, genetic variation associated with intrahost dengue virus (DENV) populations has been postulated to influence viral fitness and disease pathogenesis. Previous attempts to investigate intrahost genetic variation in DENV characterized only a few viral genes or a limited number of full-length genomes. We developed a whole-genome amplification approach coupled with deep sequencing to capture intrahost diversity across the entire coding region of DENV-2. Using this approach, we sequenced DENV-2 genomes from the serum of 22 Nicaraguan individuals with secondary DENV infection and captured ～75% of the DENV genome in each sample (range, 40 to 98%). We identified and quantified variants using a highly sensitive and specific method and determined that the extent of diversity was considerably lower than previous estimates. Significant differences in intrahost diversity were detected between genes and also between antigenically distinct domains of the Envelope gene. Interestingly, a strong association was discerned between the extent of intrahost diversity in a few genes and viral clade identity. Additionally, the abundance of viral variants within a host, as well as the impact of viral mutations on amino acid encoding and predicted protein function, determined whether intrahost variants were observed at the interhost level in circulating Nicaraguan DENV-2 populations, strongly suggestive of purifying selection across transmission events. Our data illustrate the value of high-coverage genome-wide analysis of intrahost diversity for high-resolution mapping of the relationship between intrahost diversity and clinical, epidemiological, and virological parameters of viral infection.     

p21 promotes error-free replication-coupled DNA double-strand break repair

p21 is a well-established regulator of cell cycle progression. The role of p21 in DNA repair, however, remains poorly characterized. Here, we describe a critical role of p21 in a replication-coupled DNA double-strand break (DSB) repair that is mechanistically distinct from its cell cycle checkpoint function. We demonstrate that p21-deficient cells exhibit elevated chromatid-type aberrations, including gaps and breaks, dicentrics and radial formations, following exposure to several DSB-inducing agents. p21(-/-) cells also exhibit an increased DNA damage-inducible DNA-PK(CS) S2056 phosphorylation, indicative of elevated non-homologous DNA end joining. Concomitantly, p21(-/-) cells are defective in replication-coupled homologous recombination (HR), exhibiting decreased sister chromatid exchanges and HR-dependent repair as determined using a crosslinked GFP reporter assay. Importantly, we establish that the DSB hypersensitivity of p21(-/-) cells is associated with increased cyclin-dependent kinase (CDK)-dependent BRCA2 S3291 phosphorylation and MRE11 nuclear foci formation and can be rescued by inhibition of CDK or MRE11 nuclease activity. Collectively, our results uncover a novel mechanism by which p21 regulates the fidelity of replication-coupled DSB repair and the maintenance of chromosome stability distinct from its role in the G1-S phase checkpoint.     

Only Low Frequency Event-Related EEG Activity Is Compromised in Multiple Sclerosis: Insights from an Independent Component Clustering Analysis

Cognitive impairment (CI), often examined with neuropsychological tests such as the Paced Auditory Serial Addition Test (PASAT), affects approximately 65% of multiple sclerosis (MS) patients. The P3b event-related potential (ERP), evoked when an infrequent target stimulus is presented, indexes cognitive function and is typically compared across subjects'' scalp electroencephalography (EEG) data. However, the clustering of independent components (ICs) is superior to scalp-based EEG methods because it can accommodate the spatiotemporal overlap inherent in scalp EEG data. Event-related spectral perturbations (ERSPs; event-related mean power spectral changes) and inter-trial coherence (ITCs; event-related consistency of spectral phase) reveal a more comprehensive overview of EEG activity. Ninety-five subjects (56 MS patients, 39 controls) completed visual and auditory two-stimulus P3b event-related potential tasks and the PASAT. MS patients were also divided into CI and non-CI groups (n = 18 in each) based on PASAT scores. Data were recorded from 128-scalp EEG channels and 4 IC clusters in the visual, and 5 IC clusters in the auditory, modality were identified. In general, MS patients had significantly reduced ERSP theta power versus controls, and a similar pattern was observed for CI vs. non-CI MS patients. The ITC measures were also significantly different in the theta band for some clusters. The finding that MS patients had reduced P3b task-related theta power in both modalities is a reflection of compromised connectivity, likely due to demyelination, that may have disrupted early processes essential to P3b generation, such as orientating and signal detection. However, for posterior sources, MS patients had a greater decrease in alpha power, normally associated with enhanced cognitive function, which may reflect a compensatory mechanism in response to the compromised early cognitive processing.     

Variants of the ankyrin repeat domain 6 gene (ANKRD6) and muscle and physical activity phenotypes among European-derived American adults

Ankyrin repeat domain 6 (ANKRD6) is a ubiquitous protein that associates with early development in mammals and is highly expressed in the brain, spinal cord, and heart of humans. We examined the role of 8 ANKRD6 single-nucleotide polymorphisms (SNPs) on muscle performance and habitual physical activity (PA). Single-nucleotide polymorphisms were 545 T>A (rs9362667), 485 M>L (rs61736690), 233 T>M (rs2273238), 128 I>L (rs3748085), 631 P>L (rs61739327), 122 Q>E (rs16881983), 197805 G>A (rs9344950), and 710 L>X (NOVEL). This study consisted of 922 healthy, untrained, European-derived American men (n = 376, 23.6 ± 0.3 years, 25.0 ± 0.2 kg·m(-2)) and women (n = 546, 23.2 ± 0.2 years, 24.0 ± 0.2 kg·m(-2)). Muscle strength (maximum voluntary contraction [MVC] and 1 repetition maximum [1RM]) and size (cross-sectional area [CSA]) were assessed before and after 12 weeks of unilateral resistance training (RT). A subsample (n = 536, 23.4 ± 0.2 years, 24.6 ± 0.2 kg·m(-2)) completed the Paffenbarger Physical Activity Questionnaire. Associations among ANKRD6 genotypes and muscle phenotypes were tested with repeated measure analysis of covariance (ANCOVA) and PA phenotypes with multivariate ANCOVA, with age and body mass index as covariates. ANKRD6 122 Q>E was associated with increased baseline biceps CSA. ANKRD6 545 A>T and ANKRD6 710 L>X were associated with increased 1RM and MVC in response to RT, respectively. ANKRD6 631 P>L was associated with increased biceps CSA response to RT and time spent in moderate-intensity PA among the total sample and women. ANKRD6 genetic variants were associated with the muscle size and strength response to RT and habitual PA levels. Further research is needed to validate our results and explore mechanisms for the associations we observed.     

Exercise training corrects control of spontaneous calcium waves in hearts from myocardial infarction heart failure rats

Impaired cardiac control of intracellular diastolic Ca(2+) gives rise to arrhythmias. Whereas exercise training corrects abnormal cyclic Ca(2+) handling in heart failure, the effect on diastolic Ca(2+) remains unstudied. Here, we studied the effect of exercise training on the generation and propagation of spontaneous diastolic Ca(2+) waves in failing cardiomyocytes. Post-myocardial infarction heart failure was induced in Sprague-Dawley rats by coronary artery ligation. Echocardiography confirmed left ventricular infarctions of 40 ± 5%, whereas heart failure was indicated by increased left ventricular end-diastolic pressures, decreased contraction-relaxation rates, and pathological hypertrophy. Spontaneous Ca(2+) waves were imaged by laser linescanning confocal microscopy (488 nm excitation/505-530 nm emission) in 2 μM Fluo-3-loaded cardiomyocytes at 37°C and extracellular Ca(2+) of 1.2 and 5.0 mM. These studies showed that spontaneous Ca(2+) wave frequency was higher at 5.0 mM than 1.2 mM extracellular Ca(2+) in all rats, but failing cardiomyocytes generated 50% (P < 0.01) more waves compared to sham-operated controls at Ca(2+) 1.2 and 5.0 mM. Exercise training reduced the frequency of spontaneous waves at both 1.2 and 5.0 mM Ca(2+) (P < 0.05), although complete normalization was not achieved. Exercise training also increased the aborted/completed ratio of waves at 1.2 mM Ca(2+) (P < 0.01), but not 5.0 mM. Finally, we repeated these studies after inhibiting the nitric oxide synthase with L-NAME. No differential effects were found; thus, mediation did not involve the nitric oxide synthase. In conclusion, exercise training improved the cardiomyocyte control of diastolic Ca(2+) by reducing the Ca(2+) wave frequency and by improving the ability to abort spontaneous Ca(2+) waves after their generation, but before cell-wide propagation.     

Membrane protein stability: high pressure effects on the structure and chromophore-binding properties of the light-harvesting complex LH2

Using the bacteriochlorophyll a (Bchl) cofactors as intrinsic probes to monitor changes in membrane protein structure, we investigate the response to high-pressure of the LH2 complexes from the photosynthetic bacteria Rhodobacter sphaeroides 2.4.1 and Rhodopseudomonas acidophila 10050. By FT-Raman spectroscopy, we demonstrate that high pressure does not induce significant distortion of the protein-bound 850 nm-absorbing bacteriochlorophyll molecules, or break of the hydrogen bond they are involved in. This indicates in particular that the oligomerization of the polypeptides is not perturbed up to 0.6 GPa. The pressure-induced changes in the Bchl absorption spectra are attributed to pigment-pigment interactions. In contrast, the loss of 800 nm-absorbing bacteriochlorophyll reflects pressure-induced alterations to the tertiary structure of the protein in proximity to the membrane/cytosol interface. This suggests that the LH2 protein does have two independent structural domains. The first domain is pressure independent and comprises mostly the C-terminal domain. The second domain located on the N-terminal side exhibits sensitivity to pressure and pH reminiscent of soluble proteins. The LH2 thus constitutes a suitable model system for studying in detail the stability of membrane-embedded hydrophobic helices and helices located at or close to the solvent/membrane interface.