Direct anabolic metabolism of three-carbon propionate to a six-carbon metabolite occurs in vivo across tissues and species

Anabolic metabolism of carbon in mammals is mediated via the one- and two-carbon carriers S-adenosyl methionine and acetyl-coenzyme A. In contrast, anabolic metabolism of three-carbon units via propionate has not been shown to extensively occur. Mammals are primarily thought to oxidize the three-carbon short chain fatty acid propionate by shunting propionyl-CoA to succinyl-CoA for entry into the TCA cycle. Here, we found that this may not be absolute as, in mammals, one nonoxidative fate of propionyl-CoA is to condense to two three-carbon units into a six-carbon trans-2-methyl-2-pentenoyl-CoA (2M2PE-CoA). We confirmed this reaction pathway using purified protein extracts provided limited substrates and verified the product via LC-MS using a synthetic standard. In whole-body in vivo stable isotope tracing following infusion of ¹³C-labeled valine at steady state, 2M2PE-CoA was found to form via propionyl-CoA in multiple murine tissues, including heart, kidney, and to a lesser degree, in brown adipose tissue, liver, and tibialis anterior muscle. Using ex vivo isotope tracing, we found that 2M2PE-CoA also formed in human myocardial tissue incubated with propionate to a limited extent. While the complete enzymology of this pathway remains to be elucidated, these results confirm the in vivo existence of at least one anabolic three- to six-carbon reaction conserved in humans and mice that utilizes propionate.     

Ethnic mobilization and the state: the Roma in Eastern Europe

The political mobilization of marginalized ethnic groups is a process indispensable for the realization of their political objectives. This article identifies the key criteria and conditions that promote and impede successful ethnic mobilization and analyses the determinants of state policy towards newly mobilizing ethnic minorities. The theoretical arguments receive empirical support from the findings of a comparative study of the Romani (Gypsy) minority in seven East European states.     

Cyclic Nucleotide Dependent Dephosphorylation of Regulator of G-Protein Signaling 18 in Human Platelets

Regulator of G-protein signaling 18 (RGS18) is a GTPase-activating protein that turns off Gq signaling in platelets. RGS18 is regulated by binding to the adaptor protein 14-3-3 via phosphorylated serine residues S49 and S218 on RGS18. In this study we confirm that thrombin, thromboxane A2, or ADP stimulate the interaction of RGS18 and 14-3-3 by increasing the phosphorylation of S49. Cyclic AMP- and cyclic GMP-dependent kinases (PKA, PKG) inhibit the interaction of RGS18 and 14-3-3 by phosphorylating S216. To understand the effect of S216 phosphorylation we studied the phosphorylation kinetics of S49, S216, and S218 using Phos-tag gels and phosphorylation site-specific antibodies in transfected cells and in platelets. Cyclic nucleotide-induced detachment of 14-3-3 from RGS18 coincides initially with double phosphorylation of S216 and S218. This is followed by dephosphorylation of S49 and S218. Dephosphorylation of S49 and S218 might be mediated by protein phosphatase 1 (PP1) which is linked to RGS18 by the regulatory subunit PPP1R9B (spinophilin). We conclude that PKA and PKG induced S216 phosphorylation triggers the dephosphorylation of the 14-3-3 binding sites of RGS18 in platelets.     

Quantitative Analysis of the Whole-Body Metabolic Fate of Branched-Chain Amino Acids

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The Early-Onset Myocardial Infarction Associated PHACTR1 Gene Regulates Skeletal and Cardiac Alpha-Actin Gene Expression

The phosphatase and actin regulator 1 (PHACTR1) locus is a very commonly identified hit in genome-wide association studies investigating coronary artery disease and myocardial infarction (MI). However, the function of PHACTR1 in the heart is still unknown. We characterized the mechanisms regulating Phactr1 expression in the heart, used adenoviral gene delivery to investigate the effects of Phactr1 on cardiac function, and analyzed the relationship between MI associated PHACTR1 allele and cardiac function in human subjects. Phactr1 mRNA and protein levels were markedly reduced (60%, P<0.01 and 90%, P<0.001, respectively) at 1 day after MI in rats. When the direct myocardial effects of Phactr1 were studied, the skeletal α-actin to cardiac α-actin isoform ratio was significantly higher (1.5-fold, P<0.05) at 3 days but 40% lower (P<0.05) at 2 weeks after adenovirus-mediated Phactr1 gene delivery into the anterior wall of the left ventricle. Similarly, the skeletal α-actin to cardiac α-actin ratio was lower at 2 weeks in infarcted hearts overexpressing Phactr1. In cultured neonatal cardiac myocytes, adenovirus-mediated Phactr1 overexpression for 48 hours markedly increased the skeletal α-actin to cardiac α-actin ratio, this being associated with an enhanced DNA binding activity of serum response factor. Phactr1 overexpression exerted no major effects on the expression of other cardiac genes or LV structure and function in normal and infarcted hearts during 2 weeks’ follow-up period. In human subjects, MI associated PHACTR1 allele was not associated significantly with cardiac function (n = 1550). Phactr1 seems to regulate the skeletal to cardiac α-actin isoform ratio.     

Terahertz Selective Emission Enhancement from a Metasurface-Coupled Photoconductive Emitter in Quasi-Near-Field Zone

We present a THz emission enhancement of 41 times at 0.92 THz from a metasurface made of T-shaped resonators excited in a quasi-near-field zone. Such a metasurface has an intrinsic transmission minimum with Q factor of 4 at 1.25 THz under far-field excitation. When this metasurface is coupled onto the backside of a 625-μm-thick photoconductive emitter, the metasurface is below the Fraunhofer distance to the excitation source. As such, one broad enhancement around 0.47 THz and another extremely narrow enhancement at 0.92 THz in the emission spectrum are observed owing to a quasi-near-field excitation. Theoretically, the Q factor of the latter is up to 307, which is limited by the spectral resolution in experiment. The numerical simulations indicate that the T-shaped resonators serve as an array of plasmonic antennas resulting in the aforementioned emission enhancement of THz radiation.

     

Notch Is a Critical Component of the Mouse Somitogenesis Oscillator and Is Essential for the Formation of the Somites

Segmentation of the vertebrate body axis is initiated through somitogenesis, whereby epithelial somites bud off in pairs periodically from the rostral end of the unsegmented presomitic mesoderm (PSM). The periodicity of somitogenesis is governed by a molecular oscillator that drives periodic waves of clock gene expression caudo-rostrally through the PSM with a periodicity that matches somite formation. To date the clock genes comprise components of the Notch, Wnt, and FGF pathways. The literature contains controversial reports as to the absolute role(s) of Notch signalling during the process of somite formation. Recent data in the zebrafish have suggested that the only role of Notch signalling is to synchronise clock gene oscillations across the PSM and that somite formation can continue in the absence of Notch activity. However, it is not clear in the mouse if an FGF/Wnt-based oscillator is sufficient to generate segmented structures, such as the somites, in the absence of all Notch activity. We have investigated the requirement for Notch signalling in the mouse somitogenesis clock by analysing embryos carrying a mutation in different components of the Notch pathway, such as Lunatic fringe (Lfng), Hes7, Rbpj, and presenilin1/presenilin2 (Psen1/Psen2), and by pharmacological blocking of the Notch pathway. In contrast to the fish studies, we show that mouse embryos lacking all Notch activity do not show oscillatory activity, as evidenced by the absence of waves of clock gene expression across the PSM, and they do not develop somites. We propose that, at least in the mouse embryo, Notch activity is absolutely essential for the formation of a segmented body axis.     

Positional Information Generated by Spatially Distributed Signaling Cascades

The temporal and stationary behavior of protein modification cascades has been extensively studied, yet little is known about the spatial aspects of signal propagation. We have previously shown that the spatial separation of opposing enzymes, such as a kinase and a phosphatase, creates signaling activity gradients. Here we show under what conditions signals stall in the space or robustly propagate through spatially distributed signaling cascades. Robust signal propagation results in activity gradients with long plateaus, which abruptly decay at successive spatial locations. We derive an approximate analytical solution that relates the maximal amplitude and propagation length of each activation profile with the cascade level, protein diffusivity, and the ratio of the opposing enzyme activities. The control of the spatial signal propagation appears to be very different from the control of transient temporal responses for spatially homogenous cascades. For spatially distributed cascades where activating and deactivating enzymes operate far from saturation, the ratio of the opposing enzyme activities is shown to be a key parameter controlling signal propagation. The signaling gradients characteristic for robust signal propagation exemplify a pattern formation mechanism that generates precise spatial guidance for multiple cellular processes and conveys information about the cell size to the nucleus.     

Genotype–environment interactions affect flower and fruit herbivory and plant chemistry of Arabidopsis thaliana in a transplant experiment

Large differences exist in flower and fruit herbivory between dune and inland populations of plants of Arabidopsis thaliana (Brassicaceae). Two specialist weevils Ceutorhynchus atomus and C. contractus (Curculionidae) and their larvae are responsible for this pattern in herbivory. We test, by means of a reciprocal transplant experiment, whether these differences reflect environmental influences or genetic variation in plant defense level. All plants suffered more damage after being transplanted to the dune site than after being transplanted to the inland site. Plants of inland origin suffered more flower and fruit herbivory than plants of dune origin when grown at the dune transplant site, but differences were much smaller at the inland site. Both flower damage by adult weevils and fruit damage by their larvae were subject to significant genotype × environment interactions. The observed pattern in herbivory is a strong indication for local adaption of plant defense to the level of herbivory by Ceutorhynchus. In order to identify the mechanism of defense, a quantitative analysis of glucosinolates was performed on the seeds with HPLC. Highly significant differences were found in glucosinolate types and total concentration. These patterns were mainly determined by the origin of the plants (dune or inland) and by a genotype × environment interaction. Herbivory was not significantly correlated to the concentration of glucosinolates in seeds. We therefore analyzed the total metabolic composition of seeds, using NMR spectroscopy and multivariate data analysis. Major differences in chemical composition were found in the water–methanol fractions: more glucosinolate and sucrose in the dune and more fatty acids, lipids and sinapoylmalate in the inland populations. We discuss which of these chemical factors could explain the marked differences in damage between populations.     

Animal migration: linking models and data beyond taxonomic limits

An international workshop on animal migration was held at the Lorentz Center in Leiden, The Netherlands, 2–6 March 2009, bringing together leading theoreticians and empiricists from the major migratory taxa, aiming at the identification of cutting-edge questions in migration research that cross taxonomic borders.