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PLOS Biology: New Articles

  • The glycosomal ATP-dependent phosphofructokinase of <i>Trypanosoma brucei</i> operates also in the gluconeogenic direction

    by Nicolas Plazolles, Hanna Kulyk, Edern Cahoreau, Marc Biran, Marion Wargnies, Erika Pineda, Mohammad El Kadri, Aline Rimoldi, Perrine Hervé, Corinne Asencio, Loïc Rivière, Paul A. M. Michels, Daniel Inaoka, Emmanuel Tétaud, Jean-Charles Portais, Frédéric Bringaud

    In the glucose-free environment of the midgut of the tsetse fly vector, the procyclic forms of Trypanosoma brucei primarily consume proline to feed its central carbon and energy metabolism. In this context, the parasite produces through gluconeogenesis, glucose 6-phosphate (G6P), the precursor of essential metabolic pathways, from proline catabolism. We show here that the parasite uses three different enzymes to perform the key gluconeogenic reaction producing fructose 6-phosphate (F6P) from fructose 1,6-bisphosphate, (i) fructose-1,6-bisphosphatase (FBPase), the canonical enzyme performing this reaction, (ii) sedoheptulose-1,7-bisphosphatase (SBPase), and (iii) more surprisingly ATP-dependent phosphofructokinase (PFK), an enzyme considered to irreversibly catalyze the opposite reaction involved in glycolysis. These three enzymes, as well as six other glycolytic/gluconeogenic enzymes, are located in peroxisome-related organelles, named glycosomes. Incorporation of 13C-enriched glycerol (a more effective alternative to proline for monitoring gluconeogenic activity) into F6P and G6P was more affected in the PFK null mutant than in the FBPase null mutant, suggesting the PFK contributes at least as much as FBPase to gluconeogenesis. We also showed that glucose deprivation did not affect the quantities of PFK substrates and products, whereas an approximately 500-fold increase in the substrate/product ratio was expected for PFK to carry out the gluconeogenic reaction. In conclusion, we show for the first time that ATP-dependent PFK can function in vivo in the gluconeogenic direction, even in the presence of FBPase activity. This particular feature, which precludes loss of ATP through a futile cycle involving PFK and FBPase working simultaneously in the glycolytic and gluconeogenic directions, respectively, is possibly due to the supramolecular organization of the metabolic pathway within glycosomes to overcome thermodynamic barriers through metabolic channeling.

  • Analysis of gene expression within individual cells reveals spatiotemporal patterns underlying <i>Vibrio cholerae</i> biofilm development

    by Grace E. Johnson, Chenyi Fei, Ned S. Wingreen, Bonnie L. Bassler

    Bacteria commonly exist in multicellular, surface-attached communities called biofilms. Biofilms are central to ecology, medicine, and industry. The Vibrio cholerae pathogen forms biofilms from single founder cells that, via cell division, mature into three-dimensional structures with distinct, yet reproducible, regional architectures. To define mechanisms underlying biofilm developmental transitions, we establish a single-molecule fluorescence in situ hybridization (smFISH) approach that enables accurate quantitation of spatiotemporal gene-expression patterns in biofilms at cell-scale resolution. smFISH analyses of V. cholerae biofilm regulatory and structural genes demonstrate that, as biofilms mature, overall matrix gene expression decreases, and simultaneously, a pattern emerges in which matrix gene expression becomes largely confined to peripheral biofilm cells. Both quorum sensing and c-di-GMP-signaling are required to generate the proper temporal pattern of matrix gene expression. Quorum sensing signaling is uniform across the biofilm, and thus, c-di-GMP-signaling alone sets the regional matrix gene expression pattern. The smFISH strategy provides insight into mechanisms conferring particular fates to individual biofilm cells.

  • Is pathogen prediction possible?

    by Arturo Casadevall

    As humanity comes into contact with new microbes, there is a need to identify which might be future pathogenic threats. Host–microbe interactions manifest emergent properties and chaotic dynamics, posing limits on prediction. However, probabilistic predictions are possible. To what extent can we predict future pathogenic microbes? This Perspective discusses why complex requirements for virulence and dynamic host-microbe interactions make probabilistic predictions difficult, but not impossible.

  • Phosphatase-independent activity of smooth-muscle calcineurin orchestrates a gene expression program leading to hypertension

    by Paula Sofía Yunes-Leites, Yilin Sun, Sara Martínez-Martínez, Álvaro Alfayate, Marta Toral, María José Méndez-Olivares, Ángel Colmenar, Ana Isabel Torralbo, Dolores López-Maderuelo, Sergio Mateos-García, David N. Cornfield, Jesús Vázquez, Juan Miguel Redondo, Miguel R. Campanero

    Angiotensin-II (Ang-II) drives pathological vascular wall remodeling in hypertension and abdominal aortic aneurysm (AAA) through mechanisms that are not completely understood. Previous studies showed that the phosphatase activity of calcineurin (Cn) mediates Ang-II-induced AAA, but the cell type involved in the action of Cn in AAA formation remained unknown. Here, by employing newly created smooth muscle cell (SMC)-specific and endothelial cell (EC)-specific Cn-deficient mice (SM-Cn−/− and EC-Cn−/− mice), we show that Cn expressed in SMCs, but not ECs, was required for Ang-II-induced AAA. Unexpectedly, SMC Cn also played a structural role in the early onset and maintenance of Ang-II-induced hypertension, independently of its known phosphatase activity. Among the signaling pathways activated by Ang-II, Cn signaling is essential in SMCs, as nearly 90% of the genes regulated by Ang-II in the aorta required Cn expression in SMCs. Cn orchestrated, independently of its enzymatic activity, the induction by Ang-II of a transcriptional program closely related to SMC contractility and hypertension. Cn deletion in SMCs, but not its pharmacological inhibition, impaired the regulation of arterial contractility. Among the genes whose regulation by Ang-II required Cn expression but not its phosphatase activity, we discovered that Serpine1 was critical for Ang-II-induced hypertension. Indeed, pharmacological inhibition of PAI-1, the protein encoded by Serpine1, impaired SMCs contractility and readily regressed hypertension. Mechanistically, Serpine1 induction was mediated by Smad2 activation via the structural role of Cn. These findings uncover an unexpected role for Cn in vascular pathophysiology and highlight PAI-1 as a potential therapeutic target for hypertension.

  • Molecular states underlying neuronal cell type development and plasticity in the postnatal whisker cortex

    by Salwan Butrus, Hannah R. Monday, Christopher J. Yoo, Daniel E. Feldman, Karthik Shekhar

    Mouse whisker somatosensory cortex (wS1) is a major model system to study the experience-dependent plasticity of cortical neuron physiology, morphology, and sensory coding. However, the role of sensory experience in regulating neuronal cell type development and gene expression in wS1 remains poorly understood. We assembled a transcriptomic atlas of wS1 during postnatal development comprising 45 molecularly distinct neuronal types that can be grouped into eight excitatory and four inhibitory neuron subclasses. Between postnatal day (P) 12, the onset of active whisking, and P22, when classical critical periods close, ~ 250 genes were regulated in a neuronal subclass-specific fashion when whisker experience was normal. At the resolution of neuronal types, only the composition of layer (L) 2/3 glutamatergic neurons, but not other neuronal types, changed substantially between P12 and P22. These postnatal compositional changes in L2/3 neuronal types resemble those observed previously in the primary visual cortex (V1), and the temporal gene expression changes were also highly conserved between the regions. Unlike V1, however, cell type maturation in wS1 is not substantially dependent on sensory experience, as 10-day full-face whisker deprivation from P12 to P22 did not influence the transcriptomic identity nor composition of L2/3 neuronal types. A one-day competitive whisker deprivation protocol from P21 to P22 also did not affect cell type identity but induced moderate changes in plasticity-related gene expression. Thus, developmental maturation of cell types is similar in V1 and wS1, but sensory deprivation minimally affects cell type development in wS1.