Neurons and Glial Cells

Implication of the glutamine synthetase ⁄ glutamate synthase pathway in conditioning the amino acid metabolism in bundle sheath and mesophyll cells of maize leaves Marie-He ´ le ` ne Valadier 1 , Ayako Yoshida 2 , Olivier Grandjean 3 , Halima Morin 3 , Jocelyne Kronenberger 3 , Ste ´ phanie Boutet 1 , Adeline Raballand 1 , Toshiharu Hase 2 , Tadakatsu Yoneyama 4 and Akira Suzuki 1 1 Unite ´ de Nutrition Azote ´ e des Plantes, Institut National de la Recherche Agronomique, Versailles, France 2 Institute for Protein Research, Osaka University, Japan 3 Laboratoire Commun de Cytologie, Institut National de la Recherche Agronomique, Versailles, France 4 Department of Applied Biological Chemistry, University of Tokyo, Japan In the C 4 plant maize, inorganic nitrate reduction to ammonium and subsequent ammonium assimilation into amino acids occur in two different photosyn- thetic cells: bundle sheath cells (BSCs) and mesophyll cells (MCs). Nitrate taken up by roots moves in part, via the vascular bundle, to leaves for reduction. Keywords amino acid translocation; compartmentation; glutamine and glutamate synthesis; nitrogen assimilation; Zea mays L Correspondence A. Suzuki, Unite ´ de Nutrition Azote ´ e des Plantes, Institut National de la Recherche Agronomique, Route de St-Cyr, 78026 Versailles cedex, France Fax: +33 1 30 83 30 96 Tel: +33 1 30 83 30 87 E-mail: suzuki@versailles.inra.fr (Received 20 February 2008, revised 16 April 2008, accepted 17 April 2008) doi:10.1111/j.1742-4658.2008.06472.x We investigated the role of glutamine synthetases (cytosolic GS1 and chlo- roplast GS2) and glutamate synthases (ferredoxin-GOGAT and NADH- GOGAT) in the inorganic nitrogen assimilation and reassimilation into amino acids between bundle sheath cells and mesophyll cells for the remo- bilization of amino acids during the early phase of grain filling in Zea mays L. The plants responded to a light ⁄ dark cycle at the level of nitrate, ammo- nium and amino acids in the second leaf, upward from the primary ear, which acted as the source organ. The assimilation of ammonium issued from distinct pathways and amino acid synthesis were evaluated from the diurnal rhythms of the transcripts and the encoded enzyme activities of nitrate reductase, nitrite reductase, GS1, GS2, ferredoxin-GOGAT, NADH-GOGAT, NADH-glutamate dehydrogenase and asparagine synthe- tase. We discerned the specific role of the isoproteins of ferredoxin and ferredoxin:NADP + oxidoreductase in providing ferredoxin-GOGAT with photoreduced or enzymatically reduced ferredoxin as the electron donor. The spatial distribution of ferredoxin-GOGAT supported its role in the nitrogen (re)assimilation and reallocation in bundle sheath cells and mesophyll cells of the source leaf. The diurnal nitrogen recycling within the plants took place via the specific amino acids in the phloem and xylem exudates. Taken together, we conclude that the GS1 ⁄ ferredoxin-GOGAT cycle is the main pathway of inorganic nitrogen assimilation and recycling into glutamine and glutamate, and preconditions amino acid inter- conversion and remobilization. Abbreviations AS, asparagine synthetase (EC 6.3.5.4); BSC, bundle sheath cells; DIG, digoxigenin; Fd, ferredoxin; Fd-NiR, ferredoxin-nitrite Neurons and Glial Cells Neurons and Glial Cells Bởi: OpenStaxCollege Nervous systems throughout the animal kingdom vary in structure and complexity, as illustrated by the variety of animals shown in [link] Some organisms, like sea sponges, lack a true nervous system Others, like jellyfish, lack a true brain and instead have a system of separate but connected nerve cells (neurons) called a “nerve net.” Echinoderms such as sea stars have nerve cells that are bundled into fibers called nerves Flatworms of the phylum Platyhelminthes have both a central nervous system (CNS), made up of a small “brain” and two nerve cords, and a peripheral nervous system (PNS) containing a system of nerves that extend throughout the body The insect nervous system is more complex but also fairly decentralized It contains a brain, ventral nerve cord, and ganglia (clusters of connected neurons) These ganglia can control movements and behaviors without input from the brain Octopi may have the most complicated of invertebrate nervous systems—they have neurons that are organized in specialized lobes and eyes that are structurally similar to vertebrate species 1/11 Neurons and Glial Cells Nervous systems vary in structure and complexity In (a) cnidarians, nerve cells form a decentralized nerve net In (b) echinoderms, nerve cells are bundled into fibers called nerves In animals exhibiting bilateral symmetry such as (c) planarians, neurons cluster into an anterior brain that processes information In addition to a brain, (d) arthropods have clusters of nerve cell bodies, called peripheral ganglia, located along the ventral nerve cord Mollusks such as squid and (e) octopi, which must hunt to survive, have complex brains containing millions of neurons In (f) vertebrates, the brain and spinal cord comprise the central nervous system, while neurons extending into the rest of the body comprise the peripheral nervous system (credit e: modification of work by Michael Vecchione, Clyde F.E Roper, and Michael J Sweeney, NOAA; credit f: modification of work by NIH) Compared to invertebrates, vertebrate nervous systems are more complex, centralized, and specialized While there is great diversity among different vertebrate nervous systems, they all share a basic structure: a CNS that contains a brain and spinal cord and a PNS made up of peripheral sensory and motor nerves One interesting difference between the nervous systems of invertebrates and vertebrates is that the nerve cords of many invertebrates are located ventrally whereas the vertebrate spinal cords are located dorsally There is debate among evolutionary biologists as to whether these different nervous system plans evolved separately or whether the invertebrate body plan arrangement somehow “flipped” during the evolution of vertebrates Link to Learning 2/11 Neurons and Glial Cells Watch this video of biologist Mark Kirschner discussing the “flipping” phenomenon of vertebrate evolution The nervous system is made up of neurons, specialized cells that can receive and transmit chemical or electrical signals, and glia, cells that provide support functions for the neurons by playing an information processing role that is complementary to neurons A neuron can be compared to an electrical wire—it transmits a signal from one place to another Glia can be compared to the workers at the electric company who make sure wires go to the right places, maintain the wires, and take down wires that are broken Although glia have been compared to workers, recent evidence suggests that also usurp some of the signaling functions of neurons There is great diversity in the types of neurons and glia that are present in different parts of the nervous system There are four major types of neurons, and they share several important cellular components Neurons The nervous system of the common laboratory fly, Drosophila melanogaster, contains around 100,000 neurons, the same number as a lobster This number compares to 75 million in the mouse and 300 million in the octopus A human brain contains around 86 billion neurons Despite these very different numbers, the nervous systems of these animals control many of the same behaviors—from basic reflexes to more complicated behaviors like finding food and courting mates The ability of neurons to communicate with each other as well as with other types of cells underlies all of these behaviors Most neurons share the same cellular components But neurons are also highly specialized—different types of neurons have different sizes and shapes that relate to their functional roles Parts of a Neuron Like other cells, each neuron has a cell body (or soma) that contains a nucleus, smooth and rough endoplasmic reticulum, Golgi apparatus, mitochondria, and other cellular components Neurons also contain unique structures, illustrated in [link] for receiving and sending the electrical signals that make neuronal communication possible 3/11 Neurons and Glial Cells Dendrites are tree-like structures ...Transport and Translocation of Water and Solutes UNIT I [...]... stress (see Chapter 23) (After Hsiao 1979.) FIGURE 3. 12 Protein synthesis Well-watered plants Plants under mild water stress Plants in arid, desert climates –4 Water and Plant Cells lation of solutes, closing of stomata, and inhibition of photosynthesis Water potential is one measure of how hydrated a plant is and thus provides a relative index of the water stress the plant is experiencing (see Chapter. .. permeability to water, is one of the factors determining the velocity of water movements in plants 3. 7 Wilting and Plasmolysis Plasmolysis is a major structural change resulting from major water loss by osmosis Chapter References Dainty, J (1976) Water relations of plant cells In Transport in Plants, Vol 2, Part A: Cells (Encyclopedia of Plant Physiology, New Series, Vol 2.), U Lüttge and M G Pitman,... (1996) Cotransport of water by the Na+/glucose cotransporter Proc Natl Acad Sci USA 93: 133 67– 133 70 Nobel, P S (1999) Physicochemical and Environmental Plant Physiology, 2nd ed Academic Press, San Diego, CA Schäffner, A R (1998) Aquaporin function, structure, and expression: Are there more surprises to surface in water relations? Planta 204: 131 – 139 Stein, W D (1986) Transport and Diffusion across Cell... Steudle, E., and Smith, J A C (1999) Plant aquaporins: Their molecular biology, biophysics and significance for plant water relations J Exp Bot 50: 1055–1071 Tyree, M T., and Jarvis, P G (1982) Water in tissues and cells In Physiological Plant Ecology, Vol 2: Water Relations and Carbon Assimilation (Encyclopedia of Plant Physiology, New Series, Vol 12B), O L Lange, P S Nobel, C B Osmond, and H Ziegler,... and water within sieve tubes occurs along gradients in hydrostatic 43 Water and Plant Cells (turgor) pressure rather than by osmosis Thus, within the phloem, water can be transported from regions with lower water potentials (e.g., leaves) to regions with higher water potentials (e.g., roots) These situations notwithstanding, in the vast majority of cases water in plants moves from higher to lower water. .. provides us with a better understanding of the water relations literature 3. 4 The Matric Potential A brief discussion of the concept of matric potential, used to quantify the chemical potential of water in soils, seeds, and cell walls 3. 5 Measuring Water Potential A detailed description of available methods to measure water potential in plant cells and tissues 3. 6 Understanding Hydraulic Conductivity... transport, water potential is a useful measure of the water status of plants As we will see in Chapter 4, diffusion, bulk flow, and osmosis all 46 Chapter 3 help move water from the soil through the plant to the atmosphere Web Material Web Topics 3. 1 Calculating Capillary Rise Quantification of capillary rise allows us to assess the functional role of capillary rise in water movement of plants 3. 2 Calculating... drier, the plant similarly becomes less hydrated (attains a lower Yw) If this were not the case, the soil would begin to extract water from the plant The Components of Tachykinin-related peptide precursors in two cockroach species Molecular cloning and peptide expression in brain neurons and intestine Reinhard Predel 1 , Susanne Neupert 1 , Steffen Roth 1 , Christian Derst 1 and Dick R. Na ¨ ssel 2 1 Saxon Academy of Sciences, Research Group Jena, Germany 2 Department of Zoology, Stockholm University, Sweden Tachykinins constitute a family of multifunctional neuropeptides whose signaling mechanisms seem to be partially conserved through evolution [1–5]. Although the tachykinin peptides display only limited sequence identities when comparing invertebrates and mammals, their G-protein-coupled receptors (GPCRs) display more striking similarities, suggesting ancestral relation- ships [4,5]. The three principal mammalian tachyki- nins, substance P, neurokinin A and neurokinin B, are processed from two precursors, preprotachykinin A and B and they act with preferential affinities on three different GPCRs, NK1–NK3 [5]. More recently, addi- tional tachykinins, the hemokinins, were identified on a third precursor encoding gene, preprotachykinin C, expressed in hematopoietic cells of mouse, rat and humans [6,7]. In invertebrates the tachykinins exist in two major forms: (a) the tachykinin-related peptides (TKRPs; pre- viously termed TRPs) that differ from the mammalian tachykinins by having a C-terminus FXGXRamide (X ¼ variable residues), rather than FXGLMamide and (b) invertebrate tachykinins (Inv-TKs) with an Keywords brain-gut peptides; insect neuropeptide; neurochemistry; mass spectrometry; Periplaneta americana; Leucophaea maderae Correspondence R. Predel, Saxon Academy of Sciences, Research Group Jena, Erbertstraße 1, 07743 Jena, Germany Tel: +49 3641 949191 Fax: +49 3641 949192 E-mail: B6PRRE@pan.zoo.uni-jena.de (Received 1 March 2005, revised 22 April 2005, accepted 6 May 2005) doi:10.1111/j.1742-4658.2005.04752.x Tachykinins and tachykinin-related peptides (TKRPs) play major roles in signaling in the nervous system and intestine of both invertebrates and ver- tebrates. Here we have identified cDNAs encoding precursors of multiple TKRPs from the cockroaches Leucophaea maderae and Periplaneta ameri- cana. All nine LemTKRPs that had been chemically isolated in earlier experiments could be identified on the precursor of L. maderae. Four previ- ously unidentified LemTKRPs were found in addition on the precursor. The P. americana cDNA displayed an open reading frame very similar to that of L. maderae with 13 different TKRPs. MALDI-TOF mass spectra from tissues of both species confirms the presence of all the TKRPs enco- ded on the precursor plus two additional peptides that are cleavage prod- ucts of the N-terminally extended TKRPs. A tissue-specific distribution of TKRPs was observed in earlier experiments at isolation from brain and midgut of L. maderae. Our data do not suggest a differential gene expression but a different efficacy in processing of LemTKRP-2 and Lem ⁄ PeaTKRP-3 in the brain and intestine, respectively. This results in a gut-specific accumulation of these extended peptides, whereas in the brain their cleavage products, LemTKRP-1 and LemTKRP-3 11)19 , are most abundant. Mass spectrometric analysis demonstrated the occurrence of the different TKRPs in single glomeruli of the tritocerebrum and in cells of the optical lobe. Abbreviations ESI-Q-TOF MS, electrospray ionization quadrupole time-of-flight mass spectrometry; GPCR, G-protein-coupled receptors; TKRP, tachykinin- related peptide. FEBS Journal 272 (2005) 3365–3375 ª 2005 FEBS 3365 FXGLMamide C-terminus [2,4]. As there is no evidence that the insect and molluscan Inv-TKs display biological activity in the native organism, Multidentate pyridinones inhibit the metabolism of nontransferrin-bound iron by hepatocytes and hepatoma cells Anita C. G. Chua 1 , Helen A. Ingram 1 , Kenneth N. Raymond 2 and Erica Baker 1 1 Physiology, School of Biomedical and Chemical Sciences, University of Western Australia, Crawley, Western Australia, Australia, 2 Department of Chemistry, University of California, Berkeley, California, USA The therapeutic effect of iron (Fe) chelators on the poten- tially toxic plasma pool of nontransferrin-bound iron (NTBI), often present in Fe overload diseases and in some cancer patients during chemotherapy, is of considerable interest. In the present investigation, several multidentate pyridinones were synthesized and compared with their bidentate analogue, deferiprone (DFP; L1, orally active) and desferrioxamine (DFO; hexadentate; orally inactive) for their effect on the metabolism of NTBI in the rat hepato- cyte and a hepatoma cell line (McArdle 7777, Q7). Hepa- toma cells took up much less NTBI than the hepatocytes (< 10%). All the chelators inhibited NTBI uptake (80–98%) much more than they increased mobilization of Fe from cells prelabelled with NTBI (5–20%). The hexadentate pyridinone, N,N,N-tris(3-hydroxy-1-methyl-2(1H)-pyridi- none-4-carboxaminoethyl)amine showed comparable acti- vity to DFO and DFP. There was no apparent correlation between Fe status, Fe uptake and chelator activity in hepatocytes, suggesting that NTBI transport is not regulated by cellular Fe levels. The intracellular distribution of iron taken up as NTBI changed in the presence of chelators suggesting that the chelators may act intracellularly as well as at the cell membrane. In conclusion (a) rat hepatocytes have a much greater capacity to take up NTBI than the rat hep- atoma cell line (Q7), (b) all chelators bind NTBI much more effectively during the uptake phase than in the mobilization of Fe which has been stored from NTBI and (c) while DFP is the most active chelator, other multidentate pyridinones have potential in the treatment of Fe overload, particularly at lower, more readily clinically available concentrations, and during cancer chemotherapy, by removing plasma NTBI. Keywords: non-transferrin bound iron; liver cells; iron che- lation therapy; chemotherapy. Iron (Fe) is transported in blood plasma bound tightly in a nontoxic form to the plasma iron-binding protein, trans- ferrin (Tf). Under normal conditions, Tf is 20–50% saturatedwithFe.However,insomecases,particularly when the concentration of Fe in the plasma exceeds the Fe-binding capacity of Tf, there is additional Fe circulating in non-Tf bound forms (NTBI). This is of particular concern in diseases of Fe overload such as the genetic disorder hemochromatosis [1–3], in which there is an abnormally high absorption of Fe leading to saturation of the plasma Tf. Patients with the hereditary anemia thalassemia [4,5] also have increased plasma Fe, primarily due to the obligatory treatment of the anemia with blood transfusions. The contribution of plasma NTBI to the toxicity associated with Fe overload in these disorders is uncertain, as is the form of NTBI. Significant levels of NTBI in plasma also occur in cancer as a result of some chemotherapeutic regimes [6–8]. The source of this Fe, its toxicity, and whether it can be cleared by the liver or taken up by cancer cells and used in Fe-dependent reactions essential for growth and Enzymes of creatine biosynthesis, arginine and methionine metabolism in normal and malignant cells Soumen Bera 1 , Theo Wallimann 2 , Subhankar Ray 1 and Manju Ray 1 1 Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata, India 2 Institute of Cell Biology, ETH Zurich, Switzerland In a previous study concerning the status of the crea- tine ⁄ creatine kinase (CK) system in relation to sar- coma development, we demonstrated that creatine, phosphocreatine (PCr) and creatine kinase decreased progressively in sarcoma tissue compared to normal contralateral muscle [1]. Protein and mRNA expres- sion levels of creatine kinase isoforms were signifi- cantly downregulated. From that study, it appeared that the creatine ⁄ PCr ⁄ CK system is gradually and stea- dily downregulated in sarcoma during tumor growth. Based on this finding, the question naturally arises as to the status of creatine transport and synthesis in Keywords arginine; creatine; methionine; normal muscle; sarcoma Correspondence M. Ray, Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India Fax: +91 33 2473 2805 Tel: +91 33 2473 4971 E-mail: bcmr@mahendra.iacs.res.in (Received 19 August 2008, revised 24 September 2008, accepted 30 September 2008) doi:10.1111/j.1742-4658.2008.06718.x The creatine ⁄ creatine kinase system decreases drastically in sarcoma. In the present study, an investigation of catalytic activities, western blot and mRNA expression unambiguously demonstrates the prominent expression of the creatine-synthesizing enzymes l-arginine:glycine amidinotransferase and N-guanidinoacetate methyltransferase in sarcoma, Ehrlich ascites carci- noma and Sarcoma 180 cells, whereas both enzymes were virtually unde- tectable in normal muscle. Compared to that of normal animals, these enzymes remained unaffected in the kidney or liver of sarcoma-bearing mice. High activity and expression of mitochondrial arginase II in sarcoma indicated increased ornithine formation. Slightly or moderately higher levels of ornithine, guanidinoacetate and creatinine were observed in sar- coma compared to muscle. Despite the intrinsically low level of creatine in Ehrlich ascites carcinoma and Sarcoma 180 cells, these cells could signifi- cantly take up and release creatine, suggesting a functional creatine trans- port, as verified by measuring mRNA levels of creatine transporter. Transcript levels of arginase II, ornithine-decarboxylase, S-adenosyl-homo- cysteine hydrolase and methionine-synthase were significantly upregulated in sarcoma and in Ehrlich ascites carcinoma and Sarcoma 180 cells. Over- all, the enzymes related to creatine and arginine ⁄ methionine metabolism were found to be significantly upregulated in malignant cells. However, the low levels of creatine kinase in the same malignant cells do not appear to be sufficient for the building up of an effective creatine ⁄ phosphocreatine pool. Instead of supporting creatine biosynthesis, l-arginine:glycine ami- dinotransferase and N-guanidinoacetate methyltransferase appear to be geared to support cancer cell metabolism in the direction of polyamine and methionine synthesis because both these compounds are in high demand in proliferating cancer cells. Abbreviations 3MC, 3-methylcholanthrene; AGAT, L-arginine:glycine ... myelin sheath, and satellite cells, which provide nutrients and structural support to neurons 9/11 Neurons and Glial Cells (a) Astrocytes and (b) oligodendrocytes are glial cells of the central nervous... of the nervous system (and across species), as illustrated by the neurons shown in [link] 5/11 Neurons and Glial Cells There is great diversity in the size and shape of neurons throughout the... the fluid between the spinal cord and the brain, and is a component for the choroid plexus Glial cells support neurons and maintain their environment Glial cells of the (a) central nervous system