Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.49 (reverse transcriptase)
31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Before becoming acyclic, middle-aged rats display an attenuated LH surge and a decreased number of activated GnRH neurons. The present study examined whether the decreased activation of GnRH neurons in middle-aged rats could be due to defective glutamate neurosignaling in the hypothalamus. Arcuate nucleus/median eminence (ARC/ME) fragments were isolated from young (2-month-old) and middle-aged (9- to 11-month-old) rats at 1700 h on proestrus and incubated in vitro with or without the specific glutamate agonists, D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (1 mM), kainate (1 mM), and N-methyl-D-aspartate (NMDA; 50 mM). The results showed that basal GnRH release was similar in the two age groups. In contrast, stimulated GnRH release by D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid, kainate, and NMDA was significantly attenuated in middle-aged vs. young rats. KCl stimulation at the end of the experiments confirmed the viability of all ARC/ME fragments. Quantitative reverse transcriptase-PCR revealed that messenger RNA levels for the major NMDA receptor subunit (NMDAR1) were significantly lower in the preoptic area and ARC/ME of the middle-aged rat on proestrus afternoon. As a whole, these findings suggest that a defect in hypothalamic glutamate neurosignaling may be an important mechanism leading to age-related defects in LH secretion and acyclicity in female animals.
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PMID:Decreased gonadotropin-releasing hormone neurosecretory response to glutamate agonists in middle-aged female rats on proestrus afternoon: a possible role in reproductive aging? 864 Nov 83

Receptor proteins for photoreception have been studied for several decades. More recently, putative receptors for olfaction have been isolated and characterized. In contrast, no receptors for taste have been identified yet by molecular cloning. This report describes experiments aimed at identifying a receptor responsible for the taste of monosodium glutamate (MSG). Using reverse transcriptase (RT)-PCR, we found that several ionotropic glutamate receptors are present in rat lingual tissues. However, these receptors also could be detected in lingual tissue devoid of taste buds. On the other hand, RT-PCR and RNase protection assays indicated that a G-protein-coupled metabotropic glutamate receptor, mGluR4, also is expressed in lingual tissues and is limited only to taste buds. In situ hybridization demonstrated that mGluR4 is detectable in 40-70% of vallate and foliate taste buds but not in surrounding nonsensory epithelium, confirming the localization of this metabotropic receptor to gustatory cells. Expression of mGluR4 in taste buds is higher in preweaning rats compared with adult rats. This may correspond to the known higher sensitivity to the taste of MSG in juvenile rodents. Finally, behavioral studies have indicated that MSG and L-2-amino-4-phosphonobutyrate (L-AP4), a ligand for mGluR4, elicit similar tastes in rats. We conclude that mGluR4 may be a chemosensory receptor responsible, in part, for the taste of MSG.
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PMID:The taste of monosodium glutamate: membrane receptors in taste buds. 865 76

In plants tetrapyrrole synthesis is initially light regulated on the level of 5-aminolevulinate (ALA) synthesis. ALA is formed from glutamate in three enzymatic steps. Glutamyl tRNA reductase (GluTR) catalyses the NADPH-dependent reduction of glutamyl tRNA to glutamate 1-semialdehyde. GluTR is encoded by a low-copy gene family consisting of three to four genes. Three different cDNA clones are presented. Full-length clones BHA1 and 87 differ in the length of the 3' untranslated region and code for a 58.5 kDa protein. The sequence of the partial clone, BHA13, contains at least 87 base mismatches in the coding region for the mature GluTR resulting in 11 amino acid substitutions. Synthesis of a recombinant mature and a truncated GluTR lacking the first 19 amino terminal amino acids in Escherichia coli lead only in the latter case to complementation of an E. coli hemA mutant. Steady-state level of BHA1- and BHA13-specific mRNA encoding GluTR were analysed by Northern blot hybridization using cDNA-specific oligo nucleotides and quantitative reverse transcriptase-polymerase chain reaction. Accumulation of the two RNA species is light induced in greening barley and controlled during cellular development. In contrast to BHA13, BHA1 transcripts are present in roots and are elevated after cytokinin treatment of dark-grown seedlings. Furthermore, BHA1 mRNA shows oscillation under circadian growth conditions. GluTR transcript levels correlate with the capacity for ALA synthesis indicating that the rate-limiting substrate flux through the ALA synthesizing pathway can be at least partially attributed to GluTR expression. Consequences of the initial control of the chlorophyll metabolic pathway on the level of ALA formation are discussed.
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PMID:Members of a low-copy number gene family encoding glutamyl-tRNA reductase are differentially expressed in barley. 869 65

Selection of the IIIB strain of human immunodeficiency virus type (HIV-1) resistant to the (alkylamino)piperidine-bis(heteroaryl)piperazine (AAP-BHAP) U-104489 results in substitution of a glycine to glutamate at residue 190 (G190E) of reverse transcriptase (RT). The AAP-BHAP resistant HIV-1 displays reduced in vitro replication capacity [Olmsted, R. A., et. al. (1966) J. Virol. 70, 3698-3705]. We report here that the G190E mutation in recombinant heterodimeric HIV-1 RT, compared to the wild-type RT (G190) or a G190A control mutant, results in a 40% and 80% reduction in the polymerase and RNase H specific enzymatic activities, respectively. A primer-extension assay that allowed determination of DNA elongation by the G190E mutant RT on a heteropolymeric HIV-1 gag-based RNA template showed an overall decrease in DNA polymerization. The size distribution of products generated by G190E RT-associated RNase H digestion of RNA from [35S]poly(rA).poly(dT) was markedly distinct from that of the G190A RT and was consistent with the observed reduction in RT-associated RNase H activity of the G190E RT. When challenged with unlabeled substrates, the G190E RT was relatively nonprocessive with respect to DNA synthesis and RNA degradation. It is concluded that the deleterious effect of the G190E resistance mutation on both of these RT functions is most likely involved in the observed retarded replication capacity of the AAP-BHAP-(U-104489-) resistant HIV-1.
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PMID:A drug resistance mutation in the inhibitor binding pocket of human immunodeficiency virus type 1 reverse transcriptase impairs DNA synthesis and RNA degradation. 870 45

We evaluated expression of N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptor (GluR) genes by reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern blotting in nine established cell lines: rat CG-4 (oligodendroglial lineage) and RINm5F insulinoma cells; human CHP134, SMS-KCNR, SKNSH, and Nb69 neuroblastoma cells; and human D384Med, D425Med, and D458Med medulloblastoma cells. CG-4 expressed mRNAs encoding GluR2-7, KA-1, and KA-2 non-NMDA GluR (Yoshioka et al.: J Neurochem 64:2442-2448, 1995) and NR1 (NMDAR1) and NR2D NMDA GluR. After differentiation to oligodendrocyte-like cells, CG-4 also expressed NR2B mRNA. Rat insulinoma cells expressed GluR5 and KA-2 non-NMDA and NR1 and NR2D NMDA GluR mRNAs. The four human neuroblastoma lines all expressed mRNAs encoding GluR2-4, 6, 7 and KA-1 non-NMDA and NR1 NMDA GluR, and the three human medulloblastoma cell lines all expressed mRNAs encoding GluR1, 6 and KA-1, but none of the NMDA GluRs. Whereas CG-4 is susceptible to kainate excitotoxicity, treatment of insulinoma, neuroblastoma, and medulloblastoma lines with L-glutamate, kainate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), or NMDA failed to cause cell damage or to augment 45Ca2+ influx. Thus, despite expressing a variety of non-NMDA and NMDA GluR genes, the human neuroblastoma and medulloblastoma and rat insulinoma lines failed to assemble Ca(2+)-permeable NMDA or non-NMDA GluR channels. This failure confers protection against excitotoxicity and may contribute to progression of tumors of these types.
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PMID:Expression of N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptor genes in neuroblastoma, medulloblastoma, and other cells lines. 891 93

The gamma-aminobutyric acid (GABA)-synthesizing enzyme glutamate decarboxylase (GAD) was studied during development of the chick telencephalon. By means of reverse-phase HPLC analysis, we showed that GABA indeed accumulates during embryogenesis, whereas the levels of glutamate, the substrate for GAD, are more or less unchanged up to later developmental stages. The enzyme activity increased approximately 25-fold from embryonic day 3 to embryonic day 17. Immunoblotting data revealed that two GAD proteins, of approximately 65 and 67 kDa, were present during the period investigated. Furthermore, Northern blot analysis with probes obtained from rat cDNA sequences, as well as a chicken-specific probe for GAD65 generated by means of reverse transcriptase-polymerase chain reaction (RT-PCR), strengthened the interpretation that the chick embryo expresses genes corresponding to GAD65 and GAD67. The rat probes recognized transcript sizes of 3.9 kb (GAD65) and 5.6 kb (GAD67), sizes which are different from those of the rat brain (Erlander et al., Neuron, 7, 91-100, 1991). Sequencing of the RT-PCR products revealed a high level of homology (82% at the nucleotide level) between the mammalian and chick GAD65 genes. Taken together, these findings suggest that the chick embryo expresses two GAD genes during embryogenesis. The functional properties of each gene product remain to be investigated.
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PMID:Two glutamate decarboxylase forms corresponding to the mammalian GAD65 and GAD67 are expressed during development of the chick telencephalon. 892 2

GluR2 is the key subunit of heteromeric AMPA-preferring glutamate receptors. GluR2 mRNA has been shown by in situ hybridization histochemistry to be decreased in the hippocampal formation in schizophrenics. Here, a quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method was used to investigate GluR2 expression further and to examine the relative abundance of its alternatively spliced mRNA isoforms ('flip' and 'flop') in 11 schizophrenics and 11 matched controls. Compared to the controls, schizophrenics showed reduced expression of both isoforms relative to cyclophilin mRNA, but a greater loss of the flop isoform led to a higher flip:flop ratio. These differences were observed having controlled for the confounding effects of brain pH and age upon the mRNAs. We also found that the abundance of GluR2 mRNA correlates with that of the encoded subunit. This study has confirmed that, in schizophrenia, hippocampal GluR2 mRNA is reduced, and indicates that GluR2 subunits are composed of a higher proportion of the flip variant. These data extend the evidence for glutamatergic dysfunction in the disease. They suggest that signal transduction through hippocampal AMPA receptors is impaired in schizophrenia both by an overall loss of GluR2 expression, and by the change in flip:flop ratio which is predicted to alter the desensitization kinetics of the remaining GluR2 subunits.
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PMID:GluR2 glutamate receptor subunit flip and flop isoforms are decreased in the hippocampal formation in schizophrenia: a reverse transcriptase-polymerase chain reaction (RT-PCR) study. 903 Jul 2

Cell surface proteoglycans (PGs) have been implicated in neuronal growth, migration and differentiation and can play pivotal roles both in cell-cell and cell-substrate interactions during the development of the nervous system. We have previously shown that glutamate activation of excitatory amino acid receptors induces the synthesis and release of PGs with neurite-promoting activity from hippocampal neurones. In this study, we have investigated the activity-dependent regulation of mRNA expression of two PGs in fetal hippocampal neurones using a competitive reverse transcriptase-polymerase chain reaction and correlated this expression with neuronal growth. Both cerebroglycan (CBG), a glycosylphatidylinositol-anchored heparan sulphate PG, and neurocan, a developmentally regulated chondroitin sulphate PG, are expressed in hippocampal neurones. Exposure of hippocampal neurones to 100 microM glutamate for 5 min resulted in an increase in CBG mRNA levels and an increase in axonal and dendritic length. The increase in CBG mRNA levels following glutamate exposure was mediated via both N-methyl-D-aspartate and metabotropic receptor activation.
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PMID:Differential regulation of neuronal proteoglycans by activation of excitatory amino acid receptors. 910 42

In this study, we analysed the molecular heterogeneity and synaptic localization of the N-methyl-D-aspartate receptor subunit 1 and the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor subunit 1 in the olfactory bulb glomerular synaptic circuitry. Semiquantitative reverse transcriptase polymerase chain reaction showed that approximately 40% of the N-methyl-D-aspartate receptor subunit 1 messenger RNA splice variants contain the N1 exon, which conveys specific functional properties on the channel. In other forebrain and hindbrain regions that we examined, the ratio of the N1-containing (receptor subunit 1(1XX)) to N1-lacking (receptor subunit 1(0XX)) N-methyl-D-aspartate receptor subunit 1 messenger RNAs varied considerably. The cellular and subcellular distribution of N-methyl-D-aspartate receptor subunit 1 and AMPA receptor subunit 1 was investigated with antibodies generated against the C-terminal domain of the individual subunits [Petralia R. S. et al. (1994) J. Neurosci. 14, 667 696; Wenthold R. J. et al. (1992) J. biol Chem. 267, 501 507]. Both N-methyl-D-aspartate receptor subunit 1 and AMPA receptor subunit 1 were localized to the postsynaptic density of asymmetric synapses established by olfactory receptor neuron terminals with the dendrites of mitral and tufted cells. Not all of these synapses, however, were labelled. These results are consistent with the notion that glutamate is the neurotransmitter at the olfactory nerve to mitral and tufted cell synapses, and suggest a high heterogeneity in the expression of the postsynaptic glutamate receptors.
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PMID:Glutamate receptors in the olfactory bulb synaptic circuitry: heterogeneity and synaptic localization of N-methyl-D-aspartate receptor subunit 1 and AMPA receptor subunit 1. 913 51

The channel properties of the multimeric ionotropic glutamate receptors can be regulated by their subunit composition. The relationship between the structure and physiological functions of glutamate receptors, however, is difficult to study in the CNS because of the large number of these subunits, their widespread distribution, and neuronal heterogeneity. To avoid these difficulties, and to uncover possible novel functions of ionotropic glutamate receptors in sensory neurons, we examined the expression of non-N-methyl-D-aspartate glutamate receptor subunits in a simple neuronal system: the olfactory epithelium. It contains only one neuronal type, the olfactory receptor neuron, that receives no synaptic innervation within the epithelium and therefore should not require conventional postsynaptic glutamate receptors. The axons of these neurons, however, terminate and release glutamate in the glomerular region of the olfactory bulb, and may contain presynaptic glutamate receptors. By reverse transcriptase-polymerase chain reaction amplification and RNase protection assays, we showed that a subset of non-N-methyl-D-aspartate receptor subunits is expressed in the olfactory epithelium. The most abundant is KA2, which can form kainate-selective ion channels with GluR5 or GluR6. Messenger RNAs for GluR6, and for the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate/kainate-type (AMPA/KA) GluR2 and GluR3 subunits, are also present, but at levels lower than that of KA2 by an order of magnitude. In situ hybridization and immunocytochemistry localized KA2 to only the olfactory receptor neurons, and not to any other cell type in the olfactory epithelium. Surprisingly, antibodies against KA2 or GluR5/6/7 primarily stained the olfactory neuron dendritic knobs that are specialized for odorant signalling at the sensory epithelial lumenal surface, and the olfactory neuron axon bundles that project to the olfactory bulb. The presence of a limited subset of non-N-methyl-D-aspartate receptor subunits in the olfactory epithelium, and the localization of a kainate-selective receptor to both the axons and specialized dendritic knobs of olfactory receptor neurons, which receive no known synaptic input, suggest that these non-N-methyl-D-aspartate receptor subtypes may mediate either novel non-synaptic functions in the olfactory neuron dendrites or presynaptic functions in the olfactory nerve terminals or axons. These data also suggest that the olfactory sensory system, possessing a relatively simple anatomical organization and a limited number of glutamate receptor subunits, may be useful for elucidating facets of the complex relationships between subunit composition and physiological function of ionotropic glutamate receptors.
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PMID:Expression of non-N-methyl-D-aspartate glutamate receptor subunits in the olfactory epithelium. 920 Jul 25


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