(1/44) Requirement of circadian genes for cocaine sensitization in Drosophila.
The circadian clock consists of a feedback loop in which clock genes are rhythmically expressed, giving rise to cycling levels of RNA and proteins. Four of the five circadian genes identified to date influence responsiveness to freebase cocaine in the fruit fly, Drosophila melanogaster. Sensitization to repeated cocaine exposures, a phenomenon also seen in humans and animal models and associated with enhanced drug craving, is eliminated in flies mutant for period, clock, cycle, and doubletime, but not in flies lacking the gene timeless. Flies that do not sensitize owing to lack of these genes do not show the induction of tyrosine decarboxylase normally seen after cocaine exposure. These findings indicate unexpected roles for these genes in regulating cocaine sensitization and indicate that they function as regulators of tyrosine decarboxylase. (+info)
(2/44) The trace amine tyramine is essential for sensitization to cocaine in Drosophila.
BACKGROUND: Sensitization to psychostimulant drugs of abuse is thought to be an important aspect of human addiction, yet how it develops is still unclear. The development of sensitization to cocaine in the fruit fly Drosophila melanogaster is strikingly similar to that observed in vertebrates. By taking advantage of the powerful genetic approaches that are possible in Drosophila, we are able to identify and characterize mutants that fail to develop sensitization. RESULTS: We found that the Drosophila mutant inactive (iav) failed to become sensitized to cocaine. Mutant flies had reduced amounts of the trace amine tyramine in the brain because of reduced activity of the enzyme tyrosine decarboxylase (TDC), which converts tyrosine to tyramine. Furthermore, cocaine exposure induced TDC enzyme activity in a time-dependent manner that paralleled the development of behavioral sensitization. The sensitization failure of iav flies could be rescued by feeding the flies with tyramine; other biogenic amines or amine precursors did not have the same effect. CONCLUSIONS: These results indicate an essential role for tyramine in cocaine sensitization in Drosophila. (+info)
(3/44) Expression of tryptophan decarboxylase and tyrosine decarboxylase genes in tobacco results in altered biochemical and physiological phenotypes.
The substrate specificity of tryptophan (Trp) decarboxylase (TDC) for Trp and tyrosine (Tyr) decarboxylase (TYDC) for Tyr was used to modify the in vivo pools of these amino acids in transgenic tobacco. Expression of TDC and TYDC was shown to deplete the levels of Trp and Tyr, respectively, during seedling development. The creation of artificial metabolic sinks for Trp and Tyr also drastically affected the levels of phenylalanine, as well as those of the non-aromatic amino acids methionine, valine, and leucine. Transgenic seedlings also displayed a root-curling phenotype that directly correlated with the depletion of the Trp pool. Non-transformed control seedlings could be induced to display this phenotype after treatment with inhibitors of auxin translocation such as 2,3,5-triiodobenzoic acid or N-1-naphthylphthalamic acid. The depletion of aromatic amino acids was also correlated with increases in the activities of the shikimate and phenylpropanoid pathways in older, light-treated transgenic seedlings expressing TDC, TYDC, or both. These results provide in vivo confirmation that aromatic amino acids exert regulatory feedback control over carbon flux through the shikimate pathway, as well as affecting pathways outside of aromatic amino acid biosynthesis. (+info)
(4/44) Induction of hydroxycinnamoyl-tyramine conjugates in pepper by Xanthomonas campestris, a plant defense response activated by hrp gene-dependent and hrp gene-independent mechanisms.
Inoculation of pepper leaves, Capsicum annuum cv. Early Calwonder ECW 10R, with strains of Xanthomonas campestris led to an accumulation of the phenolic conjugates feruloyltyramine (FT) and p-coumaroyltyramine (CT) 24 h postinoculation in nonhost- and gene-for-gene-determined incompatible interactions with X. campestris pv. campestris and X. campestris pv. vesicatoria, respectively. In contrast, neither compound was detected in compatible interactions with X. campestris pv. vesicatoria. The accumulation of FT and CT was preceded by an increase in the extractable activity of tyrosine decarboxylase as well as increases in the transcription of genes encoding phenylalanine ammonia-lyase and tyramine hydroxycinnamoyl transferase. No such changes were detected in compatible interactions. Very rapid accumulation of FT and CT occurred (4 h postinoculation) in pepper in response to a X. campestris pv. campestris mutant carrying a deletion of the hrp gene cluster. In contrast, hrp mutants of X. campestris pv. vesicatoria failed to elicit the production of FT and CT. These observations suggest the existence of hrp gene-dependent and -independent activation mechanisms of a defense response involving hydroxycinnamoyltyramines. (+info)
(5/44) Identification of the Enterococcus faecalis tyrosine decarboxylase operon involved in tyramine production.
Screening of a library of Enterococcus faecalis insertional mutants allowed isolation of a mutant affected in tyramine production. The growth of this mutant was similar to that of the wild-type E. faecalis JH2-2 strain in Maijala broth, whereas high-performance liquid chromatography analyses showed that tyramine production, which reached 1,000 microg ml(-1) for the wild-type strain, was completely abolished. Genetic analysis of the insertion locus revealed a gene encoding a decarboxylase with similarity to eukaryotic tyrosine decarboxylases. Sequence analysis revealed a pyridoxal phosphate binding site, indicating that this enzyme belongs to the family of amino acid decarboxylases using this cofactor. Reverse transcription-PCR analyses demonstrated that the gene (tdc) encoding the putative tyrosine decarboxylase of E. faecalis JH2-2 is cotranscribed with the downstream gene encoding a putative tyrosine-tyramine antiporter and with the upstream tyrosyl-tRNA synthetase gene. This study is the first description of a tyrosine decarboxylase gene in prokaryotes. (+info)
(6/44) Dopamine-beta-oxidase activity in man, using hydroxyamphetamine as substrate.
Hydroxyamphetamine was administered orally to five human subjects in daily doses of 26 to 118 mg. Approximately half the dosage administered was recoverable in the urine as unchanged drug (free plus conjugated) and 3.7 to 9.1% was excreted as the beta-hydroxylated metabolite, hydroxynorephedrine (free plus conjugated). Since conversion of hydroxyamphetamine to hydroxynorephedrine occurs in vitro by the action of dopamine-beta-oxidase, a simple method is suggested for measuring the activity of this enzyme and the effect of its inhibitors in man. No impairment of beta-hydroxylation was noted in an adrenalectomized subject. The beta-hydroxylation of hydroxyamphetamine in vivo has not been described previously. (+info)
(7/44) TYROSINASE INHERITANCE IN STREPTOMYCES SCABIES. I. GENETIC RECOMBINATION.
Gregory, Kenneth F. (Ontario Agricultural College, Guelph, Ontario, Canada), and Jay C. C. Huang. Tyrosinase inheritance in Streptomyces scabies. I. Genetic recombination. J. Bacteriol. 87:1281-1286. 1964.-Mutants derived from Streptomyces scabies strain A26 recombined with other derivatives of A26, but not with nine other strains of S. scabies nor with eight strains of other streptomycetes. Most of the spore progeny of heterogenomic mycelia formed from complementary diauxotrophic strains of S. scabies A26 were capable of forming tyrosinase (tye(+)), provided either of the parents was tye(+). About 99.8% of these spores carried the nutritional markers of either one or the other of the two parents. All recombinant classes between nutritional and streptomycin susceptibility markers were like-wise predominantly tye(+). We suggest that the tye(+) characteristic is carried in a small genetic unit, which is unlinked to most other genes and capable of replicating faster than the rest of the S. scabies genome. (+info)
(8/44) TYROSINASE INHERITANCE IN STREPTOMYCES SCABIES. II. INDUCTION OF TYROSINASE DEFICIENCY BY ACRIDINE DYES.
Gregory, Kenneth F. (Ontario Agricultural College, Guelph, Ontario, Canada), and Jay C. C. Huang. Tyrosinase inheritance in Streptomyces scabies. II. Induction of tyrosinase deficiency by acridine dyes. J. Bacteriol. 87:1287-1294. 1964.-Growth in minimal medium containing 1 mug of acriflavine per ml resulted in a large increase (up to 62%) in the frequency of tyrosinase-deficient (tye(-)) mutants in all of ten strains of Streptomyces scabies and eight unidentified streptomycetes studied. This increased frequency did not result from the selection of preformed mutants, since tye(-) clones were usually inhibited by lower concentrations of acriflavine than were tyrosinase-producing (tye(+)) clones, and no significant difference in mycelial yields occurred between the two types growing in a 1 mug/ml concentration of the dye. The mutations induced by X rays and acriflavine were either allelic or closely linked. This tye(-) phenotype was not caused by the production of an enzyme inhibitor, lack of a cofactor, or defect in the conversion of a protyrosinase to tyrosinase. Tye(-) mutants formed no detectable tyrosinase under a variety of conditions, including the presence of possible inducers. Mutants were able to oxidize glucose and succinate. The S. scabies tyrosinase was heat-labile (half-life at 59 C = 1.6 min) and not particle-bound. We conclude that acriflavine induces the loss of, or alteration in, a structural gene for tyrosinase production present as an extrachromosomal factor. (+info)