Structure of the mouse tyrosine hydroxylase gene

Catecholamines and Parkinson's disease: tyrosine hydroxylase (TH) over tetrahydrobiopterin (BH4) and GTP cyclohydrolase I (GCH1) to cytokines, neuromelanin, and gene therapy: a historical overview

The author identified the genes and proteins of human enzymes involved in the biosynthesis of catecholamines (dopamine, norepinephrine, epinephrine) and tetrahydrobiopterin (BH4): tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), dopamine β-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT), and GTP cyclohydrolase I (GCH1). In Parkinson's disease (PD), the activities and levels of mRNA and protein of all catecholamine-synthesizing enzymes are decreased, especially in dopamine neurons in the substantia nigra. Hereditary GCH1 deficiency results in reductions in the levels of BH4 and the activities of TH, causing decreases in dopamine levels. Severe deficiencies in GCH1 or TH cause severe decreases in dopamine levels leading to severe neurological symptoms, whereas mild decreases in TH activity in mild GCH1 deficiency or in mild TH deficiency result in only modest reductions in dopamine levels and symptoms of DOPA-responsive dystonia (DRD, Segawa disease) or juvenile Parkinsonism. DRD is a treatable disease and small doses of L-DOPA can halt progression. The death of dopamine neurons in PD in the substantia nigra may be related to (i) inflammatory effect of extra neuronal neuromelanin, (ii) inflammatory cytokines which are produced by activated microglia, (iii) decreased levels of BDNF, and/or (iv) increased levels of apoptosis-related factors. This review also discusses progress in gene therapies for the treatment of PD, and of GCH1, TH and AADC deficiencies, by transfection of TH, AADC, and GCH1 via adeno-associated virus (AAV) vectors.

The role of tyrosine hydroxylase as a key player in neuromelanin synthesis and the association of neuromelanin with Parkinson's disease

The dark pigment neuromelanin (NM) is abundant in cell bodies of dopamine (DA) neurons in the substantia nigra (SN) and norepinephrine (NE) neurons in the locus coeruleus (LC) in the human brain. During the progression of Parkinson's disease (PD), together with the degeneration of the respective catecholamine (CA) neurons, the NM levels in the SN and LC markedly decrease. However, questions remain among others on how NM is associated with PD and how it is synthesized. The biosynthesis pathway of NM in the human brain has been controversial because the presence of tyrosinase in CA neurons in the SN and LC has been elusive. We propose the following NM synthesis pathway in these CA neurons: (1) Tyrosine is converted by tyrosine hydroxylase (TH) to L-3,4-dihydroxyphenylalanine (L-DOPA), which is converted by aromatic L-amino acid decarboxylase to DA, which in LC neurons is converted by dopamine β-hydroxylase to NE; (2) DA or NE is autoxidized to dopamine quinone (DAQ) or norepinephrine quinone (NEQ); and (3) DAQ or NEQ is converted to eumelanic NM (euNM) and pheomelanic NM (pheoNM) in the absence and presence of cysteine, respectively. This process involves proteins as cysteine source and iron. We also discuss whether the NM amounts per neuromelanin-positive (NM+) CA neuron are higher in PD brain, whether NM quantitatively correlates with neurodegeneration, and whether an active lifestyle may reduce NM formation.

Genes critical for development and differentiation of dopaminergic neurons are downregulated in Parkinson's disease

We performed transcriptome analysis using RNA sequencing on substantia nigra pars compacta (SNpc) from mice after acute and chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment and from Parkinson's disease (PD) patients. Acute and chronic exposure to MPTP resulted in decreased expression of genes involved in sodium channel regulation. However, upregulation of pro-inflammatory pathways was seen after single dose but not after chronic MPTP treatment. Dopamine biosynthesis and synaptic vesicle recycling pathways were downregulated in PD patients and after chronic MPTP treatment in mice. Genes essential for midbrain development and determination of dopaminergic phenotype such as, LMX1B, FOXA1, RSPO2, KLHL1, EBF3, PITX3, RGS4, ALDH1A1, RET, FOXA2, EN1, DLK1, GFRA1, LMX1A, NR4A2, GAP43, SNCA, PBX1, and GRB10 were downregulated in human PD and overexpression of GFP tagged LMX1B rescued MPP⁺ induced death in SH-SY5Y neurons. Downregulation of gene ensemble involved in development and differentiation of dopaminergic neurons indicate their potential involvement in pathogenesis and progression of human PD.

NAD+ cellular redox and SIRT1 regulate the diurnal rhythms of tyrosine hydroxylase and conditioned cocaine reward

The diurnal regulation of dopamine is important for normal physiology and diseases such as addiction. Here we find a novel role for the CLOCK protein to antagonize CREB-mediated transcriptional activity at the tyrosine hydroxylase (TH) promoter, which is mediated by the interaction with the metabolic sensing protein, Sirtuin 1 (SIRT1). Additionally, we demonstrate that the transcriptional activity of TH is modulated by the cellular redox state, and daily rhythms of redox balance in the ventral tegmental area (VTA), along with TH transcription, are highly disrupted following chronic cocaine administration. Furthermore, CLOCK and SIRT1 are important for regulating cocaine reward and dopaminergic (DAergic) activity, with interesting differences depending on whether DAergic activity is in a heightened state and if there is a functional CLOCK protein. Taken together, we find that rhythms in cellular metabolism and circadian proteins work together to regulate dopamine synthesis and the reward value for drugs of abuse.

Human tyrosine hydroxylase in Parkinson's disease and in related disorders

Parkinson's disease (PD) is an aging-related movement disorder mainly caused by a deficiency of neurotransmitter dopamine (DA) in the striatum of the brain and is considered to be due to progressive degeneration of nigro-striatal DA neurons. Most PD is sporadic without family history (sPD), and there are only a few percent of cases of young-onset familial PD (fPD, PARKs) with the chromosomal locations and the genes identified. Tyrosine hydroxylase (TH), tetrahydrobiopterin (BH4)-dependent and iron-containing monooxygenase, catalyzes the conversion of L-tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA), which is the initial and rate-limiting step in the biosynthesis of catecholamines (DA, noradrenaline, and adrenaline). PD affects specifically TH-containing catecholamine neurons. The most marked neurodegeneration in patients with DA deficiency is observed in the nigro-striatal DA neurons, which contain abundant TH. Accordingly, TH has been speculated to play some important roles in the pathophysiology in PD. However, this decrease in TH is thought to be secondary due to neurodegeneration of DA neurons caused by some as yet unidentified genetic and environmental factors, and thus, TH deficiency may not play a direct role in PD. This manuscript provides an overview of the role of human TH in the pathophysiology of PD, covering the following aspects: (1) structures of the gene and protein of human TH in relation to PD; (2) similarity and dissimilarity between the phenotypes of aging-related sPD and those of young-onset fPD or DOPA-responsive dystonia due to DA deficiency in the striatum with decreased TH activity caused by mutations in either the TH gene or GTP cyclohydrolase I (GCH1) gene; and (3) genetic variants of the TH gene (polymorphisms, rare variants, and mutations) in PD, as discovered recently by advanced genome analysis.

Dnmt3a in Sim1 neurons is necessary for normal energy homeostasis

Obesity rates continue to rise throughout the world. Recent evidence has suggested that environmental factors contribute to altered energy balance regulation. However, the role of epigenetic modifications to the central control of energy homeostasis remains unknown. To investigate the role of DNA methylation in the regulation of energy balance, we investigated the role of the de novo DNA methyltransferase, Dnmt3a, in Single-minded 1 (Sim1) cells, including neurons in the paraventricular nucleus of the hypothalamus (PVH). Dnmt3a expression levels were decreased in the PVH of high-fat-fed mice. Mice lacking Dnmt3a specifically in the Sim1 neurons, which are expressed in the forebrain, including PVH, became obese with increased amounts of abdominal and subcutaneous fat. The mice were also found to have hyperphagia, decreased energy expenditure, and glucose intolerance with increased serum insulin and leptin. Furthermore, these mice developed hyper-LDL cholesterolemia when fed a high-fat diet. Gene expression profiling and DNA methylation analysis revealed that the expression of tyrosine hydroxylase and galanin were highly upregulated in the PVH of Sim1-specific Dnmt3a deletion mice. DNA methylation levels of the tyrosine hydroxylase promoter were decreased in the PVH of the deletion mice. These results suggest that Dnmt3a in the PVH is necessary for the normal control of body weight and energy homeostasis and that tyrosine hydroxylase is a putative target of Dnmt3a in the PVH. These results provide evidence for a role for Dnmt3a in the PVH to link environmental conditions to altered energy homeostasis.

Systemic gene delivery to the central nervous system using Adeno-associated virus

Adeno-associated virus (AAV)-mediated gene delivery has emerged as an effective and safe tool for both preclinical and clinical studies of neurological disorders. The recent discovery that several serotypes are able to cross the blood–brain barrier when administered systemically has been a real breakthrough in the field of neurodegenerative diseases. Widespread transgene expression after systemic injection could spark interest as a therapeutic approach. Such strategy will avoid invasive brain surgery and allow non-focal gene therapy promising for CNS diseases affecting large portion of the brain. Here, we will review the recent results achieved through different systemic routes of injection generated in the last decade using systemic AAV-mediated delivery and propose a brief assessment of their values. In particular, we emphasize how the methods used for virus engineering could improve brain transduction after peripheral delivery.

Epigenetic, transcriptional and posttranscriptional regulation of the tyrosine hydroxylase gene

The activity of tyrosine hydroxylase (TH, EC 1.14.16.2) gene and protein determines the catecholamine level, which, in turn, is crucial for the organism homeostasis. The TH gene expression is regulated by near all possible regulatory mechanisms on epigenetic, transcriptional and posttranscriptional levels. Ongoing molecular characteristic of the TH gene reveals some of the cis and trans elements necessary for its proper expression but most of them especially these responsible for tissue specific expression remain still obscure. This review will focus on some aspects of TH regulation including spatial chromatin organization of the TH locus and TH gene, regulatory elements mediating basal, induced and cell-specific activity, transcriptional elongation, alternative TH RNA processing, and the regulation of TH RNA stability in the cell.

Mutations in the cyclic adenosine monophosphate response element of the tyrosine hydroxylase gene

Tyrosine hydroxylase (TH) deficiency (OMIM 191290) is one cause of early-onset dopa-responsive dystonia. We describe seven cases from five unrelated families with dopa-responsive dystonia and low homovanillic acid in cerebrospinal fluid who were suspected to suffer from TH deficiency. Analysis of part of the TH promotor showed five homozygous and two heterozygous mutations in the highly conserved cyclic adenosine monophosphate response element. Our data suggest that, if no mutations are found in the coding regions of the gene in patients strongly suspected of TH deficiency, the search for pathogenic mutations should be extended to regulatory promotor elements.

A comparative genomics approach to identifying the plasticity transcriptome

Background

Neuronal activity regulates gene expression to control learning and memory, homeostasis of neuronal function, and pathological disease states such as epilepsy. A great deal of experimental evidence supports the involvement of two particular transcription factors in shaping the genomic response to neuronal activity and mediating plasticity: CREB and zif268 (egr-1, krox24, NGFI-A). The gene targets of these two transcription factors are of considerable interest, since they may help develop hypotheses about how neural activity is coupled to changes in neural function.

Results

We have developed a computational approach for identifying binding sites for these transcription factors within the promoter regions of annotated genes in the mouse, rat, and human genomes. By combining a robust search algorithm to identify discrete binding sites, a comparison of targets across species, and an analysis of binding site locations within promoter regions, we have defined a group of candidate genes that are strong CREB- or zif268 targets and are thus regulated by neural activity. Our analysis revealed that CREB and zif268 share a disproportionate number of targets in common and that these common targets are dominated by transcription factors.

Conclusion

These observations may enable a more detailed understanding of the regulatory networks that are induced by neural activity and contribute to the plasticity transcriptome. The target genes identified in this study will be a valuable resource for investigators who hope to define the functions of specific genes that underlie activity-dependent changes in neuronal properties.

Covalent genomic DNA modification patterns revealed by denaturing gradient gel blots

Several approaches are used to survey genomic DNA methylation patterns, including Southern blot, PCR, and microarray strategies. All of these methods are based on the use of methylation-sensitive isoschizomer restriction enzyme pairs and/or sodium bisulfite treatment of genomic DNA. They have many limitations, including PCR bias, lack of comprehensive assessment of methylated sites, labor-intensive protocols, and/or the need for expensive equipment. Since the presence of 5-methylcytosine alters the melting properties of DNA molecules, denaturing gradient gel blots (DGG blots), a gene scanning technique which detects differences in DNA fragments based on differential melting behavior, were used to examine genomic modification patterns in normal tissues. Variations in melting behavior, observed as restriction fragment melting polymorphisms (RFMPs), were detected in various tissues from single individuals in all human and mouse genes tested, suggesting the presence of widespread differential cell type-specific DNA modification. Additional DGG blot experiments comparing genomic DNA to unmethylated cloned DNA suggested that the melting variants were most likely caused by DNA methylation differences. The results suggest that the use of DGG blots can provide a comprehensive and rapid method for comparing complex in vivo DNA modification patterns in normal adult somatic cells.

Transgenic expression of Cre recombinase from the tyrosine hydroxylase locus

Catecholaminergic neurons are affected in several neurological and psychiatric diseases. Tyrosine hydroxylase (TH) is the first, rate-limiting enzyme in catecholamine synthesis. We report a knockin mouse expressing Cre-recombinase from the 3'-untranslated region of the endogenous Th gene by means of an internal ribosomal entry sequence (IRES). The resulting Cre expression matches the normal pattern of TH expression, while the pattern and level of TH are not altered in the knockin mouse. Crossings with two different LacZ reporter mice demonstrated Cre-mediated genomic recombination in TH expressing tissues. In addition, LacZ was found in some unexpected cell populations (including oocytes), indicating recombination due to transient developmental TH expression. Our novel knockin mouse can be used for generation of tissue-specific or general knockouts (depending on scheme of crossing) in mice carrying genes flanked by loxP sites. This knockin mouse can also be used for tracing cell lineages expressing TH during development.

Two tyrosine hydroxylase genes in teleosts

We report the finding of two non-allelic genes encoding tyrosine hydroxylase (TH) from the diploid teleost barramundi Lates calcarifer. Barramundi TH1 is the homologue of the higher vertebrate TH genes and encodes a protein of 489 amino acids that shares 90% sequence identity to the THs of other teleost species. A second non-allelic tyrosine hydroxylase gene (TH2) encodes a protein of 472 amino acids and shares 62% identity with TH1 and the vertebrate THs. TH1 mRNA is found in the brain and kidney of barramundi while TH2 mRNA is found only in brain. The TH2 gene is also present in the genomes of the pufferfish Takifugu and zebrafish Danio. Estimates of the rates of nucleotide substitution suggest the teleost TH2 genes are selectively constrained although not to the degree seen in the TH1 genes. Differential regulation of the two TH genes is, however, indicated by differences in transcript distribution, the nature of the Ca2+-responsive elements found in the proximal promoter region and the lack of recognised phosphorylation sites in TH2. Preservation of two apparently functional TH genes in phylogenetically distant teleost species is consistent with the notion of partitioning of function between duplicate genes.

Molecular genetics of dopa-responsive dystonia

The causative genes of two types of hereditary dopa-responsive dystonia (DRD) due to dopamine (DA) deficiency in the nigrostriatum DA neurons have been elucidated. Autosomal dominant DRD (AD-DRD) was originally described by Segawa as hereditary progressive dystonia with marked diurnal fluctuation (HPD). We cloned the human GTP cyclohydrolase I (GCH1) gene, and mapped the gene to chromosome 14q22.1-q22.2 within the HPD/DRD locus, which had been identified by linkage analysis. GCH1 isthe rate-limiting enzyme for the biosynthesis of tetrahydrobiopterin (BH4), the cofactor for tyrosine hydroxylase (TH), which is the first and rate-limiting enzyme of DA synthesis. We proved that the GCH1 gene is the causative gene for HPD/DRD based on the identification of mutations of the gene in the patients and decreases in the enzyme activity expressed in mononuclear blood cells to 2-20% of the normal value. About 60 different mutations (missense, nonsense, and frameshift mutations) in the coding region or in the exon-intron junctions of the GCH1 gene have been reported in patients with AD-DRD all over the world. Recent findings indicate that the decreased GCH1 activity in AD-DRD may be caused by the negative interaction of the mutated subunit with the wild-type one, i.e., a dominant negative effect, and/or by decreases in the levels of GCH1 mRNA and protein caused by inactivation of one allele of the GCH1 gene. Autosomal recessive DRD (AR-DRD) with Segawa's syndrome was discovered in Germany. The AR-DRD locus was mapped to chromosome 11p15.5 in the chromosomal site of the TH gene. In the AR-DRD with Segawa's syndrome, a point mutation in TH (Gln381Lys) resulted in a pronounced decrease in TH activity to about 15% of that of the wild type. Several missense mutations in the TH gene have been found in AR-DRD in Europe. The phenotype of AR-DRD with the Leu205Pro mutation in the TH gene, which produces a severe decrease in TH activity to 1.5% of that of the wild type, was severe, not dystonia/Segawa's syndrome, but early-onset parkinsonism. However, a marked improvement of all clinical symptoms with a low dose of L-dopa was reported in AR-DRD/parkinsonism patients. These findings on DRD indicate that the nigrostriatal DA neurons may be most susceptible to the decreases in GCH1 activity, BH4 level, TH activity, and DA level, and that DRD is the DA deficiency without neuronal death in contrast to juvenile parkinsonism or Parkinson's disease with DA cell death.

Alternative sulfonylurea receptor expression defines metabolic sensitivity of K-ATP channels in dopaminergic midbrain neurons

ATP-sensitive potassium (K-ATP) channels couple the metabolic state to cellular excitability in various tissues. Several isoforms of the K-ATP channel subunits, the sulfonylurea receptor (SUR) and inwardly rectifying K channel (Kir6.X), have been cloned, but the molecular composition and functional diversity of native neuronal K-ATP channels remain unresolved. We combined functional analysis of K-ATP channels with expression profiling of K-ATP subunits at the level of single substantia nigra (SN) neurons in mouse brain slices using an RT-multiplex PCR protocol. In contrast to GABAergic neurons, single dopaminergic SN neurons displayed alternative co-expression of either SUR1, SUR2B or both SUR isoforms with Kir6.2. Dopaminergic SN neurons expressed alternative K-ATP channel species distinguished by significant differences in sulfonylurea affinity and metabolic sensitivity. In single dopaminergic SN neurons, co-expression of SUR1 + Kir6.2, but not of SUR2B + Kir6.2, correlated with functional K-ATP channels highly sensitive to metabolic inhibition. In contrast to wild-type, surviving dopaminergic SN neurons of homozygous weaver mouse exclusively expressed SUR1 + Kir6.2 during the active period of dopaminergic neurodegeneration. Therefore, alternative expression of K-ATP channel subunits defines the differential response to metabolic stress and constitutes a novel candidate mechanism for the differential vulnerability of dopaminergic neurons in response to respiratory chain dysfunction in Parkinson's disease.

Structure/function relationship of the cAMP response element in tyrosine hydroxylase gene transcription

Expression of tyrosine hydroxylase (TH) is limited to catecholamine-producing neurons and neuroendocrine cells in a cell type-specific manner and is inducible by the cAMP-regulated signaling pathway. Previous results indicated that the cAMP response element (CRE) residing at -45 to -38 base pairs upstream of the transcription initiation site is essential for both basal and cAMP-inducible promoter activity of the 2.4-kilobase or shorter upstream sequence of the TH gene (Kim, K. S., Lee, M. K., Carroll, J. , and Joh, T. H. (1993) J. Biol. Chem. 268, 15689-15695; Lazaroff, M. , Patankar, S., Yoon, S. O., and Chikaraishi, D. M. (1995) J. Biol. Chem. 270, 21579-21589). Here, we further report that the CRE is critical for the promoter activity of the 5.6- or 9.0-kilobase upstream sequences of the rat TH gene, which had been shown to direct the cell-specific TH expression in vivo. To define the structure/function relationship of the CRE in transcriptional activation of the TH gene, we performed saturated mutational analyses of 12 nucleotides encompassing the CRE. Mutation of any nucleotide within the octamer motif results in a significant decrease of both basal and cAMP-inducible transcriptional activity of the TH reporter gene construct. Among the four nucleotides adjacent to the CRE (two 5' and two 3'), only the G residue at the immediate 3' position is important for full transcriptional activity. DNase I footprint analysis indicates a positive correlation between in vivo promoter activity and in vitro interaction between the CRE motif and its cognate protein factor(s). Reconstruction experiments using a TH promoter in which the native CRE was rendered inactive show that the CRE can transactivate transcription in either orientation through a window of approximately 200 base pairs upstream of the transcription initiation site, suggesting that CRE supports transcriptional activation of the TH gene in a distance-dependent manner. Finally, when the distance between the CRE and TATA box was changed by inserting an additional 5 or 10 bases, it was observed that both insertional mutations increased activity by approximately 3-fold. The cAMP inducibility was as intact as the wild type construct. Together, these results are consistent with a model in which transcriptional activation of the TH gene by the CRE requires that it be located within a certain proximity of the CAP site but does not depend on a stringent stereospecific alignment in relationship to the TATA element.

A novel basal promoter element is required for expression of the rat tyrosine hydroxylase gene

Transcription of the rat tyrosine hydroxylase (TH) gene is controlled by enhancer sequences in its 5' flanking region; these enhancers include the AP1, dyad, and cAMP response element (CRE) motifs. We show that a novel basal promoter element (-17 GCCTGCCTGGCGA -5) positioned between the TATA box and +1 works in conjunction with the upstream AP1-dyad and CRE enhancers but cannot support transcription by itself. A mutation of this element, termed partial dyad, reduces basal expression of a reporter gene in TH-positive cell lines and TH-negative lines but has no effect on cAMP- or KCl-induced expression. A double mutant at positions -17 and -11 of the partial dyad reduces transcriptional activation by 80%. Conversely, insertion of this element into a heterologous promoter restores basal expression to levels mediated by the native TH promoter. The partial dyad is a novel activational element that is required for full expression of the TH gene and may assist in the function of the AP1, dyad, and CRE motifs and also other enhancers further upstream. Hence, the rat TH gene is unusual in that its enhancers will not function with a heterologous promoter but require a specific TH promoter sequence for full activation.

Tissue-specific methylation occurs in the essential promoter element of the tyrosine hydroxylase gene

Expression of tyrosine hydroxylase (TH) is regulated in a tissue-specific manner by multiple mechanisms. In catecholaminergic cells, the expression of TH-mRNA is up-regulated by forskolin (FK) and is suppressed by retinoic acid (RA). We have previously provided evidence that, in N-18 cells, the expression of TH-mRNA is suppressed by DNA methylation of the TH gene itself. In the present study, using a catecholaminergic cell line, N1E-115, we performed deletional and mutational analyses on the 5'-flanking region of the mouse TH gene. The results indicate that a cAMP response element (CRE) mediates constitutive transcription of the TH gene, as well as responsiveness to FK and RA. Using bisulfite sequencing methods, we analyzed the methylation status of the TH gene 5'-flanking region in various cell lines and rat tissues. We found that three cytosine residues in the domain surrounding the CRE of the TH gene promoter were specifically methylated in N-18 cells and TH non-expressing rat tissues. In contrast, these cytosines were undermethylated in TH expressing cell lines and tissues. The inverse correlation between the frequency of cytosine methylation at these specific sites and the levels of TH expression supports a role for DNA methylation in the regulation of tissue-specific gene expression.

Targeted disruption of the tyrosine hydroxylase locus results in severe catecholamine depletion and perinatal lethality in mice

Tyrosine 3-hydroxylase (TH, EC 1.14.16.2) catalyzes the first and rate-limiting step of the catecholamine biosynthetic pathway in the nervous and endocrine systems. The TH locus was disrupted in mouse embryonic stem cells by homologous recombination. Mice heterozygous for the TH mutation were apparently normal. In these mice, TH activity in the embryos and adult tissues was less than 50% of the wild-type values, but the catecholamine level was decreased only moderately in the developing animals and was maintained normally at adulthood, suggesting the presence of a regulatory mechanism for ensuring the proper catecholamine level during animal development. In contrast, the homozygous mutant mice died at a late stage of embryonic development or shortly after birth. Both TH mRNA and enzyme activity were lacking in the homozygous mutants, which thus explained the severe depletion of catecholamines. These changes, however, did not affect gross morphological development of the cells that normally express high catecholamine levels. Analysis of electrocardiograms of surviving newborn mutants showed bradycardia, suggesting an alteration of cardiac functions in the homozygous mice that may lead to the lethality of this mutation. In addition, transfer of a human TH transgene into the homozygous mice corrected the mutant phenotype, showing recovery of TH activity by expression of the human enzyme. These results indicate that TH is essential for survival of the animals during the late gestational development and after birth.

The cyclic AMP response element directs tyrosine hydroxylase expression in catecholaminergic central and peripheral nervous system cell lines from transgenic mice

Enhancer elements regulating the neuronal gene, tyrosine hydroxylase (TH), were identified in TH-expressing peripheral nervous system PATH and central nervous system CATH cell lines. Mutational analysis in which rat TH 5'-flanking sequences directed chloramphenicol acetyltransferase (CAT) reporter gene expression demonstrated that mutating the cyclic AMP response element (CRE) at -45 base pair reduced expression by 80-90%. A CRE linked to an enhancerless TH promoter fully supported expression. Cotransfection of a dominant-negative CREB protein reduced expression 50-60%, suggesting that the CRE is bound by CREB or a CREB dimerization partner. Although mutating the AP1/dyad (AD) element at -205 base pair only modestly reduced CAT levels, AD minimal enhancer constructs gave 45-80% of wild type expression when positioned at -91 or -95. However, in its native context at -205, the AD could not support expression. In contrast, a CRE, moved from its normal position at -45 to -206, gave full activity. These results indicate that the CRE is critical for TH transcription in central nervous system CATH and peripheral nervous system PATH cells, whereas the AD is less important and its enhancer activity is context-and/or position-dependent. These results represent the first attempts to map regulatory elements directing TH expression in central nervous system cell lines.

Human and mouse dopamine transporter genes: conservation of 5'-flanking sequence elements and gene structures

Synaptic reaccumulation of the neurotransmitter dopamine is mediated by the dopamine transporter (DAT), a member of the family of twelve transmembrane domain, sodium- and chloride-dependent neurotransmitter transporters. Several DAT features, including its exclusive expression in dopaminergic neurons, implication in cocaine action, and prominent role in the mechanisms of Parkinsonism-inducing neurotoxins, make understanding of the DAT gene of interest. Isolation and characterization of the human and mouse DAT genes has allowed elucidation of similarities between each and other members of this transporter gene family. Sequences 5' to transcriptional start sites contain G-C rich, TATA-less, CAAT-less regions with striking conservation between human and mouse gene flanking regions. These studies suggest sequence elements that are candidates to contribute to the dopamine transporter's dopaminergic cell-specific expression.

Targeted disruption of the tyrosine hydroxylase gene reveals that catecholamines are required for mouse fetal development

Tyrosine hydroxylase catalyses the initial, rate-limiting step in the catecholamine biosynthetic pathway. Catecholamines, which include dopamine, noradrenaline, and adrenaline, are important neurotransmitters and hormones that regulate visceral functions, motor coordination and arousal in adults. The gene encoding tyrosine hydroxylase becomes transcriptionally active in developing neuroblasts during mid-gestation of rodent embryos, before the onset of neurotransmission. Here we show that inactivation of both tyrosine hydroxylase alleles results in mid-gestational lethality: about 90% of mutant embryos die between embryonic days 11.5 and 15.5, apparently of cardiovascular failure. Administration of L-DOPA (dihydroxyphenylalanine), the product of the tyrosine hydroxylase reaction, to pregnant females results in complete rescue of mutant mice in utero. Without further treatment, however, they die before weaning. We conclude that catecholamines are essential for mouse fetal development and postnatal survival.

Differential induction of gene expression of catecholamine biosynthetic enzymes and preferential increase in norepinephrine by forskolin

We examined the effect of forskolin, an adenylate cyclase activator, on gene expression and the activities of the three enzymes specific for catecholamine biosynthesis [tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT)] and on the amounts of available catecholamines in primary cultured bovine adrenomedullary chromaffin cells. The results showed that TH was increased by 4.7 +/- 0.7-fold and 69% in mRNA and activity levels, respectively, compared with the untreated control. DBH was elevated by 3.2 +/- 0.2-fold in mRNA and 45% in activity. The increase in PNMT, on the other hand, was smaller: 1.7 +/- 0.2-fold in mRNA and 13% in activity. This relatively small increase in PNMT was reflected in the catecholamine levels in that the total epinephrine (EPI) was elevated by only 16% while norepinephrine (NE) was elevated by 99%, which caused a shift in the molar ratio of EPI to NE from 7.0 in the untreated control to 4.1 after forskolin treatment. A large portion of the elevated catecholamines was found in the medium, which represented a 10.1-fold increase for NE and a 6.4-fold increase for EPI compared with the control. Interestingly, this caused the remaining intracellular NE and EPI to be only 117 and 66% of the control, respectively. Thus, forskolin caused coordinate up-regulation of gene expression and enzyme activities of the three catecholamine-synthesizing enzymes but to different degrees, resulting in a relatively larger increase in NE than in EPI, both of which were released dramatically. This large enhancement of catecholamine release, as well as the dramatic shift in their ratio, implicates an important physiological role for cAMP in the regulation of in vivo sympathetic activities.

Expression of human tyrosine hydroxylase-chloramphenicol acetyltransferase (CAT) fusion gene in the brains of transgenic mice as examined by CAT immunocytochemistry

We have produced transgenic (Tg) mice carrying 5.0-kb fragment from the 5'-flanking region of the human tyrosine hydroxylase (hTH) gene fused to a reporter gene, chloramphenicol acetyltransferase (CAT) [Sasaoka et al. (1992) Mol Brain Res 16: 274-286]. In the brain of the Tg mice, CAT expression has been observed in catecholaminergic (CAnergic) neurons and also in non-CAnergic neurons. The aim of the present study is to examine in detail the cell-type specific expression of the hTH-CAT fusion gene in the brain of the Tg mice, by use of immunohistochemistry for CAT, TH, and aromatic L-amino acid decarboxylase (AADC). CAT-immunoreactive cells were found in CAnergic brain regions which contained TH-positive cells, and also in non-CAnergic brain regions which contained no TH-labeled cells. The non-CAnergic brain regions that represented CAT-stained cells were further divided into two groups: (i) regions containing AADC-labeled cells, for example, bed nucleus of the stria terminalis, nucleus suprachiasmaticus, mammillary body, nucleus raphe dorsalis, inferior colliculus, and nucleus parabrachialis, and (ii) regions containing no AADC-positive cells, for example, main olfactory bulb (except A16), accessory olfactory bulb, nucleus olfactorius anterior, caudoputamen, septum, nucleus accumbens, hippocampus, medial nucleus of the amygdala, entorhinal cortex, nucleus supraopticus, and parasubiculum. The results indicate that the 5.0-kb DNA fragment flanking the 5' end of the hTH gene may contain the element(s) specific for neuron-specific TH expression but which may be insufficient to attenuate ectopic expression.

Nicotine-induced regulation of tyrosine hydroxylase activity in adrenal gland of transgenic mouse carrying human tyrosine hydroxylase gene

We investigated the effect of subcutaneous injection of nicotine on in vitro tyrosine hydroxylase (TH) activity in adrenal gland and brain of the transgenic mice carrying an 11-kb fragment containing the entire human TH gene. Injection of 5 mg nicotine/kg (as free base) for 3 days caused a statistically significant increase in vitro TH activity in the adrenal gland, whereas brain TH activity was not affected at all. The adrenal gland of non-transgenic C57BL/6J mice treated in the same way as for transgenic mice tended to enhance TH activity, although not to a significant level. This observation might indicate the possibility that the machinery used by nicotine in regulating the properties or expression of TH in the adrenal gland should be similar between transgenic and non-transgenic mice.

Chicken tyrosine hydroxylase gene: isolation and functional characterization of the 5' flanking region

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the biosynthesis of catecholamines. We describe here the isolation of the chicken TH gene and the analysis of 3 kb of its 5' flanking region. The chicken TH transcription unit spans 19 kb. The 60-bp proximal promoter contains a TATA box and a cyclic AMP response element (CRE) sequence. The 5' flanking region contains several AP1-, AP2-, and octamer-like sequences as well as a glucocorticoid response element at position -1.4 kb. A construct containing the 3-kb 5' flanking DNA fused to the chloramphenicol acetyltransferase (CAT) gene was transiently transfected into PC12 cells, and the effect of various effectors was tested. Only forskolin increased the CAT activity, likely owing to the presence of the CRE sequence. Constructs prepared by progressively deleting the 5' flanking DNA were transfected into PC12 and QT6 (quail transformed fibroblasts) cells. In both cell types, the transcriptional activity increased with deletion of the 5' flanking region. These results show that the 60-bp region containing the TATA box and the CRE is sufficient to act as a constitutive promoter for the chicken TH gene and that this region appears to be negatively controlled by upstream sequences.

Four isoforms of tyrosine hydroxylase are expressed in human brain

In contrast to nonprimate species, the RNA for human tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, can undergo alternative splicing to produce four different types of mRNA. Although types 1 and 2 of these human tyrosine hydroxylase mRNAs have been identified in human brain, whether types 3 and 4 human tyrosine hydroxylase mRNAs are present in the central nervous system remains controversial. Furthermore, little is known about the expression of the protein products of these mRNAs in human brain. In this study we used antibodies raised against different octapeptide sequences from each of the predicted human tyrosine hydroxylase protein forms to determine the presence and distribution of each human tyrosine hydroxylase isoforms in several regions of human brain. Control immunocytochemical and blot immunolabeling experiments demonstrated that each antibody selectively recognized the human tyrosine hydroxylase isoform against which it was directed. In immunocytochemical studies, all four human tyrosine hydroxylase isoforms were clearly detectable in neurons of both the substantia nigra and locus coeruleus. The presence of all four isoforms in these nuclei was confirmed with blot immunolabeling studies. Single-label immunocytochemical studies of adjacent sections as well as dual-label comparisons of immunoreactivity for human tyrosine hydroxylase type 1 with type 2, type 3, or type 4 suggested that at least some neurons in these brain regions contain all four human tyrosine hydroxylase isoforms. In contrast, some neurons of the mesencephalon appeared to be selectively immunoreactive with the antibodies against type 1. In the caudate nucleus and putamen, the terminal zones of the dopaminergic projection from the substantia nigra, all four isoforms were detected, although in immunocytochemical studies type 1 appeared to be the predominant isoform present in axons and terminals. These findings demonstrate that human brain contains four distinct isoforms of human tyrosine hydroxylase and that the presence or relative amount of each isoform may differ among catecholaminergic cell populations and between catecholaminergic neurons and terminal fields. These patterns of expression may have important implications for understanding the regulation of catecholamine biosynthesis in human brain both in normal and pathological states.

Analysis of the human tyrosine hydroxylase promoter-chloramphenicol acetyltransferase chimeric gene expression in transgenic mice

To investigate cis-elements responsible for catecholaminergic (CAnergic) neuron-specific expression of the tyrosine hydroxylase (TH) gene, we produced lines of transgenic mice carrying 5.0-kb, 2.5-kb and 0.2-kb fragments from the 5'-flanking region of the human TH gene fused to a reporter gene, chloramphenicol acetyltransferase (CAT), and designated them as TC 50, TC 25, and TC 02, respectively, and reporter gene expression in transgenic mice was analyzed by CAT assay by immunocytochemistry with anti-CAT antibody. High-level CAT expression was observed in the brain and adrenal gland using the 5.0-kb promoter of the TC 50 mice, but ectopic expression was consistently observed in several somatic tissues, e.g. thymus, colon, and testis. In brain, expression was achieved in CAnergic neurons with the largest construct (5.0 kb), but not with 2.5 kb or 0.2 kb of 5' flanking sequence. However, TC 50 mice also expressed CAT immunoreactivity in non-CAnergic neurons. In the TC 25 line CAT immunoreactivity was detected only in some non-CAnergic neurons. In the TC 02 line no CAT immunoreactivity was detected in any of the tissues examined. These results indicate that the 5.0-kb DNA fragment of the TH gene upstream region contains activity to express CAT in CAnergic neurons and surprisingly, lacks some regulatory elements attenuating ectopic expression, and that the 2.5-kb and 0.2-kb fragment are not sufficient for the proper expression. We discuss the presence of the tissue-specific regulatory elements in the structure portion of the TH gene and/or 3'-flanking region.

Cold-induced alterations in the binding of adrenomedullary nuclear proteins to the promoter region of the tyrosine hydroxylase gene

It is well documented that cold stress induces a rapid trans-synaptically mediated increase in the relative abundance of rat adrenomedullary tyrosine hydroxylase (TH) mRNA. To investigate the transcriptional mechanisms regulating the cold stress response, we have employed a gel mobility shift assay, using DNA fragments prepared from the proximal 5' flanking region of the bovine TH gene as a heterologous molecular probe. In pilot studies, this region of the bovine TH promoter (nucleotides -246 to +21) was fused to the bacterial reporter gene, chloramphenicol acetyltransferase, and the chimeric construct transfected into human neuroblastoma SK-N-BE(2)-C, hepatoma HepG2, and rat pheochromocytoma PC-12 cells. Results of this analysis indicate that the proximal 5' flanking region of the bovine TH gene contains sufficient information to drive transient reporter gene expression in both human and rat catecholaminergic clonal cell lines. The findings derived from the gel mobility shift studies demonstrate that cold exposure causes rapid and selective alterations in the binding of adrenomedullary nuclear proteins to the proximal 5' flanking region of the TH gene. The most striking cold stress-induced alteration in DNA/nucleoprotein binding occurs in a region of the TH promoter (nucleotides -246 to -189) which contains an element bearing marked sequence similarity to an AP1 binding site and is highly conserved among animal species. This alteration occurs within 1 hr of cold exposure and persists for up to 48 hr after the onset of stress. The results of adrenal denervation experiments indicate that the cold-induced change in DNA/nucleoprotein binding is neurally mediated, requiring intact sympathetic innervation of the gland.(ABSTRACT TRUNCATED AT 250 WORDS)