Sequences distal to the AP1/E box motif are involved in the cell type-specific expression of the rat tyrosine hydroxylase gene

A tyrosine hydroxylase-yellow fluorescent protein knock-in reporter system labeling dopaminergic neurons reveals potential regulatory role for the first intron of the rodent tyrosine hydroxylase gene

Degeneration of the dopaminergic neurons of the substantia nigra is a hallmark of Parkinson's disease. To facilitate the study of the differentiation and maintenance of this population of dopaminergic neurons both in vivo and in vitro, we generated a knock-in reporter line in which the yellow fluorescent protein (YFP) replaced the first exon and the first intron of the tyrosine hydroxylase (TH) gene in one allele by homologous recombination. Expression of YFP under the direct control of the entire endogenous 5' upstream region of the TH gene was predicted to closely match expression of TH from the wild type allele, thus marking functional dopaminergic neurons. We found that YFP was expressed in dopaminergic neurons differentiated in vitro from the knock-in mouse embryonic stem cell line and in dopaminergic brain regions in knock-in mice. Surprisingly, however, YFP expression did not overlap completely with TH expression, and the degree of overlap varied in different TH-expressing brain regions. Thus, the reporter gene did not identify functional TH-expressing cells with complete accuracy. A DNaseI hypersensitivity assay revealed a cluster of hypersensitivity sites in the first intron of the TH gene, which was deleted by insertion of the reporter gene, suggesting that this region may contain cis-acting regulatory sequences. Our results suggest that the first intron of the rodent TH gene may be important for accurate expression of TH.

Development of catecholaminergic systems in the spinal cord of the dogfish Scyliorhinus canicula (Elasmobranchs)

The development of catecholamine-synthesizing cells and fibers in the spinal cord of dogfish (Scyliorhinus canicula L.) was studied by means of immunohistochemistry using antibodies against tyrosine hydroxylase (TH). The only TH-immunoreactive (TH-ir) cells already present in the spinal cord of stage 26 embryos were of cerebrospinal fluid-contacting (CSF-c) type. These cells were the first catecholaminergic neurons of the dogfish CNS. The number of these TH-ir cells increased very considerably in later embryos and adult dogfish. In later embryos (stage 33; prehatching), faintly TH-ir non-CSF-contacting neurons were observed in the ventral horn throughout most of the spinal cord. In adult dogfish, some non-CSF-contacting TH-ir cells were observed ventral or lateral to the central canal. In the rostral spinal cord, the catecholaminergic neurons observed in dorsal regions were continuous with caudal rhombencephalic populations. Numerous TH-ir fibers were observed in the spinal cord of later embryos and in adults, both intrinsic and descending from the brain, innervating many regions of the cord including the dorsal and ventral horns. In addition, some TH-ir fibers innervated the marginal nucleus of the spinal cord. The early appearance of catecholaminergic cells and fibers in the embryonic spinal cord of the dogfish, and the large number of these elements observed in adults, suggests an important role for catecholamines through development and adulthood in sensory and motor functions.

The human tyrosine hydroxylase gene promoter

13.329 kilobases of the single copy human tyrosine hydroxylase (hTH) gene were isolated from a genomic library. The 5' flanking 11 kilobases fused to the reporter green fluorescent protein (GFP) drove high level expression in TH+ cells of the substantia nigra of embryonic and adult transgenic mice as determined by double label fluorescence microscopy. To provide a basis for future analysis of polymorphisms and structure-function studies, the previously unreported distal 10.5 kilobases of the hTH promoter were sequenced with an average coverage of 20-fold, the remainder with 4-fold coverage. Sequence features identified included four perfect matches to the bicoid binding element (BBE, consensus: BBTAATCYV) all of which exhibited specific binding by electrophoretic mobility shift assay (EMSA). Comparison to published sequences of mouse and rat TH promoters revealed five areas of exceptional homology shared by these species in the upstream TH promoter region -2 kb to -9 kb relative to the transcription start site. Within these conserved regions (CRs I-V), potential recognition sites for NR4A2 (Nurr1), HNF-3beta, HOXA4, and HOXA5 were shared across human, mouse, and rat TH promoters.

Regulation of the tyrosine hydroxylase and dopamine beta-hydroxylase genes by the transcription factor AP-2

The retinoic acid-inducible and developmentally regulated transcription factor AP-2 plays an important role during development. In adult mammals, AP-2 is expressed in both neural and non-neural tissues. However, the function of AP-2 in different neuronal phenotypes is poorly understood. In this study, transcriptional regulation of tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) genes by AP-2 was investigated. AP-2 binding sites were identified in the upstream regions of both genes. Electrophoretic mobility shift assays (EMSA) and DNase I footprinting analyses indicate that the AP-2 interaction with these motifs is more prominent in catecholaminergic SK-N-BE(2)C and CATH.a than in non-catecholaminergic HeLa and HepG2 cell lines. Exogenous expression of AP-2 robustly transactivated TH and DBH promoter activities in non-catecholaminergic cell lines. While AP-2 regulates the DBH promoter activity via a single site, transactivation of the TH promoter by AP-2 appears to require multiple sites. In support of this, mutation of multiple AP-2 binding sites but not that of single site diminished the basal promoter activity of the TH gene in cell lines that express TH and abolished transactivation by exogenous AP-2 expression in cell lines that do not express TH. In contrast, mutation of a single AP-2 binding site of the DBH gene completely abolished transactivation by AP-2. Double-label immunohistochemistry showed that AP-2 is coexpressed with TH in noradrenergic and adrenergic neurons in both the central and peripheral nervous systems of adult rodents. Numerous non-catecholaminergic cell groups within the spinal cord, medulla, cerebellum, and pons also express AP-2. The concentration of AP-2 in dorsomedial locations along the neuraxis suggests a regionally specific role for this transcription factor in the regulation of neuronal function. Based on these findings we propose that AP-2 may coregulate TH and DBH gene expression and thus participate in expression/maintenance of neurotransmitter phenotypes in (nor)adrenergic neurons and neuroendocrine cells.

A response element for the homeodomain transcription factor Ptx3 in the tyrosine hydroxylase gene promoter

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the biosynthesis of catecholamines, which takes place in different types of neuronal systems and nonneuronal tissues. The transcriptional regulation of the TH gene, which is complex and highly variable among different tissues, reflects this heterogeneity. We recently isolated a homeodomain transcription factor, named Ptx3, that is uniquely expressed in the dopaminergic neurons of the substantia nigra pars compacta and ventral tegmental area, which together form the mesencephalic dopaminergic system. This strict localization and its coinciding induction of expression with the TH gene during development suggested a possible role for this transcription factor in the control of the TH gene. We report here the presence of a responsive element for Ptx3 located at position -50 to -45 of the rat TH promoter. Transient transfections using TH promoter constructs and electrophoretic mobility shift assays using Ptx3-containing nuclear extracts demonstrated that this region binds Ptx3 protein and confers a transcriptional effect on the TH gene. Depending on the cell type, the effect of Ptx3 was an eight- to 12-fold enhancement of TH promoter activity in Neuro2A neuroblastoma cells, or a 60-80% repression in nonneuronal human embryonic kidney 293 cells. Despite the close association of the Ptx3-binding site and the major cyclic AMP-response element in the TH gene, no interplay was found between Ptx3 and cyclic AMP-modulating agents. In combination with the orphan nuclear receptor Nurr1, which is required for the induction of the TH gene in mesencephalic dopaminergic neurons, the TH promoter activity to Ptx3 was enhanced in Neuro2A cells. Nurr1 alone displayed only very weak activity on the TH promoter in this cell type. The results demonstrate that the homeodomain protein Ptx3 has the potential to act on the promoter of the TH gene in a markedly cell type-dependent fashion. This suggests that Ptx3 contributes to the regulation of TH expression in mesencephalic dopaminergic neurons.

HIV-1 Tat-mediated inhibition of the tyrosine hydroxylase gene expression in dopaminergic neuronal cells

Treatment of dopaminergic rat PC12 cells with human immunodeficiency virus, type 1 (HIV-1) Tat protein or tat cDNA inhibited the expression of tyrosine hydroxylase (TH), the rate-limiting enzyme for the dopamine biosynthetic pathway, as well as the production and release of dopamine into the culture medium. Moreover, the Tat addition to PC12 cells up-regulated the expression of the inducible cAMP early repressor (ICER), a specific member of the cAMP-responsive element modulator transcription factor family, in a cAMP-dependent manner. In turn, ICER overexpression abrogated the transcription activity of the TH promoter in PC12 cells, strongly suggesting ICER involvement in Tat-mediated inhibition of TH gene expression. In vivo injection of synthetic HIV-1 Tat protein into the striatum of healthy rats induced a subclinical Parkinson's-like disease that became manifested only when the animals were treated with amphetamine. As early as one week postinjection, the histochemical examination of the rat substantia nigra showed a reduced staining of neurons expressing TH followed by a loss of TH(+) neurons at later time points. As Tat protein can be locally released into the central nervous system by HIV-1-infected microglial cells, our findings may contribute to the explanation of the pathogenesis of the motorial abnormalities often reported in HIV-1 seropositive individuals.

4.5 kb of the rat tyrosine hydroxylase 5' flanking sequence directs tissue specific expression during development and contains consensus sites for multiple transcription factors

To delineate DNA sequences responsible for developmentally correct expression of the rat tyrosine hydroxylase (TH) gene, we analyzed a line of transgenic mice expressing high levels of human placental alkaline phosphatase (AP) under control of 4.5 kb of 5' flanking DNA from the rat TH gene in embryos and adults. Several regions, such as the accessory olfactory bulb, which were not thought to synthesize TH protein or do so only transiently, were shown to express TH protein using an improved method of antigen retrieval for TH immunohistochemistry. Many of these regions had been shown to express TH-driven reporter genes in transgenic mice. In the central nervous system, AP was detected in essentially all TH-expressing cell groups throughout development and in adults. In the peripheral nervous system, transgene expression paralleled endogenous TH expression in the developing adrenal medulla and sympathetic ganglia but not in transiently TH-positive cells in dorsal root ganglia. Peripheral expression in the adult adrenal medulla was very weak and absent in sympathetic ganglia. The specificity with which the 4.5 kb region directs transgene expression in embryos is comparable to that observed with longer 5' flanking promoter regions, implying that this region contains the control elements for appropriate expression during development. Sequence analysis of the region demonstrates a GT dinucleotide repeat, an element that resembles the neural restrictive silencer element (NRSE), which restricts transcription of neuronal genes in non-neuronal cells, and consensus sites for three families of transcription factors, Ptx1/3, Nurr1 and Gli1/2, which are required for the early differentiation of mesencephalic neurons.

Genomic structure and chromosomal mapping of the human and mouse hippocalcin genes

In an attempt to elucidate the possible relationship of hippocalcin to neurological disorders, we isolated and analyzed the human and mouse hippocalcin genes. The human and mouse hippocalcin genes contain three exons and two introns, and span approximately 7 and 8kb, respectively. The exon/intron splice junctions of the human and mouse genes are all situated in exactly the same position and are not consistently placed with respect to the coding regions of the tandemly repeated EF-hand motifs. The amino acid sequences of human and mouse hippocalcins deduced from the genes are 100% identical. Within the 2-kb 3'-flanking sequences of the human and mouse genes, one conserved polyadenylation signal was identified at positions 762 and 823bp downstream from TAG, respectively. Within the 2.6-kb 5'-flanking sequences of the human and mouse genes, neither a canonical 'TATA' box nor a 'CAAT' box was found. Southern blot analysis of the human and mouse genomic DNAs demonstrated that the positive bands coincide exactly with those expected from the sequence of the cloned genes, indicating that the human and mouse hippocalcin genes are present as a single-copy gene. Fluorescence in-situ hybridization revealed that the human hippocalcin gene is located at chromosome 1 p34.2-35 and the mouse hippocalcin gene at chromosome 4 D2-D3.

CRE and TRE sequences of the rat tyrosine hydroxylase promoter are required for TH basal expression in adult mice but not in the embryo

Tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of catecholamine neurotransmitters, is expressed in a restricted number of areas, and subject to numerous regulations during development and in adulthood. Two transcription factor binding sites present in the proximal region of the TH gene, the TPA-responsive element (TRE) and the c-AMP responsive element (CRE), have been shown to play important roles in TH gene regulation in vitro. In order to elucidate in vivo the role of these two sites, we produced transgenic mice bearing a 5.3-kb fragment from the 5' flanking sequence of the TH gene with mutations in either the CRE-or TRE-sites. Using the intact 5.3-kb fragment fused to two different reporter genes (HSV1-tk and lacZ), we show that this promoter fragment is able to specifically direct expression in catecholaminergic tissues both in adult mice and embryos. Interestingly, the CRE- and TRE-mutated transgenes were not expressed in adult mice, contrary to the situation in embryos where they were specifically expressed in catecholaminergic regions. These results demonstrate that the CRE and TRE play an essential role in basal TH expression in adult tissues in vivo. Moreover, they suggest that distinct transcription factors are involved in TH regulation in developing and adult tissues. In support of this, gel mobility shift experiments revealed a complex present only in embryonic tissues. Taken together, these data highlight the diversity of the mechanisms underlying the establishment and maintenance of the catecholaminergic phenotype.

Adenovirus vector-mediated gene transfer into human epileptogenic brain slices: prospects for gene therapy in epilepsy

As a first step in the development of a gene therapy approach to epilepsy, we evaluated the ability of adenovirus vectors to direct the transfer into and expression of a marker gene in human brain slices obtained from patients undergoing surgery for medically intractable epilepsy. Following injection of adenovirus vectors containing the Escherichia coli lacZ gene into hippocampal and cortical brain slices, lacZ mRNA, beta-galactosidase protein, and enzymatic activity were detected, confirming successful gene transfer, transcription, and translation into a functional protein. Transfected cells were predominantly glial, with some neurons expressing beta-galactosidase as well. These results support the potential of adenovirus vectors to transfer genetic information into human epileptogenic brain, resulting in expression of the gene into a functional protein. These findings also have implications for the development of gene therapy approaches to certain seizure disorders. A number of potential therapeutic approaches are discussed, including the elevation of inhibitory neurotransmitter or neuropeptide levels, expression or modulation of postsynaptic receptors, and manipulation of signal transduction systems.

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.

Inducible cAMP early repressor can modulate tyrosine hydroxylase gene expression after stimulation of cAMP synthesis

Members of the CREB/CREM/ATF family of transcription factors either enhance or repress transcription after binding to the cAMP response elements (CREs) of numerous genes. The rat gene for tyrosine hydroxylase (TH) bears a canonical CRE, at base pairs -38 through -45 from the transcription initiation site, that is essential for basal and cAMP-stimulated transcription (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). The current study identifies CRE-binding proteins induced in pharmacological paradigms characterized by TH activation. PC12- and rat adrenal gland-derived nuclear proteins retarded a TH-CRE oligonucleotide in gel mobility shift assays with virtually identical patterns. These differed substantially from patterns exhibited by extracts from locus ceruleus or from neuroblastoma (SK-N-BE()C) and locus ceruleus-derived (CATH.a) cell lines. Forskolin stimulation of PC12 cells and reserpine treatment of rats increased, in nuclear extracts derived from cells and adrenal glands, respectively, the amount of a fast moving CRE/protein complex that was supershifted by an anti-CREM antibody. Subsequent Western, Northern, and polymerase chain reaction analyses indicated that a specific member of the CREM family, the inducible cAMP early repressor (ICER), was strongly induced in both systems. Cotransfection of PC12 cells with TH2400CAT plasmid and the expression vector pCMV-ICER-Ib demonstrated that ICER efficiently represses the transcriptional activity of the TH gene promoter. In addition, PKA-stimulated transcriptional activity of the promoter was effectively suppressed by ICER. These results suggest that ICER can modulate cAMP-stimulated transcription of the TH gene and provide a model accounting for rapid reversal of increased TH transcription following elevations in cAMP.

Rapid down-regulation of tyrosine hydroxylase expression in the olfactory bulb of naris-occluded adult rats

In most sensory systems, afferent innervation regulates morphological and biochemical characteristics of target cells for a limited time during development. Sensory deprivation experiments in adult rats also have suggested a critical period for afferent influences on olfactory bulb structure and function. Previous odorant deprivation studies that employed unilateral naris closure in neonatal rats demonstrated down-regulation of the catecholamine biosynthetic enzyme tyrosine hydroxylase (TH) in dopamine neurons intrinsic to the olfactory bulb. Accompanying the altered biochemical parameters was a decrease in bulb size. To distinguish between deprivation-induced alterations in TH expression secondary to developmental sequelae and those occurring in mature neurons, the consequences of unilateral naris closure were assessed in young adult rats. In agreement with previous studies significant postnatal increases occurred in TH expression and total protein, an indication of bulb size. At 30 days post-closure, total protein was unaltered in the ipsilateral olfactory bulb but showed a small (12.9%), significant decline at 60 days. In contrast to the limited morphological consequences of odor deprivation, profound reductions occurred in TH expression. TH activity ipsilateral to the closure decreased significantly by 14 days post-closure and remained depressed for up to 6 months. In parallel with enzyme activity, TH immunoreactivity did not decline in the first few days post-closure. In situ hybridization revealed that TH mRNA levels decreased rapidly, i.e., by 2 days post-closure, reached a nadir at 1 month, and remained depressed for at least 6 months. The capacity of odor deprivation in the adult rat olfactory system to down-regulate TH expression suggests that this phenotypic alteration occurs independently of a presumed critical period.

Promoter elements and second messenger pathways involved in transcriptional activation of tyrosine hydroxylase by ionomycin

Membrane depolarization, or agents which increase intracellular calcium, elicit transcriptional activation of tyrosine hydroxylase (TH). In this study we analyze the factors involved in the regulation of the TH promoter by a calcium ionophore. PC12 cells were transiently transfected with plasmids containing wild type or mutated 5' flanking sequences of the rat TH gene, fused to bacterial chloramphenicol acetyl transferase (CAT). Point mutations introduced into the consensus cAMP-regulatory element (CRE) abolished the induction of CAT by ionomycin indicating that it is essential for mediating the calcium response. An intact and functional AP1 site did not confer calcium inducibility when the CRE/CaRE sequence was mutated. The extent and kinetics of the increase in intracellular calcium as well as the induction of CAT activity under the control of TH promoter by ionomycin were similar in PC12 cells and in the A123.7, protein kinase A (PKA) deficient cell line. In both cell lines addition of ionomycin rapidly increased the phosphorylation of transcription factor CREB at Ser-133. These results suggest that the activation of TH transcription by ionomycin does not require PKA. However, KN62 an inhibitor of Ca2+/calmodulin dependent (CaM) kinases prevented the induction indicating possible involvement of CAM kinases in the calcium response.

A herpes simplex virus-1 vector containing the rat tyrosine hydroxylase promoter directs cell type-specific expression of beta-galactosidase in cultured rat peripheral neurons

A defective herpes simplex virus-1 (HSV-1) vector system was used to study cell type-specific expression of the tyrosine hydroxylase (TH) gene. HSV-1 particles containing 663 bp (pTHlac 663), 278 bp (pTHlac 278), or 181 bp (pTHlac 181) of the rat TH promoter driving E. coli LacZ were used to infect superior cervical ganglia (SCG: TH-expressing tissue) and dorsal root ganglia (DRG:non-TH-expressing tissue) cultures. One day after infection, expression of beta-galactosidase was visualized by X-gal cytochemistry. Following viral transduction with pTHlac 663 at a multiplicity of infection of 0.2, 14.4% of the SCG neurons were X-gal positive whereas only about 0.9% of DRG neurons were X-gal positive. Infection with either pTHlac278 or 181 resulted in 3-fold more X-gal-positive DRG neurons. These results suggest that (i) the defective HSV-1 vector system may be useful in defining regulatory promoter motifs; (ii) 663 bp of the rat TH promoter contains sufficient information for cell type-specific expression in peripheral nervous system neurons; and (iii) sequences between -278 and -663 contain an element(s) that represses gene expression in non-catecholamingeric neurons.

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.