Upstream sequencing and functional characterization of the human cholinergic gene locus

Association of Choline Acetyltransferase Gene Polymorphisms (SNPs rs868750G/A, rs1880676G/A, rs2177369G/A and rs3810950G/A) with Alzheimer's Disease Risk: A Meta-Analysis

BACKGROUND

Epidemiological studies have investigated the role of choline acetyltransferase (ChAT) in Alzheimer's disease (AD). ChAT gene polymorphisms (SNPs rs868750G/A, rs1880676G/A, rs2177369G/A, and rs3810950G/A) may be associated with the risk of AD. In this meta-analysis, we determined the relationship between the four polymorphisms and the risk of AD.

METHODS

We searched MEDLINE, EMBASE, and HuGEnet databases for studies linking the four polymorphisms with AD risk. We included 16 articles in our meta-analysis to assess the association between the four polymorphisms and susceptibility to AD by calculating the pooled odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

The combined results showed no significant association with rs1880676G/A and rs2177369G/A polymorphisms. The risk of AD (GG+GA versus AA: OR = 0.01, 95%CI = 0.01-0.02, P < 0.05; GG versus GA+AA: OR = 0.85, 95%CI = 0.72-1.00, P = 0.05; GA versus AA: OR = 0.60, 95% CI = 0.37-0.98, P = 0.04) with rs868750G/A polymorphism, or the association of rs3810950G/A polymorphism with AD risk in the overall population (GA versus AA: OR = 0.64, 95% CI = 0.44-0.93, P = 0.02; GG+GA versus AA: OR = 0.62, 95% CI = 0.39-0.97, P = 0.04) or Asian group (GA versus AA: OR = 0.50, 95% CI = 0.32-0.76, P = 0.001, and GG+GA versus AA: OR = 0.46, 95% CI = 0.30-0.09, P = 0.0002) was demonstrated.

CONCLUSIONS

Our meta-analysis suggested that rs1880670G/A, and rs2177369 G/A polymorphisms were not risk factors for AD. However, rs3810950G/A, or rs868750G/A genetic polymorphism was a genetic risk factor for the development of AD. The rs3810950G/A polymorphism had a negative effect on the risk of AD for GA or GG+GA genotypes compared with AA in the overall population or Asians.

REST/NRSF-induced changes of ChAT protein expression in the neocortex and hippocampus of the 3xTg-AD mouse model for Alzheimer's disease

AIMS

The cholinergic system is one of the neurotransmitter systems altered in Alzheimer's disease (AD), the most common form of human dementia. The objective of this work was to determine the REST/NRSF involvement in altered ChAT expression in the neocortex and hippocampus of an AD transgenic mouse (homozygous 3xTg-AD) that over-expresses 3 proteins, amyloid-β precursor protein, presenilin-1, and tau, all of which are associated with AD and cause cellular degeneration.

MAIN METHODS

Two groups (WT and 3xTg-AD) of 11-month-old female mice were analyzed and compared. Half of the brains of each group were used for ChAT immunohistochemistry, and Western Blot analyses of ChAT and REST/NRSF were performed on the other half.

KEY FINDINGS

We observed significant decreases in the number of ChAT-immunoreactive cells in the Meynert nucleus and of fibers in the frontal motor cortex and hippocampal CA1 area in transgenic mice compared with control mice. An increased level of REST/NRSF protein and a reduction of ChAT protein expression in the 3xTg-AD mice compared with their controls were also found in both in the latter two cerebral regions.

SIGNIFICANCE

The increased REST/NRSF expression reported here and its effect on the regulatory region for ChAT transcription could explain the decreased expression of ChAT in the 3xTg-AD mouse; these findings may be associated with the degeneration observed in AD.

Neural restrictive silencer factor and choline acetyltransferase expression in cerebral tissue of Alzheimer's Disease patients: A pilot study

Decreased Choline Acetyltransferase (ChAT) brain level is one of the main biochemical disorders in Alzheimer’s Disease (AD). In rodents, recent data show that the CHAT gene can be regulated by a neural restrictive silencer factor (NRSF). The aim of the present work was to evaluate the gene and protein expression of CHAT and NRSF in frontal, temporal, entorhinal and parietal cortices of AD patient brains. Four brains from patients with AD and four brains from subjects without dementia were studied. Cerebral tissues were obtained and processed by the guanidine isothiocyanate method for RNA extraction. CHAT and NRSF gene and protein expression were determined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting. CHAT gene expression levels were 39% lower in AD patients as compared to the control group (p < 0.05, U test). ChAT protein levels were reduced by 17% (p = 0.02, U test). NRSF gene expression levels were 86% higher in the AD group (p = 0.001, U test) as compared to the control group. In the AD subjects, the NRSF protein levels were 57% higher (p > 0.05, U test) than in the control subjects. These findings suggest for the first time that in the brain of AD patients high NRSF protein levels are related to low CHAT gene expression levels.

The sympathetic neurotransmitter switch depends on the nuclear matrix protein Satb2

Sympathetic neurons can switch their neurotransmitter phenotype from noradrenergic to cholinergic on exposure to neuropoietic cytokines in vitro and in vivo. Here, we provide evidence that this transspecification is regulated by the chromatin architecture protein Satb2. Treatment with the neuropoietic cytokines ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor rapidly and strongly increases Satb2 transcript and protein levels in cultures of rat superior cervical ganglia neurons. Knockdown of endogenous Satb2 by short interfering RNA prevents the upregulation of choline acetyltransferase (Chat) and vesicular acetylcholine transporter (Vacht) by CNTF as well as the loss of norepinephrine transporter (Net). Conversely, overexpression of Satb2 in the noradrenergic sympathetic phenotype results in a marked increase of Chat and Vacht expression and reduced Net mRNA levels in the absence of neuropoietic cytokines. Chromatin immunoprecipitation analysis in primary sympathetic neurons reveals that Satb2 binds to matrix attachment regions (MARs) within the Chat locus. In vivo, in the rat stellate ganglion, Satb2 is expressed exclusively in sudomotor cholinergic neurons innervating the sweat glands and only after establishment of contact between neurons and target. These findings demonstrate a function of the MAR-binding protein Satb2 in growth factor-dependent neurotransmitter plasticity in postmitotic neurons.

82-kDa choline acetyltransferase is in nuclei of cholinergic neurons in human CNS and altered in aging and Alzheimer disease

Cholinergic neurons express choline acetyltransferase (ChAT) which synthesizes acetylcholine. We show here for the first time that primate-specific 82-kDa ChAT is expressed in nuclei of cholinergic neurons in human brain and spinal cord; isoform-specific antibodies were used to compare localization patterns and temporal expression of the more abundant 69-kDa ChAT and primate-specific 82-kDa ChAT in necropsy tissues. The 82-kDa ChAT co-localizes with 69-kDa ChAT in well-characterized cholinergic areas, but is also found in the claustrum which does not contain 69-kDa ChAT. Cholinergic neuron function changes with increasing age and are targeted in neurodegenerative diseases such as AD, thus we compared expression and subcellular localization of 69- and 82-kDa ChAT in necropsy brain samples from control subjects of varying ages and from Alzheimer disease (AD) subjects. The 82-kDa ChAT protein was expressed in cholinergic neurons in brain from birth until the eighth decade of life and in AD, but the subcellular staining pattern and proportion of neurons that were immunopositive changed with increasing age and in AD.

Regulation of cholinergic gene expression by nerve growth factor depends on the phosphatidylinositol-3'-kinase pathway

Nerve growth factor (NGF) exerts anti-apoptotic, trophic and differentiating actions on sympathetic neurons and cholinergic cells of the basal forebrain and activates the expression of genes regulating the synthesis and storage of the neurotransmitter acetylcholine (ACh). We have been studying the intracellular signaling pathways involved in this process. Although, in the rat pheochromocytoma cell line PC12, NGF strongly activates the mitogen-activated protein kinase (MAPK) pathway, prolonged inhibition of MAPK kinase (MEK) activity by PD98059 or U0126 did not affect the ability of NGF to up-regulate choline acetyltransferase (ChAT) or to increase intracellular ACh levels. In contrast, the treatment with the phosphatidylinositol 3'-kinase (PI3K) inhibitor LY294002, but not with its inactive analogue LY303511, completely abolished the NGF-induced production of ACh. Inhibition of PI3K also eliminated the NGF effect on the intracellular ACh level in primary cultures of septal neurons from E18 mouse embryos. Blocking the PI3K pathway prevented the activation of cholinergic gene expression, as demonstrated in RT/PCR assays and in transient transfections of PC12 cells with cholinergic locus promoter-luciferase reporter constructs. These results indicate that the PI3K pathway, but not the MEK/MAPK pathway, is the mediator of NGF-induced cholinergic differentiation.

Mechanisms and perspectives on differentiation of autonomic neurons

Neurons share many features in common but are distinguished by expression of phenotypic characteristics that define their specific function, location, or connectivity. One aspect of neuronal fate determination that has been extensively studied is that of neurotransmitter choice. The generation of diversity of neuronal subtypes within the developing nervous system involves integration of extrinsic and intrinsic instructive cues resulting in the expression of a core set of regulatory molecules. This review focuses on mechanisms of growth and transcription factor regulation in the generation of peripheral neural crest-derived neurons. Although the specification and differentiation of noradrenergic neurons are the focus, I have tried to integrate these into a larger picture providing a general roadmap for development of autonomic neurons. There is a core of DNA binding proteins required for the development of sympathetic, parasympathetic, and enteric neurons, including Phox2 and MASH1, whose specificity is regulated by the recruitment of additional transcriptional regulators in a subtype-specific manner. For noradrenergic neurons, the basic helix-loop-helix DNA binding protein HAND2 (dHAND) appears to serve this function. The studies reviewed here support the notion that neurotransmitter identity is closely linked to other aspects of neurogenesis and reveal a molecular mechanism to coordinate expression of pan-neuronal genes with cell type-specific genes.

Comparative study of gene expression of cholinergic system-related molecules in the human spinal cord and term placenta

By reverse transcription-polymerase chain reaction, Southern blot analysis, direct sequencing, and immunohistochemistry, we studied the expression of cholinergic neuronal markers (choline acetyltransferase [ChAT], vesicular acetylcholine transporter [VAChT], and a high-affinity choline transporter [CHT1]), and gene regulatory molecules (repressor element-1 silencing transcription factor/neuron-restrictive silencer factor [REST/NRSF] and CoREST) in the human spinal cord and term placenta, both of which are well known to contain cells synthesizing acetylcholine. H-type, M-type, N2-type, and R-type ChAT mRNAs, VAChT mRNA, and CHT1 mRNA were detected in the spinal cord, but only H-type, M-type, and N2-type ChAT mRNAs, in the term placenta. REST/NRSF and CoREST were detected in the spinal cord and the placenta, but the amounts of both mRNAs were greater in the placenta than in the spinal cord. Further microdissection analyses revealed that the placental trophoblastic cells contained more REST/NRSF and CoREST transcripts than the spinal large motor neurons. Large motor neurons in the anterior horn of the spinal cord were immunohistochemically stained for ChAT and VAChT. In the placenta, stromal fibroblasts, endothelial cells, and trophoblastic cells of the chorionic villi were positively stained with anti-ChAT antibody but not with anti-VAChT antibody. These findings suggest that transcriptions of the R-type ChAT and VAChT mRNAs are coordinately suppressed in the human term placenta, which might be regulated in part by a REST/NRSF complex that binds to a consensus sequence of repressor element 1/neuron-restrictive silencer element (RE1/NRSE) in the 5' region upstream from exon R, whereas transcriptions of the H-type, M-type, and N2-type ChAT mRNAs might be independent of control by RE1/NRSE. It is possible that at least two separate regulatory mechanisms of gene expression are present for the human cholinergic gene locus, which might be selected by different combinations of DNA motifs and binding proteins to function in neuronal and non-neuronal cells.

VAChT-Cre. Fast and VAChT-Cre.Slow: postnatal expression of Cre recombinase in somatomotor neurons with different onset

The cholinergic gene locus (CGL) consists of the genes encoding the choline acetyltransferase (ChAT) and the vesicular acetylcholine transporter (VAChT). To establish a cholinergic-specific Cre-expressing mouse, we constructed a transgene expression vector (VAChT-Cre) with 11.3 kb human CGL in which a Cre-IRES-EGFP unit was inserted in the VAChT open reading frame. The activity of Cre, whose expression was driven by the VAChT promoter, was examined by crossing a reporter mouse (CAG-CAT-Z) in which expression of LacZ is activated upon Cre-mediated recombination. Transgenic lines with the VAChT-Cre construct displayed the restricted Cre expression in a subset of cholinergic neurons in the somatomotor nuclei and medial habenular nucleus, but absent in visceromotor and other central and peripheral cholinergic neurons. Cre expression was first observed at postnatal day 7 and later detected in approximately 40-60% of somatomotor neurons. Based on the onset of Cre expression, we generated two mouse lines (two alleles; VAChT-Cre. Fast and VAChT-Cre.Slow) in which Cre expression reaches maximal levels fast and slow, respectively. The use of VAChT-Cre mice should allow us to deliver Cre to a subset of postnatal motor neurons, thereby bypassing lethality and facilitating analysis of gene function in adult motor neurons.

A restrictive element 1 (RE-1) in the VIP gene modulates transcription in neuronal and non-neuronal cells in collaboration with an upstream tissue specifier element

The vasoactive intestinal peptide (VIP) gene has been studied extensively as a prototype neuronal gene containing multiple cis-active elements that confer responsiveness to cell lineage, neurotrophic, and activity-dependent intrinsic and extrinsic cues. However, reporter genes containing the presumptive complete regulatory region 5' to the start of transcription do not confer tissue-specific gene expression in vivo. We therefore sought cis-regulatory elements downstream of the transcriptional start that might confer additional tissue-specific and tissue-restrictive properties to the VIP transcriptional unit. We report here a repressor element, similar to the canonical restrictive element-1 (RE-1), located within the first non-coding exon of the human VIP gene. The ability of this element to regulate VIP reporter gene expression in neuroblastoma and fibroblastic cells was examined. Endogenous VIP expression is high in SH-EP neuroblastoma cells, low but inducible in SH-SY5Y cells, and absent in HeLa cells. Endogenous RE-1 silencer factor (REST) expression was highest in SH-EP and HeLa cells, and significantly lower in SH-SY5Y cells. Transient transfection of a VIP reporter gene containing a mutated RE-1 sequence revealed an RE-1-dependent regulation of VIP gene expression in all three cell types, with regulation greatest in cells (SH-EP, HeLa) with highest levels of REST expression. Serial truncation of the VIP reporter gene further revealed a specific interaction between the RE-1 and a tissue-specifier element located 5 kb upstream in the VIP gene. Thus, REST can regulate VIP gene expression in both neuroblastic and non-neuronal cells, but requires coupling to the upstream tissue specifier element.

Identification of a region from the human cholinergic gene locus that targets expression of the vesicular acetylcholine transporter to a subset of neurons in the medial habenular nucleus in transgenic mice

We use a transgenic mouse model system to elucidate the regulatory regions within the human cholinergic gene locus responsible for vesicular acetylcholine transporter gene expression in vivo. In this report we characterized two transgenes for their ability to confer cholinergic-specific expression of the encoded vesicular acetylcholine transporter. An 11.2 kb transgene (named hV11.2) that spanned from about 5 kb upstream of the start of vesicular acetylcholine transporter translation down to the first choline acetyltransferase coding exon gave expression in the somatomotor neurons and a subpopulation of cholinergic neurons in the medial habenular nucleus. The second transgene (named hV6.7), a 5-prime truncated version of hV11.2 that was devoid of 4.5 kb of gene-regulatory sequences completely lacked vesicular acetylcholine transporter expression in vivo. Our data indicate that vesicular acetylcholine transporter expression in somatomotor neurons and in the medial habenular nucleus is uniquely specified within the cholinergic gene locus, and separable from cholinergic expression elsewhere. The identification of these two subdivisions of the cholinergic nervous system suggests that other cholinergic neurons in the CNS and PNS are similarly regulated by additional discrete domains within the cholinergic gene locus.

Congenital myasthenic syndrome due to a novel missense mutation in the gene encoding choline acetyltransferase

Congenital myasthenic syndromes are caused by different genetic defects affecting proteins expressed at the neuromuscular junction. Recently, the first molecular genetic defect resulting in a presynaptic congenital myasthenic syndrome has been reported: Recessive loss-of-function mutations in CHAT, the gene encoding choline acetyltransferase, were described in five congenital myasthenic syndrome families. In this study, we investigated three patients from two independent Turkish kinships. Clinically, all patients presented with moderate myasthenic symptoms including ptosis and muscle weakness with increased fatigability. Multiple episodes of sudden apnea were reported for all patients. One child suffering from a second, unrelated disorder, i.e. hepatocellular carcinoma, showed a severe myasthenic phenotype, requiring permanent ventilation. Genetically, we identified a novel missense mutation (I336T) in the CHAT gene homozygously in all three patients. Haplotype analysis revealed that the mutant allele cosegregates with the clinical phenotype in both families (maximum combined two-point LOD-score of 2.46 for D10S1793). In summary, we confirm that CHAT mutations are responsible for a clinically distinct form of congenital myasthenic syndrome, characterized by episodic apnea. Infections and stress may lead to a life-threatening failure of neuromuscular transmission in congenital myasthenic syndrome with episodic apnea. The observation of the same mutation (I336T) in two independent Turkish kinships may suggest a common origin, i.e. founder.

Developmental expression of nicotinic receptors in the chick and human spinal cord

Naturally occurring programmed cell death of lumbar motor neurons in the chick spinal cord occurs between embryonic day (E) 6 and E12; whereas, a peak of motor neuron degeneration in the human spinal cord occurs between 12 and 16 weeks gestation. One of the major neurotransmitters, acetylcholine, is released from the embryonic motor neuron early in development and is thought to be responsible for early muscle activity that serves as a signal for regulating motor neuron survival. The effects of acetylcholine are mediated by two functionally distinct classes of receptors; namely, muscarinic and nicotinic with nicotinic receptors being used at the neuromuscular synapse. In this study, we determined the developmental expression profile of nicotinic acetylcholine receptor subunits in the chick and human lumbar motor neurons and skeletal muscle using reverse transcription polymerase chain reaction, immunoblots, and immunocytochemistry. Our results show that, in the chick, nicotinic receptor subunits alpha1, alpha4, alpha7, alpha8, and beta2 appear to be regulated during the process of naturally occurring motor neuron cell death in the spinal cord. A new finding was the expression of alpha8 mRNA and protein from E4.5 through E7 in chick motor neurons. Interestingly, we also found that, at E14, alpha8 protein was localized only in sensory dorsal horn neurons. In the developing human spinal cord, we determined that nicotinic receptor subunits alpha1, alpha2, alpha3, alpha4, alpha7, beta2, and beta3 were expressed before the programmed cell death period, and alpha2, alpha4, alpha7, beta2, beta3, and beta4 were expressed during the programmed cell death period. Our data demonstrate that neuronal and muscle nicotinic receptor mRNAs and proteins are expressed during important embryonic periods. This finding raises the possibility that nicotinic receptors play an important role in the spinal cord and skeletal muscle during early development.

PACAP and NGF regulate common and distinct traits of the sympathoadrenal lineage: effects on electrical properties, gene markers and transcription factors in differentiating PC12 cells

To determine the possible role of pituitary adenylate cyclase-activating polypeptide (PACAP) in the development of the sympathoadrenal cell lineage, we have examined the effects of this neurotrophic peptide, in comparison to nerve growth factor (NGF), on the morphology, electrophysiological properties, expression of neuronal and neuroendocrine marker genes, and activity of transcription factors during differentiation of sympathoadrenal-derived cells, using the rat pheochromocytoma PC12 cell model. Both PACAP and NGF elicited rapid neurite outgrowth, which was accompanied by induction of cell excitability and the development of both sodium and calcium currents. Concurrently, PACAP and NGF increased the expression of a marker of synaptic vesicles. By contrast, PACAP, but not NGF, regulated the expression of different constituents of neuroendocrine large dense core vesicles in PC12 cells. Furthermore, PACAP and NGF differentially regulated the expression of mammalian achaete-scute homologue and paired homeobox 2b genes, transcription factors instrumental for sympathoadrenal development. To compare downstream effectors activated by PACAP and NGF, we studied the effects of these factors on the binding activity of consensus 12-O-tetradecanoylphorbol-13-acetate- and cAMP-responsive elements to nuclear extracts of differentiating PC12 cells. We found that both PACAP and NGF markedly increase the binding activity of these cis-regulatory sequences and that PACAP preferentially recruits activator protein-1-like transcription factors to these elements. Taken together, these results show that PACAP and NGF exert common as well as different effects on neuronal and neuroendocrine traits in differentiating PC12 cells, strongly suggesting that these two trophic factors could play complementary roles in the development of the sympathoadrenal cell lineage.

Abnormal chemosensory jump 6 is a positive transcriptional regulator of the cholinergic gene locus in Drosophila olfactory neurons

Cholinergic neurons acquire their neurotransmitter phenotype, in part, by expressing the cholinergic gene locus. Previous studies have indicated that the 5' flanking DNA of the locus contains both positive and negative regulatory elements important for expression in different subsets of cholinergic neurons in Drosophila and other animals. Approximately 300 bases of proximal 5' flanking DNA control expression in Drosophila CNS neurons essential for viability, whereas more distal regulatory elements are important for expression in PNS sensory neurons. In this study we identify the POU domain transcription factor abnormal chemosensory jump 6 (Acj6) as a necessary positive transcriptional regulator for cholinergic locus expression in primary olfactory neurons. Choline acetyltransferase enzyme activity, protein levels, mRNA, and a fluorescent cholinergic reporter gene are all decreased in olfactory neurons of acj6 mutants. Decreased cholinergic expression was observed in both adults and larvae. The presence of a specific Acj6 binding site has been identified in the cholinergic locus 5' flanking DNA, suggesting that Acj6 may play a direct role in specifying the cholinergic neurotransmitter phenotype of most olfactory neurons. Transgenic expression of two different isoforms of Acj6 restricted to olfactory neurons indicates that additional trans factors may be required for cholinergic locus expression. Transgenic expression in all cholinergic neurons, however, results in lethality when a POU IV box element is absent but is essentially benign when present, indicating the importance of this motif in specifying different functional roles for Acj6.

Independent patterns of transcription for the products of the rat cholinergic gene locus

The cholinergic phenotype requires the expression of the vesicular acetylcholine transporter and choline acetyltransferase proteins. Both genes are encoded at one chromosomal location called the cholinergic gene locus. We have identified by in situ hybridization histochemistry distinct patterns of transcription from the cholinergic gene locus in the subdivisions of the rat cholinergic nervous system. The vesicular acetylcholine transporter and choline acetyltransferase are co-expressed in cholinergic neurons at all developmental stages in all major types of cholinergic neurons. The relative levels of vesicular acetylcholine transporter and choline acetyltransferase transcripts, however, change substantially during development in the CNS. They also differ dramatically in distinct subdivisions of the mature cholinergic nervous system, with vesicular acetylcholine transporter mRNA expressed at high levels relative to choline acetyltransferase mRNA in the peripheral nervous system, but at equivalent levels in the CNS. Expression of the R-exon, the presumptive first non-coding exon common to both the vesicular acetylcholine transporter and choline acetyltransferase, was not detectable at any developmental stage in any of the cholinergic neuronal subtypes in the rat nervous system. Thus, in contrast to less complex metazoan organisms, production of the vesicular acetylcholine transporter and choline acetyltransferase via a common differentially spliced transcript does not seem to occur to a significant extent in the rat. We suggest that separate transcriptional start sites within the cholinergic gene locus control vesicular acetylcholine transporter and choline acetyltransferase transcription, while additional elements are responsible for the specific transcriptional control of the entire locus in cholinergic versus non-cholinergic neurons. Independent transcription of the vesicular acetylcholine transporter and choline acetyltransferase genes provides a mechanism for regulating the relative expression of these two proteins to fine-tune acetylcholine quantal size in different types of cholinergic neurons, both centrally and peripherally.

The neuron-restrictive silencer element-neuron-restrictive silencer factor system regulates basal and endothelin 1-inducible atrial natriuretic peptide gene expression in ventricular myocytes

Induction of the atrial natriuretic peptide (ANP) gene is a common feature of ventricular hypertrophy. A number of cis-acting enhancer elements for several transcriptional activators have been shown to play central roles in the regulation of ANP gene expression, but much less is known about contributions made by transcriptional repressors. The neuron-restrictive silencer element (NRSE), also known as repressor element 1, mediates repression of neuronal gene expression in nonneuronal cells. We found that NRSE, which is located in the 3' untranslated region of the ANP gene, mediated repression of ANP promoter activity in ventricular myocytes and was also involved in the endothelin 1-induced increase in ANP gene transcription. The repression was conferred by a repressor protein, neuron-restrictive silencer factor (NRSF). NRSF associated with the transcriptional corepressor mSin3 and formed a complex with histone deacetylase (HDAC) in ventricular myocytes. Trichostatin A (TSA), a specific HDAC inhibitor, relieved NRSE-mediated repression of ANP promoter activity, and chromatin immunoprecipitation assays revealed the involvement of histone deacetylation in NRSE-mediated repression of ANP gene expression. Furthermore, in myocytes infected with recombinant adenovirus expressing a dominant-negative form of NRSF, the basal level of endogenous ANP gene expression was increased and a TSA-induced increase in ANP gene expression was apparently attenuated, compared with those in myocytes infected with control adenovirus. Our findings show that an NRSE-NRSF system plays a key role in the regulation of ANP gene expression by HDAC in ventricular myocytes and provide a new insight into the role of the NRSE-NRSF system outside the nervous system.

Choline acetyltransferase mutations cause myasthenic syndrome associated with episodic apnea in humans

Choline acetyltransferase (ChAT; EC ) catalyzes the reversible synthesis of acetylcholine (ACh) from acetyl CoA and choline at cholinergic synapses. Mutations in genes encoding ChAT affecting motility exist in Caenorhabditis elegans and Drosophila, but no CHAT mutations have been observed in humans to date. Here we report that mutations in CHAT cause a congenital myasthenic syndrome associated with frequently fatal episodes of apnea (CMS-EA). Studies of the neuromuscular junction in this disease show a stimulation-dependent decrease of the amplitude of the miniature endplate potential and no deficiency of the ACh receptor. These findings point to a defect in ACh resynthesis or vesicular filling and to CHAT as one of the candidate genes. Direct sequencing of CHAT reveals 10 recessive mutations in five patients with CMS-EA. One mutation (523insCC) is a frameshifting null mutation. Three mutations (I305T, R420C, and E441K) markedly reduce ChAT expression in COS cells. Kinetic studies of nine bacterially expressed ChAT mutants demonstrate that one mutant (E441K) lacks catalytic activity, and eight mutants (L210P, P211A, I305T, R420C, R482G, S498L, V506L, and R560H) have significantly impaired catalytic efficiencies.

Somatomotor neuron-specific expression of the human cholinergic gene locus in transgenic mice

We examined the expression pattern of the vesicular acetylcholine transporter in the mouse nervous system, using rodent-specific riboprobes and antibodies, prior to comparing it with the distribution of vesicular acetylcholine transporter expressed from a human transgene in the mouse, using riboprobes and antibodies specific for human. Endogenous vesicular acetylcholine transporter expression was high in spinal and brainstem somatomotor neurons, vagal visceromotor neurons, and postganglionic parasympathetic neurons, moderate in basal forebrain and brainstem projection neurons and striatal interneurons, and low in intestinal intrinsic neurons. Vesicular acetylcholine transporter expression in intrinsic cortical neurons was restricted to the entorhinal cortex. The sequence of the mouse cholinergic gene locus to 5.1kb upstream of the start of transcription of the vesicular acetylcholine transporter gene was determined and compared with the corresponding region of the human gene. Cis-regulatory domains implicated previously in human or rat cholinergic gene regulation are highly conserved in mouse, indicating their probable relevance to the regulation of the mammalian cholinergic gene locus in vivo. Mouse lines were established containing a human transgene that included the vesicular acetylcholine transporter gene and sequences spanning 5kb upstream and 1.8kb downstream of the vesicular acetylcholine transporter open reading frame. In this transgene, the intact human vesicular acetylcholine transporter was able to act as its own reporter. This allowed elements within the vesicular acetylcholine transporter open reading frame itself, shown previously to affect transcription in vitro, to be assessed in vivo with antibodies and riboprobes that reliably distinguished between human and mouse vesicular acetylcholine transporters and their messenger RNAs. Expression of the human vesicular acetylcholine transporter was restricted to mouse cholinergic somatomotor neurons in the spinal cord and brainstem, but absent from other central and peripheral cholinergic neurons. The mouse appears to be an appropriate model for the study of the genetic regulation of the cholinergic gene locus, and the physiology and neurochemistry of the mammalian cholinergic nervous system, although differences exist in the distribution of cortical cholinergic neurons between the mouse and other mammals. The somatomotor neuron-specific expression pattern of the transgenic human vesicular acetylcholine transporter suggests a mosaic model for cholinergic gene locus regulation in separate subdivisions of the mammalian cholinergic nervous system.

The cholinergic neuronal phenotype in Alzheimer's disease

The synthesis, storage and release of acetylcholine (ACh) requires the expression of several specialized proteins, including choline acetyltransferase (ChAT) and the vesicular ACh transporter (VAChT). The VAChT gene is located within the first intron of the ChAT gene. This unique genomic organization permits coordinated activation of expression of the two genes by extracellular factors. Much less is known about factors that reduce the expression of the cholinergic phenotype. A cholinergic deficit is one of the primary features of Alzheimer's disease (AD), and AD brains are characterized by amyloid deposits composed primarily of A beta peptides. Although A beta peptides are neurotoxic, part of the cholinergic deficit in AD could be attributed to the suppression of cholinergic markers in the absence of cell death. Indeed, we and others demonstrated that synthetic A beta peptides, at submicromolar concentrations that cause no cytotoxicity, reduce the expression of cholinergic markers in neuronal cells. Another feature of AD is abnormal phospholipid turnover, which might be related to the progressive accumulation of apolipoprotein E (apoE) within amyloid plaques, leading perhaps to the reduction of apoE content in the CSF of AD patients. ApoE is a component of very low density lipoproteins (VLDL). As a first step in investigating a potential neuroprotective function of apoE, we determined the effects of VLDL on ACh content in neuronal cells. We found that VLDL increases ACh levels, and that it can partially offset the anticholinergic actions of A beta peptides.

Identification and transgenic analysis of a murine promoter that targets cholinergic neuron expression

Choline acetyltransferase (ChAT) is a specific phenotypic marker of cholinergic neurons. Previous reports showed that different upstream regions of the ChAT gene are necessary for cell type-specific expression of reporter genes in cholinergic cell lines. The identity of the mouse ChAT promoter region controlling the establishment, maintenance, and plasticity of the cholinergic phenotype in vivo is not known. We characterized a promoter region of the mouse ChAT gene in transgenic mice, using beta-galactosidase (LacZ) as a reporter gene. A 3,402-bp segment from the 5'-untranslated region of the mouse ChAT gene (from -3,356 to +46, +1 being the translation initiation site) was sufficient to direct the expression of LacZ to selected neurons of the nervous system; however, it did not provide complete cholinergic specificity. A larger fragment (6,417 bp, from -6,371 to +46) of this region contains the requisite regulatory elements that restrict expression of the LacZ reporter gene only in cholinergic neurons of transgenic mice. This 6.4-kb DNA fragment encompasses 633 bp of the 5'-flanking region of the mouse vesicular acetylcholine transporter (VAChT), the entire open reading frame of the VAChT gene, contained within the first intron of the ChAT gene, and sequences upstream of the start coding sequences of the ChAT gene. This promoter will allow targeting of specific gene products to cholinergic neurons to evaluate the mechanisms of diseases characterized by dysfunction of cholinergic neurons and will be valuable in design strategies to correct those disorders.

Cis-regulatory elements controlling basal and inducible VIP gene transcription

The cis-acting elements of the VIP gene important for basal and stimulated transcription have been studied by transfection of VIP-reporter gene constructs into distinct human neuroblastoma cell lines in which VIP transcription is constitutively high, or can be induced to high levels by protein kinase stimulation. The 5.2 kb flanking sequence of the VIP gene conferring correct basal and inducible VIP gene expression onto a reporter gene in these cell lines was systematically deleted to define its minimal components. A 425-bp fragment (-4656 to -4231) fused to the proximal 1.55 kb of the VIP promoter-enhancer was absolutely required for cell-specific basal and inducible transcription. Four additional components of the VIP gene were required for full cell-specific expression driven by the 425 bp TSE (region A). Sequences from -1.55 to -1.37 (region B), -1.37 to -1.28 (region C), -1.28 to -.094 (region D), and the CRE-containing proximal 94 bp (region E) were deleted in various combinations to demonstrate the specific contributions of each region to correct basal and inducible VIP gene expression. Deletion of region B, or mutational inactivation of the CRE in region E, resulted in constructs with low transcriptional activity in VIP-expressing cell lines. Deletion of regions B and C together resulted in a gain of transcriptional activity, but without cell specificity. All five domains of the VIP gene were also required for cell-specific induction of VIP gene expression with phorbol ester. Gelshift analysis of putative regulatory sequences in regions A-D suggests that both ubiquitous and neuron-specific trans-acting proteins participate in VIP gene regulation.

From the cholinergic gene locus to the cholinergic neuron

The cholinergic gene locus (CGL) was first identified in 1994 as the site (human chromosome 10q11.2) at which choline acetyltransferase and a functional vesicular acetylcholine transporter are co-localized. Here, we present recent neuroanatomical, developmental, and evolutionary insights into the chemical coding of cholinergic neurotransmission that have been gleaned from the study of the CGL, and its protein products VAChT and ChAT, which comprise a synthesis-sequestration pathway that functionally defines the cholinergic phenotype.