Rat nurr1 is prominently expressed in perirhinal cortex, and differentially induced in the hippocampal dentate gyrus by electroconvulsive vs. kindled seizures

Nurr1 Is Not an Essential Regulator of BDNF in Mouse Cortical Neurons

Nurr1 and brain-derived neurotrophic factor (BDNF) play major roles in cognition. Nurr1 regulates BDNF in midbrain dopaminergic neurons and cerebellar granule cells. Nurr1 and BDNF are also highly expressed in the cerebral cortex, a brain area important in cognition. Due to Nurr1 and BDNF tissue specificity, the regulatory effect of Nurr1 on BDNF in different brain areas cannot be generalized. The relationship between Nurr1 and BDNF in the cortex has not been investigated previously. Therefore, we examined Nurr1-mediated BDNF regulation in cortical neurons in activity-dependent and activity-independent states. Mouse primary cortical neurons were treated with the Nurr1 agonist, amodiaquine (AQ). Membrane depolarization was induced by KCl or veratridine and reversed by nimodipine. AQ and membrane depolarization significantly increased Nurr1 (p < 0.001) and BDNF (pAQ < 0.001, pKCl < 0.01) as assessed by real-time qRT-PCR. However, Nurr1 knockdown did not affect BDNF gene expression in resting or depolarized neurons. Accordingly, the positive correlation between Nurr1 and BDNF expression in AQ and membrane depolarization experiments does not imply co-regulation because Nurr1 knockdown did not affect BDNF gene expression in resting or depolarized cortical neurons. Therefore, in contrast to midbrain dopaminergic neurons and cerebellar granule cells, Nurr1 does not regulate BDNF in cortical neurons.

Developmental Patterning and Neurogenetic Gradients of Nurr1 Positive Neurons in the Rat Claustrum and Lateral Cortex

The claustrum is an enigmatic brain structure thought to be important for conscious sensations. Recent studies have focused on gene expression patterns, connectivity, and function of the claustrum, but relatively little is known about its development. Interestingly, claustrum-enriched genes, including the previously identified marker Nurr1, are not only expressed in the classical claustrum complex, but also embedded within lateral neocortical regions in rodents. Recent studies suggest that Nurr1 positive neurons in the lateral cortex share a highly conserved genetic expression pattern with claustrum neurons. Thus, we focus on the developmental progression and birth dating pattern of the claustrum and Nurr1 positive neurons in the lateral cortex. We comprehensively investigate the expression of Nurr1 at various stages of development in the rat and find that Nurr1 expression first appears as an elongated line along the anterior-posterior axis on embryonic day 13.5 (E13.5) and then gradually differentiates into multiple sub-regions during prenatal development. Previous birth dating studies of the claustrum have led to conflicting results, therefore, we combine 5-ethynyl-2'-deoxyuridine (EdU) labeling with in situ hybridization for Nurr1 to study birth dating patterns. We find that most dorsal endopiriform (DEn) neurons are born on E13.5 to E14.5. Ventral claustrum (vCL) and dorsal claustrum (dCL) are mainly born on E14.5 to E15.5. Nurr1 positive cortical deep layer neurons (dLn) and superficial layer neurons (sLn) are mainly born on E14.5 to E15.5 and E15.5 to E17.5, respectively. Finally, we identify ventral to dorsal and posterior to anterior neurogenetic gradients within vCL and DEn. Thus, our findings suggest that claustrum and Nurr1 positive neurons in the lateral cortex are born sequentially over several days of embryonic development and contribute toward charting the complex developmental pattern of the claustrum in rodents.

Nuclear receptors of NR1 and NR4 subfamilies in the regulation of microglial functions and pathology

This review provides an overview of researches on the NR1 and NR4 nuclear receptors involved in the regulation of microglial functions. Nuclear receptors are attractive candidates for drug targets in the therapies of the central nervous system disorders, because the activation of these receptors is expected to regulate the functions and the phenotypes of microglia, by controlling the expression of specific gene subsets and also by regulating the cellular signaling mechanisms in a nongenomic manner. Several members of NR1 nuclear receptor subfamily have been examined for their ability to regulate microglial functions. For example, stimulation of vitamin D receptor inhibits the production of pro-inflammatory factors and increases the production of anti-inflammatory cytokines. Similar regulatory actions of nuclear receptor ligands on inflammation-related genes have also been reported for other NR1 members such as retinoic acid receptors, peroxisome proliferator-activated receptors (PPARs), and liver X receptors (LXRs). In addition, stimulation of PPARγ and LXRs may also result in increased phagocytic activities of microglia. Consistent with these actions, the agonists at nuclear receptors of NR1 subfamily are shown to produce therapeutic effects on animal models of various neurological disorders such as experimental allergic encephalomyelitis, Alzheimer's disease, Parkinson's disease, and ischemic/hemorrhagic stroke. On the other hand, increasing lines of evidence suggest that the stimulation of NR4 subfamily members of nuclear receptors such as Nur77 and Nurr1 also regulates microglial functions and alleviates neuropathological events in several disease models. Further advancement of these research fields may prove novel therapeutic opportunities.

Quantitative Immunohistochemistry to Measure Regional Expression of Nurr1 in the Brain and the Effect of the Nurr1 Heterozygous Genotype

The transcription factor Nurr1 is a member of the steroid hormone nuclear receptor superfamily. Ablation of Nurr1 expression arrests mesencephalic dopamine neuron differentiation while attenuation of Nurr1 in the subiculum and hippocampus impairs learning and memory. Additionally, reduced Nurr1 expression has been reported in patients with Parkinson's disease and Alzheimer's disease. In order to better understand the overall function of Nurr1 in the brain, quantitative immunohistochemistry was used to measure cellular Nurr1 protein expression, across Nurr1 immunoreactive neuronal populations. Additionally, neuronal Nurr1 expression levels were compared between different brain regions in wild-type mice (+/+) and Nurr1 heterozygous mice (+/-). Regional Nurr1 protein was also investigated at various time points after a seizure induced by pentylenetetrazol (PTZ). Nurr1 protein is expressed in various regions throughout the brain, however, a wide range of Nurr1 expression levels were observed among various neuronal populations. Neurons in the parietal and temporal cortex (secondary somatosensory, insular, auditory, and temporal association cortex) had the highest relative Nurr1 expression (100%) followed closely by the claustrum/dorsal endopiriform cortex (85%) and then subiculum (76%). Lower Nurr1 protein levels were found in neurons in the substantia nigra pars compacta and ventral tegmental area (39%) followed by CA1 (25%) and CA3 (19%) of the hippocampus. Additionally, in the parietal and temporal cortex, two distinct populations of high and medium Nurr1 expressing neurons were observed. Comparisons between +/- and +/+ mice revealed Nurr1 protein was reduced in +/- mice by 27% in the parietal/temporal cortex, 49% in the claustrum/dorsal endopiriform cortex, 25% in the subiculum, 33% in substantia nigra pars compacta, 22% in ventral tegmental area, and 21% in CA1 region of the hippocampus. Based on these data, regional mechanisms appear to exist which can compensate for a loss of a Nurr1 allele. Following a single PTZ-induced seizure, Nurr1 protein in the dentate gyrus peaked around 2 h and returned to baseline by 8 h. Since altered Nurr1 expression has been implicated in neurologic disorders and Nurr1 agonists have showed protective effects, understanding regional protein expression of Nurr1, therefore, is necessary to understand how changes in Nurr1 expression can alter brain function.

The early overgrowth theory of autism spectrum disorder: Insight into convergent mechanisms from valproic acid exposure and translational models

The development of new approaches for the clinical management of autism spectrum disorder (ASD) can only be realized through a better understanding of the neurobiological changes associated with ASD. One strategy for gaining deeper insight into the neurobiological mechanisms associated with ASD is to identify converging pathogenic processes associated with human idiopathic clinicopathology that are conserved in translational models of ASD. In this chapter, we first present the early overgrowth theory of ASD. Second, we introduce valproic acid (VPA), one of the most robust and well-known environmental risk factors associated with ASD, and we summarize the rapidly growing body of animal research literature using VPA as an ASD translational model. Lastly, we will detail the mechanisms of action of VPA and its impact on functional neural systems, as well as discuss future research directions that could have a lasting impact on the field.

A Nurr1 agonist amodiaquine attenuates inflammatory events and neurological deficits in a mouse model of intracerebral hemorrhage

Inflammatory responses are considered to play pivotal roles in the pathogenesis of intracerebral hemorrhage (ICH). Here we show that a nuclear receptor Nurr1 (NR4A2) was expressed prominently in microglia/macrophages and astrocytes in the perihematomal region in the striatum of mice after ICH. Daily administration of a Nurr1 agonist amodiaquine (40 mg/kg, i.p.) from 3 h after ICH induction diminished perihematomal activation of microglia/macrophages and astrocytes. Amodiaquine also suppressed ICH-induced mRNA expression of IL-1β, CCL2 and CXCL2, and ameliorated motor dysfunction of mice. These results suggest that Nurr1 serves a novel target for ICH therapy.

Rationally Engineered AAV Capsids Improve Transduction and Volumetric Spread in the CNS

Adeno-associated virus (AAV) is the most common vector for clinical gene therapy of the CNS. This popularity originates from a high safety record and the longevity of transgene expression in neurons. Nevertheless, clinical efficacy for CNS indications is lacking, and one reason for this is the relatively limited spread and transduction efficacy in large regions of the human brain. Using rationally designed modifications of the capsid, novel AAV capsids have been generated that improve intracellular processing and result in increased transgene expression. Here, we sought to improve AAV-mediated neuronal transduction to minimize the existing limitations of CNS gene therapy. We investigated the efficacy of CNS transduction using a variety of tyrosine and threonine capsid mutants based on AAV2, AAV5, and AAV8 capsids, as well as AAV2 mutants incapable of binding heparan sulfate (HS). We found that mutating several tyrosine residues on the AAV2 capsid significantly enhanced neuronal transduction in the striatum and hippocampus, and the ablation of HS binding also increased the volumetric spread of the vector. Interestingly, the analogous tyrosine substitutions on AAV5 and AAV8 capsids did not improve the efficacy of these serotypes. Our results demonstrate that the efficacy of CNS gene transfer can be significantly improved with minor changes to the AAV capsid and that the effect is serotype specific.

Repeated exposure to low doses of kainic acid activates nuclear factor kappa B (NF-κB) prior to seizure in transgenic NF-κB/EGFP reporter mice

Predicting seizurogenic properties of pharmacologically active compounds is difficult due to the complex nature of the mechanisms involved and because of the low sensitivity and high variability associated with current behavioral-based methods. To identify early neuronal signaling events predictive of seizure, we exposed transgenic NF-κB/EGFP reporter mice to multiple low doses of kainic acid (KA), postulating that activation of the stress-responsive NF-κB pathway could be a sensitive indicator of seizurogenic potential. The sub-threshold dose level proximal to the induction of seizure was determined as 2.5mg/kg KA, using video EEG monitoring. Subsequent analysis of reporter expression demonstrated significant increases in NF-κB activation in the CA3 and CA1 regions of the hippocampus 24h after a single dose of 2.5mg/kg KA. This response was primarily observed in pyramidal neurons with little non-neuronal expression. Neuronal NF-κB/EGFP expression was observed in the absence of glial activation, indicating a lack of neurodegeneration-induced neuroinflammation. Protein expression of the immediate-early gene, Nurr1, increased in neurons in parallel to NF-κB activation, supporting that the sub-threshold doses of KA employed directly caused neuronal stress. Lastly, KA also stimulated NF-κB activation in organotypic hippocampal slice cultures established from NF-κB/EGFP reporter mice. Collectively, these data demonstrate the potential advantages of using genetically encoded stress pathway reporter models in the screening of seizurogenic properties of new pharamacologically active compounds.

Nur transcription factors in stress and addiction

The Nur transcription factors Nur77 (NGFI-B, NR4A1), Nurr1 (NR4A2), and Nor-1 (NR4A3) are a sub-family of orphan members of the nuclear receptor superfamily. These transcription factors are products of immediate early genes, whose expression is rapidly and transiently induced in the central nervous system by several types of stimuli. Nur factors are present throughout the hypothalamus-pituitary-adrenal (HPA) axis where are prominently induced in response to stress. Drugs of abuse and stress also induce the expression of Nur factors in nuclei of the motivation/reward circuit of the brain, indicating their participation in the process of drug addiction and in non-hypothalamic responses to stress. Repeated use of addictive drugs and chronic stress induce long-lasting dysregulation of the brain motivation/reward circuit due to reprogramming of gene expression and enduring alterations in neuronal function. Here, we review the data supporting that Nur transcription factors are key players in the molecular basis of the dysregulation of neuronal circuits involved in chronic stress and addiction.

Differential roles for Nr4a1 and Nr4a2 in object location vs. object recognition long-term memory

Nr4a1 and Nr4a2 are transcription factors and immediate early genes belonging to the nuclear receptor Nr4a family. In this study, we examine their role in long-term memory formation for object location and object recognition. Using siRNA to block expression of either Nr4a1 or Nr4a2, we found that Nr4a2 is necessary for both long-term memory for object location and object recognition. In contrast, Nr4a1 appears to be necessary only for object location. Indeed, their roles in these different types of long-term memory may be dependent on their expression in the brain, as NR4A2 was found to be expressed in hippocampal neurons (associated with object location memory) as well as in the insular and perirhinal cortex (associated with object recognition memory), whereas NR4A1 showed minimal neuronal expression in these cortical areas. These results begin to elucidate how NR4A1 and NR4A2 differentially contribute to object location versus object recognition memory.

Controlled cortical impact injury and craniotomy result in divergent alterations of pyruvate metabolizing enzymes in rat brain

Dysregulated glucose metabolism and energy deficit is a characteristic of severe traumatic brain injury (TBI) but its mechanism remains to be fully elucidated. Phosphorylation of pyruvate dehydrogenase (PDH) is the rate-limiting mitochondria enzyme reaction coupling glycolysis to the tricarboxylic acid cycle. Phosphorylation of PDH E1α1 subunit catalyzed by PDH kinase (PDK) inhibits PDH activity, effectively decoupling aerobic glycolysis whereas dephosphorylation of phosphorylated PDHE1α1 by PDH phosphatase (PDP) restores PDH activity. We recently reported altered expression and phosphorylation of pyruvate dehydrogenase (PDH) following TBI. However, little is known about PDK and PDP involvement. We determined PDK (PDK1-4) and PDP isoenzyme (PDP1-2) mRNA and protein expression in rat brain using immunohistochemistry and in situ hybridization techniques. We also quantified PDK and PDP mRNA and protein levels in rat brain following TBI using quantitative real-time PCR and Western blot, respectively. Controlled cortical impact-induced TBI (CCI-TBI) and craniotomy significantly enhanced PDK1-2 isoenzyme mRNA expression level but significantly suppressed PDP1 and PDK4 mRNA expression after the injury (4h to 7days). CCI-TBI and craniotomy also significantly increased PDK1-4 isoenzyme protein expression but suppressed PDP1-2 protein expression in rat brain. In summary, the divergent changes between PDK and PDP expression indicate imbalance between PDK and PDP activities that would favor increased PDHE1α1 phosphorylation and enzyme inhibition contributing to impaired oxidative glucose metabolism in TBI as well as craniotomy.

Identification of an intronic cis-acting element in the human dopamine transporter gene

The human dopamine transporter gene (hDAT) encodes the dopamine transporter in dopamine (DA) neurons to regulate DA transmission. hDAT expression varies significantly from neuron to neuron, and from individual to individual so that dysregulation of hDAT is related to many neuropsychiatric disorders. It is critical to identify hDAT-specific cis-acting elements that regulate the hDAT expression. Previous studies showed that hDAT Intron 1 displayed inhibitory activity for reporter gene expression. Here we report that the hDAT Intron 1 contains a 121-bp fragment that down-regulated both SV40 and hDAT promoter activities by 80% in vitro. Subfragments of 121-bp still down-regulated the SV40 promoter but not the hDAT promoter, as supported by nuclear protein-binding activities. Collectively, 121-bp is a silencer in vitro that might coordinate with transcriptional activities both inside and outside 121-bp in regulation of hDAT.

NR4A gene expression is dynamically regulated in the ventral tegmental area dopamine neurons and is related to expression of dopamine neurotransmission genes

The NR4A transcription factors NR4A1, NR4A2, and NR4A3 (also known as Nur77, Nurr1, and Nor1, respectively) share similar DNA-binding properties and have been implicated in regulation of dopamine neurotransmission genes. Our current hypothesis is that NR4A gene expression is regulated by dopamine neuron activity and that induction of NR4A genes will increase expression of dopamine neurotransmission genes. Eticlopride and γ-butyrolactone (GBL) were used in wild-type (+/+) and Nurr1-null heterozygous (+/−) mice to determine the mechanism(s) regulating Nur77 and Nurr1 expression. Laser capture microdissection and real-time PCR was used to measure Nurr1 and Nur77 mRNA levels in the ventral tegmental area (VTA). Nur77 expression was significantly elevated 1 h after both GBL (twofold) and eticlopride (fourfold). In contrast, GBL significantly decreased Nurr1 expression in both genotypes, while eticlopride significantly increased Nurr1 expression only in the +/+ mice. In a separate group of mice, haloperidol injection significantly elevated Nur77 and Nor1, but not Nurr1 mRNA in the VTA within 1 h and significantly increased tyrosine hydroxylase (TH) and dopamine transporter (DAT) mRNA expression by 4 h. These data demonstrate that the NR4A genes are dynamically regulated in dopamine neurons with maintenance of Nurr1 expression requiring dopamine neuron activity while both attenuation of dopamine autoreceptors activation and dopamine neuronal activity combining to induce Nur77 expression. Additionally, these data suggest that induction of NR4A genes could regulate TH and DAT expression and ultimately regulate dopamine neurotransmission.

The role of NR4A transcription factors in memory formation

In various physiological contexts, Nr4a genes are transcribed in response to external stimuli as part of an immediate early response that initiates a cascade of gene expression ultimately leading to distinct physiological outcomes in each of these contexts. The signaling pathway that initiates Nr4a gene expression in most of these contexts consists of elevated intracellular cAMP activating PKA, which in turn leads to phosphorylation of CREB and new gene synthesis. This cAMP-PKA-CREB pathway is a central molecular pathway in the formation of a long-term memory. Indeed, learning induces Nr4a family gene expression, and long-term memory formation requires at least two waves of transcription after learning, suggesting that NR4A nuclear receptors may contribute to the second of these waves of gene expression. In this article, we review insights gained in other physiological contexts regarding Nr4a function and regulation, and highlight how these lessons can be applied to the study of memory formation.

Comparative molecular neuroanatomy of mammalian neocortex: what can gene expression tell us about areas and layers?

It is over 100 years since Brodmann proposed the homology of layer and area structure of the cerebral cortex across species. His proposal was based on the extensive comparative analyses of various mammalian brains. Although such homology is now well accepted, the recent data in our laboratory showed striking variations of gene expression patterns across areas and species. Are cortical layers and areas really homologous? If they are, to what extent and how are they similar or different? We are trying to answer these questions by identifying the homologous neuronal types common to various areas and species. Toward this goal, we started to classify the cortical pyramidal neurons by expression of particular sets of genes. By using fluorescent double in situ hybridization combined with retrograde tracers, we are characterizing the gene expression phenotypes and projection specificity of cortical excitatory neuron types. In this review, I discuss the recent findings in our laboratory in light of the past and present knowledge about cortical cell types, which provides insight to the homology (and lack thereof) of the mammalian neocortical organization.

Analysis of area-specific expression patterns of RORbeta, ER81 and Nurr1 mRNAs in rat neocortex by double in situ hybridization and cortical box method

BACKGROUND

The mammalian neocortex is subdivided into many areas, each of which exhibits distinctive lamina architecture. To investigate such area differences in detail, we chose three genes for comparative analyses, namely, RORbeta, ER81 and Nurr1, mRNAs of which have been reported to be mainly expressed in layers 4, 5 and 6, respectively. To analyze their qualitative and quantitative coexpression profiles in the rat neocortex, we used double in situ hybridization (ISH) histochemistry and cortical box method which we previously developed to integrate the data of different staining and individuals in a standard three-dimensional space.

PRINCIPAL FINDINGS

Our new approach resulted in three main observations. First, the three genes showed unique area distribution patterns that are mostly complementary to one another. The patterns revealed by cortical box method matched well with the cytoarchitectonic areas defined by Nissl staining. Second, at single cell level, RORbeta and ER81 mRNAs were coexpressed in a subpopulation of layer 5 neurons, whereas Nurr1 and ER81 mRNAs were not colocalized. Third, principal component analysis showed that the order of hierarchical processing in the cortex correlates well with the expression profiles of these three genes. Based on this analysis, the dysgranular zone (DZ) in the somatosensory area was considered to exhibit a profile of a higher order area, which is consistent with previous proposal.

CONCLUSIONS/SIGNIFICANCE

The tight relationship between the expression of the three layer specific genes and functional areas were revealed, demonstrating the usefulness of cortical box method in the study on the cerebral cortex. In particular, it allowed us to perform statistical evaluation and pattern matching, which would become important in interpreting the ever-increasing data of gene expression in the cortex.

Knockdown of Nurr1 in the rat hippocampus: implications to spatial discrimination learning and memory

Nurr1 expression is up-regulated in the brain following associative learning experiences, but its relevance to cognitive processes remains unclear. In these studies, rats initially received bilateral hippocampal infusions of control or antisense oligodeoxynucleotides (ODNs) 1 h prior to training in a holeboard spatial discrimination task. Such pre-training infusions of nurr1 antisense ODNs caused a moderate effect in learning the task and also impaired LTM tested 7 d later. In a second experiment, ODN infusions were given immediately after the animals had received two sessions of training, during which all animals showed normal learning. Although antisense treated rats were significantly impaired during the post-infusion stages of acquisition of the task, no group differences were observed during the LTM test given 7 d later. These animals were subjected 3 d later to reversal training in the same maze in the absence of any additional treatments. Remarkably, rats previously treated with antisense ODNs displayed perseveration: The animals were fixated with the previously learned pattern of baited holes, causing them to be significantly impaired in the extinction of acquired spatial preferences and future learning. We postulate that Nurr1 function in the hippocampus is important for normal cognitive processes.

Comparative analysis of layer-specific genes in Mammalian neocortex

We examined the expression patterns of 4 layer-specific genes in monkey and mouse cortices by fluorescence double in situ hybridization. Based on their coexpression profiles, we were able to distinguish several subpopulations of deep layer neurons. One group was characterized by the expression of ER81 and the lack of Nurr1 mRNAs and mainly localized to layer 5. In monkeys, this neuronal group was further subdivided by 5-HT2C receptor mRNA expression. The 5-HT2C(+)/ER81(+) neurons were located in layer 5B in most cortical areas, but they intruded layer 6 in the primary visual area (V1). Another group of neurons, in monkey layer 6, was characterized by Nurr1 mRNA expression and was further subdivided as Nurr1(+)/connective tissue growth factor (CTGF)(-) and Nurr1(+)/CTGF(+) neurons in layers 6A and 6B, respectively. The Nurr1(+)/CTGF(+) neurons coexpressed ER81 mRNA in monkeys but not in mice. On the basis of tracer injections in 3 monkeys, we found that the Nurr1(+) neurons in layer 6A send some corticocortical, but not corticopulvinar, projections. Although the Nurr1(+)/CTGF(-) neurons were restricted to lateral regions in the mouse cortex, they were present throughout the monkey cortex. Thus, an architectonic heterogeneity across areas and species was revealed for the neuronal subpopulations with distinct gene expression profiles.

Gene induction during differentiation of human pulmonary type II cells in vitro

Mature alveolar type II cells that produce pulmonary surfactant are essential for adaptation to extrauterine life. We profiled gene expression in human fetal lung epithelial cells cultured in serum-free medium containing dexamethasone and cyclic AMP, a treatment that induces differentiation of type II cells. Microarray analysis identified 388 genes that were induced > 1.5-fold by 72 h of hormone treatment. Induced genes represented all categories of molecular function and subcellular location, with increased frequency in the categories of ionic channel, cell adhesion, surface film, lysosome, extracellular matrix, and basement membrane. In time-course experiments, self-organizing map analysis identified a cluster of 17 genes that were slowly but highly induced (5- to approximately 190-fold) and represented four functional categories: surfactant-related (SFTPC, SFTPA, PGC, SFTPB, LAMP3, LPL), regulatory (WIF2, IGF2, IL1RL1, NR4A2, HIF3A), metabolic (MAOA, ADH1B, SEPP1), and transport (SCNN1A, CLDN18, AQP4). Induction of both mRNA and protein for these genes, which included nine newly identified regulated genes, was confirmed, and cellular localization was determined in both fetal and postnatal tissue. Induction of lysosomal-associated membrane protein 3 required both hormones, and expression was localized to limiting membranes of lamellar bodies. Hormone-induced differentiation of human type II cells is associated with genome-wide increased expression of genes with diverse functions.

Reduction of dopamine-related transcription factors Nurr1 and NGFI-B in the prefrontal cortex in schizophrenia and bipolar disorders

Abnormal cortical and subcortical dopaminergic activities are among the most consistent neuropathological findings in schizophrenia. The molecular mechanisms remain unspecified. NGFI-B and Nurr1 are two closely related transcription factors involved in dopaminergic cell differentiation, maturation, and apoptosis. NGFI-B knockout mice show attenuated behavioral response to dopamine receptor agonists, whereas Nurr1 knockout disrupts midbrain dopaminergic neuron development. To further understand the role of Nurr1 and NGFI-B in schizophrenia and bipolar disorders, we measured Nurr1 and NGFI-B mRNA in the prefrontal cortex Brodmann's areas 9 (BA 9) and BA 46 by in situ hybridization, and the protein levels in BA 9 by Western blotting, of patients with schizophrenia, major depression, and bipolar disorders, and non-psychiatric control subjects (n=15 per group). NGFI-B mRNA (P<0.05) and protein (P<0.01) were significantly lower in patients with schizophrenia (BA 9), and NGFI-B mRNA was lower in bipolar disorder (BA 9 and BA 46) than in the controls. In the deep cortical layers of BA 46, Nurr1 mRNA was significantly (P<0.05) lower in patients with bipolar disorder and schizophrenia than in the controls. Nurr1 protein in BA 9 was significantly lower in major depression (P<0.05) and lower at a trend level in schizophrenia (P=0.056) than in the controls. These data show a deficient prefrontal NGFI-B and Nurr1 expression in schizophrenia and bipolar disorder. Further study may elucidate if and how these deficiencies could be associated with abnormal dopaminergic functions seen in both illnesses.

Early postnatal isolation reduces dopamine levels, elevates dopamine turnover and specifically disrupts prepulse inhibition in Nurr1-null heterozygous mice

Sensorimotor gating is a phenomenon that is linked with dopamine neurotransmission in limbic and cortical areas, and disruption of sensorimotor gating has been consistently demonstrated in schizophrenia patients. The nuclear receptor Nurr1 is essential for development of dopamine neurons and, using Nurr1-null heterozygous mice, has been found to be important for normal dopamine neurotransmission as null heterozygous mice have reduced limbic and cortical dopamine levels and elevated open-field locomotor activity. The current investigation compared sensorimotor gating, as measured by prepulse inhibition of the acoustic startle response, in Nurr1 wild-type and null heterozygous mice. When mice were weaned between 19 and 21 days of age either into isolation or groups of three to five and tested 12 weeks later, prepulse inhibition was elevated in group-raised null heterozygous mice and significantly disrupted in isolated null heterozygous mice as compared with isolation-raised wild-type mice and group-raised null heterozygous mice. Isolation had no effect on prepulse inhibition in wild-type mice. Isolation reduced tissue dopamine levels and elevated dopamine turnover in the nucleus accumbens and striatum in both wild-type and null heterozygous mice. In the prefrontal cortex, isolation reduced dopamine and 3,4-dihydroxyphenylacetic acid levels in null heterozygous as compared with isolation-raised wild-type mice, whereas no differences were observed between group-raised wild-type and null heterozygous mice. Neither the null heterozygous genotype nor isolation had any effect on basal or stress-induced corticosterone levels. These data suggest that the Nurr1 null heterozygous genotype predisposes these mice to isolation-induced disruption of prepulse inhibition that may be related to the interactions between intrinsic deficiencies in dopamine neurotransmission as a result of the null heterozygous genotype and isolation-induced changes in dopamine neurotransmission. Post-weaning isolation of Nurr1 null heterozygous mice provides a model to explore the interactions of genetic predisposition and environment/neurodevelopment on dopamine function that has important relevance to neuropsychiatric disorders.

Factors involved in the determination of the neurotransmitter phenotype of developing neurons of the CNS: Applications in cell replacement treatment for Parkinson's disease

The developmental stages involved in the conversion of stem cells to fully functional neurons of specific neurotransmitter phenotype are complex and not fully understood. Over the past decade many studies have been published that demonstrate that in vitro manipulation of the epigenetic environment of the stem cells allows experimental control of final neuronal phenotypic choice. This review presents the evidence for the involvement of a number of endogenous neurobiochemicals, which have been reported to potently influence DAergic (and other neurotransmitter) phenotype expression in vitro. They act at different stages on the pathway to neurotransmitter phenotype determination, and in different ways. Many are better known for their involvement in other aspects of development, and in other biochemical roles. Their proper place, and precise roles, in neurotransmitter phenotype determination in vivo will no doubt be determined in the future. Meanwhile, considerable medical benefits are offered from producing large, long-term, viable cryostores of self-regenerating multipotential neural precursor cells (i.e., brain stem cells), which can be used for cell replacement therapies in the treatment of degenerative brain diseases, such as Parkinson's disease.

nor-1 regulates hippocampal axon guidance, pyramidal cell survival, and seizure susceptibility

The nuclear receptor transcription factor, nor-1, is expressed during mammalian development predominantly in the nervous system and is induced in a cell-specific manner in nonneuronal cells in response to a variety of extracellular stimuli. To elucidate the essential developmental functions of this transcription factor, we have analyzed the consequences of its elimination on central nervous system development in mice. Here we show that null mutant mice lacking nor-1 respond with increased limbic seizure activity to the excitotoxic glutamate receptor agonist kainic acid. We demonstrate that these abnormalities are associated with defective postnatal hippocampal development exemplified by abnormal axonal guidance of dentate gyrus granule and mossy cells, disorganization of the pyramidal cell layer, and early postnatal death of pyramidal neurons in the CA1 field of the hippocampus. Our data indicate that nor-1 plays a critical role in neuronal survival and axonal guidance in the developing murine hippocampus and that hippocampal dysgenesis in nor-1-/- mice may be an underlying cause of seizure susceptibility.

Nurr1, an orphan nuclear receptor with essential functions in developing dopamine cells

Nurr1 is a transcription factor that is expressed in the embryonic ventral midbrain and is critical for the development of dopamine (DA) neurons. It belongs to the conserved family of nuclear receptors but lacks an identified ligand and is therefore referred to as an orphan receptor. Recent structural studies have indicated that Nurr1 belongs to a class of ligand-independent nuclear receptors that are unable to bind cognate ligands. However, Nurr1 can promote signaling via its heterodimerization partner, the retinoid X receptor (RXR). RXR ligands can promote the survival of DA neurons via a process that depends on Nurr1-RXR heterodimers. In developing DA cells, Nurr1 is required for the expression of several genes important for DA synthesis and function. However, Nurr1 is probably also important for the maintenance of adult DA neurons and plays additional less-well-elucidated roles in other regions of the central nervous system and in peripheral tissues.

Modulation of nurr1 gene expression in mesencephalic dopaminergic neurones

The transcription factor/nuclear receptor Nurr1 is essential for the differentiation of midbrain dopaminergic neurones. Here we demonstrate that, during the ontogeny of rat ventral mesencephalon, nurr1 gene expression is developmentally regulated and its levels show a sharp peak between embryonic day E13 and E15, when most dopaminergic neurones differentiate. In addition, in primary cultures from embryonic rat mesencephalon, nurr1 gene follows a temporal pattern of expression comparable to that observed in vivo. We also report that exposure of embryonic mesencephalic cultures to depolarizing stimuli leads to a robust increase in nurr1 mRNA and protein. The depolarizing effect is also detected in mesencephalic cultures enriched in dopaminergic neurones by using a combination of bFGF and Sonic hedgehog. The latter further increases the number of dopaminergic neurones in these 'expanded' cultures, an effect abolished in the presence of anti-Sonic hedgehog antibodies. Our data show that nurr1 gene is highly expressed in midbrain dopaminergic neurones in a sharp temporal window and that its expression is plastic, both in vivo and in vitro. In addition we show that Sonic hedgehog can direct dopaminergic differentiation in proliferating dopaminergic neuroblasts in vitro.

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Organization and development of corticocortical associative neurons expressing the orphan nuclear receptor Nurr1

The developmental mechanism that contributes to the highly organized axonal connections within the cerebral cortex is not well understood. This is partly due to the lack of molecular markers specifically expressed in corticocortical associative neurons during the period of circuit formation. We have shown previously that latexin, a carboxypeptidase A inhibitor, is expressed in intrahemispheric corticocortical neurons from the second postnatal week in the rat (Arimatsu et al. [1999] Cereb. Cortex 9:569-576). In the present study, we first demonstrate in the adult rat that the orphan nuclear receptor Nurr1 is coexpressed in latexin-expressing neurons located in layer V, sublayer VIa, and the white matter of the lateral sector of the neocortex, and also in latexin-negative early born neurons in sublayer VIb of the entire neocortex. Virtually all Nurr1-expressing neurons exhibit immunoreactivity for phosphate-activated glutaminase but not for gamma-aminobutyric acid, suggesting that they are glutamatergic-excitatory neurons. By combining Nurr1 immunohistochemistry and 5-bromo-2'-deoxyuridine-birthdating, we then show that Nurr1 is expressed in (early born) subplate neurons and (later born) presumptive latexin-expressing neurons from embryonic day 18 onward. Finally, by combination of Nurr1 immunohistochemistry and retrograde tracing, we show that Nurr1-expressing neurons, including those in sublayer VIb, contribute predominantly to long-range intrahemispheric corticocortical projections. These results raise the possibility that Nurr1 plays a role in the establishment and maintenance of normal corticocortical circuitry and function.

Rapid increase of Nurr1 expression in the substantia nigra after 6-hydroxydopamine lesion in the striatum of the rat

Nurr1 is a transcription factor essential for the genesis of ventral dopaminergic neurons. In this study, we investigated the expression of Nurr1 protein and mRNA in the adult rat brain by using immunohistochemistry and in situ hybridization, respectively. Another aim of our study was to investigate Nurr1 expression in substantia nigra after dopamine depletion induced by the injection of 6-hydroxydopamine in the striatum. We observed that Nurr1 mRNA and protein are expressed in several brain regions, including cortex, hippocampus, substantia nigra, and ventral tegmental area, in agreement with previous reports using in situ hybridization. Additionally, we found that Nurr1 is expressed in brain regions that have not been previously reported, such as striatum, septum, and superior colliculus. Highest levels of expression were found in cortex, medial septum, dentate gyrus, some hypothalamic nuclei, and substantia nigra. Interestingly, we observed that, in the superior colliculus, Nurr1 protein is localized in the cytoplasm of cells, whereas, in other regions, it was localized mainly in the nuclei, suggesting that Nurr1 subcellular localization is regulated and may have functional implications. Dopamine depletion induced by an injection of 6-hydroxydopamine into the striatum produced an increase in the number of cells expressing Nurr1 mRNA and protein in both substantia nigra compacta and substantia nigra reticulata, ipsilateral and contralateral to the lesioned side, measured 24 hr after the 6-hydroxydopamine injection. These results suggest that Nurr1 may be involved in many neuronal functions in the adult central nervous system and, in particular, might be related to the compensation processes that take place in dopaminergic cells in order to normalize extracellular dopamine levels in the striatum.

The constitutive and inducible expression of Nurr1, a key regulator of dopaminergic neuronal differentiation, in human neural and non-neural cell lines

Nur-related factor 1 (Nurr1), nerve growth factor-induced gene B (NGFI-B) and neuron-derived orphan receptor-1 (NOR-1) constitute the orphan nuclear receptor subfamily of transcription factors. Previous studies showed that midbrain dopaminergic neuronal precursor cells failed to differentiate in Nurr1-deficient mice. To investigate a role of Nurr1 in human neuronal function, Nurr1 mRNA expression was studied in human neural cell lines by RT-PCR and northern blot analysis. Nurr1, NGFI-B and NOR-1 mRNA were coexpressed in all human neural and nonneural cell lines under the serum-containing culture condition, except for SK-N-SH neuroblastoma, in which Nurr1 mRNA was undetectable. The levels of Nurr1, NGFI-B and NOR-1 mRNA were elevated markedly in NTera2 teratocarcinoma-derived neurons (NTera2-N), a model of differentiated human neurons, following a 1.5 or 3 h-exposure to 1 mM dibutyryl cyclic AMP or 100 nm phorbol 12-myristate 13-acetate. NGFI-B mRNA levels were also elevated in NTera2-N cells by exposure to 100 ng/mL brain-derived neurotrophic factor (BDNF). To identify Nurr1-target genes, the mRNA expression of 27 genes potentially involved in dopaminergic neuronal differentiation and survival, including BDNF, glia-derived neurotrophic factor, their receptors, tyrosine hydroxylase and alpha-synuclein, were studied in HEK293 cells following overexpression of Nurr1. None of these genes examined, however, showed significant changes. These results indicate that Nurr1, NGFI-B and NOR-1 mRNA are expressed constitutively in various human neural and non-neural cell lines under the serum-containing culture condition, and their levels are up-regulated in human neurons by activation of protein kinase A or protein kinase C pathway, although putative coactivators expressed in dopaminergic neuronal precursor cells might be required for efficient transcriptional activation of Nurr1-target genes.

Region-specific phosphorylation of ATF-2, Elk-1 and c-Jun in rat hippocampus and cerebellum after electroconvulsive shock

There have been reports of regional differences in the activation of mitogen activated protein kinases (MAPKs) and in the induction of immediate early genes after electroconvulsive shock (ECS) in the rat brain. This study was performed to determine whether ECS induce the region-specific phosphorylation of MAPK-downstream transcription factors, ATF-2, Elk-1, c-Jun, in rat hippocampus and cerebellum. Following ECS, the phosphorylation of ATF-2 was highly increased in the hippocampus but slightly in the cerebellum. The phosphorylation of Elk-1 was increased in the cerebellum but not in the hippocampus. In contrast, the phosphorylation of c-Jun was increased only in the hippocampus. These results indicate that ECS can induce the region-specific phosphorylation of MAPK-downstream transcription factors in rat hippocampus and cerebellum.

The effects of isolation rearing on glutamate receptor NMDAR1A mRNA expression determined by in situ hybridization in Fawn hooded and Wistar rats

Rats reared in social isolation exhibit a syndrome of behavioral and biochemical effects indicative of enhanced mesolimbic dopamine (DA) function. The precise nature of the neurodevelopmental changes that produce this state are unknown but result in enhanced DA neurotransmission in the nucleus accumbens (NAC). It was hypothesized that this may be the indirect result of chronic changes in glutamate NMDA receptor function. The same prediction has been made for Fawn hooded (FH) rats that exhibit some of the characteristic effects of isolation-reared rats when compared to Wistar rats. Therefore, mRNA levels of the NMDAR1A receptor subunit were determined by in situ hybridization and were quantified in the striatum, hippocampus and prefrontal cortex of FH and Wistar rats. Isolation rearing alone was not found to have an effect on the expression of NMDAR1A, while FH rats had reduced levels across most brain regions examined. In some areas of the striatum and prefrontal cortex, this effect was greater in FH isolates than in FH socials, while in the hippocampus, the opposite was observed.

Decreased prefrontal CaMKII alpha mRNA in bipolar illness

Ca2+/calmodulin-dependent protein kinase II (CaMKII) plays critical roles in neurotransmission, synaptic plasticity, learning and memory. The aim of this study was to examine, by in situ hybridization, prefrontal cortical expression of CaMKII alpha mRNA in postmortem brains of unipolar, bipolar, schizophrenic, and control subjects. Compared to controls, bipolar patients had significantly lower levels of CaMKII alpha mRNA in laminae I-VI of Brodmann's area 9 and laminae I-III and VI of area 46. Unipolar patients also exhibited significantly lower levels of CaMKII alpha mRNA in laminae I-IV of area 9 than did controls. The significant decrease in CaMKII alpha mRNA in bipolar patients could be associated with some of the affective and cognitive alterations that have been linked to prefrontal cortical dysfunction in bipolar disorder, although this requires further direct examination.

ECT for the treatment of psychiatric symptoms in Basedow's disease

To treat psychiatric symptoms associated with hyperthyroidism, we administered electroconvulsive therapy (ECT) to a patient with Basedow's disease. After unsuccessful treatment with an oral antithyroid drug, neuroleptics, and mood stabilizer, the patient recovered completely after three ECTs and did not relapse in the 40-day follow-up period. Although hyperthyroidism has been considered to induce psychiatric symptoms by enhancement of the sensitivity and turnover in catecholaminergic neurotransmission, we suggest another possible mechanism, involving translational and activational regulation of functional proteins in the brain.

Induction of cell cycle arrest and morphological differentiation by Nurr1 and retinoids in dopamine MN9D cells

Dopamine cells are generated in the ventral midbrain during embryonic development. The progressive degeneration of these cells in patients with Parkinson's disease, and the potential therapeutic benefit by transplantation of in vitro generated dopamine cells, has triggered intense interest in understanding the process whereby these cells develop. Nurr1 is an orphan nuclear receptor essential for the development of midbrain dopaminergic neurons. However, the mechanism by which Nurr1 promotes dopamine cell differentiation has remained unknown. In this study we have used a dopamine-synthesizing cell line (MN9D) with immature characteristics to analyze the function of Nurr1 in dopamine cell development. The results demonstrate that Nurr1 can induce cell cycle arrest and a highly differentiated cell morphology in these cells. These two functions were both mediated through a DNA binding-dependent mechanism that did not require Nurr1 interaction with the heterodimerization partner retinoid X receptor. However, retinoids can promote the differentiation of MN9D cells independently of Nurr1. Importantly, the closely related orphan receptors NGFI-B and Nor1 were also able to induce cell cycle arrest and differentiation. Thus, the growth inhibitory activities of the NGFI-B/Nurr1/Nor1 orphan receptors, along with their widespread expression patterns both during development and in the adult, suggest a more general role in control of cell proliferation in the developing embryo and in adult tissues.

A clonal line of mesencephalic progenitor cells converted to dopamine neurons by hematopoietic cytokines: a source of cells for transplantation in Parkinson's disease

Neural progenitor cells potentially provide a limitless, on-demand source of cells for grafting into patients with Parkinson's disease (PD) if the signals needed to control their conversion into dopamine (DA) neurons could be identified. We have recently shown that cytokines which instruct cell division and differentiation within the hematopoeitic system may provide similar functions in the central nervous system. We have shown that mitotic progenitor cells can be isolated from embryonic rat mesencephalon and that these cells respond to a combination of interleukin-1, interleukin-11, leukemia inhibitory factor, and glial cell line-derived neurotrophic factor yielding a tyrosine hydroxylase-immunoreactive (THir) phenotype in 20-25% of total cells. In the present study, 24 clonal cell lines derived from single cells of mesencephalic proliferation spheres were examined for their response to the cytokine mixture. The clone yielding the highest percentage of THir neurons (98%) was selected for further study. This clone expressed several phenotypic characteristics of DA neurons and expression of Nurr1. The response to cytokines was stable for several passages and after cryopreservation for several months. When grafted into the striatum of DA-depleted rats, these cells attenuated rotational asymmetry to the same extent as freshly harvested embryonic DA neurons. These data demonstrate that mesencephalic progenitor cells can be clonally expanded in culture and differentiated in the presence of hematopoietic cytokines to yield enriched populations of DA neurons. When transplanted, these cells provide significant functional benefit in the rat model of PD.

Parathyroid hormone induces expression of the nuclear orphan receptor Nurr1 in bone cells

Following PTH treatment, immediate changes in osteoblast gene expression involve induction of primary response genes. Primary gene products subsequently mediate the osteoblast response to PTH. Using representational difference analysis (RDA) to isolate primary genes induced by PTH in osteoblasts, we identified Nurr1, a member of the NGFI-B nuclear orphan receptor subfamily. Nurr1 binds DNA as a monomer but also heterodimerizes with the 9-cis retinoic acid receptor (RXR). Nurr1's importance in retinoic acid, vitamin D, and thyroid hormone signaling has been hypothesized. Nurr1 messenger RNA (mRNA) levels were maximal at 1 h and at 10 nM of PTH in primary mouse osteoblasts (MOB). Activation of the PKA and PKC pathways by 10 microM forskolin and 1 microM PMA, respectively, induced Nurr1 mRNA levels. However, inhibition of the PKA but not the PKC pathway significantly inhibited the PTH induction of Nurr1. Moreover, PTH(3-34) at 1-100 nM did not induce Nurr1 mRNA levels. Thus, PTH induction of Nurr1 in primary mouse osteoblasts is mediated primarily through the cAMP/PKA pathway. PTH also stimulated Nurr1 protein in MOB cells and Nurr1 mRNA in calvarial organ cultures. Nurr1 induction represents a potential cross-talk mechanism between PTH and steroid hormone signaling at the transcription factor level.

Nigrostriatal innervation is preserved in Nurr1-null mice, although dopaminergic neuron precursors are arrested from terminal differentiation

Various factors, including the orphan nuclear receptor Nurr1, have been implicated in dopamine biosynthesis, but many of the specific events involved in this process have to be determined. Using genetic manipulations in mice, the obligatory role for Nurr1 in dopamine (DA) biosynthesis has been documented; however, the mechanism remains unclear. DA biosynthetic enzymes, transporters and receptors are absent in the substantia nigra (SN) and the ventral tegmental area (VTA) of Nurr1-null neonates. The current study establishes that the loss of Nurr1 function does not affect the normal ventralization of neuroepithelial cells to the ventral midbrain, their differentiation into neurons, and their topographical pattern in the SN and VTA. Futhermore, the absence of Nurr1 does not affect the survival of these DA precursor cells in the ventral midbrain, as determined by quantitative analysis of cells, expressing the general neuronal nuclear marker (NeuN) and the TUNEL assay for apoptosis. These neurons express cholecystokinin (CCK), a co-transmitter of dopaminergic neurons in this area. The untranslated exon 1-2 of the Nurr1 gene, which remains intact after homologous recombination, revealed the presence of dopaminergic precursors in the ventral midbrain of the Nurr1-null mice. In addition, these neurons establish their nigrostriatal projections, as shown by axonal transport of a fluorescent tracer, DiI. These results provide evidence that Nurr1 is essential for terminal differentiation of the dopaminergic neurons in the ventral midbrain but does not affect the early steps of their neurogenesis, migration, survival and striatal projections. Our findings suggest that activation of Nurr1 might be therapeutically useful in Parkinson's disease.

Hippocampal expression of the orphan nuclear receptor gene hzf-3/nurr1 during spatial discrimination learning

The immediate-early gene hzf-3, also known as nurr1, is a member of the inducible orphan nuclear receptor family and is one candidate in the search for genes associated with learning and memory processes. Here we report that acquisition of a spatial food search task is accompanied by elevated levels of hzf-3 mRNA in the hippocampus. Adult male Long-Evans rats were handled, food-restricted, and allowed to habituate to the maze prior to training. During acquisition, rats were given one training session per day for 5 days. Each training session consisted of five trials in which animals searched the maze for food located in 4 of 16 holes in the floor of the maze. Training resulted in spatial acquisition of the task. Northern blot analysis showed significant increases in hippocampal hzf-3 mRNA 3 h after training in the maze. Next, brains were obtained from Naive, Habituated, Day 1, Day 3, and Day 5 animals and processed for in situ hybridization. The results showed significant increases of hzf-3 mRNA in CA1 and CA3 subregions of the dorsal hippocampus during acquisition of the task. We conclude that expression of the hzf-3 gene in the brain is associated with long-term spatial memory processes. The present results are the first to implicate an orphan nuclear receptor in long-term information storage in the hippocampus.

Identification of nuclear orphan receptors as regulators of expression of a neurotransmitter receptor gene

Nuclear orphan receptors are known to be important mediators of neurogenesis, but the target genes of these transcription factors in the vertebrate nervous system remain largely undefined. We have previously shown that a 500-base pair fragment in the first intron of the GRIK5 gene, which encodes the kainate-preferring glutamate receptor subunit KA2, down-regulates gene expression. In our present studies, mutation of an 11-base pair element within this fragment resulted in a loss of nuclear protein binding and reverses negative regulation by the intron. Using yeast one-hybrid screening, we have identified intron-binding proteins from rat brain as COUP-TFI, EAR2, and NURR1. Gel shift studies with postnatal day 2 rat brain extract indicate the presence of COUP-TFs, EAR2, and NURR1 in the DNA-protein complex. Competition assays with GRIK5-binding site mutations show that the recombinant clones exhibit differential binding characteristics and suggest that the DNA-protein complex from postnatal day 2 rat brain may consist primarily of EAR2. The DNA binding activity was also observed to be enriched in rat neural tissue and developmentally regulated. Co-transfection assays showed that recombinant nuclear orphan receptors function as transcriptional repressors in both CV1 cells and rat CG4 oligodendrocyte cells. Direct interaction of the orphan receptors with and relief of repression by TFIIB indicate likely role(s) in active and/or transrepression. Our findings are thus consistent with the notion that multiple nuclear orphan receptors can regulate the transcription of a widely expressed neurotransmitter receptor gene by binding a common element in an intron and directly modulating the activity of the transcription machinery.

Organization of the human orphan nuclear receptor Nurr1 gene

Recent reports have revealed that Nurr1 (also known as NOT/TINUR/RNR-1/HZF-3), a member of the steroid/thyroid hormone nuclear receptor superfamily, is predominantly expressed in the midbrain; substantia nigra (SN) and ventral tegmental area (VTA). Nurr1 null mice are born lethal, lacking the midbrain dopamine (DA) neurons, suggesting that Nurr1 is essential for the development and differentiation of midbrain DA neurons. Human Nurr1 gene has been mapped on chromosome 2q22-23, which is reported to associate weakly with schizophrenia. We cloned and sequenced the human Nurr1 gene, which is approximately 8.3kb long, consisting of eight exons and seven introns. Comparisons of the human Nurr1 with the mouse Nurr1, mouse Nur77 and human NOR-1 revealed that their genomic structures were highly conserved. The 5'-flanking region of the human Nurr1 included three transcriptional regulatory elements, cAMP-response element (CRE), CArG-like element and Sp-1 site, which were surrounded by CpG island, and showed a strong homology with the mouse Nurr1. We performed a primer extension analysis using mRNA from HeLa S3 cells stimulated with phorbol 12-myristate 13-acetate (PMA), Ca2+ ionophore A23187 and cycloheximide (CHX) in order to induce the Nurr1 mRNA expression, and determined one transcription initiation site within CRE. The transient transfection assay indicates that the regulatory elements in the 5'-flanking region are robust for mitogen-induced expression of the human Nurr1. Further analysis of the polymorphism of the human Nurr1 gene may reveal the association with diseases characterized by changes of the DA system, such as Parkinson's disease and schizophrenia.

Nurr1 mRNA expression in neonatal and adult rat brain following kainic acid-induced seizure activity

Nurr1 is an immediate early gene encoding a member of the steroid-thyroid hormone receptor family. In PC12 cells, Nurr1 is readily induced by membrane depolarization, but not by growth factors. Nurr1 is predominantly expressed in the brain, and is essential to the differentiation of midbrain dopaminergic neurons. However, Nurr1 is also expressed in brain regions unrelated to dopaminergic neurons, e.g., hippocampus and cerebral cortex, and its immediate induction following seizure activity suggests a potential involvement of this transcription factor in modulating gene expression in the nervous system. To investigate the response of Nurr1 to neuronal activation, we analyzed Nurr1 mRNA expression in neonatal and adult rat brain following kainic acid (KA)-induced seizure. In P7 animals, systemic injection of KA increased Nurr1 mRNA levels in a few hilar cells of the dentate gyrus and some pyramidal cells of the CA3 region of the hippocampus. In older animals, Nurr1 induction progressively expanded to all hippocampal regions (P14, P21) and eventually to cortical regions (adult). The increase was rapid and transient in the dentate gyrus, a structure resistant to the neurotoxic effect of KA, and was more prolonged in other regions more susceptible to KA toxicity. Induction of Nurr1 at early postnatal stages and rapid increase in the dentate gyrus following KA-induced seizure, suggest that Nurr1 expression is modulated by neuronal activity. On the other hand, prolonged Nurr1 induction in regions sensitive to KA toxicity indicates a possible involvement of Nurr1 in selective neuronal vulnerability.