Focal brain injury induces multiple immediate early genes encoding zinc finger transcription factors

Global Impairment of Immediate-Early Genes Expression in Rett Syndrome Models and Patients Linked to Myelination Defects

Rett syndrome (RTT) is a severe neurodevelopmental disease caused almost exclusively by mutations to the MeCP2 gene. This disease may be regarded as a synaptopathy, with impairments affecting synaptic plasticity, inhibitory and excitatory transmission and network excitability. The complete understanding of the mechanisms behind how the transcription factor MeCP2 so profoundly affects the mammalian brain are yet to be determined. What is known, is that MeCP2 involvement in activity-dependent expression programs is a critical link between this protein and proper neuronal activity, which allows the correct maturation of connections in the brain. By using RNA-sequencing analysis, we found several immediate-early genes (IEGs, key mediators of activity-dependent responses) directly bound by MeCP2 at the chromatin level and upregulated in the hippocampus and prefrontal cortex of the Mecp2-KO mouse. Quantification of the IEGs response to stimulus both in vivo and in vitro detected an aberrant expression pattern in MeCP2-deficient neurons. Furthermore, altered IEGs levels were found in RTT patient's peripheral blood and brain regions of post-mortem samples, correlating with impaired expression of downstream myelination-related genes. Altogether, these data indicate that proper IEGs expression is crucial for correct synaptic development and that MeCP2 has a key role in the regulation of IEGs.

CaMKIV mediates spine growth deficiency of hippocampal neurons by regulation of EGR3/BDNF signal axis in congenital hypothyroidism

Congenital hypothyroidism (CH) will cause cognitive impairment in the condition of delayed treatment. The hippocampus is one of the most affected tissues by CH, in which the functional structures of hippocampal neurons manifest deficiency due to aberrant expression of effector molecules. The Ca²⁺/Calmodulin-dependent protein kinase, CaMKIV, is downregulated in the hippocampal neurons, influencing the growth of dendritic spines in response to CH. However, the underlying mechanism is not fully elucidated. In the present study, the early growth response factor 3 (EGR3) was regulated by CaMKIV in the hippocampal neurons of CH rat pups, as was analyzed by transcriptome sequencing and in vitro cell experiments. EGR3 localized within hippocampal neurons in CA1, CA3, and dentate gyrus regions. Deficient EGR3 in the primary hippocampal neurons significantly reduced the density of dendritic spines by downregulating the expression of BDNF, and such effects could be rescued by supplementing recombinant BDNF protein. Taken together, CH mediates cognitive impairment of pups through the inactivation of CaMKIV in the hippocampal neurons, which decreases the expression of EGR3 and further reduces the production of BDNF, thereby impairing the growth of dendritic spines. Identifying CaMKIV/EGR3/BDNF pathway in the hippocampal neurons in the context of CH will benefit the drug development of intellectual disability caused by CH.

The role of NURR1 in metabolic abnormalities of Parkinson's disease

A constant metabolism and energy supply are crucial to all organs, particularly the brain. Age-dependent neurodegenerative diseases, such as Parkinson’s disease (PD), are associated with alterations in cellular metabolism. These changes have been recognized as a novel hot topic that may provide new insights to help identify risk in the pre-symptomatic phase of the disease, understand disease pathogenesis, track disease progression, and determine critical endpoints. Nuclear receptor-related factor 1 (NURR1), an orphan member of the nuclear receptor superfamily of transcription factors, is a major risk factor in the pathogenesis of PD, and changes in NURR1 expression can have a detrimental effect on cellular metabolism. In this review, we discuss recent evidence that suggests a vital role of NURR1 in dopaminergic (DAergic) neuron development and the pathogenesis of PD. The association between NURR1 and cellular metabolic abnormalities and its implications for PD therapy have been further highlighted.

Slide-seq: A scalable technology for measuring genome-wide expression at high spatial resolution

Spatial positions of cells in tissues strongly influence function, yet a high-throughput, genome-wide readout of gene expression with cellular resolution is lacking. We developed Slide-seq, a method for transferring RNA from tissue sections onto a surface covered in DNA-barcoded beads with known positions, allowing the locations of the RNA to be inferred by sequencing. Using Slide-seq, we localized cell types identified by single-cell RNA sequencing datasets within the cerebellum and hippocampus, characterized spatial gene expression patterns in the Purkinje layer of mouse cerebellum, and defined the temporal evolution of cell type-specific responses in a mouse model of traumatic brain injury. These studies highlight how Slide-seq provides a scalable method for obtaining spatially resolved gene expression data at resolutions comparable to the sizes of individual cells.

Long 3'UTR of Nurr1 mRNAs is targeted by miRNAs in mesencephalic dopamine neurons

The development of mesencephalic dopamine neurons and their survival later in life requires the continuous presence of the transcription factor Nurr1 (NR4A2). Nurr1 belongs to the nuclear receptors superfamily. However, it is an orphan member that does not require a ligand to regulate the transcription of its target genes. Therefore, controlling the expression of Nurr1 is an important manner to control its function. Several reports have shown that microRNAs (miRNAs) regulate Nurr1 expression. However, Nurr1 has several splicing variants, posing the question what variants are subjected to miRNA regulation. In this work, we identified a long 3'UTR variant of rat Nurr1 mRNA. We used bioinformatics analysis to identify miRNAs with the potential to regulate Nurr1 expression. Reporter assays performed with the luciferase gene fused to the short (658 bp) or long (1,339 bp) 3'UTR of rat Nurr1 mRNAs, showed that miR-93, miR-204 and miR-302d selectively regulate the mRNA with the longest 3'UTR. We found that the longest variant of Nurr1 mRNA expresses in the rat mesencephalon as assessed by PCR. The transfection of rat mesencephalic neurons with mixed miR-93, miR-204 and miR-302d resulted in a significant reduction of Nurr1 protein levels. In conclusion, Nurr1 mRNA variant with the longest 3'UTR undergoes a specific regulation by miRNAs. It is discussed the importance of fine-tuning Nurr1 protein levels in mesencephalic dopamine neurons.

NR4A1 Knockdown Suppresses Seizure Activity by Regulating Surface Expression of NR2B

Nuclear receptor subfamily 4 group A member 1 (NR4A1), a downstream target of CREB that is a key regulator of epileptogenesis, has been implicated in a variety of biological processes and was previously identified as a seizure-associated molecule. However, the relationship between NR4A1 and epileptogenesis remains unclear. Here, we showed that NR4A1 protein was predominantly expressed in neurons and up-regulated in patients with epilepsy as well as pilocarpine-induced mouse epileptic models. NR4A1 knockdown by lentivirus transfection (lenti-shNR4A1) alleviated seizure severity and prolonged onset latency in mouse models. Moreover, reciprocal coimmunoprecipitation of NR4A1 and NR2B demonstrated their interaction. Furthermore, the expression of p-NR2B (Tyr1472) in epileptic mice and the expression of NR2B in the postsynaptic density (PSD) were significantly reduced in the lenti-shNR4A1 group, indicating that NR4A1 knockdown partly decreased surface NR2B by promoting NR2B internalization. These results are the first to indicate that the expression of NR4A1 in epileptic brain tissues may provide new insights into the molecular mechanisms underlying epilepsy.

■ REVIEW : Long-Term Modulation of Gene Expression in Epilepsy

Molecular genetics has led to major advances in the study of neurological disease over the last 2 decades. Initial advances were made in understanding specific mutations that were associated with disease, such as epilepsy and other neurological conditions. In addition to specific mutations, recent research has focused on long-lasting or permanent changes in genetic expression as an underlying substrate of acquired diseases such as epilepsy. In symptomatic epilepsy, normal brain tissue is permanently altered and develops spon taneous recurrent seizures. Evidence indicates that long-lasting changes in gene expression at both tran scriptional and post-transcriptional levels are associated with epileptogenesis. The expression of transcription factors and other regulatory proteins represent a molecular mechanism for mediating these changes. Understanding the effects of severe environmental stresses on the multiple sites of transcriptional and post-transcriptional regulation of gene expression is likely to provide important insights into the devel opment of altered neuronal function in a number of important disease states, including epilepsy. NEURO SCIENTIST 5:86-99, 1999

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.

Activation and function of immediate-early genes in the nervous system

Immediate-early genes have important roles in processes such as brain development, learning, and responses to drug abuse. Further, immediate-early genes play an essential role in cellular responses that contribute to long-term neuronal plasticity. Neuronal plasticity is a characteristic of the nervous system that is not limited to the first stages of brain development but persists in adulthood and seems to be an inherent feature of everyday brain function. The plasticity refers to the neuron's capability of showing short- or long-lasting phenotypic changes in response to different stimuli and cellular scenarios. In this review, we focus on the immediate-early genes encoding transcription factors (AP-1 and Egr) that are relevant for neuronal responses. Our current understanding of the mechanisms involved in the induction of the immediate-early genes is presented.

NR4A orphan nuclear receptors as mediators of CREB-dependent neuroprotection

Induced expression of neuroprotective genes is essential for maintaining neuronal integrity after stressful insults to the brain. Here we show that NR4A nuclear orphan receptors are induced after excitotoxic and oxidative stress in neurons, up-regulate neuroprotective genes, and increase neuronal survival. Moreover, we show that NR4A proteins are induced by cAMP response element binding protein (CREB) in neurons exposed to stressful insults and that they function as mediators of CREB-induced neuronal survival. Animals with null mutations in three of six NR4A alleles show increased oxidative damage, blunted induction of neuroprotective genes, and increased vulnerability in the hippocampus after treatment with kainic acid. We also demonstrate that NR4A and the transcriptional coactivator PGC-1alpha independently regulate distinct CREB-dependent neuroprotective gene programs. These data identify NR4A nuclear orphan receptors as essential mediators of neuroprotection after exposure to neuropathological stress.

NR4A orphan nuclear receptors influence retinoic acid and docosahexaenoic acid signaling via up-regulation of fatty acid binding protein 5

The orphan nuclear receptor (NR) Nurr1 is expressed in the developing and adult nervous system and is also induced as an immediate early gene in a variety of cell types. In silico analysis of human promoters identified fatty acid binding protein 5 (FABP5), a protein shown to enhance retinoic acid-mediated PPARbeta/delta signaling, as a potential Nurr1 target gene. Nurr1 has previously been implicated in retinoid signaling via its heterodimerization partner RXR. Since NRs are commonly involved in cross-regulatory control we decided to further investigate the regulatory relationship between Nurr1 and FABP5. FABP5 expression was up-regulated by Nurr1 and other NR4A NRs in HEK293 cells, and Nurr1 was shown to activate and bind to the FABP5 promoter, supporting that FABP5 is a direct downstream target of NR4A NRs. We also show that the RXR ligand docosahexaenoic acid (DHA) can induce nuclear translocation of FABP5. Moreover, via up-regulation of FABP5 Nurr1 can enhance retinoic acid-induced signaling of PPARbeta/delta and DHA-induced activation of RXR. We also found that other members of the NR4A orphan NRs can up-regulate FABP5. Thus, our findings suggest that NR4A orphan NRs can influence signaling events of other NRs via control of FABP5 expression levels.

Induction of transcription factor Egr-1 gene expression in astrocytoma cells by Murine coronavirus infection

Mouse hepatitis virus (MHV) causes encephalitis and demyelination in the central nervous system (CNS) of susceptible rodents. Astrocytes are one of the major targets for MHV infection in the CNS, and respond to MHV infection by expressing diverse molecules that may contribute to CNS pathogenesis. Here we characterized the activation of an immediate-early transcription factor Egr-1 by MHV infection in an astrocytoma cell line. We found that the expression of Egr-1 was dramatically increased following virus infection. Using various inhibitors of mitogen-activated protein kinases, we identified that the extracellular signal-regulated kinases 1/2 were involved in the activation of Egr-1 transcription by MHV infection. Experiments with ultraviolet light-inactivated virus revealed that the induction of Egr-1 did not require virus replication and was likely mediated during cell entry. We further found that over-expression of Egr-1 suppressed the expression of BNip3, a pro-apoptotic member of the Bcl-2 family. This finding may provide an explanation for our previously observed down-regulation of BNip3 by MHV infection in astrocytoma cells (Cai, Liu, Yu, and Zhang, Virology 316:104-115, 2003). Furthermore, knockdown of Egr-1 by an siRNA inhibited MHV propagation, suggesting the biological relevance of Egr-1 induction to virus replication. In addition, the persistence/demylinating-positive strains (JHM and A59) induced Egr-1 expression, whereas the persistence/demylinating-negative strain (MHV-2) did not. These results indicate a correlation between the ability of MHVs to induce Egr-1 expression and their ability to cause demyelination in the CNS, which may suggest a potential role for the induction of Egr-1 in viral pathogenesis.

Expression of proinflammatory cytokines tumor necrosis factor-α and interleukin-1β in the brain during experimental Group B streptococcal meningitis

We performed mRNA in situ hybridization for TNF-alpha and IL-1beta from infant rats with group B streptococcal meningitis. Induction of both cytokines was seen in the ependyma and the meninges at 4 h. Both cytokines were expressed in the brain parenchyma at 12 h. Induction of IL-1beta mRNA was seen in vessels within the brain cortex. Neutrophilic infiltrate at all time points examined was minimal and could not account for the observed cytokine expression.

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.

Mediators of ischemic preconditioning identified by microarray analysis of rat spinal cord

Spinal ischemia is a frequent cause of paralysis. Here we explore the biological basis of ischemic preconditioning (IPC), the phenomenon in which a brief period of ischemia can confer protection against subsequent longer and normally injurious ischemia, to identify mediators of endogenous neuroprotection. Using microarrays, we examined gene expression changes induced by brief spinal ischemia using a rat balloon occlusion model. Among the nearly 5000 genes assayed, relatively few showed two-fold changes, and three groups stood out prominently. The first group codes for heat shock protein 70, which is induced selectively and robustly at 30 min after brief ischemia, with increases up to 100-fold. A second group encodes metallothioneins 1 and 2. These mRNAs are increased at 6 and 12 h after ischemia, up to 12-fold. The third group codes for a group of immediate-early genes not previously associated with spinal ischemia: B-cell translocation gene 2 (BTG2), the transcription factors early growth response 1 (egr-1) and nerve growth factor inducible B (NGFI-B), and a mitogen-activated protein kinase phosphatase, ptpn16, an important cell signaling regulator. These mRNAs peak at 30 min and return to baseline or are decreased 6 h after ischemia. Several other potentially protective genes cluster with these induced mRNAs, including small heat shock proteins, and many have not been previously associated with IPC. These results provide both putative mediators of IPC and molecular targets for testing preconditioning therapies.

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.

Early gene expression in the rat cortex after experimental traumatic brain injury and hypotension

To determine c-fos and egr-1 mRNA levels in the rat cortex after traumatic brain injury (TBI) and TBI plus hemorrhagic hypotension (HH). Sprague-Dawley rats were subjected to TBI. HH was induced by removing 5 ml of blood from the jugular vein for a duration of 20 min. Cortical tissue was harvested at 0 and 120 min, and mRNA levels of the immediate early genes c-fos, egr-1 were obtained. Rats that sustained TBI alone had increased c-fos and egr-1 mRNA expression at 120 min that was significant. Additionally, c-fos mRNA levels after TBI alone were significantly higher than c-fos mRNA levels after TBI+HH at 120 min. Levels of egr-1 mRNA after TBI alone at 120 min were not significantly higher than egr-1 mRNA levels after TBI+HH at 120 min.

How necessary is the activation of the immediate early gene zif268 in synaptic plasticity and learning?

The immediate early genes (IEGs) are activated rapidly and transiently in response to a multitude of stimuli. The zif268 belongs to a category of regulatory IEGs that activate downstream target genes and is considered to be a triggering mechanism to activate the genomic response in neurons. Several studies have shown that zif268 mRNA is upregulated during different forms of associative learning, and following tetanic stimulation that induces long-lasting LTP. To date, there is a general consensus that zif268 activation may constitute a critical mechanism for the encoding of long-lasting memories, however this is based on relatively few studies. Given the fact that zif268 can be activated by a number of different types of stimuli, it becomes important to determine exactly how it may be implicated in memory. Examination of the current literature suggests that zif268 is necessary in the processing of several types of memory, however, it is not entirely clear what aspects of memory zif268 may be implicated in. Here, we review the existing literature and emphasise that understanding the signalling pathways that lead to activation of the IEGs and the downstream targets of these genes will advance our understanding of how functional activation of zif268 may be implicated in processing long-term memories.

Cloning and characterization of the bovine EGR4 gene and evaluation as candidate gene for bovine spinal dysmyelination

Genes of the early growth response (EGR) family encode transcription factors with a highly conserved DNA binding zinc finger domain, which regulate a variety of genes, e.g. late myelin genes. Here, the cloning, genomic structure and expression of the bovine orthologue of the EGR4 gene are reported. The gene consists of two exons and encodes a 482 amino acid protein with a Cys2His2 zinc finger structure. The predicted protein shares between 80 and 87% identity to mouse, rat and human EGR4 proteins and all four species share almost complete identity in the DNA-binding domain. The bovine transcript is alternatively spliced by retaining intronic sequence, giving rise to two different mRNAs differing in three nucleotides and resulting in an extra alanine residue in the longer variant of the predicted protein. The gene was mapped by radiation hybrid (RH) mapping to markers on bovine chromosome 11. EGR4 transcripts were detected by reverse transcriptase polymerase chain reaction (RT-PCR) in the frontal cortex and cerebellum, and a low expression level was also detected in the liver. The EGR4 gene was evaluated as a candidate gene for bovine spinal dysmyelination (BSD). Sequencing of the gene from a homozygous affected animal and a heterozygous carrier revealed a single base mutation that leads to an amino acid substitution at residue 322 in EGR4. Genotype analysis of this polymorphism in a pedigree segregating for BSD, as well as in a panel of different cattle breeds, and sequence analysis of the entire coding region suggested that the EGR4 is not the gene responsible for BSD. Furthermore, 87 animals of different cattle breeds were screened for single-nucleotide polymorphisms (SNPs) resulting in the identification of two SNPs in EGR4.

Enhanced expression of TNF-R1 protein in NMDA-mediated cell death in the retina

Multiple apoptosis-related genes are expressed in the retina after exposure to N-methyl-D-aspartic acid (NMDA). For example, the mRNAs for TNF-R1, FasL, and Nur77 are up-regulated between 2.8 and 7-fold [Mol. Brain Res. 91 (2001) 34-42]. The purpose of the present study is to examine prospective changes in protein expression for these genes and to determine their cellular localizations subsequent to NMDA stimulation. Following anesthesia, a single intravitreal injection of 4 mM NMDA was administered into the right eye of anesthetized rats. The left eye was injected with phosphate-buffered saline. Retinae were harvested at 2 and 24 h postinjection. Western-blot and immunocytochemical techniques were used to detect changes in protein expression levels, and to localize their distributions within the retina. Analyses of Western blots demonstrated a significant increase in TNF-R1 (100 and 80%) compared to the sham-controls at 2 and 24 h postinjection with NMDA. Immunolabeling of TNF-R1 was observed in the inner nuclear layer (INL) at 2 h postinjection with NMDA. TNF-R1 was also clearly evident in cells within the INL and ganglion cell layers (GCL) at 24 h post-injection with NMDA. In contrast to these changes in TNF-R1 there were no significant changes in the levels or distributions of FasL or Nur77 in NMDA-stimulated animals at either 2 or 24 h when compared to the sham-controls. These results implicate the TNF-R1 signal transduction pathway in NMDA-induced cell death in the INL and GCL of the retina.

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.

Functional regulatory regions of human transcription factor MEF2C

Myocyte enhancer-binding factor 2C (MEF2C), a transcription factor expressed at high levels in muscle and brain, is implicated in the terminal differentiation and post-mitotic survival of neurons. In this study MEF2C deletion mutants and naturally-occurring isoforms were transfected into COS and P19 cells with two different reporter genes, to test the relative transcriptional activities of the MEF2C constructs. Deletion of parts of the carboxy terminus, in particular amino acids 387-473, enhanced transcriptional activation. A region rich in serine, threonine, proline, and tyrosine from amino acids 312-367 was sufficient to activate transcription at low levels when coupled to amino acids 1-86, which contain the DNA-binding (MADS/MEF) domain of MEF2C, but also depended on amino acids 87-311 for full effect. A construct with amino acids 312-350 missing showed significantly less transcriptional activation than proteins containing this sequence. MEF2C constructs were uniformly localized to the cell nucleus by immunostaining with an antibody to the constant N-terminal region of MEF2C. Western blot and gel shift studies of extracts from transfected cells and from in vitro transcription/translation suggest that variation in the amount of protein expressed or in DNA-binding properties does not account for observed differences in transcriptional activation. This structural information may be useful for elucidating the mechanisms of MEF2C in interacting with other factors to regulate target genes.

Characterization of apoptosis-genes associated with NMDA mediated cell death in the adult rat retina

Calcium/calmodulin-dependent protein kinase II containing a nuclear localizing signal (CaMKII-alphaB) is altered in retinal neurons exposed to N-methyl-D-aspartate (NMDA). AIP (myristoylated autocamtide-2-related inhibitory peptide), a specific inhibitor of CaMKII provides neuroprotection against NMDA-mediated neurotoxicity. In this study, gene-arrays were used to investigate which apoptosis-associated genes are altered after exposure to NMDA. The data indicate an increased expression (2-7-fold) of five such genes encoding proteins that could be involved in NMDA induced cell death. The up-regulated genes are: FasL; GADD45; GADD153; Nur77 and TNF-R1. Treatment with AIP blocked their altered expression. The results suggest that multiples genes are involved in NMDA-induced excitotoxicity and that AIP, a specific inhibitor for CaMKII, regulates the expression of these apoptosis-associated genes in the retina.

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.

Stress induces zinc finger immediate early genes in the rat adrenal gland

The secretion of steroid hormones from the adrenal cortex as well as cathecolamines from the adrenal medulla is stimulated by stress. In this study, we studied the effect of capsaicin-induced stress on the expression of the immediate-early genes (IEGs) NGFI-A, -B, -C, egr-2, -3 and Nurr1 in the rat adrenal gland using in situ hybridization. All of these IEGs except egr-2 were rapidly induced in the adrenal cortex and medulla. The temporal patterns of the IEG induction in medulla varied significantly. NGFI-A was induced in medulla within 15 min after stress, NGFI-B, egr-3 and Nurr1 were induced by 30 min, whereas NGFI-C was induced by 2 h. Surprisingly, only NGFI-B and Nurr1 were induced in the glucocorticoid secreting regions of zonae reticularis and fasciculata of the cortex, starting 15 min after the stress. All of the inducible IEGs were induced in the aldosterone secreting zona glomerulosa 15-30 min after the capsaicin injection. NGFI-A, NGFI-B and Nurr1 expression persisted for 6 h. Since the IEGs studied had major differences in their temporospatial induction pattern, they are likely to be induced by distinct stress-elicited factors and have separate target genes and roles in stress-induced glucocorticoid and catecholamine secretion.

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.

Decreased c-fos expression in experimental neonatal hydrocephalus: evidence for reduced neuronal activation

Although neonatal hydrocephalus often results in residual neurological impairments, little is known about the cellular mechanisms responsible for these deficits. The immediate early gene, fos (c-fos), functions as a “third messenger” to regulate protein synthesis and is a good marker for neuronal activation. To identify functional changes in neurons at the cellular level, the authors quantified fos RNA expression and localized fos protein in the H-Tx rat model of congenital hydrocephalus. Tissue samples from sensorimotor and auditory regions were obtained from hydrocephalic rats and age-matched, normal litter mates at 1, 6, 12, and 21 days of age (four-six animals in each group) and processed for immunohistochemical analysis of fos and Northern blot analysis of RNA. At 12 days of age, hydrocephalic animals exhibited significant decreases in the ratio of fos immunoreactive cells to Nissl-stained neurons from both cortical regions, but no statistical differences were noted in fos expression. At 21 days of age, both the ratio of fos immunoreactive cells to Nissl-stained neurons and fos expression decreased significantly. The number of fos-positive neurons decreased in all cortical layers but was most prominent in layers V through VI. This decrease did not appear to be caused by neuronal death because examination of Nissl-stained sections revealed many viable neurons within the areas where fos immunoreactivity was absent. These results suggest that progressive neonatal hydrocephalus reduces the capacity for neuronal activation in the cerebral cortex, primarily in those neurons that provide corticofugal projections, and that this impairment may begin during relatively early stages of ventriculomegaly.

Brain gene expression during REM sleep depends on prior waking experience

In most mammalian species studied, two distinct and successive phases of sleep, slow wave (SW), and rapid eye movement (REM), can be recognized on the basis of their EEG profiles and associated behaviors. Both phases have been implicated in the offline sensorimotor processing of daytime events, but the molecular mechanisms remain elusive. We studied brain expression of the plasticity-associated immediate-early gene (IEG) zif-268 during SW and REM sleep in rats exposed to rich sensorimotor experience in the preceding waking period. Whereas nonexposed controls show generalized zif-268 down-regulation during SW and REM sleep, zif-268 is upregulated during REM sleep in the cerebral cortex and the hippocampus of exposed animals. We suggest that this phenomenon represents a window of increased neuronal plasticity during REM sleep that follows enriched waking experience.

Neuronal death and survival in two models of hypoxic-ischemic brain damage

Two unilateral hypoxic-ischemia (HI) models (moderate and severe) in immature rat brain have been used to investigate the role of various transcription factors and related proteins in delayed neuronal death and survival. The moderate HI model results in an apoptotic-like neuronal death in selectively vulnerable regions of the brain while the more severe HI injury consistently produces widespread necrosis resulting in infarction, with some necrosis resistant cell populations showing evidence of an apoptotic type death. In susceptible regions undergoing an apoptotic-like death there was not only a prolonged induction of the immediate early genes, c-jun, c-fos and nur77, but also of possible target genes amyloid precursor protein (APP751) and CPP32. In contrast, increased levels of BDNF, phosphorylated CREB and PGHS-2 were found in cells resistant to the moderate HI insult suggesting that these proteins either alone or in combination may be of importance in the process of neuroprotection. An additional feature of both the moderate and severe brain insults was the rapid activation and/or proliferation of glial cells (microglia and astrocytes) in and around the site of damage. The glial response following HI was associated with an upregulation of both the CCAAT-enhancer binding protein alpha (microglia only) and NFkappaB transcription factors.

Activity and injury-dependent expression of inducible transcription factors, growth factors and apoptosis-related genes within the central nervous system

This review primarily discusses work that has been performed in our laboratories and that of our direct collaborators and therefore does not represent an exhaustive review of the current literature. Our aim is to further discuss the role that gene expression plays in neuronal plasticity and pathology. In the first part of this review we examine activity-dependent changes in the expression of inducible transcription factors (ITFs) and neurotrophins with long-term potentiation (LTP) and kindling. This work has identified particular ITFs (Krox-20 and Krox-24) and neurotrophin systems (particularly the brain-derived neurotrophic factor (BDNF)/tyrosine receptor kinase-B, Trk-B system) that may be involved in stabilizing long-lasting LTP (i.e. LTP3). We also show that changes in the expression of other ITFs (Fos, Jun-D and Krox-20) and the BDNF/trkB neurotrophin system may play a central role in the development of hippocampal kindling, an animal model of human temporal lobe epilepsy. In the next part of this review we examine changes in gene expression after neuronal injuries (ischemia, prolonged seizure activity and focal brain injury) and after nerve transection (axotomy). We identify apoptosis-related genes (p53, c-Jun, Bax) whose delayed expression selectively increases in degenerating neurons, further suggesting that some forms of neuronal death may involve apoptosis. Moreover, since overexpression of the tumour-suppressor gene p53 induces apoptosis in a wide variety of dividing cell types we speculate that it may perform the same function in post-mitotic neurons following brain injuries. Additionally, we show that neuronal injury is associated with rapid, transient, activity-dependent expression of neurotrophins (BDNF and activinA) in neurons, contrasting with a delayed and more persistent injury-induced expression of certain growth factors (IGF-1 and TGFbeta) in glia. In this section we also describe results linking ITFs and neurotrophic factor expression. Firstly, we show that while BDNF and trkB are induced as immediate-early genes following injury, the injury-induced expression of activinA and trkC may be regulated by ITFs. We also discuss whether loss of retrograde transport of neurotrophic factors such as nerve growth factor following nerve transection triggers the selective and prolonged expression of c-Jun in axotomized neurons and whether c-Jun is responsible for regeneration or degeneration of these axotomized neurons. In the last section we further examine the role that gene expression may play in memory formation, epileptogenesis and neuronal degeneration, lastly speculating whether the expression of various growth factors after brain injury represents an endogenous neuroprotective response of the brain to injury. Here we discuss our results which show that pharmacological enhancement of this response with exogenous application of IGF-1 or TGF-beta reduces neuronal loss after brain injury.

Prolonged expression of zinc finger immediate-early gene mRNAs and decreased protein synthesis following kainic acid induced seizures

In the present study in situ hybridization was used to study the effect of kainic acid induced seizures on the expression of the zinc finger immediate-early genes (IEGs) NGFI-A, NGFI-B, NGFI-C, egr-2; egr-3 and Nurr1. Kainic acid markedly induced these IEGs especially in hippocampus, cortex and amygdala by 30 min. This induction gradually decreased and returned to baseline by 24 h in most regions. However, in the CA1 and CA3 subfields of hippocampus known to be damaged by kainic acid the expression of all the IEGs except egr-2 remained elevated for 24 h. NGFI-A, NGFI-B, NGFI-C and to a lesser extent, Nurr1, remained elevated also in the subcortical region of the temporal lobe. By 24 h incorporation of 14C-leucine decreased in the piriform cortex, amygdala, and in the CA1 and CA3 subfields, but not in CA2 and dentate gyrus. These areas showing decreased protein synthesis in the hippocampus by 24 h showed prolonged IEG induction, whereas IEG expression returned to control levels in areas showing normal protein synthesis. In the temporal lobe decreased protein synthesis coexisted with decreased IEG expression, whereas areas in the vicinity of the region showing decreased protein synthesis demonstrated elevated IEG expression. The decreased protein synthesis was localized in areas where extensive neuronal death has occurred. This prolonged IEG induction in the hippocampus, which has been linked with neuronal death, could solely represent a prolonged mRNA turnover caused by disrupted protein synthesis. The prolonged IEG expression in the temporal lobe appeared to be localized in regions where the cells are in stress, but still viable. The sustained IEG expression might therefore either represent a stress response by which the neurons are trying to protect themselves or, alternatively, the IEG response may be an early sign indicating that these cells are initiating a pathway leading to programmed cell death.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Differential expression of Nur77 family members in human T-lymphotropic virus type 1-infected cells: transactivation of the TR3/nur77 gene by Tax protein

We analyzed the differential expression and regulation of three members of the Nur77 transcription factor family by the human T-lymphotropic virus type 1 (HTLV-1) Tax protein. We have demonstrated that in both HTLV-1-infected cells and Tax-expressing JPX-9 cells, TR3/nur77 is highly expressed, whereas neither NOR-1 nor NOT expression is detectable. Transient transfection analysis further confirmed the Tax transactivation of the TR3/nur77 promoter but not the NOR-1 promoter in different cell types. Furthermore, expression of a luciferase reporter gene driven by the NGFI-B (rat homolog of TR3/Nur77) response element (NBRE) provided evidence that Tax-mediated transactivation resulted in the induction of a functional protein. Cotransfection assays with the TR3/nur77 promoter sequence or the NBRE binding motif together with a series of Tax mutants have shown that Tax-induced TR3/nur77 expression is mediated by CREB/ATF-related transcription factors.

Microglial NO induces delayed neuronal death following acute injury in the striatum

We have established a novel injury model in the central nervous system by a stereotaxic injection of ethanol into rat striatum to induce necrosis. With this model, we clarify a function of inducible nitric oxide synthase (iNOS) in a healing mechanism around a necrotic lesion. A semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) revealed that the iNOS mRNA arose at 6 h, peaked at 24 h, and declined to a lower level 48 h after an intrastriatal 5-microL ethanol injection. From in situ hybridization, this iNOS mRNA was expressed in the area surrounding the injury. By immunohistochemistry, mononuclear cells at this boundary area of necrosis were stained with anti-iNOS antibody on the first day after the injury. These cells turned out to be reactive microglia from the positive staining of GSA-I-B4, ED-1 and OX-42. Haematoxylin-eosin (HE) staining showed that neurons in this boundary area gradually disappear up to 5 days after the injury with an increment of microglial cells, and this area became cavernous. Nuclei of neurons in this area were stained positive by the terminal deoxynucleotidyl-transferase-mediated dUTP-biotin nick end-labelling (TUNEL) assay on the first day after the injury. These TUNEL-positive neurons gradually disappeared toward the third day, while microglial cells increased. L-Ng-nitro-arginine methylester (L-NAME), a competitive NOS inhibitor, administration diminished the elimination of neurons by microglia in this boundary area surrounding necrosis. Microglial NO may act as a neurotoxic agent to eliminate damaged neurons near the necrosis in the form of delayed neuronal death, and may reintegrate the neuronal circuits with functionally intact neurons.

Analysis of c-Fos and glial fibrillary acidic protein (GFAP) expression following topical application of potassium chloride (KCl) to the brain surface

Application of high K+ concentrations to a limited area of the brain surface is known to trigger spreading depression. We used this model to observe the response of cortical areas, distant to the exposed site, at the cellular level. Immunostaining of glial fibrillary acidic protein (GFAP) and of the proto-oncogene c-Fos was analyzed in brain sections at different times after K+ application. Piriform and parietal cortices, as observed in coronal sections located 3 mm rostrally from the center of the stimulated area and ipsilateral to it, showed a dramatic increase in immunostaining for both markers. However, the time course for such increments was different. c-Fos protein(s) expression was high at 1.5 h and decreased at 24 h after K+ exposure and c-fos mRNA expression correlated with the immunohistochemical results. At these initial times GFAP immunoreactivity was still low but began to rise between 2 and 7 days after treatment in exactly the same areas where c-Fos expression had been up-regulated. No significant effect, for either marker, was evident in the contralateral piriform or parietal cortices. In addition, we studied the effects of the NMDA antagonist MK-801 (4 mg/kg i.p.) on the expression of mRNA for GFAP and c-fos and demonstrated a marked reduction in the upregulation of these genes.

Blood-brain barrier disruption, HSP70 expression and apoptosis due to 3-nitropropionic acid, a mitochondrial toxin

3-Nitropropionic acid (3-NP), a mitochondrial toxin, induces apoptosis in the striatum. We wanted to determine if there was a relationship between mitochondrial dysfunction, disruption of the blood-brain barrier (BBB), and apoptosis. BBB disruption following intrastriatal injection of 3-NP was assessed by Evans blue leakage, brain water content, and by the expression of the 70 kDa heat shock protein (HSP70) and mRNA. Apoptosis was assessed by in situ terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling (TUNEL) and gel electrophoresis to detect internucleosomal DNA fragmentation. Microscopic evidence of Evans blue leakage due to 3-NP was present only 3 hr after injection. Both internucleosomal DNA fragmentation and TUNEL-labeling did not appear until 24 hr after injection. HSP70 (protein and mRNA) was also elevated by 24 hr. There was a quantitative increase in Evans blue leakage and brain water content due to 3-NP by 3 days after injection. Our results suggest that BBB disruption is an early event followed by increased HSP70 expression and apoptosis. We speculate that 3-NP damages endothelial cells, leading to vasogenic edema and apoptosis.

Egr transcription factors in the nervous system

The Egr proteins, Egr-1, Egr-2, Egr-3 and Egr-4, are closely related members of a subclass of immediate early gene-encoded, inducible transcription factors. They share a highly homologous DNA-binding domain which recognises an identical DNA response element. In addition, they have several less-well conserved structural features in common. As immediate early proteins, the Egr transcription factors are rapidly induced by diverse extracellular stimuli within the nervous system in a discretely controlled manner. The basal expression of the Egr proteins in the developing and adult rat brain and the induction of Egr proteins by neurotransmitter analogue stimulation, physiological mimetic and brain injury paradigms is reviewed. We review evidence indicating that Egr proteins are subject to tight differential control through diverse mechanisms at several levels of regulation. These include transcriptional, translational and post-translational (including glycosylation, phosphorylation and redox) mechanisms and protein-protein interaction. Ultimately the differentially co-ordinated Egr response may lead to discrete effects on target gene expression. Some of the known target genes of Egr proteins and functions of the Egr proteins in different cell types are also highlighted. Future directions for research into the control and function of the different Egr proteins are also explored.

Coordinate suppression of striatal ngfi-a and c-fos produces locomotor asymmetry and up-regulation of IEGs in the globus pallidus

We have studied the effects of inhibition of c-Fos and NGFI-A expression by intrastriatal infusion of end-capped antisense oligodeoxynucleotides to determine if their coordinate expression is conferred independently or through regulatory influences exerted between these two proteins. The previously reported locomotor bias that has been associated with unilateral c-Fos suppression was also investigated in animals receiving antisense oligodeoxynucleotides targeted to ngfi-a to determine if the behavior is specific to alterations in c-Fos expression, or if its cause may be a generalized imbalance of striatal IEGs. We show here that while unilateral suppression of c-Fos has negligible effects on NGFI-A, oligodeoxynucleotides targeted to ngfi-a markedly inhibit both NGFI-A and c-Fos expression. Animals with extensive unilateral reduction of either or both proteins demonstrated robust ipsiversive rotation when challenged with D-amphetamine. Infusions of random oligodeoxynucleotides produced neither a reduction in c-Fos or NGFI-A expression, nor a significant rotational bias following D-amphetamine challenge. Surprisingly, animals with extensive striatal IEG suppression were found to have marked up-regulation of c-Fos and NGFI-A in the ipsilateral globus pallidus, a finding which may ultimately shed light on the mechanism of antisense-induced rotational behavior.

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

We isolated a rat orphan nuclear hormone receptor from a brain cortex cDNA library. The sequence of the cDNA insert was 2154 bp with an open reading frame of 1794 bp encoding a putative protein of 598 amino acids and predicted molecular mass of 65 kDa. The deduced amino acid sequence showed a strong homology to the mouse nurr1 and human NOT1 orphan nuclear hormone receptors of the NGFI-B/nur77/NAK1 gene subfamily. We refer to this rat clone as r-nurr1. Northern blot analysis showed that r-nurr1 mRNA was highly expressed in the brain and moderately in the lung as a 4.0 kb transcript. A smaller transcript of 2.5 kb was also detected in the testes. The level of r-nurr1 transcript in the heart, skeletal muscle, liver, kidney and spleen was marginal. In situ hybridization showed that r-nurr1 mRNA was constitutively expressed in various regions of the CNS, particularly in the deeper layers (IV to VI) of the perirhinal cortex and area 2 of parietal cortex. We further evaluated the modulation of r-nurr1 expression in CNS by an electroconvulsive seizure (ECS) and by an amgydala-kindled seizure. A single ECS administered via earclip electrodes induced a rapid and transient increase of r-nurr1 mRNA in the granule cells of the dentate gyrus, being significant at 15 min after the seizure, maximal approximately 1 h and back to baseline at 4 h. The amygdala kindled seizure revealed a less robust and restricted nurr-1 induction in the CNS, as only two of the four kindled animals showed a unilateral induction of nurr1 mRNA in the dentate gyrus. These results suggest that r-nurr1 is an immediate-early gene that is differentially induced by ECS vs. kindled seizures. In addition, as r-nurr1 is prominently expressed in the specific brain sites associated with memory acquisition and consolidation, it may play a role in memory processing.

Expression of zinc finger immediate early genes in rat brain after permanent middle cerebral artery occlusion

The prolonged expression of the leucine zipper fos/jun immediate early genes (IEG) has been correlated with neuronal death after cerebral ischemia. In this study, the expression of six zinc finger IEG was examined using in situ hybridization in adult rats after middle cerebral artery occlusion (MCAO) with the suture model. NGFI-A, NGFI-B, NGFI-C, egr-2, egr-3, and Nurr1 mRNA were all induced throughout the ipsilateral cortex at 1 hour to 12 hours after MCAO. The cortical induction for most of the genes was greatest in the anterior cingulate and the anterior cerebral artery (ACA) and middle cerebral artery (MCA) transition zone. All of the zinc finger IEG were induced at 1 hour in all regions of hippocampus. NGFI-A and NGFI-B were induced in ipsilateral thalamus. Within areas of infarction, the basal IEG mRNA expression, and expression of the housekeeping gene cyclophilin A mRNA, decreased below control levels by 12 hours after the ischemia. Immediate early gene expression outside areas of infarction returned to control levels in most brain regions by 24 hours except for egr-3, which continued to be induced in the MCA/ ACA transition zone for 24 hours, and NGFI-A, which continued to be expressed in specific regions of the thalamus for 72 hours. The induction of these IEG in the cortex is likely caused by ischemia-induced cortical spreading depression, with the hippocampal and thalamic IEG induction being caused by activation of efferent cortical pathways to these regions. The prominent induction of NGFI-B, NGFI-C, egr-2, and egr-3 in the anterior cingulate cortex, the ACA/MCA transition zone, and medial striatum could reflect the ischemic regions around MCA infarcts. The prolonged NGFI-A expression observed in thalamus in this study, and in CA1 of hippocampus after global ischemia in the gerbil in a previous study, suggests that the prolonged NGFI-A, expression could be the result of or the cause of the delayed cell death. Prolonged NGFI-A expression, like c-fos and c-jun, seems to provide a marker for slowly dying neurons.

Differential and time-dependent changes in gene expression for type II calcium/calmodulin-dependent protein kinase, 67 kDa glutamic acid decarboxylase, and glutamate receptor subunits in tetanus toxin-induced focal epilepsy

To study potential molecular mechanisms of epileptogenesis in the neocortex, the motor cortex of rats was injected with tetanus toxin (TT), and gene expression for 67 kDa glutamic acid decarboxylase (GAD-67), type II calcium/calmodulin-dependent protein kinase (CaMKII), NMDA receptor subunit 1 (NR1), and AMPA receptor subunit 2 (GluR2) was investigated by in situ hybridization histochemistry. Injections of 20-35 ng TT induced recurrent seizures after a postoperative period ranging from 4 to 13 d. A majority of rats perfused 5-7 d after TT injection showed altered gene expression, but the changes varied in their areal extent, ranging from most neocortical areas on the injected side in some rats to mainly the frontoparietal cortex or the motor cortex in others. Epileptic rats perfused 14 d after TT injection showed a focus of increased GAD-67 and NR1, and of decreased alpha-CaMKII and GluR2 mRNA levels at the injection site. A zone of cortex surrounding the focus showed changes in alpha-CaMKII, GAD-67, and NR1 mRNA levels that were reciprocal to those in the focus. The results suggest that TT-induced seizure activity initially spread to a variable extent but was gradually restricted 2-3 d after seizure onset. The focus and the surround showing reciprocal changes in gene expression are thought to correspond to the electrophysiologically identified epileptic focus and inhibitory surround, respectively. The findings suggest that lateral inhibition between neighboring cortical regions will be affected and contribute to a neurochemical segregation of an epileptic focus from surrounding cortex.

Distribution of messenger RNAs for the orphan nuclear receptors Nurr1 and Nur77 (NGFI-B) in adult rat brain using in situ hybridization

Nurr1 and Nur77 (NGFI-B) are orphan nuclear receptors, belonging to the steroid/thyroid hormone receptor gene superfamily. They have conserved amino acid sequence in the zinc-finger DNA binding domains and similar COOH-terminal regions, but have no known ligands. However, different expression patterns during brain development and tissue distributions of these messenger RNAs imply that they might reflect a different transcriptional role in the brain. In this study, the regional and cellular expression of messenger RNAs encoding these two proteins in rat brain has been determined by in situ hybridization. Nurr1 messenger RNA is highly expressed in the piriform and entorhinal cortices, hippocampus, medial habenular and paraventricular thalamic nuclei. Moderate labeling was detected in layers II-V of most of the cerebral cortex, and in the dorsal lateral geniculate nucleus, substantia nigra (pars compacta and reticularis) and interpeduncular nucleus. No Nurr1 hybridization signal was seen in the rhombencephalon. In the cerebellum, Nurr1 messenger RNA is present in the internal granular cell layer and Purkinje cell layer. In contrast, Nur77 has a widespread distribution, with the highest level of expression in the cerebral cortex. Moderate hybridization signals were detected in the hippocampus, the lateral dorsal and posterior nuclei, reuniens thalamic nuclei, and paraventricular and supraoptic hypothalamic nuclei. In the rhombencephalon, higher signals were present in the medial and lateral vestibular, dorsal cochlear and facial, and raphe magnus nuclei. Nur77 signal was also detected in the nucleus of the spinal tract of the trigeminal nerve. In the cerebellum, Nur77 messenger RNA is highly expressed in the Purkinje cell layer and lateral deep nucleus of the cerebellum. Our results show that Nurr1 and Nur77 messenger RNAs have both overlapping and different distribution patterns within the brain, suggesting that they might regulate different sets of responsive genes.

Excitotoxic lesion of rat brain with quinolinic acid induces expression of p53 messenger RNA and protein and p53-inducible genes Bax and Gadd-45 in brain areas showing DNA fragmentation

Several recent studies have demonstrated that expression of the tumour-suppressor gene p53 increases within the nervous system after injury. In various cell lines wild-type-p53, induced by DNA damage, has been shown to function to halt cell-cycle progression and under certain circumstances to induce programmed-cell death or apoptosis. Since wild type-p53 can act as a transcription factor to regulate the expression of p53-responsive genes it is possible that either, or both, functions of p53 are mediated by down-stream effector genes. However wild-type-p53 only weakly activates transcription and it remains to be determined whether p53-responsive genes are expressed in lesioned brain. Here we report that excitotoxic lesion of rat brain with the N-methyl-D-aspartate receptor agonist, quinolinic acid, induces expression of p53 messenger RNA and protein in brain regions showing delayed DNA fragmentation and that expression of p53 messenger RNA precedes DNA damage detected by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labelling. In addition, using in situ hybridization and immunocytochemistry we demonstrate increased expression of the p53-responsive gene Gadd-45 (preceding p53 expression) and re-expression of the p53-responsive gene Bax (following p53 expression), in these same areas. Bax has been shown to promote neuronal death by interacting with Bcl-2 family members while Gadd-45 expression has been associated with suppression of the cell-cycle and DNA repair. These results suggest that p53 protein may function as an active transcription factor in lesioned brain perhaps initiating the re-expression of Bax in injured brain regions. However, since Gadd-45 precedes p53 expression it appears unlikely that p53 is involved in regulating the early expression of Gadd-45. Taken together however, these results suggest that p53, Bax and Gadd-45 may play important roles in the response (damage/recovery) of the brain following excitotoxic injury.

Cellular expression of the immediate early transcription factors Nurr1 and NGFI-B suggests a gene regulatory role in several brain regions including the nigrostriatal dopamine system

Nurr1 and NGFI-B are closely related orphan members of the steroid-thyroid hormone receptor family involved in immediate early responses to stimuli such as growth factors. In-situ hybridization in the developing and adult mouse and rat demonstrated Nurr1 mRNA in several regions during early central nervous system (CNS) development. Expression persisted through the pre- and postnatal periods and was also found in several areas in the adult CNS. Positive areas include the olfactory bulb, parts of the cortex, the hippocampal formation and substantia nigra where Nurr1 and tyrosine hydroxylase mRNAs were co-expressed. 6-Hydroxydopamine-induced degeneration of mesencephalic dopamine neurons led to a corresponding loss of Nurr1 mRNA, demonstrating a link between Nurr1 and dopaminergic neurons. NGFI-B mRNA was not found in the prenatal CNS but was highly expressed in the adult brain in many areas including the olfactory bulb, cortex, basal ganglia and hippocampus. The spatiotemporal distribution of Nurr1 and NGFI-B mRNAs suggests that these transcription factors are involved in the development and maturation of specific sets of CNS neurons. The experimental data imply that one of these functions may be to control gene regulatory events important for development and function of those neurons that degenerate in patients with Parkinson's disease.

Effects of phencyclidine on immediate early gene expression in the brain

The N-methyl-D-aspartate receptor antagonist phencyclidine (PCP) is a psychotomimetic drug which produces schizophrenia-like psychosis. In animal studies it is toxic to neurons in the posterior cingulate and retrosplenial cortex and to cerebellar Purkinje cells. To find clues about the mechanism and pathways of PCP action, we studied the effect of systemic PCP administration (10 and 50 mg/kg, intraperitoneal) on the expression of immediate-early genes (IEGs) (c-fos, c-jun, egr-2, egr-3, NGFI-A, NGFI-B, NGFI-C, and Nurr1) using in situ hybridization histochemistry. PCP, 50 mg/kg, produced a biphasic IEG induction: an early induction in the hippocampus, cerebral cortex, and cerebellar granule cell layer, and a delayed induction in the posterior cingulate cortex and cerebellar Purkinje cell layer. The early induction of all eight IEGs was observed 30 min after drug treatment in the cerebral cortex and in the hippocampus. c-fos, NGFI-A, and NGFI-B were also induced in thalamic nuclei, and c-fos was also induced in the cerebellar granule cell layer. In contrast, a delayed induction of c-fos, c-jun, NGFI-A, NGFI-B, NGFI-C, and Nurr1 in the posterior cingulate cortex was observed 2-6 hr after PCP, 50 mg/kg. egr-2 and egr-3 were not induced in the posterior cingulate cortex. c-fos induction in the cerebellar Purkinje cell layer peaked 2 hr after PCP, 50 mg/kg. In addition, PCP induced c-fos, egr-3, NGFI-A, NGFI-B, NGFI-C, and Nurr1 in the inferior olivary nucleus. PCP-induced IEG expression returned to baseline by 24 hr. A lower PCP dose, 10 mg/kg, induced lower levels of IEG expression, with similar anatomical and biphasic temporal pattern as with the higher PCP dose of 50 mg/kg. However, no IEG induction was observed in the hippocampus following 10 mg/kg PCP. These results demonstrate that PCP produces neural activation not only in the cingulate and retrosplenial cortex, but also in many other regions of forebrain and cerebellum. Moreover, prolonged IEG expression in the posterior cingulate cortex and cerebellar Purkinje cells, the sites of PCP toxicity, suggests that IEGs could mediate neurotoxic/neuroprotective effects in these brain regions.

Stimulus-dependent, reciprocal up- and downregulation of glutamic acid decarboxylase and Ca2+/calmodulin-dependent protein kinase II gene expression in rat cerebral cortex

Long-train tetanic stimulation of the cerebral cortex induces long-term changes in the excitability of cortical neurons, while short-train electrical stimulation does not. In the present study, we show that both forms of stimulation when applied to rat motor cortex for 4 h enhance c-fos expression, but only tetanic stimulation, when imposed upon short-train stimulation, modulates gene expression for 67-kDa glutamic acid decarboxylase (GAD) and alpha Ca2+/calmodulin-dependent protein kinase II (CaMKII alpha). Gene expression for beta Ca2+/calmodulin-dependent protein kinase II is not affected by either stimulation mode. GAD messenger RNA (mRNA) is increased from 1 h after the end of tetanization to the longest poststimulus survival time investigated (14 h). CaMKII alpha mRNA is decreased 1-3 h after the end of tetanization but thereafter returns to prestimulus levels. These results imply not only that mechanisms underlying neocortical plasticity are stimulus-dependent but also that they involve reciprocal changes in molecules regulating the balance of excitation and inhibition.

Global ischemia induces immediate-early genes encoding zinc finger transcription factors

Ischemia induces immediate-early genes (IEGs) in brain. Since prolonged expression of some IEGs may precede neuronal death, some researchers have suggested that these IEGs mediate neuronal death. We therefore examined the effect of 5 and 10 min of global ischemia on the expression of the IEGs NGFI-A, NGFI-B, NGFI-C, egr-2, egr-3, and Nurr1 in gerbil brain. All of the IEGs were induced after 30 min of reperfusion in the hippocampus. Most of them were induced in several other regions as well, including cortex, hypothalamus, thalamus, and amygdala. The acute IEG induction decreased in most brain areas by 2-6 h. However, at 24 h following 5 min of ischemia NGFI-A continued to be expressed in the CA1 region and dentate gyrus. In the dentate gyrus, NGFI-C continued to be expressed for 24 h and egr-3 for as long as 72 h. In other brain areas, all of the IEGs returned to control levels by 72 h except in CA1, where most messenger RNA (mRNA) levels were decreased; this decrease correlated with marked neuronal loss. The persistent expression of NGFI-A in CA1 neurons destined to die and the persistent expression of NGFI-A, NGFI-C, and egr-3 genes in dentate granule cell neurons that survive may indicate that some transcription factors modulate cell death whereas others support cell survival when expressed for prolonged periods. The protein products of several transcription factors, including c-fos, are known to downregulate their own expression. The persistent expression of NGFI-A in the CA1 neurons destined to die could therefore be due to ischemia-induced transcriptional activation caused by, e.g., increased intracellular calcium levels plus a lack of negative feedback caused by the blockade of the translation of NGFI-A mRNA into protein.