REST: a mammalian silencer protein that restricts sodium channel gene expression to neurons

The canonical Wnt pathway directly regulates NRSF/REST expression in chick spinal cord

Neural precursor cells actively proliferate in the ventricular zone to self-renew the stem cell population, and in parallel, maintain their undifferentiated state. This progenitor pool generates postmitotic cells that migrate to the mantle layer and differentiate into mature neurons. The growth of these stem cells is strictly controlled by the canonical Wnt signaling cascade, in part mediated by the direct regulation of Cyclin D1, a critical regulator of cell cycle progression. Here, we report that the canonical Wnt pathway directly controls the expression of NRSF/REST. The Wnt-activated beta-catenin/TCF complex up-regulates this gene through a conserved element found in its exon 1a, a critical result obtained by a novel in ovo transcriptional assay. Hence, our data show that the canonical Wnt signaling cascade directly regulates the NRSF/REST and Cyclin D1 genes, thereby controlling the progenitor cells. In addition, we show that our in ovo transcription assay is a powerful way to analyze gene regulation in a natural in vivo context.

REST/NRSF-interacting LIM domain protein, a putative nuclear translocation receptor

The transcriptional repressor REST/NRSF (RE-1 silencing transcription factor/neuron-restrictive silencer factor) and the transcriptional regulator REST4 share an N-terminal zinc finger domain structure involved in nuclear targeting. Using this domain as bait in a yeast two-hybrid screen, a novel protein that contains three LIM domains, putative nuclear localization sequences, protein kinase A phosphorylation sites, and a CAAX prenylation motif was isolated. This protein, which is localized around the nucleus, is involved in determining the nuclear localization of REST4 and REST/NRSF. We propose the name RILP, for REST/NRSF-interacting LIM domain protein, to label this novel protein. RILP appears to serve as a nuclear receptor for REST/NRSF, REST4, and possibly other transcription factors.

Interaction of the repressor element 1-silencing transcription factor (REST) with target genes

The repressor element 1-silencing transcription factor (REST) has been proposed to restrict expression of repressor element 1 (RE1) bearing genes to differentiated neurons by silencing their expression in non-neural tissue. Here, we have examined the interaction of REST with the M(4) muscarinic acetylcholine receptor gene. We show that REST binds to the RE1 of the M(4) gene in those cell lines and brain regions where the M(4) gene is expressed but not in those where the M(4) is not expressed. Furthermore, in cells that express M(4), the presence of REST represses but is insufficient to silence transcription of M(4). In non-neural cells REST is absent from the RE1 of the silent M(4) gene and perturbation of REST function fails to induce M(4) expression. We propose that REST acts to regulate expression levels of some RE1-bearing genes in neural cells, thereby playing an important role in defining neuronal activity.

Distinct RE-1 Silencing Transcription Factor-containing Complexes Interact with Different Target Genes

Establishment of neuronal identity requires co-ordinated expression of specific batteries of genes. These programs of gene expression are executed by activation of neuron-specific genes in neuronal cells and their repression in non-neuronal cells. Such co-ordinate regulation requires that individual activators and repressors regulate transcription from specific subsets of their potential target genes, yet we know little of the mechanisms that underlie this selective process. The RE-1 silencing transcription factor (REST) is a repressor that is proposed to silence transcription of numerous neuron-specific genes in non-neuronal cells via recruitment of two independent histone deacetylase (HDAC)-containing co-repressor complexes. However, in vivo, REST appears to be an obligate silencer for only a minority of RE-1-bearing genes. Here we examine the interaction of REST, Co-REST, Sin3A, HDAC1, and HDAC2 with two archetypical endogenous target genes, the M4 muscarinic receptor and the sodium type II channel (NaV1.2) genes. We find that these genes are present in distinct chromosomal domains. The NaV1.2 gene is actively transcribed but repressed by REST independently of histone deacetylation or DNA methylation and does not co-localize with epigenetic markers of silence, including dimethylation of H3K9 and HP1. In contrast, the M4 gene is maintained in a silent state independently of REST and co-localizes with dimethylated H3K9 and HP1alpha and HP1gamma, characteristic of silenced or senescent euchromatic DNA. This contrasts with the coordinate REST-dependent regulation of this locus reported previously. Taken together, we infer that distinct repressor complexes and mechanisms are operative at particular loci even in cell lines derived from a common embryological origin.

SREBP contributes to induction of collagen VI transcription by serum starvation

Collagen VI is a main extracellular matrix protein whose mutation is linked to myopathic diseases. In myoblasts and other cell types, collagen VI gene transcription peaks during cell-cycle exit that precedes differentiation, upon serum withdrawal or confluence. To get insight into this transcriptional regulation, we characterized a growth arrest responsive region (GARR) in the Col6a1 promoter responsible for this effect. In this work, we identify sterol regulatory element binding protein (SREBP) as a GARR binding protein and provide evidence that SREBP contributes to induction of Col6a1 transcription in serum free conditions. Furthermore, our data unveil a previously unexpected link between extracellular matrix production and LDL signaling.

Critical role of the transcriptional repressor neuron-restrictive silencer factor in the specific control of connexin36 in insulin-producing cell lines

Connexin36 (Cx36) is specifically expressed in neurons and in pancreatic beta-cells. Cx36 functions as a critical regulator of insulin secretion and content in beta-cells. In order to identify the molecular mechanisms that control the beta-cell expression of Cx36, we initiated the characterization of the human 5' regulatory region of the CX36 gene. A 2043-bp fragment of the human CX36 promoter was identified from a human BAC library and fused to a luciferase reporter gene. This promoter region was sufficient to confer specific expression to the reporter gene in insulin-secreting cell lines. Within this 5' regulatory region, a putative neuron-restrictive silencer element conserved between rodent and human species was recognized and binds the neuron-restrictive silencing factor (NRSF/REST). This factor is not expressed in insulin-secreting cells and neurons; it functions as a potent repressor through the recruitment of histone deacetylase to the promoter of neuronal genes. The NRSF-mediated repression of Cx36 in HeLa cells was abolished by trichostatin A, confirming the functional importance of histone deacetylase activity. Ectopic expression, by viral gene transfer, of NRSF/REST in different insulin-secreting beta-cell lines induced a marked reduction in Cx36 mRNA and protein content. Moreover, mutations in the Cx36 neuron-restrictive silencer element relieved the low transcriptional activity of the human CX36 promoter observed in HeLa cells and in INS-1 cells expressing NRSF/REST. The data showed that cx36 gene expression in insulin-producing beta-cell lines is strictly controlled by the transcriptional repressor NRSF/REST indicating that Cx36 participates to the neuronal phenotype of the pancreatic beta-cells.

Regulation of Pax4 paired homeodomain gene by neuron-restrictive silencer factor

An elucidation of the key regulatory factors in pancreas development is critical for understanding the pathogenesis of diabetes mellitus. This study examined whether a specific regulatory mechanism that exists in neuronal development also plays a role in the pancreas. In non-neuronal cells, neuron-restrictive silencer factor (NSRF) actively represses gene transcription via a sequence-specific DNA motif known as the neuron-restrictive silencer element (NRSE). This DNA motif has been identified in many genes that are specific markers for cells of neuronal and neuroendocrine lineage. We identified several genes involved in pancreas development that also harbor NRSE-like motifs, including pdx-1, Beta2/NeuroD, and pax4. The paired homeodomain transcription factor Pax4 is implicated in the differentiation of the insulin-producing beta-cell lineage because disruption of the pax4 gene results in a severe deficiency of beta-cells and the manifestation of diabetes mellitus in mice. The NRSE-like motif identified in the upstream pax4 promoter is highly conserved throughout evolution, forms a DNA-protein complex with NRSF, and confers NRSF-dependent transcriptional repression in the context of a surrogate gene promoter. This cis-activating NRSE element also confers NRSF-dependent modulation in the context of the native pax4 gene promoter. Together with earlier reports, these new findings suggest an important functional role for NRSF in the expression of the pax4 gene and infer a role for NRSF in pancreatic islet development.

Huntingtin interacts with REST/NRSF to modulate the transcription of NRSE-controlled neuronal genes

Huntingtin protein is mutated in Huntington disease. We previously reported that wild-type but not mutant huntingtin stimulates transcription of the gene encoding brain-derived neurotrophic factor (BDNF; ref. 2). Here we show that the neuron restrictive silencer element (NRSE) is the target of wild-type huntingtin activity on BDNF promoter II. Wild-type huntingtin inhibits the silencing activity of NRSE, increasing transcription of BDNF. We show that this effect occurs through cytoplasmic sequestering of repressor element-1 transcription factor/neuron restrictive silencer factor (REST/NRSF), the transcription factor that binds to NRSE. In contrast, aberrant accumulation of REST/NRSF in the nucleus is present in Huntington disease. We show that wild-type huntingtin coimmunoprecipitates with REST/NRSF and that less immunoprecipitated material is found in brain tissue with Huntington disease. We also report that wild-type huntingtin acts as a positive transcriptional regulator for other NRSE-containing genes involved in the maintenance of the neuronal phenotype. Consistently, loss of expression of NRSE-controlled neuronal genes is shown in cells, mice and human brain with Huntington disease. We conclude that wild-type huntingtin acts in the cytoplasm of neurons to regulate the availability of REST/NRSF to its nuclear NRSE-binding site and that this control is lost in the pathology of Huntington disease. These data identify a new mechanism by which mutation of huntingtin causes loss of transcription of neuronal genes.

Reduced expression of the neuron restrictive silencer factor permits transcription of glycine receptor alpha1 subunit in small-cell lung cancer cells

Small-cell lung cancer (SCLC) cells express various markers of neuronal differentiation associated with deficient activity of the neuron-restricted silencer factor (NRSF). Here, we characterize mechanisms by which NRSF target genes are upregulated in SCLC and their functional consequences for cell survival. Since the glycine receptor (GlyR) alpha1 subunit gene, GLRA1, contains a sequence motif for NRSF binding (NRSE) within its 5' UTR, it served as a cellular surrogate marker for NRSF activity. Expression of GLRA1 in nontransformed cells is largely restricted to cells in the spinal cord, retina and brain stem. In experiments described here, we detected GLRA1 transcripts in three out of four SCLC-derived cell lines and in three of five biopsy samples obtained from SCLCs. In contrast, no GLRA1 transcripts were found in 10 nonmalignant nor 15 non-small-cell lung cancer biopsies. Consistent with this observation, NRSF-mediated suppression of an expression construct harbouring the NRSE of the GLRA1 (GLRA1 NRSE) gene was impaired in three of four 'classic' SCLC cell lines, whereas exogenous overexpression of NRSF in NRSF-deficient SCLC cell lines reconstituted silencing of the reporter plasmid. The level of NRSF transcripts as well as the level of specifically bound NRSF to the NRSE correlated with the level of GLRA1 transcripts in SCLC cell lines. Splice variants encoding truncated NRSF proteins and expressed in some SCLC did not antagonize the repression of NRSE-containing genes. Most interestingly, reconstitution of NRSF expression induced apoptosis in SCLC cells, suggesting that inhibition of NRSF activity is a crucial step in the carcinogenesis of a subgroup of SCLC.

Structural and functional characterization of mouse glutamate decarboxylase 67 gene promoter

Neuronal expression of the mouse glutamate decarboxylase 67 (mGAD67) gene occurs exclusively in neurons that synthesize and release GABA (GABAergic neurons). This gene is also expressed in pancreatic islet cells and testicular spermatocytes. In order to elucidate the molecular mechanisms underlying the regulation of mGAD67 gene expression, we isolated and characterized the 5'-flanking region of this gene. Sequence analysis of a 10.2-kb DNA fragment of this gene containing a promoter region (8.4 kb) and noncoding exons 0A and 0B revealed the presence of numerous potential neuron-specific cis-regulatory elements. Functional analysis of the 5'-flanking region of exons 0A and 0B by transient transfection into cultured cells revealed that the region -98 to -52 close to exon 0A is important for the transcriptional activity of both exons 0A and 0B. In addition, we used transgenic mice to examine the expression pattern conferred by the 10.2 kb DNA fragment of the mGAD67 gene fused to the bacterial lacZ reporter gene. Transgene expression was observed in neurons of particular brain regions containing abundant GABAergic neurons such as the basal ganglia, in pancreatic islet cells and in testicular spermatocytes and spermatogonia. These results suggest that the 10.2 kb DNA fragment of the mGAD67 gene contains regulatory elements essential for its targeted expression in GABAergic neurons, islet cells and spermatocytes.

The role of the RE1 element in activation of the NR1 promoter during neuronal differentiation

To understand the genetic mechanism controlling the expression of the NMDA subtype of glutamate receptors during neuronal differentiation, we studied activation of the N-methyl-D-aspartate receptor subunit 1 (NR1) gene and the role of the repressor element-1 (RE1) element in NR1 promoter activation. Following neuronal differentiation of P19 embryonic carcinoma cells, the NR1 transcription rate and mRNA level were significantly increased, while the nuclear level of the repressor RE1 silencing transcription factor (REST)/neuron-restriction silencer factor (NRSF) was reduced. Nuclear REST/NRSF from undifferentiated cells formed a large complex with the NR1 RE1 element. While this complex was significantly reduced after the differentiation, REST/NRSF from differentiated cells formed a new, faster migrating complex. In transient transfections, deletion of the RE1 element increased activity of the 5.4-kb NR1 promoter sixfold in undifferentiated cells, but only induced approximately 1.4-fold increase in differentiated cells. Forced expression of REST/NRSF in differentiated cells suppressed the promoter, while forced expression of a dominant-negative REST/NRSF induced promoter activity as well as the mRNA of the NR1 gene in undifferentiated cells. In stable transfectants, the wild-type promoter showed a robust increase in activity following differentiation in a pattern similar to the NR1 mRNA increase. Conversely, the promoter lacking the RE1 element showed only a moderate increase. Our data suggest that the NR1 gene up-regulation during neuronal differentiation is controlled by its promoter activation, which is largely determined by the interaction between the RE1 element and the repressor REST/NRSF.

Ischemic insults derepress the gene silencer REST in neurons destined to die

A subset of genes implicated in genetic and acquired neurological disorders encode proteins essential to neural patterning and neurogenesis. The gene silencing transcription factor neuronal repressor element-1 silencing transcription factor (REST)/neuron-restrictive silencer factor (NRSF) plays a critical role in elaboration of the neuronal phenotype. In neural progenitor and non-neural cells, REST acts by repression of a subset of neural genes important to synaptic plasticity and synaptic remodeling, including the AMPA receptor (AMPAR) subunit GluR2. Here we show that global ischemia triggers REST mRNA and protein expression. REST suppresses GluR2 promoter activity and gene expression in neurons destined to die. Because the GluR2 subunit governs AMPAR Ca2+ permeability, these changes are expected to have profound effects on neuronal survival. In keeping with this concept, acute knockdown of the REST gene by antisense administration prevents GluR2 suppression and rescues post-ischemic neurons from ischemia-induced cell death in an in vitro model. To our knowledge, our study represents the first example of ischemia-induced induction of a master transcriptional regulator gene and its protein expression critical to neural differentiation and patterning in adult neurons. Derepression of REST is likely to be an important mechanism of insult-induced neuronal death.

Expression of stathmin family genes in human tissues: non-neural-restricted expression for SCLIP

The stathmin family consists of phosphoproteins highly conserved in vertebrates and thought to be implicated in the development and functional regulation of various organs, most notably the nervous system. This family includes stathmin, SCG10, SCLIP, and RB3, phosphoproteins that are related by structural and functional homologies. They all sequester tubulin and interfere with microtubule dynamics, a property due to their shared stathmin-like domain. Little is known about the expression of the stathmin gene family in humans. Herein, we describe for the first time, for a collection of human tissues, the expression of each member of this family, using real-time quantitative RT-PCR. We found that stathmin is ubiquitously expressed, whereas SCG10 and RB3 are neural enriched, expression patterns similar to those reported for other mammals. Surprisingly, SCLIP, whose expression is thought to be neural-specific, exhibits a broader tissue distribution. Analyses of the SCLIP gene (approved symbol STMN3) show that it contains several NRSE-like elements that display low or no affinity for the cognate binding protein NRSF. The substantial expression of SCLIP in most tissues points out a novel function for this protein outside the nervous system and raises the possibility that its coexpression with stathmin could provide some degree of functional redundancy.

Identification of repressor element 1 in cytochrome P450 genes and their negative regulation by RE1 silencing transcription factor/neuron-restrictive silencer factor

RE1 silencing transcription factor/neuron-restrictive silencing factor (REST/NRSF) mediates transcriptional repression in many neuron-specific genes by interaction with the repressor element 1/neuron-restrictive silencing element (RE1/NRSE). This element has been identified at least in 20 neuron specific genes. REST/NRSF is highly expressed in non-neuronal tissues, where it is thought to repress gene transcription. We performed a BLAST search to look for the presence of RE1/NRSE elements in the rat cytochrome P450 genes. We identified the presence of RE1/NRSE element in the cytochrome P450 genes CYP1A1, 2A2, 2E1 and 3A2. Electrophoretic mobility shift assay and supershift assays were carried out to prove functionality of these sites and detect the interaction of REST/NRSF with this sequence. Cotransfection studies in PC12 cells with a plasmid containing the RE1 element of the CYP genes, cloned upstream of the minimal type II sodium channel promoter, in the presence of REST/NRSF, showed a marked expression inhibition of the CAT reporter gene. These data suggest that the RE1 elements that exist in these four CYP genes might be a target for the REST/NRSF transcription factor and such an interaction might play a role in the negative regulation of these genes.

RE-1 silencing transcription factor (REST) regulates human synaptophysin gene transcription through an intronic sequence-specific DNA-binding site

Synaptophysin, one of the major proteins on synaptic vesicles, is ubiquitously expressed throughout the brain. Synaptophysin and synapsin I, another synaptic vesicle protein, are also expressed by retinoic acid-induced neuronally differentiated P19 teratocarcinoma cells. Here, we show that inhibition of histone deacetylase activity in P19 cells is sufficient to activate transcription of the synaptophysin and synapsin I genes, indicating that neuronal differentiation and impairment of histone deacetylases results in a similar gene expression pattern. The transcription factor REST, a repressor of neuronal genes in non-neuronal tissues, has been shown to function via recruitment of histone deacetylases to the transcription unit, indicating that modulation of the chromatin structure via histone deacetylation is of major importance for REST function and neuron-specific gene transcription. Furthermore, REST has been shown to be the major regulator of neuronal expression of synapsin I. Here, we have identified a functional binding site for REST in the first intron of the human synaptophysin gene indicating that REST blocks human synaptophysin gene transcription through an intronic neuron-specific silencer element. The synaptophysin promoter is, however, devoid of neuron-specific genetic elements and directs transcription in both neuronal and non-neuronal cells. Using a dominant-negative approach we have identified the transcription factor Sp1 as one of the regulators responsible for constitutive transcription of the human synaptophysin gene.

Malignant rhabdoid tumor shows a unique neural differentiation as distinct from neuroblastoma

Malignant rhabdoid tumors (MRT) show a multiphenotypic diversity, including a neural phenotype. To elucidate the difference in neural characteristics between MRT and neuroblastoma, we examined the expression of synapsin I, neuron-restrictive silencer factor (NRSF), neurofilament medium-size (NF-M) and chromogranin A (CGA) in five MRT cell lines (TM87-16, STM91-01, TTC549, TTC642 and YAM-RTK1) and five neuroblastoma cell lines under differentiation-induction with 12-O-tetradecanoylphorbol-13-acetate (TPA). Our results showed TM87-16 and TTC642 cells, expressed synapsin I and NF-M before TPA induction, had a neural phenotype. After differentiation-induction, only TM87-16 cells expressed CGA. Among all neuroblastoma cells, expression of NF-M and CGA was stable at a high level throughout TPA-induced differentiation. In TM87-16 and TTC642 MRT cells, synapsin I mRNA promptly increased after TPA differentiation, with the peak level at 6 h, and thereafter, synapsin I mRNA rapidly decreased in a time-dependent manner. The decreased expression of synapsin I correlated with an increased expression of NRSF during differentiation-induction. In contrast, in some neuroblastoma cells, a significant up-regulation of synapsin I was observed concurrently with a down-regulation of NRSF. The inverse relationship between NRSF and synapsin I expression in TM87-16 and TTC642 MRT cells was opposite to that of neuroblastoma cells. Our results showed that the neural characteristics of these MRT cells are fairly distinct from those of neuroblastoma cells. These MRT cells appeared to have only limited capability for neural differentiation, and were still in an extremely early stage of neural differentiation.

Transcription factor REST dependent proteins are comparable between Down Syndrome and control brains: challenging a hypothesis

Impairment of the RE-1-silencing transcription factor (REST) and REST-dependent genes in Down Syndrome (DS) neuronal progenitor cells and neurospheres has been published recently. As dysregulation of this system has been shown at the RNA level and considering the long and unpredictable way from RNA to proteins, and as it is the proteins that do the function in brain, we decided to test this hypothesis at the protein level. Cortex of brains of patients with Down Syndrome at the early second trimester were used. REST-dependent structures as synapsin I, brain derived neurotrophic factor BDNF and neuronal growth-associated protein SCG10 were determined at the protein level using immunoblotting. Proteins were comparably expressed in fetal Down syndrome and control brains. Even when normalized versus housekeeping genes (glyceraldehyde-6-phosphate-dehydrogenease) and a marker for neuronal density (neuron-specific enolase) DS results were resembling controls. Therefore, we cannot confirm the REST-hypothesis by our studies in the 18/19th week of gestation at the protein level in brain and taking into account that the hypothesis was based upon studies in progenitor cells.

Histone deacetylase activity is necessary for oligodendrocyte lineage progression

Gene expression can be modulated by chromatin changes induced by histone acetylation and deacetylation. Acetylation of histone lysine residues by acetyltransferases is associated with transcriptionally active chromatin, whereas the removal of acetyl groups by histone deacetylases (HDACs) correlates with repressed chromatin. Recent evidence has shown that histone deacetylation is responsible for restricting neuronal gene expression, whereas histone acetylation is necessary for astrocytic differentiation We now asked whether histone acetylation or deacetylation was necessary for oligodendrocyte differentiation. Neonatal rat cortical progenitors were kept proliferating and undifferentiated in the presence of mitogens and induced to stop proliferating and differentiate into oligodendrocytes by mitogen removal. Histone deacetylation was observed during the temporal window between exit from the cell cycle and onset of differentiation, which was characterized by acquisition of branched morphology and myelin gene expression. Blocking HDAC activity during this critical window using the inhibitor trichostatin A (TSA) prevented the progression of progenitors into mature oligodendrocytes. TSA-treated progenitors were able to exit from the cell cycle but did not progress to oligodendrocytes. Their development was arrested at the progenitor stage, characterized by simple morphology and lack of myelin gene expression. The effect of TSA on progenitor differentiation was lineage specific, because TSA did not affect the ability of these cells to differentiate into type II astrocytes when cultured in the presence of serum. From these data, we conclude that histone deacetylation is a necessary component of the oligodendrocyte differentiation program.

Analysis of transcriptional regulatory sequences of the N-methyl-D-aspartate receptor 2A subunit gene in cultured cortical neurons and transgenic mice

The postnatal appearance and up-regulation of the NR2A subunit of the N-methyl-d-aspartate receptor contributes to the functional heterogeneity of the receptor during development. To elucidate the molecular mechanisms that regulate the neural and developmental specific expression of NR2A, an upstream approximately 9-kb region of the gene harboring the promoter was isolated and characterized in transgenic mice and transfected cortical neurons. Transgenic mouse lines generated with luciferase reporter constructs driven by either 9 or 1 kb of upstream sequence selectively transcribe the transgene in brain, as compared with other non-neural tissues. Reporter luciferase levels in dissociated cultures made from these mice are over 100-fold greater in neuronal/glial co-cultures than in pure glial cultures. Analysis of NR2A 5'-nested deletions in transfected cultures of cortical neurons and glia indicate that while sequences residing upstream of -1079 bp augment NR2A neuronal expression, sequences between -486 and -447 bp are sufficient to maintain neuronal preference. An RE1/NRSE element is not necessary for NR2A neuron specificity. Furthermore, comparison of the 5'-deletion constructs in cortical neurons grown for 5, 8, 11, or 14 days in vitro indicate that sequences between -1253 and -1180 bp are necessary for maturational up-regulation of NR2A. Thus, different cis-acting sequences control the regional and temporal expression of NR2A, implicating distinct regulatory pathways.

Corepressor-dependent silencing of chromosomal regions encoding neuronal genes

The molecular mechanisms by which central nervous system-specific genes are expressed only in the nervous system and repressed in other tissues remain a central issue in developmental and regulatory biology. Here, we report that the zinc-finger gene-specific repressor element RE-1 silencing transcription factor/neuronal restricted silencing factor (REST/NRSF) can mediate extraneuronal restriction by imposing either active repression via histone deacetylase recruitment or long-term gene silencing using a distinct functional complex. Silencing of neuronal-specific genes requires the recruitment of an associated corepressor, CoREST, that serves as a functional molecular beacon for the recruitment of molecular machinery that imposes silencing across a chromosomal interval, including transcriptional units that do not themselves contain REST/NRSF response elements.

Effect of the ubiquitous transcription factors, SP1 and MAZ, on NMDA receptor subunit type 1 (NR1) expression during neuronal differentiation

The silencer factor NRSF/REST has been reported to restrict expression to neurons of a variety of genes, including that encoding NMDA receptor subunit type 1 (NR1), by suppressing transcription in nonneuronal cells. However, we recently reported that in addition to the absence of NRSF/REST-binding activity, another neuron-specific mechanism is necessary for high level expression of the NR1 gene in neurons. In this study, we explored the mechanism of induction of NR1 promoter activity during neuronal differentiation of the P19 cell line. We identified a 27 base pair GC-rich region in the promoter as an important element responsible for induction of the NR1 gene after neuronal differentiation. We found that the ubiquitous transcription factors SP1 and MAZ bind to this GC-rich region. Surprisingly, the binding activities of SP1 and MAZ are not remarkably changed after neuronal differentiation. Mutations in the SP1 and MAZ sites impair binding of SP1 and MAZ proteins and also decrease NR1 promoter activity. These findings suggest that SP1 and MAZ mediate enhancement of NR1 promoter activity during neuronal differentiation despite the fact that their binding activity does not change.

NRSF/REST confers transcriptional repression of the GPR10 gene via a putative NRSE/RE-1 located in the 5' promoter region

The G protein-coupled receptor GPR10 is highly localized to areas of the brain. In an effort to reveal transcriptional determinants of this tissue specificity, we recognized a putative NRSE (neuron-restrictive silencer element) located in the 5' promoter region of the gene. The cognate NRSE binding protein NRSF (neuron-restrictive silencer factor) restricts gene expression to mature neurons and endocrine cells by repressing their transcription in non-neuronal/-endocrine cells. In cell lines where NRSF-mediated gene repression has been functionally established, the activity of the GPR10 promoter was repressed in a manner consistent with NRSE-dependent regulation. A specific point mutation to confer non-functionality of the NRSE revealed a 10-fold de-repression of reporter gene expression. In contrast, in the GPR10-expressing cell line GH3, mRNA transcripts of NRSF were undetectable and suppression of promoter activity was not observed. However, transfection of a rat NRSF expression vector resulted in significant repression of transcription, which was reversed by mutation of the NRSE. In conclusion, we demonstrate that the GPR10 gene is specifically regulated by NRSF, and suggest this to be a contributory factor in the tissue-specific distribution of GPR10 in vivo.

REST repression of neuronal genes requires components of the hSWI.SNF complex

A function of the transcription factor REST is to block the expression of neuronal phenotypic traits in non-neuronal cells. Previous studies have shown that REST-mediated repression requires histone deacetylase activity and that recruitment of deacetylases is mediated by two co-repressors, Sin3A and CoREST. In this study, we show that a repressor domain in CoREST interacts with BRG1-associated factor (BAF) 57, a component of the hSWI.SNF complex. In vivo, BAF57 occupies the neuronal sodium channel gene (Nav1.2) promoter, and targeting to this gene requires REST. In addition to BAF57, the ATPase BRG1 and BAF170, other members of the hSWI.SNF complex, are also present in the REST.CoREST repressor complex. Microinjection of specific antibodies against BRG1, BAF57, or BAF170 into Rat1 fibroblasts relieves repression of RE1 reporter genes. Together, our data suggest that ATP-dependent chromatin remodeling, as well as histone deacetylation, is needed for REST-mediated repression.

Repressor element-1 silencing transcription/neuron-restrictive silencer factor is required for neural sodium channel expression during development of Xenopus

The ability of neurons to fire rapid action potential relies on the expression of voltage-gated sodium channels; the onset of the transcription of genes that encode these channels occurs during early neuronal development. The factors that direct and regulate the specific expression of ion channels are not well understood. Repressor element-1 silencing transcription/neuron-restrictive silencer factor (REST/NRSF) is a transcriptional regulator characterized as a repressor of the expression of NaV1.2, the gene encoding the voltage-gated sodium channel most abundantly expressed in the CNS, as well as of the expression of numerous other neuronal genes. In mammals, REST/NRSF is expressed mostly in non-neural cell types and immature neurons, and it is downregulated on neural maturation. To understand the mechanisms that govern sodium channel gene transcription and to explore the role of REST/NRSF in vivo, we inhibited REST/NRSF action in developing Xenopus laevis embryos by means of a dominant negative protein or antisense oligonucleotides. Contrary to what was expected, these maneuvers result in the decrease of the expression of the NaV1.2 gene, as well as of other neuronal genes in the primary spinal neurons and cranial ganglia, without overt perturbation of neurogenesis. These results, together with the demonstration of robust REST/NRSF expression in primary spinal neurons, suggest that REST/NRSF is required for the acquisition of the differentiated functional neuronal phenotype during early development. Furthermore, they suggest that REST/NRSF may be used to activate or repress transcription of neuronal genes in distinct cellular and developmental contexts.

Neuron restrictive silencer factor as a modulator of neuropeptide gene expression

We hypothesize that the transcription factor neuron restrictive silencer factor (NRSF) is an important determinant of the expression of the preprotachykinin (PPTA) gene (encoding substance P and Neurokinin A) and arginine vasopressin (AVP) both in neuronal and nonneuronal cells. NRSF, a zinc finger repressor protein, binds the NRSE motif found in many neuronal specific genes at a variety of promoter locations. However, it is found in a similar location at the major transcriptional start site, within both PPTA and AVP peptide promoters. We have correlated modulation of NRSF activity with expression of AVP and PPTA in a variety of cell types, indicating the general mechanism by which this protein may regulate expression. Specifically, they are as follows:(1). Expression of NRSF dramatically represses PPTA promoter activity in reporter gene constructs in primary cultures of DRG neurons.(2). The PPTA promoter activity is regulated differentially in osteoarthritic compared to normal chondrocytes. This regulation correlates with the region containing the NRSE site.(3). We have correlated a splice variant of NRSF with the establishment and progression of small cell lung carcinoma (SCLC) and demonstrated that NRSF variants can directly affect the activity of the AVP promoter in reporter gene constructs. If the deregulated expression of peptides in these diseases point to the mechanism determining the pathology, then perhaps targeting protocols that correct this deregulation may also reverse the specific disease phenotypes. Our data would indicate that modulation of NRSF activity would be a target for such intervention.

REST mRNA expression in normal and regenerating avian auditory epithelium

Hair cells (HCs) and supporting cells (SCs) in the auditory epithelium initially arise from a sheet of undifferentiated cells. Although much has been learned about the initial steps leading to the fate determination of HCs and SCs, respectively, little is known about what molecular events 'finalize' cell fate determination. We investigated the role of repressor element-1 (RE-1) silencing transcription factor (REST), whose inactivation is known to be a requirement for a cell to assume a neuronal identity. Here we show by in situ hybridization (ISH) that SCs express REST messenger RNA (mRNA) but sensory HCs lack detectable expression. Using a more sensitive reverse transcription-polymerase chain reaction assay, however, we detected the presence of a neuron-specific splice variant in the epithelium, suggesting that HCs express REST mRNA at levels too low to be detectable by ISH. In regenerating auditory epithelium, we found that REST mRNA was expressed and upregulated in all remaining cells in the damaged region of the epithelium, consistent with its expression pattern during development prior to neurogenesis. Surprisingly, REST mRNA was also upregulated in SCs in the apical, undamaged region of the epithelium, and readily detectable by ISH in the HCs in this region. This finding suggests that the grossly undamaged region of the epithelium is in fact biochemically altered towards a 'less developed' state. Our results indicate that REST inactivation is an important step in finalizing HC fate in the chick inner ear.

A transcriptional response to Wnt protein in human embryonic carcinoma cells

BACKGROUND

Wnt signaling is implicated in many developmental decisions, including stem cell control, as well as in cancer. There are relatively few target genes known of the Wnt pathway.

RESULTS

We have identified target genes of Wnt signaling using microarray technology and human embryonic carcinoma cells stimulated with active Wnt protein. The ~50 genes upregulated early after Wnt addition include the previously known Wnt targets Cyclin D1, MYC, ID2 and betaTRCP. The newly identified targets, which include MSX1, MSX2, Nucleophosmin, Follistatin, TLE/Groucho, Ubc4/5E2, CBP/P300, Frizzled and REST/NRSF, have important implications for understanding the roles of Wnts in development and cancer. The protein synthesis inhibitor cycloheximide blocks induction by Wnt, consistent with a requirement for newly synthesized beta-catenin protein prior to target gene activation. The promoters of nearly all the target genes we identified have putative TCF binding sites, and we show that the TCF binding site is required for induction of Follistatin. Several of the target genes have a cooperative response to a combination of Wnt and BMP.

CONCLUSIONS

Wnt signaling activates genes that promote stem cell fate and inhibit cellular differentiation and regulates a remarkable number of genes involved in its own signaling system.

A core-BRAF35 complex containing histone deacetylase mediates repression of neuronal-specific genes

BRAF35, a structural DNA-binding protein, initially was identified as a component of a large BRCA2-containing complex. Biochemical analysis revealed the presence of a smaller core-BRAF35 complex devoid of BRCA2. Here we report the isolation of a six-subunit core-BRAF35 complex with the capacity to deacetylate histones, termed the BRAF-histone deacetylase complex (BHC), from human cells. BHC contains polypeptides reminiscent of the chromatin-remodeling complexes SWI/SNF and NuRD (nucleosome remodeling and deacetylating). Similar to NuRD, BHC contains an Mi2-like subunit, BHC80, and a PHD zinc-finger subunit as well as histone deacetylases 1/2 and an MTA-like subunit, the transcriptional corepressor CoREST. We show that BHC mediates repression of neuron-specific genes through the cis-regulatory element known as the repressor element 1 or neural restrictive silencer (RE1/NRS). Chromatin-immunoprecipitation experiments demonstrate the recruitment of BHC by the neuronal repressor REST. Expression of BRAF35 containing a single point mutation in the HMG domain of the protein abrogated REST-mediated transcriptional repression. These results demonstrate a role for core-BRAF35-containing complex in the regulation of neuron-specific genes through modulation of the chromatin structure.

Cardiac ion channels

The normal electrophysiologic behavior of the heart is determined by ordered propagation of excitatory stimuli that result in rapid depolarization and slow repolarization, thereby generating action potentials in individual myocytes. Abnormalities of impulse generation, propagation, or the duration and configuration of individual cardiac action potentials form the basis of disorders of cardiac rhythm, a continuing major public health problem for which available drugs are incompletetly effective and often dangerous. The integrated activity of specific ionic currents generates action potentials, and the genes whose expression results in the molecular components underlying individual ion currents in heart have been cloned. This review discusses these new tools and how their application to the problem of arrhythmias is generating new mechanistic insights to identify patients at risk for this condition and developing improved antiarrhythmic therapies.

Adenoviral-mediated, high-level, cell-specific transgene expression: a SYN1-WPRE cassette mediates increased transgene expression with no loss of neuron specificity

Viral vectors are excellent tools for studying gene function in the brain, although a limitation has been the ability to effectively target transgene expression to specific neuronal populations. This generally cannot be overcome by the use of neuron-specific promoters, as most are too large to be used with current viral vectors and expression from these promoters is often relatively weak. We therefore developed a composite expression cassette, comprising 495 bp of the weak human SYN1 (synapsin-1) promoter and 800 bp of the woodchuck hepatitis virus posttranscriptional regulatory element (WPRE). Studies in hippocampal cultures, organotypic cultures, and in vivo showed that the 3' addition of the WPRE to the SYN1 element greatly increased enhanced green fluorescent protein expression levels with no loss of neuronal specificity. In vivo studies also showed that transgene expression was enhanced with no loss of neuronal specificity in dentate-gyrus neurons for at least 6 weeks following transfection. Therefore, unlike most powerful promoter systems, which mediate expression in neurons and glia, this SYN1-WPRE cassette can target powerful long-term transgene expression to central nervous system neurons when delivered at relatively low titers of adenovirus. Its use should therefore facilitate both gene therapy studies and investigations of neuronal gene function.

Regulation of synaptotagmin gene expression during ascidian embryogenesis

The ascidian embryo, a model for the primitive mode of chordate development, rapidly forms a dorsal nervous system which consists of a small number of neurons. Here, we have characterized the transcriptional regulation of an ascidian synaptotagmin (syt) gene to explore the molecular mechanisms underlying development of synaptic transmission. In situ hybridization showed that syt is expressed in all neurons described in previous studies and transiently in the embryonic epidermis. Neuronal expression of syt requires induction from the vegetal side of the embryo, whereas epidermal expression occurs autonomously in isolated ectodermal blastomeres. Introduction of green fluorescent protein reporter gene constructs into the ascidian embryos indicates that a genomic fragment of the 3.4-kb 5' upstream region contains promoter elements of syt gene. Deletion analysis of the promoter suggests that syt expression in neurons and in the embryonic epidermis depends on distinct cis-regulatory regions.

RE-1 silencing transcription factor-4 (REST4) is neither a transcriptional repressor nor a de-repressor

The zinc finger protein RE-1 silencing transcription factor (REST) is a transcriptional repressor that represses neuronal genes in non-neuronal tissues. A neuronal splice form of REST, termed REST4, has been described in the rat. It encompasses the N-terminus of REST, including the N-terminal repressor domain and five of the eight zinc fingers of the DNA-binding domain. The biological function of REST4 is controversial. Transcriptional repression as well as transcriptional de-repression activity has been attributed to the REST4 protein of rat. Here, we have expressed a 'humanized' version of REST4 (hREST4) to facilitate a comparison of the biological functions of hREST4 and REST. The biological activity the human REST protein has been extensively studied in the past. Additionally, hREST4 has a high degree of homology with the REST4 protein of rat. An immunofluorescence analysis showed that hREST4 is expressed in the nucleus, indicating that the protein may have a potential impact on gene regulation. We analyzed the biological function of hREST4 in NS20Y neuroblastoma cells using human synapsin I promoter/reporter gene constructs. The human synapsin I gene is negatively regulated by REST. The results show that hREST4, in contrast to the full-length human REST protein, does not impair human synapsin I promoter activity. Moreover, co-transfection experiments with expression vectors encoding REST and hREST4 did not reveal any evidence that REST4 blocks the transcriptional repression activity of REST.

Effect of age on the gene expression of neural-restrictive silencing factor NRSF/REST

Aging affects a wide range of gene expression changes in the nervous system. Such effects could be attributed to random changes in the environment with age around each gene, but also could be caused by selective changes in a limited set of key regulatory transcription factors and/or chromatin remodeling components. To approach the question of whether neural-restrictive silencer factor NRSF, a key determinant of the neuron-specific gene expression, is involved in these changes, we examined the levels of NRSF in the rat brain and dosal root ganglia during aging by semi-quantitative reverse transcriptase-mediated polymerase chain reaction (PCR) (RT-PCR). Complementary expression profiles of transcripts of NRSF and SCG10 in the mature brain were shown by in situ hybridization. Neither the mRNA levels of NRSF nor a splicing variant NRnV were changed, at least in rats up to 26 months old. The gene expression level of SCG10, one of the NRSF targets, was also unaffected by age. The stable expression of SCG10 transcripts in aging was confirmed by in situ hybridization. The NRS-binding ability of NRSF was also unchanged significantly in the nuclear extracts of aged rat brain. These results suggest that the genetic machinery associated with the NRS-NRSF system is well maintained during aging.

REST4-mediated modulation of REST/NRSF-silencing function during BDNF gene promoter activation

Neural-restrictive silencer element (NRSE)/repressor element-1 (RE1) regulates neuron-specific gene expression by binding the transcriptional factor REST/NRSF which functions as a silencer in nonneuronal cells. In neuronal cells, a truncated, neuronal-specific REST/NRSF isoform, REST4, has been found but little is known about its function. To address this, we investigated the effect of REST/NRSF and REST4 on the activity-dependent activation of BDNF gene promoter I (BDNFp-I) using cultured rat cortical neurons. REST/NRSF markedly repressed the transcriptional activation of BDNFp-I, whereas the effect of REST4 was weak, depending upon the NRSE/RE1 sequence. In addition, REST4 enhanced the basal transcriptional activity of BDNFp-I. Coexpression of REST4 with REST/NRSF competitively inhibited the silencing effect of REST/NRSF on the activation of BDNFp-I. Although REST4 itself has a weak repressive effect on activation of the BDNF gene via NRSE/RE1, it can compete the silencing effect of REST/NRSF, suggesting a primary role for REST4 in preventing the neuron-specific gene from being inactivated by REST/NRSF and allowing gene activation in response to a variety of neuronal stimuli.

The Xiro-repressed gene CoREST is expressed in Xenopus neural territories

The iroquois (iro) genes encode evolutionary conserved homeoproteins that participate in many developmental processes [reviewed in Development 128 (2001) 2847]. In Xenopus, the Iro protein Xiro1 is a repressor, required during gastrulation for neural plate formation, that downregulates Bmp4. During neurulation, Xiro1 participates in the pattering of the neuroectoderm. In this work, we report the cloning and pattern of expression of XCoREST, another gene repressed by Xiro1. During Xenopus development, XCoREST is expressed in territories in which neurogenesis takes place.

Characterization of the rat GRIK5 kainate receptor subunit gene promoter and its intragenic regions involved in neural cell specificity

The GRIK5 (glutamate receptor ionotropic kainate-5) gene encodes the kainate-preferring glutamate receptor subunit KA2. The GRIK5 promoter is TATA-less and GC-rich, with multiple consensus initiator sequences. Transgenic mouse lines carrying 4 kilobases of the GRIK5 5'-flanking sequence showed lacZ reporter expression predominantly in the nervous system. Reporter assays in central glial (CG-4) and non-neural cells indicated that a 1200-base pair (bp) 5'-flanking region could sustain neural cell-specific promoter activity. Transcriptional activity was associated with the formation of a transcription factor IID-containing complex on an initiator sequence located 1100 bp upstream of the first intron. In transfection studies, deletion of exonic sequences downstream of the promoter resulted in reporter gene activity that was no longer neural cell-specific. When placed downstream of the GRIK5 promoter, a 77-bp sequence from the deleted fragment completely silenced reporter expression in NIH3T3 fibroblasts while attenuating activity in CG-4 cells. Analysis of the 77-bp sequence revealed a functional SP1-binding site and a sequence resembling a neuron-restrictive silencer element. The latter sequence, however, did not display cell-specific binding of REST-like proteins. Our studies thus provide evidence for intragenic control of GRIK5 promoter activity and suggest that elements contributing to tissue-specific expression are contained within the first exon.

The transcriptional repressor REST determines the cell-specific expression of the human MAPK8IP1 gene encoding IB1 (JIP-1)

Islet-brain 1 (IB1) is the human and rat homologue of JIP-1, a scaffold protein interacting with the c-Jun amino-terminal kinase (JNK). IB1 expression is mostly restricted to the endocrine pancreas and to the central nervous system. Herein, we explored the transcriptional mechanism responsible for this preferential islet and neuronal expression of IB1. A 731-bp fragment of the 5' regulatory region of the human MAPK8IP1 gene was isolated from a human BAC library and cloned upstream of a luciferase reporter gene. This construct drove high transcriptional activity in both insulin-secreting and neuron-like cells but not in unrelated cell lines. Sequence analysis of this promoter region revealed the presence of a neuron-restrictive silencer element (NRSE) known to bind repressor zinc finger protein REST. This factor is not expressed in insulin-secreting and neuron-like cells. By mobility shift assay, we confirmed that REST binds to the NRSE present in the IB1 promoter. Once transiently transfected in beta-cell lines, the expression vector encoding REST repressed IB1 transcriptional activity. The introduction of a mutated NRSE in the 5' regulating region of the IB1 gene abolished the repression activity driven by REST in insulin-secreting beta cells and relieved the low transcriptional activity of IB1 observed in unrelated cells. Moreover, transfection in non-beta and nonneuronal cell lines of an expression vector encoding REST lacking its transcriptional repression domain relieved IB1 promoter activity. Last, the REST-mediated repression of IB1 could be abolished by trichostatin A, indicating that deacetylase activity is required to allow REST repression. Taken together, these data establish a critical role for REST in the control of the tissue-specific expression of the human IB1 gene.

Directed differentiation of embryonic stem cells: genetic and epigenetic methods

Embryonic stem cells are derived from the inner cell mass of the pre-implantation blastocyst, and can both self-renew and differentiate into all the cells and tissues of the body. The embryonic stem cell is an unsurpassed starting material to begin to understand a critical, largely inaccessible, period of development, as well as an important source of cells for transplantation and gene therapy. Despite their potential, attempts to obtain specific cell types from embryonic stem cells have been only partially successful because many of the growth factor combinations and developmental control genes involved in cell type restricted differentiation are unknown. This article summarizes some of the recent advances in promoting lineage restricted differentiation of embryonic stem cells, focusing on growth factor manipulation, or genetically altering embryonic stem cells to produce a desired phenotype. The two approaches epitomize current scientific concerns regarding the therapeutic use of these cells; genetic alterations will produce more pure cells with the risk of increasing the likelihood of malignant transformation; epigenetic methods for the manipulation of stem cell phenotype are often incomplete and remaining pluripotent cells are likely to form teratomas. As more is known about lineage specification during development, it will be possible to more precisely control cell type specification.

Alternative RNA splicing in the nervous system

Tissue-specific alternative splicing profoundly effects animal physiology, development and disease, and this is nowhere more evident than in the nervous system. Alternative splicing is a versatile form of genetic control whereby a common pre-mRNA is processed into multiple mRNA isoforms differing in their precise combination of exon sequences. In the nervous system, thousands of alternatively spliced mRNAs are translated into their protein counterparts where specific isoforms play roles in learning and memory, neuronal cell recognition, neurotransmission, ion channel function, and receptor specificity. The essential nature of this process is underscored by the finding that its misregulation is a common characteristic of human disease. This review highlights the current views of the biological phenomenon of alternative splicing, and describes evidence for its intricate underlying biochemical mechanisms. The roles of RNA binding proteins and their tissue-specific properties are discussed. Why does alternative splicing occur in cosmic proportions in the nervous system? How does it affect integrated cellular functions? How are region-specific, cell-specific and developmental differences in splicing directed? How are the control mechanisms that operate in the nervous system distinct from those of other tissues? Although there are many unanswered questions, substantial progress has been made in showing that alternative splicing is of major importance in generating proteomic diversity, and in modulating protein activities in a temporal and spatial manner. The relevance of alternative splicing to diseases of the nervous system is also discussed.

Identification and localization of M-CoREST (1A13), a mouse homologue of the human transcriptional co-repressor CoREST, in the developing mouse CNS

By means of subtractive and differential hybridization techniques we have identified a novel murine gene (1A13) the expression of which is developmentally regulated in the mouse brain. Comparison of the nucleotide and predicted protein sequence revealed closest relationship of 1A13 to human CoREST, a transcriptional co-repressor required for regulation of neural-specific gene expression. Thus, we will refer to 1A13 as M-CoREST. As shown by in situ hybridization and Northern blotting, expression of M-CoREST mRNA is abundant in neural tissue at early embryonic stages but declines significantly towards birth, coincident with the progression of CNS maturation.

Biological activity of RE-1 silencing transcription factor (REST) towards distinct transcriptional activators

The zinc finger protein RE-1 silencing transcription factor (REST) is a transcriptional repressor that represses neuronal genes in non-neuronal tissues. We have analyzed the ability of REST and the REST mutants, RESTDeltaN and RESTDeltaC lacking either the N-terminal or C-terminal repression domains of REST, to inhibit transcription mediated by distinct transcriptional activator proteins. For this purpose we have designed an activator specific assay where transcription is activated as a result of only one distinct activation domain. In addition, binding sites for REST were inserted in the 5'-untranslated region or at a distant position downstream of the polyadenylation signal. The results show that REST or the REST mutants containing only one repression domain were able to block transcriptional activation mediated by the transcriptional activation domains derived from p53, AP2, Egr-1, and GAL4. Moreover, REST, as well as the REST mutants, blocked the activity of the phosphorylation-dependent activation domain of Elk1. However, the activity of the activation domain derived from cAMP response element binding protein 2 (CREB2), was not inhibited by REST, RESTDeltaN or RESTDeltaC, suggesting that REST is able to distinguish between distinct transcriptional activation domains. Additionally, the activator specific assay, together with a positive-dominant mutant of REST that activated instead of repressed transcription, was used in titration experiments to show that REST has transcriptional repression and no transcriptional activation properties when bound to the 5'-untranslated region of a gene.

Regulation of neuronal traits by a novel transcriptional complex

The transcriptional repressor, REST, helps restrict neuronal traits to neurons by blocking their expression in nonneuronal cells. To examine the repercussions of REST expression in neurons, we generated a neuronal cell line that expresses REST conditionally. REST expression inhibited differentiation by nerve growth factor, suppressing both sodium current and neurite growth. A novel corepressor complex, CoREST/HDAC2, was shown to be required for REST repression. In the presence of REST, the CoREST/HDAC2 complex occupied the native Nav1.2 sodium channel gene in chromatin. In neuronal cells that lack REST and express sodium channels, the corepressor complex was not present on the gene. Collectively, these studies define a novel HDAC complex that is recruited by the C-terminal repressor domain of REST to actively repress genes essential to the neuronal phenotype.

REST acts through multiple deacetylase complexes

The RE1 binding silencer protein REST represses neuronal-specific gene expression in nonneuronal cell types. In this issue of Neuron, Ballas et al. show that REST inhibits gene expression via the recruitment of multiple histone deacetylase complexes.

Identification of a neurorestrictive suppressor element (NRSE) in the human mu-opioid receptor gene

Analysis of the DNA sequence of the human mu-opioid receptor gene (MOR) revealed that a region overlapping the start codon was substantially homologous to a DNA element named the neurorestrictive suppressor element (NRSE) or restrictive element 1 (RE-1). Transient transfection experiments in the L929 and HEK non-neural cell lines showed that expression of a MOR promoter/reporter gene construct was suppressed in non-neural cell lines by inclusion of this MOR NRSE. Expression from a thymidine kinase promoter was also suppressed when the MOR NRSE was inserted upstream or downstream of the reporter gene. The MOR NRSE did not suppress expression of the reporter gene in neural derived cell lines, IMR-32 and Neuro 2a. The transcription factor REST which binds NRSE thereby enacting the suppression of transcription, was encoded in a plasmid and co-transfected into the IMR-32 cells. The REST co-transfected neuronal derived (IMR-32) cells became sensitive to the MOR NRSE mediated suppression of reporter gene expression. Electrophoretic mobility shift experiments revealed that oligonucleotides containing the MOR NRSE were bound by a factor from nuclear extracts of non-neural cell lines, HeLa and Jurkat. This binding was specifically competed by oligonucleotides containing NRSE sequences previously shown to suppress transcription through REST. Thus an NRSE element overlapping the human MOR start codon suppresses gene expression in non-neural cell lines and may help direct neural tissue specific expression of MOR.

Cell-type non-selective transcription of mouse and human genes encoding neural-restrictive silencer factor

Neural-restrictive silencer (NRS) has been identified in at least twenty neuron-specific genes, and its nuclear DNA-binding factor, NRSF (also known as RE1-silencing transcription factor (REST)), has been cloned from human and rat, and was shown to repress transcription by recruiting corepressors mSin3 and/or CoREST via its N- and C-terminal domains, leading to chromatin reorganization by mSin3-associated histone deacetylase, HDAC. However, it is largely unknown how NRSF gene expression is regulated. To elucidate the mechanisms for gene expression of NRSF, we isolated the transcriptional unit of the NRSF gene from mouse and human, identified three 5'-non-coding exons in addition to three coding exons, determined transcription start sites, and identified two basal promoter activities in the upstream of the first two non-coding exons. Both promoters functioned equally in neuronal and non-neuronal cells, suggesting that levels of initial transcripts of NRSF gene are similar in neuronal and non-neuronal cells. These results suggest that the level of NRSF gene expression is not determined by transcription per se, and rather is modulated at the post-transcriptional level, e.g. splicing, mRNA stability, and/or post-translational modifications, in a cell-specific manner. Consistent with this idea, NRSF protein was apparently present even in neuronal cells and tissues, but was unable to bind to the NRS element, suggesting that NRSF is regulated at least in part post-translationally.