Monoclonal antibodies to barley aleurain and homologs from other plants

Barley aleurain is contained within a specific type of vacuole characterized by acidic pH and the presence of other hydrolytic enzymes. The aleurain-containing vacuole is distinct from protein storage vacuoles, and anti-aleurain antibodies serve as markers for this organelle in barley cells. Aleurain is a unique type of cysteine protease, and other plant species have genes for homologs whose sequences are highly conserved, but little is known about these homologs at the protein level. Seven monoclonal antibodies to barley aleurain were isolated, which bind to and define aleurain homologues in Arabidopsis, Petunia, and tobacco cell extracts. Interestingly, in addition to 29-32 kDa aleurain homologs, Petunia extracts contain a protein of approximately 50 kDa and tobacco extracts a protein of approximately 40 kDa that are recognized by multiple different monoclonal antibodies, indicating an unexpected diversity to the aleurain protein family. Among the group of antibodies are some that efficiently immunoprecipitate metabolically labeled aleurain from barley cell extracts, and some that efficiently label aleurain in immunofluorescence assays using root tip cells. These antibodies should be useful for plant cell biologists who study vacuole biogenesis and function and sorting of proteins to specific vacuolar compartments, in barley as well as other plant species.

Identification of amino acids in the glutamate receptor, GluR3, important for antibody-binding and receptor-specific activation

We reported (Twyman, R. E., Gahring, L. C., Speiss, J., and Rogers, S. W. (1995) Neuron 14, 755-762) that antibodies to a subregion of the glutamate receptor (GluR) subunit GluR3 termed GluR3B (amino acids 372-395), act as highly specific GluR agonists. In this study we produced additional rabbit anti-GluR3B-specific antibodies, ranked them according to their ability to function as GluR agonists and characterized the immunoreactivity using deletion and alanine substitution mutagenesis. These anti-GluR3B antibodies bound to a subset of the residues in GluR3B (amino acids 372-386), of which glutamate 375, valine 378, proline 379, and phenylalanine (Phe) 380 were preferred. The level of GluR activation correlated with the binding of antibody to Phe-380, which suggests that immunoreactivity directed toward Phe-380 is an index for the anti-GluR agonist potential. Since the identity of this residue varies between respective GluR subunits, this suggested that this residue may be important for imparting antibody subunit specificity. To test this possibility, the alanine in GluR1 was converted to a phenylalanine, which extended the subunit specificity from GluR3 to the modified GluR1. We conclude that antibody contacts with key residues in the GluR3B region define a novel GluR subunit-specific agonist binding site and impart subunit-specific immunoreactivity.

Autoantibodies to glutamate receptor subunit GluR2 in nonfamilial olivopontocerebellar degeneration

We describe a 63-year-old man with a 5-year history of progressive sporadic olivopontocerebellar atrophy (OPCA) who exhibits high serum titers of IgM autoantibodies to the neuronal glutamate receptor subunit GluR2. Immunohistochemistry revealed intense staining of mouse cerebellar Purkinje cells and cells in the pontine nuclei and olivary complex. Glutamate receptor currents were activated in a subset of cultured mouse neurons by an anti-GluR2 IgM fraction, and they were blocked by the competitive AMPA-type glutamate receptor antagonist CNQX and by a synthetic peptide to a specific epitope region of GluR2 (AA 369-393). The patient was treated with nine courses of plasmapheresis with little improvement of symptomatology. However, IgM titers to GluR2 decreased approximately 8-fold and the serum functional activity decreased proportionally. These findings may suggest a role for autoimmunity to glutamate receptors in the pathophysiology of certain forms of progressive nervous system degeneration.

Interleukin-1alpha in the brain is induced by audiogenic seizure

We examined the expression of the sleep-inducing cytokine interleukin-1alpha (IL-1alpha) in the brains of audiogenic seizure-susceptible mice subsequent to the induction of sound-induced seizure. Animal models of epilepsy often require lesioning or trauma that may nonspecifically alter IL-1alpha expression. To avoid this, we employed the Frings mouse strain; a model of auditory-evoked reflex epilepsy. Frings mice were exposed to a high-intensity sound stimulus to induce a tonic extension seizure, and the expression of IL-1alpha transcripts in different brain regions was measured thereafter. Compared to control animals, IL-1alpha transcripts were elevated 6 to 8 h postseizure in the hypothalamus, but not hippocampus, by a dexamethasone-sensitive pathway. Similar results were obtained from the genetically distinct DBA/2J audiogenic seizure-susceptible mouse strain. These findings demonstrate that the expression of IL-1alpha is altered following generalized seizure activity, induced by noninvasive sensory stimulation, in a brain-region-specific manner.

Neuronal nicotinic receptor expression in sensory neurons of the rat trigeminal ganglion: demonstration of alpha3beta4, a novel subtype in the mammalian nervous system

The identification of a family of neuronal nicotinic receptor subunit genes establishes the potential for multiple subtypes with diverse physiological functions. Virtually all of the high affinity nicotinic receptors measured to date in the rodent CNS are composed of alpha4 and beta2 subunits only. However, the demonstration of other subunit transcripts in a variety of central and peripheral nervous tissues suggests a greater degree of receptor subtype heterogeneity than so far has been elucidated. The purpose of the present studies was to determine at the mRNA and protein levels which neuronal nicotinic receptor subunits are expressed by sensory neurons of the rat trigeminal ganglion and in what combinations these gene products associate to form neuronal nicotinic receptor subtypes in this tissue. Radioreceptor binding analysis indicated that in the adult rat trigeminal ganglion there exist at least two nicotinic receptor binding sites with differing affinities for [3H]-epibatidine. In situ hybridization histochemical studies revealed the existence of mRNA encoding the alpha3, alpha4, alpha5, beta2, and beta4 subunits, but not the alpha2 subunit. Immunoprecipitation with subunit-specific antisera demonstrated that each of the subunits present in the ganglion at the mRNA level is a constituent of nicotinic receptors capable of binding 3H-epibatidine. Various applications of these approaches yielded strong evidence that, in addition to alpha4beta2, which is thought to be the predominant neuronal nicotinic receptor subtype in the rodent CNS, trigeminal sensory neurons express as the principal subtype alpha3beta4, which has not been demonstrated previously in mammalian nervous tissue.

Neuronal expression of tumor necrosis factor alpha in the murine brain

We have examined the expression of the inflammatory cytokine, tumor necrosis factor alpha (TNF alpha) in the mouse brain. Using immunohistochemical methods developed, we found anti-TNF alpha immunoreactivity localized in the basal ganglia and other discrete brain structures. Constitutive immunoreactivity, present in normal, unstimulated brain, was observed in glial and microglial-like cells, but it was predominant in neuronal-like cells. Intravenous administration of lipopolysaccharide (LPS) increased TNF alpha transcript levels detected by RT-PCR in specific brain subregions in which contaminating blood cells were removed. The maximal increase occurred within 2 h of LPS injection; transcripts diminished to near control levels in the next 4 h. Immunocytochemical analysis and single-cell RT-PCR analysis of primary cultures of cortical neuronal cells confirmed expression of TNF alpha in cells that also express neuronal-specific enolase RNA. Addition of LPS or recombinant TNF alpha protein to neuronal cultures enhanced expression of TNF alpha transcripts. Our results indicate that in addition to glial and microglial cells, a well-defined subset of neuronal cells also express TNF alpha constitutively; this expression can be altered by both extrinsic (LPS) and intrinsic (TNF alpha itself) factors.

Kainic acid induced excitotoxicity and cfos expression in fibroblasts transfected with glutamate receptor subunit, GluR1

Glutamate receptors participate in the majority of fast excitatory neurotransmission in the mammalian brain. Excessive excitation of these receptors has been linked to neuronal dysfunction and death through a process termed excitotoxicity. In this study we demonstrate that transfection of a single non-NMDA glutamate receptor subunit, GluR1, into cultured fibroblasts is sufficient to confer kainic acid mediated excitotoxicity similar to that seen in neuronal cells. Death of transfected cells requires at least 24 h of continuous exposure to kainic acid and can be blocked with a glutamate receptor antagonist. Also, the induction of protooncogene cfos transcripts occurs 30 min following kainic acid administration, and Fos protein accumulated in the nucleus within 90 min. These observations suggest that the signaling system(s) required to initiate gene expression and kainic acid excitotoxicity from a neuronal ionotropic receptor to the nucleus is present in these nonneuronal cells. Finally, antibodies prepared to amino acids 185-449 of GluR1 are demonstrated to be useful for fluorescence-activated sorting of live cells transfected with a GluR1 expression vector. This supports the conclusion that this region of the protein is located extracellularly.

PEST sequences and regulation by proteolysis

In 1986, we proposed that polypeptide sequences enriched in proline (P), glutamic acid (E), serine (S) and threonine (T) target proteins for rapid destruction. For much of the past decade there were only sporadic experimental tests of the hypothesis. This situation changed markedly during the past two years with a number of papers providing strong evidence that PEST regions do, in fact, serve as proteolytic signals. Here, we briefly review the properties of PEST regions and some interesting examples of the conditional nature of such signals. Most of the article, however, focuses on recent experimental support for the hypothesis and on mechanisms responsible for the rapid degradation of proteins that contain PEST regions.

Nicotinic receptor subunits alpha 3, alpha 4, and beta 2 and high affinity nicotine binding sites are expressed by P19 embryonal cells

Controlled exposure to retinoic acid (RA) induces the murine embryonal carcinoma cell line P19S18O1A1 (P19) to differentiate into a variety of cell types. One of the cell types exhibits neuronal-like morphology and expresses neuronal markers including neurofilament proteins, glutamate receptors, and the cholinergic enzymes choline acetyl-transferase and acetylcholinesterase. In this study we use Northern blot analysis, double-label immunocytochemistry, and single cell RNA analysis using polymerase chain reaction to show that RA-treated P19 cells with neuronal-like morphology also express neuronal nicotinic acetylcholine receptor (nAChR) subunits alpha 3, alpha 4, and beta 2. Greater than 80% of RA-treated P19 cells with a neuronal-like phenotype express nAChR alpha 4 subunit transcripts and both alpha 4 and beta 2 protein. The RA-induced expression of alpha 3 transcripts accounts for a comparably small number of nAChR-containing cells (< 20%) of which half coexpress alpha 4 transcripts. Expression of high-levels of alpha 4 RNA is dependent upon both cell-cell contact and RA exposure. The appearance of nAChR subunits also coincides with RA-induced expression of high affinity [3H]-nicotine binding receptors. The P19 cell line offers an inducible neuronal cell system to study mammalian neuronal nicotinic receptor expression and the development of high affinity nicotinic binding sites similar to those expressed in the mammalian central nervous system.

The role of autoimmunity to glutamate receptors in neurological disease

Understanding and experimentally approaching the processes that underlie the origin and progression of many severe neurological disorders presents a challenge to both clinical and basic researchers. We have found that the origin of some neurological diseases, including a rare form of childhood epilepsy and a neurodegenerative disease associated with peripheral cancers, may be related to production of physiologically active autoantibodies that are directed towards excitatory ionotropic glutamate receptors of the brain. This suggests that some neurological diseases may result from dysfunction of the immune system.

Glutamate receptor antibodies activate a subset of receptors and reveal an agonist binding site

Two rabbits immunized with a portion of glutamate receptor (GluR) subunit GluR3 (amino acids 245-457) exhibited seizure-like behaviors, suggesting that antibodies to GluR3 may modulate neuronal excitability. Using whole-cell recording, rabbit GluR3 antisera were tested on cultured fetal mouse cortical neurons. In a subset of kainate-responsive neurons, miniperfusion of antisera and IgG evoked currents that were blocked by CNQX. Immunoreactivity to synthetic peptides prepared to subregions GluR3A (amino acids 245-274) and GluR3B (amino acids 372-395) was present in both rabbit sera. Peptide GluR3B, but not GluR3A, specifically blocked antisera- and IgG-evoked currents. Similar receptor activation and anti-GluR3 reactivity was present in sera from patients with active Rasmussen's encephalitis, an intractable pediatric epilepsy. Thus, antibodies to GluR3 define a region involved in agonist binding and specific receptor activation. These data suggest that antibodies to neuronal receptors can function as agonists and that autoantibodies to GluRs may be highly specific neurotoxicants in some neurological diseases.

Distribution of the excitatory amino acid receptor subunits GluR2(4) in monkey hippocampus and colocalization with subunits GluR5-7 and NMDAR1

Ionotropic excitatory amino acid (EAA) receptors are divided pharmacologically into three categories termed NMDA, AMPA/kainate, and high affinity kainate receptors. Each of these receptor subtypes is composed of a specific subset of subunits termed GluR1-4 (AMPA/kainate), GluR5-7, KA1-2 (high affinity kainate), and NMDAR1, 2 A-D (NMDA). Although colocalization of NMDA and non-NMDA receptors has been previously demonstrated electrophysiologically in rat, comprehensive analyses of subunit specific colocalization patterns have not been possible until the advent of appropriate antibodies. The present study investigates such immunocytochemical colocalization of several EAA receptor subunits within individual cells as well as dendritic spines in the monkey hippocampus. Double-label immunohistochemical experiments using antibodies which are specific for GluR2(4), GluR5-7, and NMDAR1 demonstrated that virtually all projection neurons in each subfield of the hippocampus contain subunits from the AMPA/kainate, kainate, and NMDA receptor families. In addition, confocal microscopy has demonstrated that individual spines may contain subunits representative of multiple EAA receptor families. Furthermore, detailed regional, cellular, and ultrastructural distribution patterns of the EAA receptor subunits GluR2 and GluR4 in monkey hippocampus are presented based on the use of a monoclonal antibody (mAb), 3A11, which was generated against the putative extracellular N-terminal domain of GluR2. Since this antibody recognizes only GluR2 in Western blots, and GluR2 as well as GluR4 in fixed transiently transfected cells, it has been designated anti-GluR2(4). Immunocytochemical labeling with mAb 3A11 revealed pyramidal cell somata and dendrites in each field of the hippocampus, as well as granule cells and polymorphic hilar cells in the dentate gyrus. Small cells with the morphologic characteristics of astroglia were also immunolabeled for GluR2(4) within the alveus and fimbria. Immunoreactivity at the ultrastructural level was localized to postsynaptic densities on dendritic spines and shafts and within the somatodendritic cytoplasm in all major hippocampal regions, as well as in a subset of dentate granule cell axons within the mossy fiber projection.

Autoantibodies to neuronal glutamate receptors in patients with paraneoplastic neurodegenerative syndrome enhance receptor activation

BACKGROUND

Paraneoplastic syndromes are "remote" complications of cancer characterized clinically by neurological disease. The sera and cerebrospinal fluid (CSF) from patients with paraneoplastic neurological syndromes (PNS) frequently contain autoantibodies to ill-defined neuronal antigens. We report here that neuronal glutamate receptors are targets for autoantibodies found in the serum from some patients with well-characterized PNS.

MATERIALS AND METHODS

We have analyzed the serum from seven patients with well-characterized PNS for the presence of autoreactive antibodies to non-NMDA glutamate receptor subunits. Autoantibodies were assessed using Western blot, immunohistochemistry, and immunocytochemistry. Whole-cell electrophysiological recordings were used to examine the effect of antibodies on glutamate receptors expressed by cortical neurons in culture.

RESULTS

Six of seven patients' serum contained autoantibodies to the non-NMDA glutamate receptor (GluR) subunits GluR1, GluR4, and/or GluR5/6. No patient had autoantibodies to GluR2, and only one patient exhibited weak immunoreactivity to GluR3. Electrophysiological analysis demonstrated that the serum from four of the six GluR-antibody-positive patients enhanced glutamate-elicited currents on cultured cortical neurons but had no effect on receptor function alone. Enhancement of glutamate-elicited currents was also produced by affinity-purified antibody to GluR5.

CONCLUSIONS

The occurrence of autoantibodies to specific neuronal neurotransmitter subunits in the sera of patients with PNS and the ability of these autoantibodies to modulate glutaminergic receptor function suggest that some paraneoplastic neurological injury could result from glutamate-mediated excitotoxicity.

Comparison of the effects of N6-methyldeoxyadenosine and N5-methyldeoxycytosine on transcription from nuclear gene promoters in barley

Methylation of deoxycytosine residues in plant nuclear DNA at CpG dinucleotides is generally assumed to suppress transcription, while deoxyadenosine methylation on recombinant reporter gene constructs transiently introduced into plant cells increases expression by uncharacterized mechanisms. A particle bombardment transient expression system was used in intact barley aleurone layers to quantitate the effects of CpG and A methylation on transcription from well-characterized hormone-regulated alpha-amylase promoters. Methylation of C in all CpG pairs had little effect on transcription. In contrast, the presence of methylated A residues in the sequence GATC scattered in the reporter plasmid outside of the promoter increased transcription two- to fivefold, regardless of the strength of the promoter, and proper hormonal regulation of transcription was maintained. The methyl-dA effect was similar when the amount of reporter construct DNA used was varied over a 20-fold range, beginning with an amount that gave only a small increment of expression above background. Similar enhancing effects for methyl-dA were seen with the CaMV 35S, maize Adh1, and maize ubiquitin promoters, though the magnitude varied for each individual promoter. Methyl-dA did not detectably affect plasmid DNA stability in aleurone cells in transient expression experiments because the enhancing effect of methyl-dA on expression was the same regardless of whether the assay was performed at 12 h or 40 h. Several proteins in wheat germ nuclear extracts bound preferentially to methylated DNA as assessed by gel retardation assays; one showed preferential binding to methyl-dA rather than methyl-CpG residues. The data indicate that the presence of methyl-dA in the vicinity of active promoters enhances transcription of nuclear genes in barley in a manner independent of the strength of the promoter. This effect may be mediated by a methyl-dA-binding protein.

Autoantibodies to glutamate receptor GluR3 in Rasmussen's encephalitis

Rasmussen's encephalitis is a progressive childhood disease of unknown cause characterized by severe epilepsy, hemiplegia, dementia, and inflammation of the brain. During efforts to raise antibodies to recombinant glutamate receptors (GluRs), behaviors typical of seizures and histopathologic features mimicking Rasmussen's encephalitis were found in two rabbits immunized with GluR3 protein. A correlation was found between the presence of Rasmussen's encephalitis and serum antibodies to GluR3 detected by protein immunoblot analysis and by immunoreactivity to transfected cells expressing GluR3. Repeated plasma exchanges in one seriously ill child transiently reduced serum titers of GluR3 antibodies, decreased seizure frequency, and improved neurologic function. Thus, GluR3 is an autoantigen in Rasmussen's encephalitis, and an autoimmune process may underlie this disease.

KEKE motifs. Proposed roles in protein-protein association and presentation of peptides by MHC class I receptors

A stretch of 28 'alternating' lysine (K) and glutamate (E) residues is found in an activator of the multicatalytic protease. Such 'KEKE sequences' are also present in subunits of the multicatalytic protease, in subunits of the 26S protease and in a variety of chaperonins. We propose that KEKE regions promote association between protein complexes. Furthermore, they may contribute to the selection of peptides presented on MHC Class I receptors.

Selective RNA editing and subunit assembly of native glutamate receptors

RNA editing and subunit assembly of ionotropic glutamate receptors (GluRs) were examined in an oligodendrocyte progenitor cell line, CG4, which expresses GluR2-GluR4, GluR6, GluR7, KA1, and KA2. AMPA-evoked currents rapidly desensitize, whereas kainate-evoked currents contain a steady-state component with a nearly linear current-voltage relation and a fast desensitizing component that is inwardly rectifying. The Q/R site is edited > 95% to the arginine codon in GluR2(Q607) mRNA, and < 5% in GluR6(Q621) mRNA. Immunoprecipitation experiments demonstrate that GluR6 and/or GluR7 subunits assemble with KA2, but not with GluR2-GluR4. These results indicate that oligodendrocyte progenitor cells selectively edit and assemble glutamate receptors into at least two functionally and structurally distinct heteromeric channels.

Nicotinic acetylcholine receptors in the ground squirrel retina: localization of the beta 4 subunit by immunohistochemistry and in situ hybridization

Immunohistochemical and in situ hybridization techniques were used to localize the beta 4 subunit of the neuronal nicotinic acetylcholine receptors (nAChRs) in the ground squirrel retina. The beta 4 nAChR subunit was detected in both transverse and horizontal sections of the retina using a subunit-specific antiserum and the avidin-biotin complex technique. Two bands of labeled processes were seen in the inner plexiform layer, corresponding approximately to the laminae where the cholinergic cells arborize. Labeled cells were found in the ganglion cell layer and the inner third of the inner nuclear layer. The cells in the ganglion cell layer were medium- to large-sized and were frequently observed to give rise to axon-like processes. Most of the labeled neurons in the inner nuclear layer were small presumptive amacrine cells, but a few medium-to-large cells were also labeled. These could constitute a different class of amacrine cells or displaced ganglion cells. The latter possibility is supported by the existence of nAChR-containing displaced ganglion cells in the avian retina. In situ hybridization with a 35S-labeled cRNA probe revealed the expression of mRNA coding for the nAChR beta 4 subunit in the ganglion cell layer and the inner third of the inner nuclear layer. This finding confirmed the immunohistochemical data of the cellular localization of beta 4 nAChR subunit. These results indicate that the beta 4 nAChR subunit is expressed by specific subtypes of neurons on the ground squirrel retina.(ABSTRACT TRUNCATED AT 250 WORDS)

The cis-acting gibberellin response complex in high pI alpha-amylase gene promoters. Requirement of a coupling element for high-level transcription

In cereal alpha-amylase gene promoters the cis-acting gibberellin response element (GARE) is required for increased transcription in the presence of gibberellin. In low-isoelectric point (pI) alpha-amylase gene promoters a second type of cis element, termed a coupling element, must also be present in a specific position near the GARE; otherwise, the level of transcription in the presence of gibberellin is only a few percent of maximum. The coupling element may help determine where and when in development high-level, hormonally regulated transcription will occur. Such coupling elements have not yet been shown to be necessary for high-level transcription from high-pI alpha-amylase gene promoters. Here we use quantitative transient expression assays to show that a high-pI promoter truncated to -300 is a weak promoter due to the absence of a functional coupling element in the vicinity of the GARE. Gibberellin-induced transcription increases substantially when coupling element function is provided, either by appending upstream regions normally attached to the promoter or by inserting a defined coupling element from a low-pI promoter. Thus, in a second type of gibberellin-regulated promoter coupling element function was found to be crucial for hormone regulation to result in high-level transcription.

Organization and quantitative analysis of kainate receptor subunit GluR5-7 immunoreactivity in monkey hippocampus

A monoclonal antibody specific for GluR5-7 (mAb-4F5) has been used to characterize the distribution of kainate class glutamate receptor subunits in monkey hippocampus. Immunolabeled neurons were present in all subfields of the hippocampus as well as the dentate gyrus and subiculum. Quantitative immunofluorescence analysis by confocal microscopy demonstrated differential levels of immunoreactivity such that the highest intensities were in neurons within CA1 and subiculum as compared with those within CA3 or dentate gyrus. The regional differences in levels of subunit immunoreactivity correlate with the relative vulnerability of hippocampal neurons in several neurodegenerative disorders.

Quantitative localization of AMPA/kainate and kainate glutamate receptor subunit immunoreactivity in neurochemically identified subpopulations of neurons in the prefrontal cortex of the macaque monkey

Excitatory amino acid transmission has been proposed as the principal synaptic mechanism for distribution of information through corticocortical and thalamocortical pathways. The following study utilized a double labeling paradigm, using antibodies that recognize non-NMDA ionotropic glutamate receptor subunits and other neuronal markers, to further define, quantitatively, the subclasses of neurons that contain immunoreactivity for the AMPA/kainate and kainate receptor subunits in the monkey prefrontal cortex. Double labeling with an antibody that recognizes common epitopes in AMPA/kainate subunits GluR2 and GluR3 (GluR2/3) in combination with an antibody that recognizes the kainate receptor subunits GluR5, GluR6, and GluR7 (GluR5/6/7) demonstrated that immunoreactivity for these two receptor classes was highly colocalized in a great majority of the pyramidal neurons in this region but present in only a minority of neurochemically identified subclasses of GABAergic interneurons. Furthermore, GluR2/3 immunoreactivity had principally a somatic distribution whereas GluR5/6/7 labeling was predominately found in the perikarya and/or particular dendritic domains. In contrast, intense GluR1 labeling was observed in a small subpopulation of interneurons and low GluR1 immunoreactivity was present in many other cortical neurons. These results demonstrate that there is a high degree of specificity in the distribution of AMPA/kainate and kainate receptor-class proteins to subclasses of neurons within the neocortex. A neuron's combination of excitatory amino acid receptor subunits may regulate its response to excitatory inputs and further defines the role of identified subclasses of neurons in the complex circuitry of the cerebral cortex and may also indicate the basis for the apparent cellular selectivity of excitotoxic degenerative processes.

Selective distribution of kainate receptor subunit immunoreactivity in monkey neocortex revealed by a monoclonal antibody that recognizes glutamate receptor subunits GluR5/6/7

A monoclonal antibody (4F5) was generated against a portion of the putative extracellular domain of glutamate receptor subunit GluR5. Western blot analyses and immunocytochemistry of transfected human embryonic kidney 293 cells confirmed that monoclonal antibody 4F5 was specific for GluR5, -6, and -7 (the three identified members of the kainate receptor subunit class), but did not recognize GluR1, -2, or -3 (the AMPA/kainate receptor subunit class). The antibody was subsequently used to examine immunocytochemically the regional, laminar, and cellular distribution of GluR5/6/7 receptor subunits at the light and electron microscopic levels in monkey neocortex. Receptor subunit immunoreactivity was present throughout all cortical areas examined, but exhibited marked cellular, laminar, and regional specificity. Typically, pyramidal cell somata and apical dendrites were well stained. Electron microscopy revealed an extensive cytoplasmic localization of GluR5/6/7 immunoprecipitate, with intense staining of many postsynaptic densities, all of which were associated with asymmetric synapses located on dendritic shafts or dendritic spines. There was no evidence of stained glial cells or presynaptic axon terminals. In most areas, labeled cells and dendrites were concentrated in layers II, III, and V while layers I, IV, and VI typically possessed the fewest and/or least intensely stained elements. A consistent feature in many areas was groups of clustered layer V pyramidal cells and bundles of ascending apical dendrites. Regionally, motor areas and higher-order association areas of the frontal, parietal, and occipital lobes were more densely stained than primary sensory areas (somatic sensory and visual cortex), which was confirmed quantitatively. These data indicate a high degree of selectivity in the distribution of kainate receptors composed of GluR5/6/7 subunits, and suggest that functional specificity and diversity in the ubiquitous excitatory amino acid-utilizing axonal systems in neocortex are achieved in part by the differential association of particular glutamate receptor subunits with specific cortical circuits. In addition, the regional, laminar, and morphological characteristics of GluR5/6/7-immunoreactive neurons bear a strong similarity to those of the neocortical neurons with heightened vulnerability in certain neurodegenerative disorders.

The expression of nicotinic acetylcholine receptors by PC12 cells treated with NGF

The expression of neuronal nicotinic ACh receptors (nAChRs) and the subunits that compose these receptors by PC12 cells exposed to NGF has been studied. The analysis of total RNA reveals that the neuronal nAChR subunits alpha 3, alpha S, beta 2, beta 3, and beta 4, but not alpha 2 and alpha 4, are expressed in our PC12 cells. Within 48 hr of adding NGF to cultures, the RNA corresponding to alpha 3, alpha 5, beta 3, and beta 4 is decreased, but the beta 2 RNA increases for up to 6 d after NGF treatment. To determine the influence of NGF treatment on subunit protein expression, subunit-specific antisera were prepared. Immunocytochemistry detected antigen for alpha 3, alpha 5, beta 2, beta 3, and beta 4 (but not alpha 2 and alpha 4) in both NGF-treated and nontreated PC12 cells. The expression of nAChR subunit proteins, as measured by direct binding of antibodies to PC12 cells, does not change subsequent to 6 d of treatment with NGF. Whole-cell recording of PC12 cells shows that both the individual cell current density and response to the agonist cytisine were not altered after 5-7 d in NGF. However, the number of cells exhibiting detectable ACh-induced currents doubled. These results indicate that NGF increases the number of PC12 cells expressing ACh-sensitive nAChR currents but the activation is not the result of altering the amounts of individual nAChR subunit proteins. These data, taken together with the decrease in most nAChR subunit RNAs (except beta 2), suggest that NGF regulation of nAChRs may be through a posttranscriptional mechanism.

Definition and functional implications of gibberellin and abscisic acid cis-acting hormone response complexes

The mechanisms by which cis-acting hormone response elements affect transcription is unclear. In this study, we demonstrated that a second "coupling element," identified as O2S, must be present to allow a single copy of either the gibberellin response element (GARE) or the abscisic acid response element (ABRE) to mediate their hormonal effects in the barley Amy32b alpha-amylase gene promoter. The interactive effects of the O2S and the GARE are constrained positionally and spatially; thus, together they form a gibberellin response complex (GARC). The absolute requirement of the O2S for function of the ABRE demonstrates that these together form an abscisic acid response complex (ABRC). A second copy of the GARE can substitute for the O2S in the GARC, but only in one orientation. By expressing the GARC-containing and ABRC-containing promoters in developing aleurone tissue, we showed that hormonal effects prevent alpha-amylase gene expression during the second half of grain development, but other mechanisms suppress expression earlier. Our results suggest that the specific sequence serving as a coupling element in a given gene promoter will greatly affect where and when the GARE or ABRE will be able to regulate transcription.

Definition and functional implications of gibberellin and abscisic acid cis-acting hormone response complexes

The mechanisms by which cis-acting hormone response elements affect transcription is unclear. In this study, we demonstrated that a second "coupling element," identified as O2S, must be present to allow a single copy of either the gibberellin response element (GARE) or the abscisic acid response element (ABRE) to mediate their hormonal effects in the barley Amy32b alpha-amylase gene promoter. The interactive effects of the O2S and the GARE are constrained positionally and spatially; thus, together they form a gibberellin response complex (GARC). The absolute requirement of the O2S for function of the ABRE demonstrates that these together form an abscisic acid response complex (ABRC). A second copy of the GARE can substitute for the O2S in the GARC, but only in one orientation. By expressing the GARC-containing and ABRC-containing promoters in developing aleurone tissue, we showed that hormonal effects prevent alpha-amylase gene expression during the second half of grain development, but other mechanisms suppress expression earlier. Our results suggest that the specific sequence serving as a coupling element in a given gene promoter will greatly affect where and when the GARE or ABRE will be able to regulate transcription.