Regulation of class I MHC gene expression in the developing and mature CNS by neural activity

Expression of T cell receptor beta locus in central nervous system neurons

MHC class I proteins are cell-surface ligands that bind to T cell receptors and other immunoreceptors and act to regulate the activation state of immune cells. Recent work has shown that MHC class I genes and CD3zeta, an obligate component of T cell receptors, are expressed in neurons, are regulated by neuronal activity, and function in neuronal development and plasticity. A search for additional neuronally expressed T cell receptor components has revealed that the T cell antigen receptor beta (TCRbeta) locus is expressed in neurons of the murine central nervous system and that this expression is dynamically regulated over development. In neonates, expression is most abundant in various thalamic nuclei. At later ages and in adults, thalamic expression fades and cortical expression is robust, particularly in layer 6. In T cells, protein-encoding transcripts are produced only after recombination of the TCRbeta genomic locus, which joins variable, diversity, and joining regions, a process that creates much of the diversity of the immune system. We detect no genomic recombination in neurons. Rather, transcripts begin in regions upstream of several joining regions, and are spliced to constant region segments. One of the transcripts encodes a hypothetical 207-aa, 23-kDa protein, which includes the TCRbeta J2.7 region, and the entire C region. These observations suggest that TCRbeta may function in neurons.

An evolutionarily conserved N-terminal acetyltransferase complex associated with neuronal development

We previously identified mNAT1 (murine N-terminal acetyltransferase 1) as an embryonic gene that is expressed in the developing brain and subsequently down-regulated, in part, by the onset of N-methyl-d-aspartate (NMDA) receptor function. By searching the data base we discovered a second closely related gene, mNAT2. mNAT1 and mNAT2 are highly homologous to yeast NAT1, a gene known to regulate entry into the G0 phase of the cell cycle. However, in the absence of further characterization, including evidence that mammalian homologues of NAT1 encode functional acetyltransferases, the significance of this relationship has been unclear. Here we focus on mNAT1. Biochemical analysis demonstrated that mNAT1 and its evolutionarily conserved co-subunit, mARD1, assemble to form a functional acetyltransferase. Transfection of mammalian cells with mNAT1 and mARD1 followed by immunofluorescent staining revealed that these proteins localize to the cytoplasm in both overlapping and separate compartments. In situ hybridization demonstrated that throughout brain development mNAT1 and mARD1 are highly expressed in areas of cell division and migration and are down-regulated as neurons differentiate. Finally, mNAT1 and mARD1 are expressed in proliferating mouse P19 embryonic carcinoma cells; treatment of these cells with retinoic acid initiates exit from the cell cycle, neuronal differentiation, and down-regulation of mNAT1 and mARD1 as the NMOA receptor 1 gene is induced. The results provide the first direct evidence that vertebrate homologues of NAT1 and ARD1 form an evolutionarily conserved N-terminal acetyltransferase and suggest that expression and down-regulation of this enzyme complex plays an important role in the generation and differentiation of neurons.

MHC-congenic mice (C57BL/6J and B6-H-2K) show differences in speed but not accuracy in learning the Hebb-Williams Maze

We compared spatial learning and memory in male and female mice of two MHC-congenic strains (C57BL/6J and B6-H-2K) in two versions of the Hebb-Williams Maze. In the food-reward paradigm, males required fewer sessions to learn than females, but there were no strain differences in acquisition. There were no strain or sex differences in the number of errors during the test phase, but the B6-H-2K mice reached the goal box faster than the C57BL/6J mice. In the water-escape paradigm, the C57BL/6J mice required more sessions than the B6-H-2K mice during acquisition. There were no strain or sex differences in the number of errors or in the latency to swim to the goal box in the test phase of the water-escape task. There were no significant correlations between the number of sessions to learn the two mazes; the number of errors made or the latencies to reach the goal box in each maze. These results indicate that these two strains show differences in performance in the Hebb-Williams Maze, but do not differ in cognitive ability.

Impaired motor coordination in mice lacking neural recognition molecule NB-3 of the contactin/F3 subgroup

The neural recognition molecule NB-3, which belongs to the contactin subgroup of the immunoglobulin superfamily, is expressed exclusively in the nervous system and mainly upregulated at the early postnatal stage during mouse brain development. The expression of NB-3 in the cerebellum increases until adulthood. In contrast, the expression in the cerebrum declines to a low level after postnatal day 7. To characterize the functional roles of NB-3 in vivo, we generated NB-3-deficient mice by substituting a part of the NB-3 gene with the beta-galactosidase (Lac Z) gene. Complete overlap of the Lac Z expression in the heterozygous mouse brain with the NB-3 immunostaining pattern in the rat cerebellum and with the previously reported pattern of in situ hybridization of NB-3 transcripts indicated that Lac Z expression reflects the expression of NB-3 in the mouse brain. NB-3-deficient mice were viable and fertile. The formation and organization of all nuclei and layers throughout the brains of mutant mice appeared normal. Behavioral tests to examine motor function showed that the mice deficient for NB-3 were slow to learn to stay on the rotating rod in the rotorod test during repeated trials, and that they displayed dysfunction of equilibrium and vestibular senses in the wire hang and horizontal rod-walking tests. In contrast, the mutant mice showed no difference of grasp force from the wild-type mice. Thus, NB-3-deficient mice are impaired in motor coordination.

Immune changes during acute cold/restraint stress-induced inhibition of host resistance to Listeria

Experiments were conducted to delineate the cellular changes modulated by acute cold/restraint stress (ACRS), a physical and psychological stressor, in response to a Listeria monocytogenes(LM) infection. In addition to wild type (WT) BALB/c mice, CD4-deficient (CD4-/-) BALB/c mice, which have no effective adaptive immunity, were used to determine the involvement of adaptive versus innate immunity. ACRS-induced suppression of host resistance to LM was not observed in CD4-/- mice, suggesting the involvement of CD4+T cells in the acute cold/restraint stress (ACRS)-induced inhibition. The in vivo splenic leukocyte phenotypes and activities of WT BALB/c mice after infection and in vitro lymphocyte responses to heat-killed LM (HKLM) also were examined. There were no significant differences in the numbers of splenic T and B lymphocytes, natural killer cells, macrophages, or neutrophils between nonstressed and ACRS-treated WT mice. However, higher levels of activated T cells and non-T lymphocytes were observed in the ACRS-treated mice; beta-adrenergic receptor (beta-ADR) antagonists (propranolol and atenolol) eliminated these elevated levels of activation, as well as the ACRS-induced suppression of host resistance. ACRS and control mice also had equivalent activation of macrophages. With in vitro HKLM stimulation, splenocytes from ACRS-treated mice produced significantly higher levels of IFNgamma and slightly higher levels of IL-6 in comparison with the nonstressed mice, although equivalent levels of lymphocyte proliferation were obtained. Additionally, ACRS-treated mice showed comparable elevation of serum nitric oxide after infection, indicating macrophage bactericidal activity similar to nonstressed mice. Thus, it appears that ACRS inhibits host resistance through regulatory CD4+ T cells and/or effector cell functions downstream of CD4+ T cell activation, as well as through beta-ADR signaling, in that blockage of these receptors appears to aid host defenses by means other than elevation of helper T cell activity. Because CD4 T cell deficiency and beta-ADR blockage produced equivalent effects, beta-ADR+ CD4+ T cells may have a negative role on host defenses after ACRS.

Differential display implicates cyclophilin A in adult cortical plasticity

Removal of retinal input from a restricted region of adult cat visual cortex leads to a substantial reorganization of the retinotopy within the sensory-deprived cortical zone. Little is known about the molecular mechanisms underlying this reorganization. We used differential mRNA display (DDRT-PCR) to compare gene expression patterns between normal control and reorganizing visual cortex (area 17-18), 3 days after induction of central retinal lesions. Systematic screening revealed a decrease in the mRNA encoding cyclophilin A in lesion-affected cortex. In situ hybridization and competitive PCR confirmed the decreased cyclophilin A mRNA levels in reorganizing cortex and extended this finding to longer postlesion survival times as well. Western blotting and immunocytochemistry extended these data to the protein level. In situ hybridization and immunocytochemistry further demonstrated that cyclophilin A mRNA and protein are present in neurons. To exclude the possibility that differences in neuronal activity per se can induce alterations in cyclophilin A mRNA and protein expression, we analyzed cyclophilin A expression in the dorsal lateral geniculate nucleus (dLGN) of retinally lesioned cats and in area 17 and the dLGN of isolated hemisphere cats. In these control experiments cyclophilin A mRNA and protein were distributed as in normal control subjects indicating that the decreased cyclophilin A levels, as observed in sensory-deprived area 17 of retinal lesion cats, are not merely a reflection of changes in neuronal activity. Instead our findings identify cyclophilin A, classically considered a housekeeping gene, as a gene with a brain plasticity-related expression in the central nervous system.

Characterisation of RT1-E2, a multigenic family of highly conserved rat non-classical MHC class I molecules initially identified in cells from immunoprivileged sites

BACKGROUND

So-called "immunoprivileged sites" are tissues or organs where slow allograft rejection correlates with low levels of expression of MHC class I molecules. Whilst classical class I molecules are recognised by cytotoxic T lymphocytes (CTL), some MHC class I molecules are called "non-classical" because they exhibit low polymorphism and are not widely expressed. These last years, several studies have shown that these can play different, more specialised roles than their classical counterparts. In the course of efforts to characterise MHC class I expression in rat cells obtained from immunoprivileged sites such as the central nervous system or the placenta, a new family of non-classical MHC class I molecules, which we have named RT1-E2, has been uncovered.

RESULTS

Members of the RT1-E2 family are all highly homologous to one another, and the number of RT1-E2 loci varies from one to four per MHC haplotype among the six rat strains studied so far, with some loci predicted to give rise to soluble molecules. The RT1n MHC haplotype (found in BN rats) carries a single RT1-E2 locus, which lies in the RT1-C/E region of the MHC and displays the typical exon-intron organisation and promoter features seen in other rat MHC class I genes. We present evidence that: i) RT1-E2 molecules can be detected at the surface of transfected mouse L cells and simian COS-7 cells, albeit at low levels; ii) their transport to the cell surface is dependent on a functional TAP transporter. In L cells, their transport is also hindered by protease inhibitors, brefeldin A and monensin.

CONCLUSIONS

These findings suggest that RT1-E2 molecules probably associate with ligands of peptidic nature. The high homology between the RT1-E2 molecules isolated from divergent rat MHC haplotypes is particularly striking at the level of their extra-cellular portions. Compared to other class I molecules, this suggests that RT1-E2 molecules may associate with well defined sets of ligands. Several characteristics point to a certain similarity to the mouse H2-Qa2 and human HLA-G molecules.

Upstream stimulatory factors are mediators of Ca2+-responsive transcription in neurons

To identify molecular mechanisms that control activity-dependent gene expression in the CNS, we have characterized the factors that mediate activity-dependent transcription of BDNF promoter III. We report the identification of a Ca(2+)-responsive E-box element, CaRE2, within BDNF promoter III that binds upstream stimulatory factors 1 and 2 (USF1/2) and show that USFs are required for the activation of CaRE2-dependent transcription from BDNF promoter III. We find that the transcriptional activity of the USFs is regulated by Ca(2+)-activated signaling pathways in neurons and that the USFs bind to the promoters of a number of neuronal activity-regulated genes in vivo. These results suggest a new function for the USFs in the regulation of activity-dependent transcription in neurons.

Multiple sclerosis and glutamate

Experimental autoimmune encephalomyelitis reproduces in rodents the features of multiple sclerosis, an immune-mediated, disabling disorder of the human nervous system. No adequate therapy is available for multiple sclerosis, despite anti-inflammatory, immunosuppressive, and immunomodulatory measures. Increasingly glutamate is implicated in the pathogenesis of neurodegenerative diseases. Here we (1) review changes in the glutamatergic system in multiple sclerosis and (2) reveal the effects of glutamate AMPA antagonists in acute and chronic rodent models of multiple sclerosis. Administration of structurally diverse competitive and non-competitive AMPA antagonists reduces neurologic disability in rodents subjected to acute experimental autoimmune encephalomyelitis. In addition, AMPA antagonists are active in both the adoptive transfer and in chronic models of experimental autoimmune encephalomyelitis in rats and mice and affect both the acute and chronic relapsing phases. Moreover, short-term therapy with AMPA antagonists leads to sustained benefit well into the progressive phases. These results imply that therapeutic strategies for multiple sclerosis should be complemented by glutamate AMPA antagonists to reduce neurologic disability.

Functional expression of murine V2R pheromone receptors involves selective association with the M10 and M1 families of MHC class Ib molecules

The vomeronasal organ (VNO) of the mouse has two neuronal compartments expressing distinct families of pheromone receptors, the V1Rs and the V2Rs. We report here that two families of major histocompatibility complex (MHC) class Ib molecules, the M10 and the M1 families, show restricted expression in V2R-expressing neurons. Our data suggest that neurons expressing a given V2R specifically co-express one or a few members of the M10 family. Biochemical and immunocytochemical analysis demonstrates that in VNO sensory dendrites M10s belong to large multi-molecular complexes that include pheromone receptors and beta2-microglobulin (beta2m). In cultured cells, M10s appear to function as escort molecules in transport of V2Rs to the cell surface. Accordingly, beta2m-deficient mice exhibit mislocalization of V2Rs in the VNO and a specific defect in male-male aggressive behavior. The functional characterization of M10 highlights an unexpected role for MHC molecules in pheromone detection by mammalian VNO neurons.

Combinatorial coexpression of neural and immune multigene families in mouse vomeronasal sensory neurons

The vomeronasal organ (VNO) is a chemosensory organ specialized in the detection of pheromones in higher vertebrates. In mouse and rat, two gene superfamilies, V1r and V2r vomeronasal receptor genes, are expressed in sensory neurons whose cell bodies are located in, respectively, the apical and basal layers of the VNO epithelium. Here, we report that neurons of the basal layer express another multigene family, termed H2-Mv, representing nonclassical class I genes of the major histocompatibility complex. The nine H2-Mv genes are expressed differentially in subsets of neurons. More than one H2-Mv gene can be expressed in an individual neuron. In situ hybridization with probes for H2-Mv and V2r genes reveals complex and nonrandom combinations of coexpression. While neural expression of Mhc class I molecules is increasingly being appreciated, the H2-Mv family is distinguished by variegated expression across seemingly similar neurons and coexpression with a distinct multigene family encoding neural receptors. Our findings suggest that basal vomeronasal sensory neurons may consist of multiple lineages or compartments, defined by particular combinations of V2r and H2-Mv gene expression.

Impaired processing of brief, rapidly presented auditory cues in infants with a family history of autoimmune disorder

Studies have shown that individuals with language disorders, such as developmental dyslexia and specific language impairment, exhibit impairments in the processing of brief, successive, or rapidly changing auditory information. It is also the case that a higher rate of autoimmune disorders have been identified in those with language-based learning disorders and, conversely, that individuals with autoimmune disorders show a higher incidence of language-related disorders. The rapid auditory processing (RAP) deficits described for older individuals with language impairments may also be used as a behavioral marker to identify infants at higher risk for language delays. Thus, we were interested in examining RAP abilities in a subset of infants with a positive family history of autoimmune disorders. Eleven infants from our ongoing prospective longitudinal studies were identified based on parental response to a question about the presence of a family history of autoimmune disease and compared to 11 matched controls. The RAP threshold of each infant was assessed at 6 and 9 months of age using a conditioned head-turn procedure (using tone pairs with brief interstimulus intervals) and an auditory-visual habituation-recognition memory task using computer-generated consonant-vowel syllables (/ba/ vs. /da/). A visual habituation-recognition memory task that did not require processing of brief temporal cues was also administered. Group differences emerged on the infant RAP tasks, and on language outcome measures at 12 and 16 months of age. Infants from families with a history of autoimmune disorder had significantly higher (i.e., poorer) RAP thresholds and lower language scores than did control infants, whereas visual discrimination scores did not differ between family history infants and controls. Moreover, when brief auditory cues were necessary for the discrimination of /ba/ vs. /da/, infants with a family history of autoimmune disorder performed significantly more poorly than did controls. These findings lend support to the hypothesis that a similar mechanism, perhaps a neural-immune interaction, may underlie the observed co-occurrence of autoimmune disorders and learning impairments.

Visual motion sensitivity and reading

Reading is more difficult than speaking because an arbitrary set of visual symbols must be rapidly identified, ordered and translated into the sounds they represent. Many poor readers have particular problems with the rapid visual processing required for these tasks because they have a mild impairment of the visual magnocellular system. This deficit has been demonstrated using neuropathological, evoked potential, functional magnetic resonance imaging and psychophysical techniques. The sensitivity of the M-system in both good and bad readers correlates with their orthographic abilities, suggesting that the M-system plays an important part in their development. This role is probably to mediate steady direction of visual attention and eye fixations on words. Thus many children with reading difficulties have unsteady eye control and this causes the letters they are trying to read to appear to move around, so that they cannot tell what order they are meant to be in. Therefore, boosting M-performance using yellow filters, or training eye fixation, can improve reading performance very significantly. Several genetic linkage studies have associated reading difficulties with the MHC control region on the short arm of chromosome 6. This system has recently been shown to help regulate the differentiation of M-cells. This association could also explain the high incidence of autoimmune conditions in poor readers. Other chromosomal sites are associated with the metabolism of polyunsaturated fatty acids (PUFAs) as found in fish oils, and this could explain why PUFA supplements can improve reading.

Trajectories of brain development: point of vulnerability or window of opportunity?

Brain development is a remarkable process. Progenitor cells are born, differentiate, and migrate to their final locations. Axons and dendrites branch and form important synaptic connections that set the stage for encoding information potentially for the rest of life. In the mammalian brain, synapses and receptors within most regions are overproduced and eliminated by as much as 50% during two phases of life: immediately before birth and during the transitions from childhood, adolescence, to adulthood. This process results in different critical and sensitive periods of brain development. Since Hebb (1949) first postulated that the strengthening of synaptic elements occurs through functional validation, researchers have applied this approach to understanding the sculpting of the immature brain. In this manner, the brain becomes wired to match the needs of the environment. Extensions of this hypothesis posit that exposure to both positive and negative elements before adolescence can imprint on the final adult topography in a manner that differs from exposure to the same elements after adolescence. This review endeavors to provide an overview of key components of mammalian brain development while simultaneously providing a framework for how perturbations during these changes uniquely impinge on the final outcome.

The rainbow trout classical MHC class I molecule Onmy-UBA*501 is expressed in similar cell types as mammalian classical MHC class I molecules

Onmy-UBA is a polymorphic classical major histocompatibility (MHC) class I locus in rainbow trout (Oncorhynchus mykiss). A common allomorph is Onmy-UBA*501, which has been detected in several wildtype strains, in the clonal homozygous rainbow trout C25 and, in the current study, in the rainbow trout gonad cell line RTG-2. The extracellular domain of this allomorph was expressed in E. coli and a murine monoclonal antibody designated H9 was generated against the recombinant protein. In Western blot analysis Mab H9 specifically recognised an n-glycosylated protein of 45 kDa in leucocytes and erythrocytes of C25 fish and in RTG-2 cells. The level of Onmy-UBA*501 expression in erythrocytes was very low. Immunocytochemistry of isolated cells indicated expression in lymphocytes, macrophages, neutrophils, erythrocytes, RTG-2 cells and Onmy-UBA *501 transfected CHO cells, but not in untransfected CHO cells. Immunohistochemistry using frozen sections of C25 fish indicated that Onmy-UBA*501 expression is strong in the lymphoid organs (thymus, head kidney and spleen) and in the epithelia and endothelia of several organs. No significant expression was observed in muscle fibres, hepatocytes or neurons. These observations demonstrate that in jawed fish, the lowest phylogenetic group possessing an MHC system, the classical MHC class I molecules are expressed in similar cell types as in higher vertebrates.

Differential expression of class I MHC mRNA in the hypothalamus of Lewis and Fischer rats

The expression of class I major histocompatibility complex (MHC) mRNA was compared in the brains of inflammatory susceptible, hypothalamic-pituitary-adrenal (HPA)-axis blunted Lewis rats and inflammatory resistant, HPA-axis hyperresponsive Fischer rats by quantitative in situ hybridization following lipopolysaccharide (LPS) or vehicle administration. Lewis rats showed lower levels of class I MHC in the hypothalamic paraventricular nucleus (PVN) and retrochiasmatic area (RCA) compared to Fischer rats under both vehicle and LPS conditions. No differences were detected in other brain structures. Differential class I MHC expression in Lewis rats suggests an alteration in mechanisms related to cellular activity of neuroendocrine cells rather than alterations specific to neuroendocrine molecules.

Aberrant transcription of unrearranged T-cell receptor ? gene in mouse brain

The nervous system and the immune system share several functional molecules involved in various cell-cell interaction events. In this study, we used in situ hybridization to identify immune molecules that are expressed by a restricted population of neurons in the mouse brain and found that mRNA for the beta subunit of T-cell receptor (TCRbeta) was predominantly and strongly localized to neurons in deep layers of the cerebral neocortex and weakly expressed in the thalamus. Developmentally, TCRbeta mRNA expression started at embryonic day 15 in the thalamic nuclei and at postnatal day 1 in the cerebral neocortex. The level of TCRbeta mRNA in the neocortex subsequently increased until postnatal day 21, and it remained high in the adult. Detailed analysis revealed that only the Cbeta2 segment of TCRbeta, not the Cbeta1 or Vbeta segments, was expressed by the brain neurons. By the 5' rapid amplification of cDNA ends method, we determined a brain-specific transcription start site in the Jbeta2 region locus, not in the Vbeta region locus. Furthermore, we confirmed that the aberrant transcription around the Jbeta2 region took place only in neurons and lymphocytes in transgenic mice. These results demonstrate that the transcriptional machinery for unrearranged TCRbeta expression is shared by the nervous and immune systems and raise a possibility of gene rearrangement in neurons under certain circumstances.

The role of nAChR-mediated spontaneous retinal activity in visual system development

In the developing vertebrate retina, nAChR synapses are among the first to appear. This early cholinergic circuitry plays a key role in generating "retinal waves," spontaneously generated waves of action potentials that sweep across the ganglion cell layer. These retinal waves exist for a short period of time during development when several circuits within the visual system are being established. Here I review the cholinergic circuitry of the developing retina and the role these early circuits play in the development of the retina itself and of retinal projections to the lateral geniculate nucleus of the thalamus.

Identification of Munc13-3 as a candidate gene for critical-period neuroplasticity in visual cortex

The first several months of life are a critical period for neuronal plasticity in the visual cortex during which anatomic and physiological development depends on visual experience. In cats, electrophysiologically assessed neuronal plasticity is minimal until approximately 3 weeks, peaks at 5 weeks, gradually declines to low levels at 20 weeks, and disappears at approximately 1 year of age (Daw, 1994). Rearing in darkness slows the entire time course of this critical period, such that at 5 weeks of age, normal cats are more plastic than dark-reared cats, whereas at 20 weeks, dark-reared cats are more plastic (Mower, 1991; Beaver et al., 2001). Thus, a stringent criterion is that genes that are important for plasticity in visual cortex will show differences in expression between normal rearing and dark rearing that are of opposite direction in young versus older animals. The present study reports the identification by differential display PCR of Munc13-3, a mammalian homolog of the Caenorhabditis elegans "uncoordinated" gene (unc-13), as a candidate gene for critical-period neuronal plasticity, the expression of which is regulated according to this criterion specifically in visual cortex and not in frontal cortex. Other members of the Munc13 family (Munc13-1 and Munc13-2) do not meet this criterion in visual cortex, indicating that Munc13-3 is the only family member that is regulated by age and dark rearing in the same manner as physiological plasticity during the visual cortical critical period.

Induced neuronal expression of class I major histocompatibility complex mRNA in acute and chronic inflammation models

Studies have demonstrated neuronal expression of class I major histocompatibility complex (MHC) mRNA and protein in normal and developing brain and in response to injury or viral infection. We report neuronal expression of class I MHC mRNA in hypothalamic paraventricular nucleus (PVN) neurons in rats following systemic infection with Trypanosoma brucei brucei parasites (chronic) and in response to intravenous 1 mg/kg lipopolysaccharide administration (acute peripheral) and in striatal neurons following intrastriatal 5 microg lipopolysaccharide injection (acute central). These results demonstrate that neurons can be a source of immune signaling molecules and establish class I MHC as part of the neuronal component of immune responses.

Transcriptional analysis in the brain: trophin-induced hippocampal synaptic plasticity

Gene profiling in the central nervous system presents unique challenges due to the unprecedented heterogeneity of cells, systems and functions in time and space. We have employed a multidisciplinary approach using whole cell patch clamp recording and transcriptional analysis to define the genomic basis of trophin-induced hippocampal synaptic plasticity. Transcriptional analysis of single cells by linear amplification of antisense RNA has added a new dimension of sensitivity and selectivity to the study of the complex and heterogeneous population of neurons. We describe different gene expression profiling techniques that offer novel approaches to monitoring thousands of genes in parallel, fostering identification of circuits involved in learning and memory.

The newt ortholog of CD59 is implicated in proximodistal identity during amphibian limb regeneration

The proximodistal identity of a newt limb regeneration blastema is respecified by exposure to retinoic acid, but its molecular basis is unclear. We identified from a differential screen the cDNA for Prod 1, a gene whose expression in normal and regenerating limbs is regulated by proximodistal location and retinoic acid: Prod 1 is the newt ortholog of CD59. Prod 1/CD59 was found to be located at the cell surface with a GPI anchor which is cleaved by PIPLC. A proximal newt limb blastema engulfs a distal blastema after juxtaposition in culture, and engulfment is specifically blocked by PIPLC, and by affinity-purified antibodies to two distinct Prod 1/CD59 peptides. Prod 1 is therefore a cell surface protein implicated in the local cell-cell interactions mediating positional identity.

The sensory basis of reading problems

Learning to read is much more difficult than learning to speak. Most children teach themselves to speak with little or no difficulty. Yet a few years later when they come to learn to read they have to be taught how to do it; they do not pick up reading by themselves. This is because we speak in words and syllables, but we write in phonemes. Syllables do not naturally break down into the sounds of letters and letter units (i.e., phonemes) because these do not correspond to physiologically distinct articulatory gestures (Liberman, Shankweiler, & Studdert-Kennedy, 1967). Alphabetic writing was only invented when people realized that syllables could be artificially divided into smaller acoustically distinguishable phonemes that could be represented by a small number of letters. But these distinctions are arbitrary cultural artifacts, and their mastery was originally confined to a select social class. And until about 100 years ago it did not matter much if the majority of people could not read; the acquisition of reading probably had no serious disadvantages. Reading requires the integration of at least two kinds of analysis (Castles & Coltheart, 1993; Ellis, 1984; Manis, Seidenberg, Doi, McBride-Chang, & Petersen, 1996; Morton, 1969; Seidenburg, 1993). First, the visual form of words, the shape of letters, their order in words, and common spelling patterns, which is termed their orthography, has to be processed visually. Their orthography yields the meaning of familiar words very rapidly without needing to sound them out. But for unfamiliar words, and all words are fairly unfamiliar to the beginning reader, the letters have to be translated into the speech sounds (i.e., phonemes) that they stand for, and then those sounds have to be melded together in inner speech to yield the word and its meaning. Reading exclusively by the phonological route is more time consuming than if words can be accessed directly without requiring phonological mediation.

Inflammation in neurodegenerative disease--a double-edged sword

Inflammation is a defense reaction against diverse insults, designed to remove noxious agents and to inhibit their detrimental effects. It consists of a dazzling array of molecular and cellular mechanisms and an intricate network of controls to keep them in check. In neurodegenerative diseases, inflammation may be triggered by the accumulation of proteins with abnormal conformations or by signals emanating from injured neurons. Given the multiple functions of many inflammatory factors, it has been difficult to pinpoint their roles in specific (patho)physiological situations. Studies of genetically modified mice and of molecular pathways in activated glia are beginning to shed light on this issue. Altered expression of different inflammatory factors can either promote or counteract neurodegenerative processes. Since many inflammatory responses are beneficial, directing and instructing the inflammatory machinery may be a better therapeutic objective than suppressing it.

Retinogeniculate axons undergo eye-specific segregation in the absence of eye-specific layers

Spontaneous retinal activity mediated by cholinergic transmission regulates the segregation of retinal ganglion cell axons in the lateral geniculate nucleus of the thalamus into eye-specific layers. The details of how the layers form are unknown. Mice lacking the beta2 subunit of the neuronal nicotinic acetylcholine receptor lack ACh-mediated waves and as a result, do not form eye-specific layers at any stage of development. However, during the second postnatal week, beta2-/- mice have glutamate-mediated waves. Here we show that after the first postnatal week, even in the absence of layers, retinothalamic axons segregate into an unlayered, patchy distribution of eye-specific regions. These results indicate that spontaneous neural activity may independently regulate eye-specific segregation and the formation of layers at the developing retinothalamic projection.

Evidence that toxicity of lipopolysaccharide upon cholinergic basal forebrain neurons requires the presence of glial cells in vitro

The cholinergic system of the basal forebrain is affected in brains of dementia patients and during neuroinflammation. The aim of this study was to establish a method to cultivate basal forebrain cholinergic neurons in dissociated, pure neuronal cultures and to apply this method to study the effect of acute and chronic experimentally-induced inflammation using lipopolysaccharide. Purity of the cultures, degrees of neuronal dissociation, connectivity and neuronal survival were investigated by immunocytochemistry for microtubule-associated protein-2 (neurons), glial fibrillary acidic protein (astroglia), complement receptor 3 (microglia), choline acetyltransferase and the neurotrophin receptor p75 (cholinergic neurons). Neuronal cultures only contained <7% astrocytes and <1% microglia when using a "sandwich-technique". Acute (1, 10 microg/ml) as well as chronic (0.1, 1 microg/ml) treatment with lipopolysaccharide did neither affect total number of neurons, nor number of p75-positive neurons or enhance expression of major histocompatibility complex I or II. Our results suggest that lipopolysaccharide-induced degeneration of both microtubule-associated protein-2-like immunoreactive as well as specific killing of cholinergic forebrain neurons in vitro are mediated by glial cells.

Ganglioside expression in tissues of mice lacking beta2-microglobulin

This study presents a comparative analysis of gangliosides from lymphoid (spleen and thymus) and other (brain, liver, lungs and muscle) tissues of C57BL/6 mice lacking the gene for beta2-microglobulin (beta2M), a constitutive component of the MHC class I molecule. Ganglioside fractions in the tissues of mice homozygous (beta2M-/-) and heterozygous (beta2M-/+) for the gene deletion were determined by high performance thin-layer chromatography (HPTLC), followed by immunostaining with specific polyclonal antibodies. Ubiquitous gangliosides GM3(Neu5Ac) and GM3(Neu5Gc) were the dominant gangliosides in the lungs of the control beta2M-/+ mice, whereas the homozygous knockout mice had substantially decreased expression of these structures. The lungs of the beta2M-/- mice also had reduced expression of T-lymphocyte-specific GM1b-type gangliosides (GM1b and GalNAc-GM1b). beta2M-deficient mice also had more GM1a and GD1a gangliosides in the liver, and several neolacto-series gangliosides were increased in the brain and lungs. This study provides in vivo evidence that the beta2M molecule can influence the acquisition of a distinct ganglioside assembly in different mouse organs, implicating its non-immunological functions.

Innate immunity: the missing link in neuroprotection and neurodegeneration?

Innate immunity was previously thought to be a nonspecific immunological programme that was engaged by peripheral organs to maintain homeostasis after stress and injury. Emerging evidence indicates that this highly organized response also takes place in the central nervous system. Through the recognition of neuronal fingerprints, the long-term induction of the innate immune response and its transition to an adaptive form might be central to the pathophysiology and aetiology of neurodegenerative disorders. Paradoxically, this response also protects neurons by favouring remyelination and trophic support afforded by glial cells.

Failure of sensory neurons to express class I MHC is due to differential SOCS1 expression

Neurons, unlike glia and most other cell types, fail to express major histocompatibility complex (MHC) molecules, even in response to IFNgamma. This study shows that sensory neurons but not glia constitutively express high levels of suppressor of cytokine signaling-1 (SOCS1), a negative regulator of IFNgamma signaling. Neurons from SOCS1 null mice expressed class I MHC in response to IFNgamma, while SOCS1 overexpression in glia inhibited MHC induction. Differential expression of SOCS1 by neurons explains their failure to express MHC. Regulation of SOCS1 induction and therefore neuronal responses to IFNgamma may be critical for neuron survival following viral infection or injury.

MHC and MHC-related proteins as pleiotropic signal molecules

Class I molecules of the major histocompatibility complex (MHC) have been studied primarily for their role in presenting peptide antigens to conventional T lymphocytes. An increasing body of evidence suggests that MHC and newly characterized MHC-related molecules have a much more varied function in the body. Many of these molecules are involved in pleiotropic interactions with other proteins, which initiate signal transduction cascades and contribute to cellular and tissue homeostasis.

Experience-dependent plasticity of mouse visual cortex in the absence of the neuronal activity-dependent marker egr1/zif268

Neuronal activity elicits a rapid increase in the expression of several immediate early genes (IEGs). To clarify a role for IEG response in activity-dependent development, we examined the contribution of the egr1/zif268 gene during visual cortical processing and plasticity in mice. We first analyzed the expression of egr1 mRNA in wild-type (WT) mice using Northern blot hybridization. In the visual cortex, expression of egr1 mRNA increased dramatically after eye opening, systemic injection of kainate, or 30 min of photostimulation after a brief (5 d) period of dark adaptation. Thus, the expression of egr1 is regulated by synaptic activity in the mouse visual cortex, as it is in other species (e.g., monkeys, cats, and rats). To evaluate whether this transcription factor is directly involved in activity-dependent plasticity, mice lacking Egr1 were deprived of the use of one eye during the developmental critical period [postnatal day 24 (P24)-P34]. Extracellular in vivo single-unit recordings from the binocular zone of the visual cortex revealed that visual responses developed normally in egr1 knock-out (KO) mice. Moreover, a similarly significant shift of responsiveness in favor of the open eye was produced in both KO and WT mice by either brief (4 d) or long-term (>2 weeks) occlusion of one eye. There was no apparent compensation among egr2, egr3, or c-fos mRNA and protein expression in the visual cortex of egr1 KO mice. Taken together, these results indicate that egr1 is a useful marker of sensory input in mice but is not intrinsically necessary for the experience-dependent plasticity of the visual cortex. Our findings underscore a mechanistic distinction between sensory plasticity and long-lasting forms of synaptic potentiation in the hippocampus, for which egr1/zif268 was recently found to be essential.

Voltage-gated channels block nicotinic regulation of CREB phosphorylation and gene expression in neurons

Synaptic activation of the transcription factor CREB and downstream gene expression usually depend on calcium influx aided by voltage-gated calcium channels. We find that nicotinic signaling, in contrast, activates CREB and gene expression in ciliary ganglion neurons both in culture and in situ only if voltage-gated channels are silent. The nicotinic response requires calcium influx and release from internal stores and acts through CaMK and MAPK pathways to sustain activated CREB. Voltage-gated channels mobilize CaMK to activate CREB initially, but they also enable calcineurin and PP1 to terminate the activation before transcription is affected. L-type voltage-gated channels dominate the outcome and block the effects of nicotinic signaling on transcription. This demonstrates a novel aspect of activity-dependent gene regulation.

The clinical spectrum and pathogenesis of paraneoplastic disorders of the central nervous system

Paraneoplastic neurologic disorders (PND) refer to neurologic disorders of unknown cause that occur at higher frequency in patients with cancer than in the general population. There is increasing evidence that many of these disorders are immune mediated and associated with cytotoxic antitumor immunity. The identification of the immune responses in these patients facilitates the diagnosis of the PND and has led to the cloning and characterization of the target antigens in the nervous system and tumor.

Electrical activity and development of neural circuits

A distinct feature of the nervous system is the intricate network of synaptic connections among neurons of diverse phenotypes. Although initial connections are formed largely through molecular mechanisms that depend on intrinsic developmental programs, spontaneous and experience-driven electrical activities in the developing brain exert critical epigenetic influence on synaptic maturation and refinement of neural circuits. Selective findings discussed here illustrate some of our current understanding of the effects of electrical activity on circuit development and highlight areas that await further study.

Neuronal plasticity and cellular immunity: shared molecular mechanisms

It is becoming evident that neurons express an unusual number of molecules that were originally thought to be specific to immune functions. One such molecule, class I major histocompatibility complex, is required in the activity-dependent refinement and plasticity of connections in the developing and adult central nervous system, demonstrating that molecules can perform critical roles in both systems. Recent studies reveal striking parallels between cellular signaling mechanisms in the immune and nervous systems that may provide unexpected insights into the development, function, and diseases of both systems.

In vivo expression of major histocompatibility complex molecules on oligodendrocytes and neurons during viral infection

Demyelination in multiple sclerosis and in animal models is associated with infiltrating CD8+ and CD4+ T cells. Although oligodendrocytes and axons are damaged in these diseases, the roles T cells play in the demyelination process are not completely understood. Antigen-specific CD8+ T cell lysis of target cells is dependent on interactions between the T cell receptor and major histocompatibility complex (MHC) class I-peptide complexes on the target cell. In the normal central nervous system, expression of MHC molecules is very low but often increases during inflammation. We set out to precisely define which central nervous system cells express MHC molecules in vivo during infection with a strain of murine hepatitis virus that causes a chronic, inflammatory demyelinating disease. Using double immunofluorescence labeling, we show that during acute infection with murine hepatitis virus, MHC class I is expressed in vivo by oligodendrocytes, neurons, microglia, and endothelia, and MHC class II is expressed only by microglia. These data indicate that oligodendrocytes and neurons have the potential to present antigen to T cells and thus be damaged by direct antigen-specific interactions with CD8+ T lymphocytes.

Paraneoplastic neurologic disease antigens: RNA-binding proteins and signaling proteins in neuronal degeneration

Studies of the disorders known as paraneoplastic neurologic degenerations exemplify the successful application of modern molecular biological techniques to diseases, yielding, even for these extremely rare disorders, wide-ranging insight into basic neurobiology, tumor immunity, and autoimmune neurologic disease. Immune responses to paraneoplastic neurologic degeneration antigens, also called onconeural antigens, have been exploited to clone and characterize a number of neuron-specific proteins, including several RNA-binding proteins and new kinds of signaling molecules. The biology and functions of these proteins are reviewed, and a model in which their functions are related to the pathogenesis of autoimmune neurologic disease is discussed.

Embryonic regionalization of the neocortex

Understanding the development of the vertebrate brain and in particular that of the neocortex, where high brain functions reside, remains one of the most difficult and exciting tasks in biology. In this review, we discuss recent experimental evidence as well as different possibilities for the intrinsic regionalization of the embryonic dorsal telencephalon, which may be related to the formation of distinct functional areas in the adult neocortex.

Genetic and functional relationships between MHC and NK receptor genes

HLA class I and NK receptors are encoded within dense clusters of immune loci. The MHC, at 6p21.3, and the complex containing the KIR loci, at 19q13.4, both feature variation in the number of genes, as well as sequence polymorphism. In addition to T cell receptors, several variable class I-related molecules interact with polymorphic NK receptors. Some of the lectin-related NK receptor genes, at 12p13.1, also have ligands belonging to the extended class I family. The expanding clusters of class I-related sequences and their receptors, some of which evolved recently, reveal further complexity in immune recognition of disease.

The CRE/CREB pathway is transiently expressed in thalamic circuit development and contributes to refinement of retinogeniculate axons

The development of precise connections in the mammalian brain proceeds through refinement of initially diffuse patterns, a process that occurs largely within critical developmental windows. To elucidate the molecular pathways that orchestrate these early periods of circuit remodeling, we have examined the role of a calcium- and cAMP-regulated transcriptional pathway. We show that there is a window of CRE/CREB-mediated gene expression in the developing thalamus, which precedes neocortical expression. In the LGN, this wave of gene expression occurs prior to visual experience, but requires retinal function. Mutant mice with reduced CREB expression show loss of refinement of retinogeniculate projections. These results suggest an important role of the CRE/CREB transcriptional pathway in the coordination of experience-independent circuit remodeling during forebrain development.

A novel p75NTR signaling pathway promotes survival, not death, of immunopurified neocortical subplate neurons

Subplate neurons of mammalian neocortex undergo pronounced cell death postnatally, long after they have matured and become incorporated into functional cortical circuits. They express the p75 neurotrophin receptor (p75NTR), which is known to signal cell death in some types of neurons via the activation of sphingomyelinase and the concomitant increase in the sphingolipid ceramide. To evaluate the role of p75NTR in subplate neurons, they were immunopurified and cultured in vitro. Contrary to its known function as a death receptor, ligand binding to p75NTR promotes subplate neuron survival. Moreover, p75NTR-dependent survival is blocked by inhibition of ceramide synthesis and rescued by addition of its precursor sphingomyelin. Inhibition of Trk signaling does not block survival, nor is Trk signaling alone sufficient to promote survival. Thus, ligand-dependent p75NTR regulation of the ceramide pathway mediates survival in certain neurons and may represent an important target for neuroprotective drugs in degenerative diseases involving p75NTR-expressing neurons, such as Alzheimer's disease.

Developmental regulation of CPG15 expression in Xenopus

Mechanisms controlling dendritic arbor formation affect the establishment of neuronal circuits. Candidate plasticity gene 15 (CPG15) is a glycosylphosphatidyl inositol (GPI)-linked activity-induced protein that has been shown to function as an intercellular signaling molecule that can promote the morphological and physiological development of the Xenopus retinotectal system. A thorough understanding of CPG15 function requires knowledge of the spatiotemporal expression of the endogenous protein. We therefore cloned Xenopus cpg15 and used RNA in situ hybridization and immunohistochemistry to determine the pattern of CPG15 expression. cpg15 mRNA and CPG15 protein are first detectable in the developing spinal cord and become widespread as development proceeds. CPG15 is expressed in sensory regions of the brain, including the visual, auditory, and olfactory systems. Within the retina, CPG15 is only expressed in retinal ganglion cells. CPG15 protein is concentrated in axon tracts, including retinal axons. These data support a model in which CPG15 expressed in retinal ganglion cells is trafficked to retinal axons, where it modulates postsynaptic dendritic arbor elaboration, and synaptic maturation.

N-methyl-D-aspartate receptors regulate a group of transiently expressed genes in the developing brain

Mammalian brain development requires the transmission of electrical signals between neurons via the N-methyl-d-aspartate (NMDA) class of glutamate receptors. However, little is known about how NMDA receptors carry out this role. Here we report the first genes shown to be regulated by physiological levels of NMDA receptor function in developing neurons in vivo: NMDA receptor-regulated gene 1 (NARG1), NARG2, and NARG3. These genes share several striking regulatory features. All three are expressed at high levels in the neonatal brain in regions of neuronal proliferation and migration, are dramatically down-regulated during early postnatal development, and are down-regulated by NMDA receptor function. NARG2 and NARG3 appear to be novel, while NARG1 is the mammalian homologue of a yeast N-terminal acetyltransferase that regulates entry into the G(o) phase of the cell cycle. The results suggest that highly specific NMDA receptor-dependent regulation of gene expression plays an important role in the transition from proliferation of neuronal precursors to differentiation of neurons.

The magnocellular theory of developmental dyslexia

Low literacy is termed 'developmental dyslexia' when reading is significantly behind that expected from the intelligence quotient (IQ) in the presence of other symptoms--incoordination, left-right confusions, poor sequencing--that characterize it as a neurological syndrome. 5-10% of children, particularly boys, are found to be dyslexic. Reading requires the acquisition of good orthographic skills for recognising the visual form of words which allows one to access their meaning directly. It also requires the development of good phonological skills for sounding out unfamiliar words using knowledge of letter sound conversion rules. In the dyslexic brain, temporoparietal language areas on the two sides are symmetrical without the normal left-sided advantage. Also brain 'warts' (ectopias) are found, particularly clustered round the left temporoparietal language areas. The visual magnocellular system is responsible for timing visual events when reading. It therefore signals any visual motion that occurs if unintended movements lead to images moving off the fovea ('retinal slip'). These signals are then used to bring the eyes back on target. Thus, sensitivity to visual motion seems to help determine how well orthographic skill can develop in both good and bad readers. In dyslexics, the development of the visual magnocellular system is impaired: development of the magnocellular layers of the dyslexic lateral geniculate nucleus (LGN) is abnormal; their motion sensitivity is reduced; many dyslexics show unsteady binocular fixation; hence poor visual localization, particularly on the left side (left neglect). Dyslexics' binocular instability and visual perceptual instability, therefore, can cause the letters they are trying to read to appear to move around and cross over each other. Hence, blanking one eye (monocular occlusion) can improve reading. Thus, good magnocellular function is essential for high motion sensitivity and stable binocular fixation, hence proper development of orthographic skills. Many dyslexics also have auditory/phonological problems. Distinguishing letter sounds depends on picking up the changes in sound frequency and amplitude that characterize them. Thus, high frequency (FM) and amplitude modulation (AM) sensitivity helps the development of good phonological skill, and low sensitivity impedes the acquisition of these skills. Thus dyslexics' sensitivity to FM and AM is significantly lower than that of good readers and this explains their problems with phonology. The cerebellum is the head ganglion of magnocellular systems; it contributes to binocular fixation and to inner speech for sounding out words, and it is clearly defective in dyslexics. Thus, there is evidence that most reading problems have a fundamental sensorimotor cause. But why do magnocellular systems fail to develop properly? There is a clear genetic basis for impaired development of magnocells throughout the brain. The best understood linkage is to the region of the Major Histocompatibility Complex (MHC) Class 1 on the short arm of chromosome 6 which helps to control the production of antibodies. The development of magnocells may be impaired by autoantibodies affecting the developing brain. Magnocells also need high amounts of polyunsaturated fatty acids to preserve the membrane flexibility that permits the rapid conformational changes of channel proteins which underlie their transient sensitivity. But the genes that underlie magnocellular weakness would not be so common unless there were compensating advantages to dyslexia. In developmental dyslexics there may be heightened development of parvocellular systems that underlie their holistic, artistic, 'seeing the whole picture' and entrepreneurial talents.

Selection of and evasion from cytotoxic T cell responses in the central nervous system

Cytotoxic CD8 T lymphocytes (CTLs) are critical for the clearance of noncytopathic viruses from infected cells. This chapter discusses one mechanism used by viruses to persist—namely, the selection of a variant virus in which changes in the sequence of a CTL epitope abrogate recognition. The unique features of cytotoxic CD8 T cell function in the central nervous system (CNS) are discussed. The role of CTL escape mutants in the viral evasion of the immune system and subsequent disease progression in non-CNS infections are summarized. The immune response in the CNS is similar to the response in extraneural tissue, but several aspects of the activation of the immune response, cellular trafficking, and antigen presentation are unique to the CNS. Although the CNS has classically been considered a site of immune privilege, surveillance of the normal CNS by circulating, activated lymphocytes occurs, with a limited number of lymphocytes being present in the normal CNS at any given time. In mice infected with mouse hepatitis virus and in some humans persistently infected with human immunodeficiency virus type1, hepatitis B virus or hepatitis C virus, CTL escape mutants play an important role in virus amplification and disease progression.