Receptor tyrosine kinase ErbB4 modulates neuroblast migration and placement in the adult forebrain

Cellular and molecular determinants of stroke-induced changes in subventricular zone cell migration

A remarkable aspect of adult neurogenesis is that the tight regulation of subventricular zone (SVZ) neuroblast migration is altered after ischemic stroke and newborn neurons emigrate towards the injury. This phenomenon is an essential component of endogenous repair and also serves to illuminate normal mechanisms and rules that govern SVZ migration. Stroke causes inflammation that leads to cytokine and chemokine release, and SVZ neuroblasts that express their receptors are recruited. Metalloproteinases create pathways and new blood vessels provide a scaffold to facilitate neuroblast migration between the SVZ and the infarct. Most experiments have studied the peri-lesion parenchyma and relatively little is known about SVZ remodeling after stroke. Migration in the SVZ is tightly regulated by cellular interactions and molecular signaling; how are these altered after stroke to allow emigration? Do ependymal cells contribute to this process, given their reported neurogenic potential? How does stroke affect ependymal cell regulation of cerebrospinal fluid flow? Given the heterogeneity of SVZ progenitors, do all types of neuroblasts migrate out, or is this confined to specific subtypes of cells? We discuss these and other questions in our review and propose experiments to address them.

Exome sequencing identifies GRIN2A as frequently mutated in melanoma

The incidence of melanoma is increasing more than any other cancer, and knowledge of its genetic alterations is limited. To systematically analyze such alterations, we performed whole-exome sequencing of 14 matched normal and metastatic tumor DNAs. Using stringent criteria, we identified 68 genes that appeared to be somatically mutated at elevated frequency, many of which are not known to be genetically altered in tumors. Most importantly, we discovered that TRRAP harbored a recurrent mutation that clustered in one position (p. Ser722Phe) in 6 out of 167 affected individuals (∼4%), as well as a previously unidentified gene, GRIN2A, which was mutated in 33% of melanoma samples. The nature, pattern and functional evaluation of the TRRAP recurrent mutation suggest that TRRAP functions as an oncogene. Our study provides, to our knowledge, the most comprehensive map of genetic alterations in melanoma to date and suggests that the glutamate signaling pathway is involved in this disease.

Neuregulin 1 promotes excitatory synapse development and function in GABAergic interneurons

Neuregulin 1 (NRG1) and its receptor ErbB4 are both susceptibility genes of schizophrenia. However, little is known about the underlying mechanisms of their malfunction. Although ErbB4 is enriched in GABAergic interneurons, the role of NRG1 in excitatory synapse formation in these neurons remains poorly understood. We showed that NRG1 increased both the number and size of PSD-95 puncta and the frequency and amplitude of miniature EPSCs (mEPSCs) in GABAergic interneurons, indicating that NRG1 stimulates the formation of new synapses and strengthens existing synapses. In contrast, NRG1 treatment had no effect on either the number or size of excitatory synapses in glutamatergic neurons, suggesting its synaptogenic effect is specific to GABAergic interneurons. Ecto-ErbB4 treatment diminished both the number and size of excitatory synapses, suggesting that endogenous NRG1 may be critical for basal synapse formation. NRG1 could stimulate the stability of PSD-95 in the manner that requires tyrosine kinase activity of ErbB4. Finally, deletion of ErbB4 in parvalbumin-positive interneurons led to reduced frequency and amplitude of mEPSCs, providing in vivo evidence that ErbB4 is important in excitatory synaptogenesis in interneurons. Together, our findings suggested a novel synaptogenic role of NRG1 in excitatory synapse development, possibly via stabilizing PSD-95, and this effect is specific to GABAergic interneurons. In light of the association of the genes of both NRG1 and ErbB4 with schizophrenia and dysfunction of GABAergic system in this disorder, these results provide insight into its potential pathological mechanism.

Prospects and limitations of using endogenous neural stem cells for brain regeneration

Neural stem cells (NSCs) are capable of producing a variety of neural cell types, and are indispensable for the development of the mammalian brain. NSCs can be induced in vitro from pluripotent stem cells, including embryonic stem cells and induced-pluripotent stem cells. Although the transplantation of these exogenous NSCs is a potential strategy for improving presently untreatable neurological conditions, there are several obstacles to its implementation, including tumorigenic, immunological, and ethical problems. Recent studies have revealed that NSCs also reside in the adult brain. The endogenous NSCs are activated in response to disease or trauma, and produce new neurons and glia, suggesting they have the potential to regenerate damaged brain tissue while avoiding the above-mentioned problems. Here we present an overview of the possibility and limitations of using endogenous NSCs in regenerative medicine.

Trafficking of stem cells

Stem cells undergo regulated trafficking from the developmental stages to the adulthood. Stem cell migration is critical to organize developing organs and likely contributes postnatally to tissue regeneration. Here, we review the molecular mechanisms underlying migration of hematopoietic stem cells, neural stem cells, and primordial germ cells, revealing common operative pathways.

Neuroplasticity signaling pathways linked to the pathophysiology of schizophrenia

Schizophrenia is a severe mental illness that afflicts nearly 1% of the world's population. One of the cardinal pathological features of schizophrenia is perturbation in synaptic connectivity. Although the etiology of schizophrenia is unknown, it appears to be a developmental disorder involving the interaction of a potentially large number of risk genes, with no one gene producing a strong effect except rare, highly penetrant copy number variants. The purpose of this review is to detail how putative schizophrenia risk genes (DISC-1, neuregulin/ErbB4, dysbindin, Akt1, BDNF, and the NMDA receptor) are involved in regulating neuroplasticity and how alterations in their expression may contribute to the disconnectivity observed in schizophrenia. Moreover, this review highlights how many of these risk genes converge to regulate common neurotransmitter systems and signaling pathways. Future studies aimed at elucidating the functions of these risk genes will provide new insights into the pathophysiology of schizophrenia and will likely lead to the nomination of novel therapeutic targets for restoring proper synaptic connectivity in the brain in schizophrenia and related disorders.

Control of neuronal migration through rostral migration stream in mice

During the nervous system development, immature neuroblasts have a strong potential to migrate toward their destination. In the adult brain, new neurons are continuously generated in the neurogenic niche located near the ventricle, and the newly generated cells actively migrate toward their destination, olfactory bulb, via highly specialized migratory route called rostral migratory stream (RMS). Neuroblasts in the RMS form chains by their homophilic interactions, and the neuroblasts in chains continually migrate through the tunnels formed by meshwork of astrocytes, glial tube. This review focuses on the development and structure of RMS and the regulation of neuroblast migration in the RMS. Better understanding of RMS migration may be crucial for improving functional replacement therapy by supplying endogenous neuronal cells to the injury sites more efficiently.

Ectopic expression of α-synuclein affects the migration of neural stem cells in mouse subventricular zone

α-Synuclein (α-syn) is a key protein in Parkinson's disease (PD), and its abnormal accumulation is implicated only not in the loss of dopaminergic neurons in the substantia nigra but also in impairment of olfactory bulb (OB) in PD. Olfactory dysfunction could arise from these OB changes as an early symptom in PD. We reported previously the impairment of neuronal stem cell (NSC) proliferation in the subventricular zone, which is upstream of OB in PD models. Reduction of NSC generation could potentially lead to olfactory dysfunction, which is commonly associated with and precedes the motor symptoms by several years in PD. Here, we investigated neurosphere formation in vitro and migration of NSCs in vivo after transduction of α-syn-encoding retroviral vector to characterize the function of α-syn in NSC. Over-expression of α-syn caused less effective formation of neurospheres and induced morphological changes. Fluorescence-activated cell sorting showed diminished NSC cell cycle progression induced by over-expression of α-syn. Intriguingly, suppression of NSC migration along the rostral migratory stream was observed when the α-syn-encoding vector was directly injected into the subventricular zone of mice in vivo. These results indicate that α-syn affects the generation of NSC and suggest that this protein could serve as a tool for the design of potentially useful therapy for PD patients.

Strategies for analyzing neuronal progenitor development and neuronal migration in the developing cerebral cortex

The emergence of functional neuronal connectivity in the developing cerebral cortex depends on 1) neural progenitor differentiation, which leads to the generation of appropriate number and types of neurons, and 2) neuronal migration, which enables the appropriate positioning of neurons so that the correct patterns of functional synaptic connectivity between neurons can emerge. In this review, we discuss 1) currently available methods to study neural progenitor development and differentiation in the developing cerebral cortex and emerging technologies in this regard, 2) assays to study the migration of descendents of progenitors (i.e., neurons) in vitro and in vivo, and 3) the use of these assays to probe the molecular control of these events in the developing brain and evaluation of gene functions disrupted in human neurodevelopmental disorders.

The neuregulin signaling pathway and schizophrenia: from genes to synapses and neural circuits

Numerous genetic linkage and association studies implicate members of the Neuregulin-ErbB receptor (NRG-ErbB) signaling pathway as schizophrenia "at risk" genes. An emphasis of this review is to propose plausible neurobiological mechanisms, regulated by the Neuregulin-ErbB signaling network, that may be altered in schizophrenia and contribute to its etiology. To this end, the distinct neurotransmitter pathways, neuronal subtypes and neural network systems altered in schizophrenia are initially discussed. Next, the review focuses on the possible significance of genetic studies associating NRG1 and ErbB4 with schizophrenia, in light of the functional role of this signaling pathway in regulating glutamatergic, GABAergic and dopaminergic neurotransmission, as well as modulating synaptic plasticity and gamma oscillations. The importance of restricted ErbB4 receptor expression in GABAergic interneurons is emphasized, particularly their expression at glutamatergic synapses of parvalbumin-positive fast-spiking interneurons where modulation of inhibitory drive could account for the dramatic effects of NRG-ErbB signaling on gamma oscillations and pyramidal neuron output. A case is made for reasons that the NRG-ErbB signaling pathway constitutes a "biologically plausible" system for understanding the pathogenic mechanisms that may underlie the complex array of positive, negative and cognitive deficits associated with schizophrenia during development.

Neurodegeneration in schizophrenia

The neurodegenerative aspect of schizophrenia presupposes gene-environmental interactions involving chromosomal abnormalities and obstetric/perinatal complications that culminate in predispositions that impart a particular vulnerability for drastic and unpredictable precipitating factors, such as stress or chemical agents. The notion of a neurodevelopmental progression to the disease state implies that early developmental insults, with neurodegenerative proclivities, evolve into structural brain abnormalities involving specific regional circuits and neurohumoral agents. This neurophysiological orchestration is expressed in the dysfunctionality observed in premorbid signs and symptoms arising in the eventual diagnosis, as well as the neurobehavioral deficits reported from animal models of the disorder. The relative contributions of perinatal insults, neonatal ventral hippocampus lesion, prenatal methylazoxymethanol acetate and early traumatic experience, as well as epigenetic contributions, are discussed from a neurodegenerative view of the essential neuropathology. It is implied that these considerations of factors that exert disruptive influences upon brain development, or normal aging, operationalize the central hub of developmental neuropathology around which the disease process may gain momentum. Nonetheless, the status of neurodegeneration in schizophrenia is somewhat tenuous and it is possible that brain imaging studies on animal models of the disorder, which may describe progressive alterations to cortical, limbic and ventricular structures similar to those of schizophrenic patients, are necessary to resolve the issue.

Dynamic imaging reveals that brain-derived neurotrophic factor can independently regulate motility and direction of neuroblasts within the rostral migratory stream

Neuronal precursors generated in the subventricular zone (SVZ) migrate through the rostral migratory stream (RMS) to the olfactory bulb (OB). Although, the mechanisms regulating this migration remain largely unknown. Studies have shown that molecular factors, such as brain-derived neurotrophic factor (BDNF) emanating from the OB, may function as chemoattractants drawing neuroblasts toward their target. To better understand the role of BDNF in RMS migration, we used an acute slice preparation from early postnatal mice to track the tangential migration of GAD65-GFP labeled RMS neuroblasts with confocal time-lapse imaging. By quantifying the cell dynamics using specific directional and motility criteria, our results showed that removal of the OB did not alter the overall directional trajectory of neuroblasts, but did reduce their motility. This suggested that additional guidance factors present locally within the RMS region also contribute to this migration. Here we report that BDNF and its high affinity receptor, tyrosine kinase receptor type 2 (TrkB), are indeed heterogeneously expressed within the RMS at postnatal day 7. By altering BDNF levels within the entire pathway, we showed that reduced BDNF signaling changes both neuroblast motility and direction, while increased BDNF levels changes only motility. Together these data reveal that during this early postnatal period BDNF plays a complex role in regulating both the motility and direction of RMS flow, and that BDNF comes from sources within the RMS itself, as well as from the olfactory bulb.

Selective populations of hippocampal interneurons express ErbB4 and their number and distribution is altered in ErbB4 knockout mice

Neuregulins (NRGs) are ligands of ErbB receptor tyrosine kinases. The NRG1-ErbB4 pathway has been shown to modulate hippocampal synaptic plasticity and network oscillations in the adult rodent brain. To identify cells that mediate these effects, here we determine the expression pattern of ErbB4 in four functionally distinct classes of interneurons that represent the majority of all inhibitory neurons in the adult hippocampus. On the basis of data from nine mice and 25,000 cells, we show that ErbB4 is expressed in cells that are positive for cholecystokinin (CCK, 54%), parvalbumin (PV, 42%), or neuronal nitric oxide synthase (nNOS, 39%) in a layer-specific and region-specific manner, whereas cells expressing somatostatin (SOM) are rarely immunoreactive for ErbB4 (1%). We next compared the numerical density (cells/mm(3)) and the distribution of interneurons between ErbB4-/- mice and wildtype controls. Based on data from 25 mice and 56,000 cells, we detected reductions of PV-positive and nNOS-positive cells in knockouts (-24% and -27%, respectively) but only a minor reduction of CCK-positive cells; no changes in SOM-positive cells were observed. The overall reduction of interneurons was verified by quantification of GAD67-immunoreactive cells (-24% in ErbB4-/- mice). The reduction of interneurons along the dorsoventral axis was more severe in intermediate and ventral portions than in the dorsal hippocampus, and regional reductions occurred in the CA1-3 regions and subiculum, whereas we found no significant changes in the dentate gyrus (DG). The expression by different populations of interneurons suggests that ErbB4 can modulate several microcircuits within the hippocampus and mediate the previously reported effects of NRG1 on network oscillations and synaptic plasticity. The selective reduction of GABAergic cells in ErbB4-/- mice is consistent with the role of NRG-ErbB4 signaling in the generation and migration of interneurons during development, and with neuronal and behavioral functional deficits in adult ErbB4 knockouts.

Common genetic variation in Neuregulin 3 (NRG3) influences risk for schizophrenia and impacts NRG3 expression in human brain

Structural and polymorphic variations in Neuregulin 3 (NRG3), 10q22-23 are associated with a broad spectrum of neurodevelopmental disorders including developmental delay, cognitive impairment, autism, and schizophrenia. NRG3 is a member of the neuregulin family of EGF proteins and a ligand for the ErbB4 receptor tyrosine kinase that plays pleotropic roles in neurodevelopment. Several genes in the NRG-ErbB signaling pathway including NRG1 and ErbB4 have been implicated in genetic predisposition to schizophrenia. Previous fine mapping of the 10q22-23 locus in schizophrenia identified genome-wide significant association between delusion severity and polymorphisms in intron 1 of NRG3 (rs10883866, rs10748842, and rs6584400). The biological mechanisms remain unknown. We identified significant association of these SNPs with increased risk for schizophrenia in 350 families with an affected offspring and confirmed association to patient delusion and positive symptom severity. Molecular cloning and cDNA sequencing in human brain revealed that NRG3 undergoes complex splicing, giving rise to multiple structurally distinct isoforms. RNA expression profiling of these isoforms in the prefrontal cortex of 400 individuals revealed that NRG3 expression is developmentally regulated and pathologically increased in schizophrenia. Moreover, we show that rs10748842 lies within a DNA ultraconserved element and homedomain and strongly predicts brain expression of NRG3 isoforms that contain a unique developmentally regulated 5' exon (P = 1.097E(-12) to 1.445E(-15)). Our observations strengthen the evidence that NRG3 is a schizophrenia susceptibility gene, provide quantitative insight into NRG3 transcription traits in the human brain, and reveal a probable mechanistic basis for disease association.

Directing traffic in neural cells: determinants of receptor tyrosine kinase localization and cellular responses

The trafficking of receptor tyrosine kinases (RTKs) to distinct subcellular locations is essential for the specificity and fidelity of signal transduction and biological responses. This is particularly important in the PNS and CNS in which RTKs mediate key events in the development and maintenance of neurons and glia through a wide range of neural processes, including survival, proliferation, differentiation, neurite outgrowth, and synaptogenesis. The mechanisms that regulate the targeting of RTKs to their subcellular destinations for appropriate signal transduction, however, are still elusive. In this review, we discuss evidence for the spatial organization of signaling machinery into distinct subcellular compartments, as well as the role for ligand specificity, receptor sorting signals, and lipid raft microdomains in RTK targeting and the resultant cellular responses in neural cells.

New neurons clear the path of astrocytic processes for their rapid migration in the adult brain

In the long-range neuronal migration of adult mammals, young neurons travel from the subventricular zone to the olfactory bulb, a long journey (millimeters to centimeters, depending on the species). How can these neurons migrate through the dense meshwork of neuronal and glial processes of the adult brain parenchyma? Previous studies indicate that young neurons achieve this by migrating in chains through astrocytic tunnels. Here, we report that young migrating neurons actively control the formation and maintenance of their own migration route. New neurons secrete the diffusible protein Slit1, whose receptor, Robo, is expressed on astrocytes. We show that the Slit-Robo pathway is required for morphologic and organizational changes in astrocytes that result in the formation and maintenance of the astrocytic tunnels. Through this neuron-glia interaction, the new neurons regulate the formation of the astrocytic meshwork that is needed to enable their rapid and directional migration in adult brain.

Olfactory ensheathing cells: attractant of neural progenitor migration to olfactory bulb

Olfactory ensheathing cells (OECs) are the glial cells that derive from the olfactory placode, envelop olfactory axons in the course of migration from the olfactory epithelium to the olfactory bulb and reside primarily in the olfactory nerve layer. OECs transplantation as a promising experimental therapy for axonal injuries has been intensively studied; however, little is known about their roles in olfactory bulb development. In this study, we examined the effects of OECs on the migration of neural progenitors in rostral migratory stream (RMS). Initially, the neurosphere migration assay showed that OEC-conditioned medium promoted progenitors to migrate from RMS neurospheres in a concentration dependent manner. Moreover, co-culturing OECs nearby the RMS explants led to asymmetric migration of explants in different developing stages. However, OECs could influence the migration in a distance not further than 1.5 mm. Finally, slice assay that mimic the circumstance in vivo revealed that OECs had a chemoattractive activity on RMS neural progenitors. Together, these results demonstrate that OECs attract neural progenitors in RMS through the release of diffusible factors and it is likely that OECs mainly influence radial migration in the olfactory bulb but not tangential migration of the RMS invivo during development. This suggests a previously unknown function for OECs in olfactory development and a novel mechanism underlying the targeting of RMS cells.

Axon guidance and neuronal migration research in China

Proper migration of neuronal somas and axonal growth cones to designated locations in the developing brain is essential for the assembly of functional neuronal circuits. Rapid progress in research of axon guidance and neuronal migration has been made in the last twenty years. Chinese researchers began their exploration in this field ten years ago and have made significant contributions in clarifying the signal transduction of axon guidance and neuronal migration. Several unique experimental approaches, including the migration assay of single isolated neurons in response to locally delivered guidance cues, have been developed by Chinese neuroscientists to investigate the molecular machinery underlying these guidance events.

Molecules and mechanisms involved in the generation and migration of cortical interneurons

The GABA (γ-aminobutyric acid)-containing interneurons of the neocortex are largely derived from the ganglionic eminences in the subpallium. Numerous studies have previously defined the migratory paths travelled by these neurons from their origins to their destinations in the cortex. We review here results of studies that have identified many of the genes expressed in the subpallium that are involved in the specification of the subtypes of cortical interneurons, and the numerous transcription factors, motogenic factors and guidance molecules that are involved in their migration.

Identification of microRNAs regulated by activin A in human embryonic stem cells

Human embryonic stem (hES) cells have the capacities to propagate for extended periods and to differentiate into cell types from all three germ layers both in vitro and in vivo. These characteristics of self-renewal and pluripotency enable hES cells having the potential to provide an unlimited supply of different cell types for tissue replacement, drug screening, and functional genomics studies. The hES-T3 cells with normal female karyotype cultured on either mouse embryonic fibroblasts (MEF) in hES medium (containing 4 ng/ml bFGF) (T3MF) or feeder-free Matrigel in MEF-conditioned medium (supplemented with additional 4 ng/ml bFGF) (T3CM) were found to express very similar profiles of mRNAs and microRNAs, indicating that the unlimited self-renewal and pluripotency of hES cells can be maintained by continuing culture on these two conditions. However, the expression profiles, especially microRNAs, of the hES-T3 cells cultured on Matrigel in hES medium supplemented with 4 ng/ml bFGF and 5 ng/ml activin A (T3BA) were found to be different from those of T3MF and T3CM cells. In T3BA cells, four hES cell-specific microRNAs miR-372, miR-302d, miR-367, and miR-200c, as well as three other microRNAs miR-199a, miR-19a, and miR-217, were found to be up-regulated, whereas five miRNAs miR-19b, miR-221, miR-222, let-7b, and let-7c were down-regulated by activin A. Thirteen abundantly differentially expressed mRNAs, including NR4A2, ERBB4, CXCR4, PCDH9, TMEFF2, CD24, and COX6A1 genes, targeted by seven over-expressed miRNAs were identified by inverse expression levels of these seven microRNAs to their target mRNAs in T3BA and T3CM cells. The NR4A2, ERBB4, and CXCR4 target genes were further found to be regulated by EGF and/or TNF. The 50 abundantly differentially expressed genes targeted by five under-expressed miRNAs were also identified. The abundantly expressed mRNAs in T3BA and T3CM cells were also analyzed for the network and signaling pathways, and roles of activin A in cell proliferation and differentiation were found. These findings will help elucidate the complex signaling network which maintains the self-renewal and pluripotency of hES cells.

Expression of ezrin radixin moesin proteins in the adult subventricular zone and the rostral migratory stream

Continuous proliferation occurs in the adult subventricular zone (SVZ) of the lateral ventricles throughout life. In the SVZ, progenitor cells differentiate into neuroblasts, which migrate tangentially along the rostral migratory stream (RMS) to reach their final destination in the olfactory bulb. These progenitor cells mature and integrate into the existing neural network of the olfactory bulb. Long distance migration of neuroblasts in the RMS requires a highly dynamic cytoskeleton with the ability to respond to surrounding stimuli. Radixin is a member of the ERM (Ezrin, Radixin, Moesin) family, which connect the actin cytoskeleton to the extracellular matrix through transmembrane proteins. The membrane-cytoskeleton linker proteins of the ERM family may regulate cellular events with a high demand on cytoskeleton plasticity, such as cell motility. Recently, specific expression of the ERM protein ezrin was shown in the RMS. Radixin however has not been characterized in this region. Here we used immunohistochemistry and confocal microscopy to examine the expression of radixin in the different cell types of the adult subventricular zone niche and in the RMS. Our findings indicate that radixin is strongly expressed in neuroblasts of the adult RMS and subventricular zone, and also in Olig2-positive cells. We also demonstrate the presence of radixin in the cerebral cortex, striatum, cerebellum, thalamus, hippocampus as well as the granular and periglomerular layers of the olfactory bulb. Our studies also reveal the localization of radixin in neurosphere culture studies and we reveal the specificity of our labeling using Western blotting. The expression pattern demonstrated here suggests a role for radixin in neuronal migration and differentiation in the adult RMS. Understanding how adult neuronal migration is regulated is of importance for the development of new therapeutic interventions using endogenous repair for neurodegenerative diseases.

Dynamic roles of FGF-2 and Anosmin-1 in the migration of neuronal precursors from the subventricular zone during pre- and postnatal development

FGF-2 and Anosmin-1 are diffusible proteins which act in cell proliferation and/or migration during CNS development. We describe their developmental expression patterns in the subventricular zone (SVZ) of the forebrain and the neuronal precursors (NPs) that migrate from this neurogenic site towards the olfactory bulb, forming the rostral migratory stream (RMS). The analysis is carried out before (E14), during (E17, P5) and after (P15) the peaks of migration along the RMS and before this acquires its mature conformation. At all these stages, FGF-2 exerts a FGFR1-mediated motogenic effect on NPs and induces the proliferation of SVZ astrocytes (putatively type B cells from triads), and Anosmin-1 works as a typical chemotropic agent for the NPs (mediated by FGFR1 at P5-P15). Altogether, our results are consistent with the notion that FGF-2 increases cell proliferation in the SVZ and would be the motogenic cue which feeds the migration of the newly produced NPs once generated, from early development (E14) and at least until P15, while Anosmin-1 cooperates in this migration attracting the NPs. In this sense, both cues should be considered as two of the first to be chronologically identified as actors in the formation of the RMS.

Schizophrenia-related endophenotypes in heterozygous neuregulin-1 'knockout' mice

Neuregulin-1 (NRG1) has been shown to play a role in glutamatergic neurotransmission and is a risk gene for schizophrenia, in which there is evidence for hypoglutamatergic function. Sensitivity to the behavioural effects of the psychotomimetic N-methyl-D-aspartate receptor antagonists MK-801 and phencyclidine (PCP) was examined in mutant mice with heterozygous deletion of NRG1. Social behaviour (sociability, social novelty preference and dyadic interaction), together with exploratory activity, was assessed following acute or subchronic administration of MK-801 (0.1 and 0.2 mg/kg) or PCP (5 mg/kg). In untreated NRG1 mutants, levels of glutamate, N-acetylaspartate and GABA were determined using high-performance liquid chromatography and regional brain volumes were assessed using magnetic resonance imaging at 7T. NRG1 mutants, particularly males, displayed decreased responsivity to the locomotor-activating effects of acute PCP. Subchronic MK-801 and PCP disrupted sociability and social novelty preference in mutants and wildtypes and reversed the increase in both exploratory activity and social dominance-related behaviours observed in vehicle-treated mutants. No phenotypic differences were demonstrated in N-acetylaspartate, glutamate or GABA levels. The total ventricular and olfactory bulb volume was decreased in mutants. These data indicate a subtle role for NRG1 in modulating several schizophrenia-relevant processes including the effects of psychotomimetic N-methyl-D-aspartate receptor antagonists.

Adult mouse subventricular zone stem and progenitor cells are sessile and epidermal growth factor receptor negatively regulates neuroblast migration

Background

The adult subventricular zone (SVZ) contains stem and progenitor cells that generate neuroblasts throughout life. Although it is well accepted that SVZ neuroblasts are migratory, recent evidence suggests their progenitor cells may also exhibit motility. Since stem and progenitor cells are proliferative and multipotential, if they were also able to move would have important implications for SVZ neurogenesis and its potential for repair.

Methodology/Principal Findings

We studied whether SVZ stem and/or progenitor cells are motile in transgenic GFP+ slices with two photon time lapse microscopy and post hoc immunohistochemistry. We found that stem and progenitor cells; mGFAP-GFP+ cells, bright nestin-GFP+ cells and Mash1+ cells were stationary in the SVZ and rostral migratory stream (RMS). In our search for motile progenitor cells, we uncovered a population of motile βIII-tubulin+ neuroblasts that expressed low levels of epidermal growth factor receptor (EGFr). This was intriguing since EGFr drives proliferation in the SVZ and affects migration in other systems. Thus we examined the potential role of EGFr in modulating SVZ migration. Interestingly, EGFr^low neuroblasts moved slower and in more tortuous patterns than EGFr-negative neuroblasts. We next questioned whether EGFr stimulation affects SVZ cell migration by imaging Gad65-GFP+ neuroblasts in the presence of transforming growth factor alpha (TGF-α), an EGFr-selective agonist. Indeed, acute exposure to TGF-α decreased the percentage of motile cells by approximately 40%.

Conclusions/Significance

In summary, the present study directly shows that SVZ stem and progenitor cells are static, that EGFr is retained on some neuroblasts, and that EGFr stimulation negatively regulates migration. This result suggests an additional role for EGFr signaling in the SVZ.

Blood vessels form a migratory scaffold in the rostral migratory stream

In adult mice, new neurons born in the subventricular zone (SVZ), lining the lateral ventricles, migrate tangentially into the olfactory bulb along a well-delineated path, the rostral migratory stream (RMS). Neuroblasts in the RMS migrate tangentially in chains, without a recognized migratory scaffold. Here we quantitatively examine the distribution of, and relationships between, cells within the RMS, throughout its rostral-caudal extent. We show that there is a higher density of blood vessels in the RMS than in other brain regions, including areas with equal cell density, and that the orientation of blood vessels parallels the RMS throughout the caudal to rostral path. Of particular interest, migratory neuroblast chains are longitudinally aligned along blood vessels within the RMS, with over 80% of vessel length in rostral areas of the RMS apposed by neuroblasts. Electron micrographs show direct contact between endothelial cells and neuroblasts, although intervening astrocytic processes are often present. Within the RMS, astrocytes arborize extensively, extending long processes that are parallel to blood vessels and the direction of neuroblast migration. Thus, the astrocytic processes establish a longitudinal alignment within the RMS, rather than a more typical stellate shape. This complementary alignment suggests that blood vessels and astrocytes may cooperatively establish a scaffold for migrating neuroblasts, as well as provide and regulate migratory cues.

Neurodevelopmental mechanisms of schizophrenia: understanding disturbed postnatal brain maturation through neuregulin-1-ErbB4 and DISC1

Schizophrenia (SZ) is primarily an adult psychiatric disorder in which disturbances caused by susceptibility genes and environmental insults during early neurodevelopment initiate neurophysiological changes over a long time course, culminating in the onset of full-blown disease nearly two decades later. Aberrant postnatal brain maturation is an essential mechanism underlying the disease. Currently, symptoms of SZ are treated with anti-psychotic medications that have variable efficacy and severe side effects. There has been much interest in the prodromal phase and the possibility of preventing SZ by interfering with the aberrant postnatal brain maturation associated with this disorder. Thus, it is crucial to understand the mechanisms that underlie the long-term progression to full disease manifestation to identify the best targets and approaches towards this goal. We believe that studies of certain SZ genetic susceptibility factors with neurodevelopmental implications will be key tools in this task. Accumulating evidence suggests that neuregulin-1 (NRG1) and disrupted-in-schizophrenia-1 (DISC1) are probably functionally convergent and play key roles in brain development. We provide an update on the role of these emerging concepts in understanding the complex time course of SZ from early neurodevelopmental disturbances to later onset and suggest ways of testing these in the future.

Neurogenesis and Alzheimer's disease: at the crossroads

While a massive and progressive neuronal loss in specific areas such as the hippocampus and cortex unequivocally underlies cognitive deterioration and memory loss in Alzheimer's disease, noteworthy alterations take place in the neurogenic microenvironments, namely, the subgranule layer of the dentate gyrus and the subventricular zone. Compromised neurogenesis presumably takes place earlier than onset of hallmark lesions or neuronal loss, and may play a role in the initiation and progression of neuropathology in Alzheimer's disease. Neurogenesis in the adult brain is thought to play a role in numerous forms and aspects of learning and memory and contribute to the plasticity of the hippocampus and olfactory system. Misregulated or impaired neurogenesis on the other hand, may compromise plasticity and neuronal function in these areas and exacerbate neuronal vulnerability. Interestingly, increasing evidence suggests that molecular players in Alzheimer's disease, including PS1, APP and its metabolites, play a role in adult neurogenesis. In addition, recent studies suggest that alterations in tau phosphorylation are pronounced in neurogenic areas, and may interfere with the potential central role of tau proteins in neuronal maturation and differentiation. On the other hand, numerous neurogenic players, such as Notch-1, ErbB4 and L1 are substrates of alpha- beta- and gamma- secretase that play a major role in Alzheimer's disease. This review will discuss current knowledge concerning alterations of neurogenesis in Alzheimer's disease with specific emphasis on the cross-talk between signaling molecules involved in both processes, and the ways by which familial Alzheimer's disease-linked dysfunction of these signaling molecules affect neurogenesis in the adult brain.

Adult neurogenesis and the olfactory system

Though initially described in the early 1960s, it is only within the past decade that the concept of continuing adult neurogenesis has gained widespread acceptance. Neuroblasts from the subventricular zone (SVZ) migrate along the rostral migratory stream (RMS) into the olfactory bulb, where they differentiate into interneurons. Neuroblasts from the subgranular zone (SGZ) of the hippocampal formation show relatively little migratory behavior, and differentiate into dentate gyrus granule cells. In sharp contrast to embryonic and perinatal development, these newly differentiated neurons must integrate into a fully functional circuit, without disrupting ongoing performance. Here, after a brief historical overview and introduction to olfactory circuitry, we review recent advances in the biology of neural stem cells, mechanisms of migration in the RMS and olfactory bulb, differentiation and survival of new neurons, and finally mechanisms of synaptic integration. Our primary focus is on the olfactory system, but we also contrast the events occurring there with those in the hippocampal formation. Although both SVZ and SGZ neurogenesis are involved in some types of learning, their full functional significance remains unclear. Since both systems offer models of integration of new neuroblasts, there is immense interest in using neural stem cells to replace neurons lost in injury or disease. Though many questions remain unanswered, new insights appear daily about adult neurogenesis, regulatory mechanisms, and the fates of the progeny. We discuss here some of the central features of these advances, as well as speculate on future research directions.

Decreased expression of ErbB4 and tyrosine hydroxylase mRNA and protein in the ventral midbrain of aged rats

Decreased availability or efficacy of neurotrophic factors may underlie an increased susceptibility of mesencephalic dopaminergic cells to age-related degeneration. Neuregulins (NRGs) are pleotrophic growth factors for many cell types, including mesencephalic dopamine cells in culture and in vivo. The functional NRG receptor ErbB4 is expressed by virtually all midbrain dopamine neurons. To determine if levels of the NRG receptor are maintained during aging in the dopaminergic ventral mesencephalon, expression of ErbB4 mRNA and protein was examined in young (3 months), middle-aged (18 months), and old (24-25 months) Brown Norway/Fischer 344 F1 rats. ErbB4 mRNA levels in the substantia nigra pars compacta (SNpc), but not the adjacent ventral tegmental area (VTA) or subtantia nigra pars lateralis (SNl), were significantly reduced in the middle-aged and old animals when compared to young rats. Protein expression of ErbB4 in the ventral midbrain was significantly decreased in the old rats when compared to the young rats. Expression of tyrosine hydroxylase (TH) mRNA levels was significantly reduced in the old rats when compared to young animals in the SNpc, but not in the VTA or SNI. TH protein levels in the ventral midbrain were also decreased in the old animals when compared to the young animals. These data demonstrate a progressive decline of ErbB4 expression, coinciding with a loss of the dopamine-synthesizing enzyme TH, in the ventral midbrain of aged rats, particularly in the SNpc. These findings may implicate a role for diminished NRG/ErbB4 trophic support in dopamine-related neurodegenerative disorders of aging such as Parkinson's disease.

Analysis of neuronal proliferation, migration and differentiation in the postnatal brain using equine infectious anemia virus-based lentiviral vectors

Ongoing neurogenesis in discrete sectors of the adult central nervous system depends on the mitotic activity of an elusive population of adult stem cells. The existence of adult neural stem cells provides an alternative approach to transplantation of embryonic stem cells in cell-based therapies. Owing to the limited intrinsic fate of adult stem cells and inhibitory nature of the adult brain for neurogenesis, accommodation for circuit replacement in the brain will require genetic and epigenetic manipulation. Here, we show that a replication-incompetent Equine Infectious Anemia Virus (EIAV) is highly suitable for stable and persistent gene transfer to adult neural stem cells. The transduced regions were free of long-lasting neuroimmune responses to EIAV. Transduction in the subventricular zone was specific to the stem cell niche, but spared the progeny of adult neural stem cells that includes transit amplifying progenitors (TAPs) and migrating neuroblasts. With time, EIAV-transduced stem cells passed on the transgene to TAPs and migrating neuroblasts, which ultimately differentiated into neurons in the olfactory bulbs. We show that EIAV is highly suitable for discovery and assessment of mechanisms that regulate proliferation, migration and differentiation in the postnatal brain.

Deficient NRG1-ERBB signaling alters social approach: relevance to genetic mouse models of schizophrenia

Growth factor Neuregulin 1 (NRG1) plays an essential role in development and organization of the cerebral cortex. NRG1 and its receptors, ERBB3 and ERBB4, have been implicated in genetic susceptibility for schizophrenia. Disease symptoms include asociality and altered social interaction. To investigate the role of NRG1-ERBB signaling in social behavior, mice heterozygous for an Nrg1 null allele (Nrg1+/−), and mice with conditional ablation of Erbb3 or Erbb4 in the central nervous system, were evaluated for sociability and social novelty preference in a three-chambered choice task. Results showed that deficiencies in NRG1 or ERBB3 significantly enhanced sociability. All of the mutant groups demonstrated a lack of social novelty preference, in contrast to their respective wild-type controls. Effects of NRG1, ERBB3, or ERBB4 deficiency on social behavior could not be attributed to general changes in anxiety-like behavior, activity, or loss of olfactory ability. Nrg1+/− pups did not exhibit changes in isolation-induced ultrasonic vocalizations, a measure of emotional reactivity. Overall, these findings provide evidence that social behavior is mediated by NRG1-ERBB signaling.

Brain injury expands the numbers of neural stem cells and progenitors in the SVZ by enhancing their responsiveness to EGF

There is an increase in the numbers of neural precursors in the SVZ (subventricular zone) after moderate ischaemic injuries, but the extent of stem cell expansion and the resultant cell regeneration is modest. Therefore our studies have focused on understanding the signals that regulate these processes towards achieving a more robust amplification of the stem/progenitor cell pool. The goal of the present study was to evaluate the role of the EGFR [EGF (epidermal growth factor) receptor] in the regenerative response of the neonatal SVZ to hypoxic/ischaemic injury. We show that injury recruits quiescent cells in the SVZ to proliferate, that they divide more rapidly and that there is increased EGFR expression on both putative stem cells and progenitors. With the amplification of the precursors in the SVZ after injury there is enhanced sensitivity to EGF, but not to FGF (fibroblast growth factor)-2. EGF-dependent SVZ precursor expansion, as measured using the neurosphere assay, is lost when the EGFR is pharmacologically inhibited, and forced expression of a constitutively active EGFR is sufficient to recapitulate the exaggerated proliferation of the neural stem/progenitors that is induced by hypoxic/ischaemic brain injury. Cumulatively, our results reveal that increased EGFR signalling precedes that increase in the abundance of the putative neural stem cells and our studies implicate the EGFR as a key regulator of the expansion of SVZ precursors in response to brain injury. Thus modulating EGFR signalling represents a potential target for therapies to enhance brain repair from endogenous neural precursors following hypoxic/ischaemic and other brain injuries.

Vasculature guides migrating neuronal precursors in the adult mammalian forebrain via brain-derived neurotrophic factor signaling

Adult neuronal precursors retain the remarkable capacity to migrate long distances from the posterior (subventricular zone) to the most anterior [olfactory bulb (OB)] parts of the brain. The knowledge about the mechanisms that keep neuronal precursors in the migratory stream and organize this long-distance migration is incomplete. Here we show that blood vessels precisely outline the migratory stream for new neurons in the adult mammalian forebrain. Real-time video imaging of cell migration in the acute slices demonstrate that neuronal precursors are retained in the migratory stream and guided into the OB by blood vessels that serve as a physical substrate for migrating neuroblasts. Our data suggest that endothelial cells of blood vessels synthesize brain-derived neurotrophic factor (BDNF) that fosters neuronal migration via p75NTR expressed on neuroblasts. Interestingly, GABA released from neuroblasts induces Ca(2+)-dependent insertion of high-affinity TrkB receptors on the plasma membrane of astrocytes that trap extracellular BDNF. We hypothesize that this renders BDNF unavailable for p75NTR-expressing migrating cells and leads to their entrance into the stationary period. Our findings provide new insights into the functional organization of substrates that facilitate the long-distance journey of adult neuronal precursors.

In situ hybridization reveals developmental regulation of ErbB1-4 mRNA expression in mouse midbrain: implication of ErbB receptors for dopaminergic neurons

Although epidermal growth factor (EGF) and neuregulin-1 are neurotrophic factors for mesencephalic dopaminergic neurons and implicated in schizophrenia, the cellular localization and developmental regulation of their receptors (ErbB1-4) remain to be characterized. Here we investigated the distributions of mRNA for ErbB1-4 in the midbrain of the developing mouse with in situ hybridization and immunohistochemistry. The expression of ErbB1 and ErbB2 mRNAs was relatively high at the perinatal stage and frequently colocalized with mRNA for S100beta and Olig2, markers for immature astrocytes or oligodendrocyte precursors. Modest signal for ErbB1 mRNA was also detected in a subset of dopaminergic neurons. ErbB3 mRNA was detectable at postnatal day 10, peaked at postnatal day 18, and colocalized with 2',3'-cyclic nucleotide 3'-phosphodiesterase, a marker for oligodendrocytes. In contrast, ErbB4 mRNA was exclusively localized in neurons throughout development. Almost all of ErbB4 mRNA-expressing cells (94%-96%) were positive for tyrosine hydroxylase in the substantia nigra pars compacta but 66%-78% in the ventral tegmental area and substantia nigra pars lateralis. Conversely, 92%-99% of tyrosine hydroxylase-positive cells expressed ErbB4 mRNA. The robust and restricted expression of ErbB4 mRNA in the midbrain dopaminergic neurons suggests that ErbB4 ligands, neuregulin-1 and other EGF-related molecules, contribute to development or maintenance of this neuronal population.

Cell migration in the normal and pathological postnatal mammalian brain

In the developing brain, cell migration is a crucial process for structural organization, and is therefore highly regulated to allow the correct formation of complex networks, wiring neurons, and glia. In the early postnatal brain, late developmental processes such as the production and migration of astrocyte and oligodendrocyte progenitors still occur. Although the brain is completely formed and structured few weeks after birth, it maintains a degree of plasticity throughout life, including axonal remodeling, synaptogenesis, but also neural cell birth, migration and integration. The subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampus are the two main neurogenic niches in the adult brain. Neural stem cells reside in these structures and produce progenitors that migrate toward their ultimate location: the olfactory bulb and granular cell layer of the DG respectively. The aim of this review is to synthesize the increasing information concerning the organization, regulation and function of cell migration in a mature brain. In a normal brain, proteins involved in cell-cell or cell-matrix interactions together with secreted proteins acting as chemoattractant or chemorepellant play key roles in the regulation of neural progenitor cell migration. In addition, recent data suggest that gliomas arise from the transformation of neural stem cells or progenitor cells and that glioma cell infiltration recapitulates key aspects of glial progenitor migration. Thus, we will consider glioma migration in the context of progenitor migration. Finally, many observations show that brain lesions and neurological diseases trigger neural stem/progenitor cell activation and migration toward altered structures. The factors involved in such cell migration/recruitment are just beginning to be understood. Inflammation which has long been considered as thoroughly disastrous for brain repair is now known to produce some positive effects on stem/progenitor cell recruitment via the regulation of growth factor signaling and the secretion of a number of chemoattractant cytokines. This knowledge is crucial for the development of new therapeutic strategies. One of these strategies could consist in increasing the mobilization of endogenous progenitor cells that could replace lost cells and improve functional recovery.

The adenomatous polyposis coli protein is an essential regulator of radial glial polarity and construction of the cerebral cortex

Radial glia are highly polarized cells that serve as neuronal progenitors and as scaffolds for neuronal migration during construction of the cerebral cortex. How radial glial cells establish and maintain their morphological polarity is unknown. Using conditional gene targeting in mice, we demonstrate that adenomatous polyposis coli (APC) serves an essential function in the maintenance of polarized radial glial scaffold during brain development. In the absence of APC, radial glial cells lose their polarity and responsiveness to the extracellular polarity maintenance cues, such as neuregulin-1. Elimination of APC further leads to marked instability of the radial glial microtubule cytoskeleton. The resultant changes in radial glial function and loss of APC in radial glial progeny lead to defective generation and migration of cortical neurons, severely disrupted cortical layer formation, and aberrant axonal tract development. Thus, APC is an essential regulator of radial glial polarity and is critical for the construction of cerebral cortex in mammals.

ErbB4 genotype predicts left frontotemporal structural connectivity in human brain

Diminished left frontotemporal connectivity is among the most frequently reported findings in schizophrenia and there is evidence that altered neuronal myelination may in part account for this deficit. Several investigations have suggested that variations of the genes that encode the Neuregulin 1 (NRG1)-ErbB4 receptor complex are associated with schizophrenia illness. As NRG1--ErbB4 has been implicated in neuronal myelination, we investigated with diffusion tensor imaging (DTI) whether fractional anisotropy (FA)--a putative measure of neuronal myelination--is predicted by a risk haplotype of the ErbB4 gene. The effects of the ErbB4 genotype were investigated in healthy subjects (N=59; mean age: 22.6+/-1.8 years). We also measured reaction time (RT) during a selective attention/working memory paradigm (visual oddball). In the schizophrenia risk genotype group, we found lower FA in the temporal lobe white matter (WM) including frontotemporal fiber tracts, predominantly in the left hemisphere. RT was increased in the risk genotype group and correlated with FA in the affected brain region. As FA is considered to index structural integrity of WM, to which neuronal fiber myelination is contributing, our results suggest that variations of the ErbB4 genotype may confer risk for schizophrenia illness via its impact on left frontotemporal connectivity in human brain. Reliability and validity of the result is suggested by our observation that (1) the FA-genotype association was not only obtained in the entire sample but also in both the split halves and (2) a statistical relationship was found among RT, genotype and FA.

The ErbB4 growth factor receptor is required for colon epithelial cell survival in the presence of TNF

BACKGROUND & AIMS

The ErbB4 receptor tyrosine kinase regulates cell growth, survival, and differentiation in several tissues, but its role in the gastrointestinal tract has not been reported. We tested the hypothesis that ErbB4 promotes intestinal cell survival and restitution following injury or inflammation.

METHODS

ErbB4 expression in human inflammatory bowel disease was determined by immunohistochemistry. Mice were subjected to dextran sulfate sodium (DSS, 3%) colitis or injected with tumor necrosis factor (TNF), and ErbB4 expression was quantified by immunohistochemistry and Western blot. Cultured young adult mouse colon (YAMC) cells were exposed to TNF, and ErbB4 messenger RNA, protein, and phosphorylation levels were measured. Cells transfected with ErbB4 small interfering RNA (siRNA), or over expressing ErbB4, were subjected to wound healing and apoptosis assays.

RESULTS

ErbB4 levels increased in Crohn's colitis and the colon epithelium of mice with DSS colitis or injected with TNF. In YAMC cells, TNF induced ErbB4 messenger RNA, protein, and phosphorylation; nuclear factor kappaB activation also stimulated ErbB4 accumulation. ErbB4 siRNA sensitized cells to TNF-stimulated apoptosis, while over expression blocked apoptosis induced by TNF plus cycloheximide. Additionally, ErbB4 siRNA decreased YAMC cell wound healing. ErbB4 knockdown attenuated, while over expression elevated, phosphorylation of Akt in response to TNF. Inhibition of the phosphatidylinositol 3-kinase/Akt signaling cascade reversed the ability of ErbB4 over expression to protect from cytokine-induced apoptosis.

CONCLUSIONS

ErbB4 expression and signaling are key elements for TNF responses in vivo and in cell culture, protecting intestinal epithelial cells from apoptosis in the inflammatory environment, possibly through Akt activation.

Deficiency of TNFalpha converting enzyme (TACE/ADAM17) causes a lean, hypermetabolic phenotype in mice

Energy homeostasis involves central nervous system integration of afferent inputs that coordinately regulate food intake and energy expenditure. Here, we report that adult homozygous TNFalpha converting enzyme (TACE)-deficient mice exhibit one of the most dramatic examples of hypermetabolism yet reported in a rodent system. Because this effect is not matched by increased food intake, mice lacking TACE exhibit a lean phenotype. In the hypothalamus of these mice, neurons in the arcuate nucleus exhibit intact responses to reduced fat mass and low circulating leptin levels, suggesting that defects in other components of the energy homeostasis system explain the phenotype of Tace(DeltaZn/DeltaZn) mice. Elevated levels of uncoupling protein-1 in brown adipose tissue from Tace(DeltaZn/DeltaZn) mice when compared with weight-matched controls suggest that deficient TACE activity is linked to increased sympathetic outflow. These findings collectively identify a novel and potentially important role for TACE in energy homeostasis.

Altered growth factor signaling pathways as the basis of aberrant stem cell maturation in schizophrenia

In recent years evidence has accumulated that the activity of the signaling cascades of Neuregulin-1, Wnt, TGF-beta, BDNF-p75 and DISC1 is different between control subjects and patients with schizophrenia. These pathways are involved in embryonic and adult neurogenesis and neuronal maturation. A review of the clinical data indicates that in schizophrenia the Wnt pathway is most likely hypoactive, whereas the Nrg1-ErbB4, the TGF-beta- and the BDNF-p75-pathways are hyperactive. Haplo-insuffiency of the DISC1 gene is currently the best established schizophrenia risk factor. Preclinical experiments indicate that suppression of DISC1 signaling leads to accelerated dendrite development in neuronal stem cells, accelerated migration and aberrant integration into the neuronal network. Other preclinical experiments show that increasing NRG1-, BDNF- and TGF-beta signaling and decreasing Wnt signaling, also promotes adult neuronal differentiation and migration. Thus deviations in these pathways detected in schizophrenia could contribute to premature neuronal differentiation, accelerated migration and inappropriate insertion into the neuronal network. Initial clinical findings are confirmatory: neuronal stem cells isolated from nasal biopsies from schizophrenia patients display signs of accelerated development, whilst increased erosion of telomeres and bone age provide further support for accelerated cell maturation in schizophrenia.

A BAC transgenic mouse model to analyze the function of astroglial SPARCL1 (SC1) in the central nervous system

Extracellular matrix associated Sparc-like 1 (SC1/SPARCL1) can influence the function of astroglial cells in the developing and mature central nervous system (CNS). To examine SC1's significance in the CNS, we generated a BAC transgenic mouse model in which Sc1 is expressed in radial glia and their astrocyte derivatives using the astroglial-specific Blbp (Brain-lipid binding protein; [Feng et al., (1994) Neuron 12:895-908]) regulatory elements. Characterization of these Blbf-Sc1 transgenic mice show elevated Sc1 transcript and protein in an astroglial selective pattern throughout the CNS. This model provides a novel in vivo system for evaluating the role of SC1 in brain development and function, in general, and for understanding SC1's significance in the fate and function of astroglial cells, in particular.

Early myoclonic encephalopathy caused by a disruption of the neuregulin-1 receptor ErbB4

The tyrosine kinase receptor ErbB4 (erythroblastic leukemia viral oncogene homolog 4) plays a crucial role in numerous neurobiological processes in the developing and adult brain. Moreover, recent molecular genetics studies implicate ErbB4 in the pathophysiology of schizophrenia. However, the phenotypic consequences of haploinsufficiency of ErbB4 are not known, as no coding mutations have been identified until now. Here, we present a patient with early myoclonic encephalopathy and profound psychomotor delay with a de novo reciprocal translocation t(2;6)(q34;p25.3), disrupting the ErbB4 gene. This patient represents the first case of haploinsufficiency for one of the ErbB family members of tyrosine kinase receptors.

Neuregulin-1 modulates hippocampal gamma oscillations: implications for schizophrenia

Alterations in gamma-frequency oscillations are implicated in psychiatric disorders, and polymorphisms in NRG-1 and ERBB4, genes encoding Neuregulin-1 (NRG-1) and one of its receptors, designated ErbB4, are associated with schizophrenia. Here we show that NRG-1 selectively increases the power of kainate-induced, but not carbachol-induced, gamma oscillations in acute hippocampal slices. NRG-1beta is more effective than NRG-1alpha, a splice variant with lower affinity for ErbB receptors, and neither isoform affects the network activity without prior induction of gamma oscillations. NRG-1beta dramatically increases gamma oscillation power in hippocampal slices from both rats (2062 +/- 496%) and mice (710 +/- 299%). These effects of NRG-1beta are blocked by PD158780, a pan-specific antagonist of ErbB receptors, and are mediated specifically via ErbB4 receptors, because mice harboring a targeted mutation of ErbB4 do not respond to NRG-1. Moreover, we demonstrate that 50% of gamma-amino butyric acidergic parvalbumin (PV)-positive interneurons, which heavily contribute to the generation of gamma oscillations, express ErbB4 receptors. Importantly, both the number of PV-immunoreactive interneurons (-31%) and the power of kainate-induced gamma oscillations (-60%) are reduced in ErbB4 knockout mice. This study provides the first plausible link between NRG-1/ErbB4 signaling and rhythmic network activity that may be altered in persons with schizophrenia.

Specific developmental reductions in subventricular zone ErbB1 and ErbB4 mRNA in the human brain

The primate postnatal subventricular zone (SVZ) lies under the ventrolateral borders of the lateral ventricles as a discrete region of cells with gliogenic and neurogenic capacity regulated by ErbB receptors. However, the specific role of each ErbB subtype in SVZ cell development remains unclear, particularly in the human brain. The postnatal spatial and temporal expression profile of ErbB subtypes in the human brain may provide valuable insight into their distinct functions in the SVZ following birth. Hence, we examined the expression profile of ErbB1, ErbB2, ErbB3 and ErbB4 mRNA in the SVZ of human postmortem brains from neonates, infants, toddlers, school age subjects, adolescents, young adults and adults using in situ hybridization. SVZ transcript levels of ErbB1 and ErbB4 were highest in neonates and diminished with age. SVZ ErbB4 mRNA quantities significantly decreased by >85% to almost undetectable levels after the first year of life, while SVZ ErbB1 transcript levels displayed more gradual reductions, stabilizing to approximately 30-40% of neonate levels after the age of 5 years. In the neonate and infant SVZ, ErbB4 mRNA was localized to cell clusters resembling migratory neuroblast aggregates whereas ErbB1 mRNA was expressed in cells along but not within these clusters. ErbB2 mRNA appeared to be constantly expressed in the human SVZ at all postnatal ages as opposed to ErbB3 transcripts, which were not detected in the human SVZ at any age following birth. These findings suggest that ErbB1 and ErbB4 may play more salient roles than ErbB2 and ErbB3 in mediating early postnatal neurodevelopmental events. In addition, ErbB1- and ErbB4-immunoreactive cells and fibers were extensive throughout the human infant SVZ, but did not appear to overlap with PSA-NCAM-immunopositive clusters. The restriction of robust SVZ ErbB4 expression to neonate and infant age groups may indicate that SVZ-derived ErbB4-dependent postnatal neuronal development is most extensive within a narrow time frame early after birth.