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

Regulation of neurogenesis by calcium signaling

Calcium (Ca(2+)) signaling has essential roles in the development of the nervous system from neural induction to the proliferation, migration, and differentiation of neural cells. Ca(2+) signaling pathways are shaped by interactions among metabotropic signaling cascades, intracellular Ca(2+) stores, ion channels, and a multitude of downstream effector proteins that activate specific genetic programs. The temporal and spatial dynamics of Ca(2+) signals are widely presumed to control the highly diverse yet specific genetic programs that establish the complex structures of the adult nervous system. Progress in the last two decades has led to significant advances in our understanding of the functional architecture of Ca(2+) signaling networks involved in neurogenesis. In this review, we assess the literature on the molecular and functional organization of Ca(2+) signaling networks in the developing nervous system and its impact on neural induction, gene expression, proliferation, migration, and differentiation. Particular emphasis is placed on the growing evidence for the involvement of store-operated Ca(2+) release-activated Ca(2+) (CRAC) channels in these processes.

Downregulation of Sphingosine 1-Phosphate Receptor 1 Promotes the Switch from Tangential to Radial Migration in the OB

Neuroblast migration is a highly orchestrated process that ensures the proper integration of newborn neurons into complex neuronal circuits. In the postnatal rodent brain, neuroblasts migrate long distances from the subependymal zone of the lateral ventricles to the olfactory bulb (OB) within the rostral migratory stream (RMS). They first migrate tangentially in close contact to each other and later radially as single cells until they reach their final destination in the OB. Sphingosine 1-phosphate (S1P) is a bioactive lipid that interacts with cell-surface receptors to exert different cellular responses. Although well studied in other systems and a target for the treatment of multiple sclerosis, little is known about S1P in the postnatal brain. Here, we report that the S1P receptor 1 (S1P1) is expressed in neuroblasts migrating in the RMS. Using in vivo and in vitro gain- and loss-of-function approaches in both wild-type and transgenic mice, we found that the activation of S1P1 by its natural ligand S1P, acting as a paracrine signal, contributes to maintain neuroblasts attached to each other while they migrate in chains within the RMS. Once in the OB, neuroblasts cease to express S1P1, which results in cell detachment and initiation of radial migration, likely via downregulation of NCAM1 and β1 integrin. Our results reveal a novel physiological function for S1P1 in the postnatal brain, directing the path followed by newborn neurons in the neurogenic niche.

SIGNIFICANCE STATEMENT

The function of each neuron is highly determined by the position it occupies within a neuronal circuit. Frequently, newborn neurons must travel long distances from their birthplace to their predetermined final location and, to do so, they use different modes of migration. In this study, we identify the sphingosine 1-phosphate (S1P) receptor 1 (S1P1) as one of the key players that govern the switch from tangential to radial migration of postnatally generated neuroblasts in the olfactory bulb. Of interest is the evidence that the ligand, S1P, is provided by nearby astrocytes. Finally, we also propose adhesion molecules that act downstream of S1P1 and initiate the transition from tangential chain migration to individual radial migration outside of the stream.

Physiological electrical signals promote chain migration of neuroblasts by up-regulating P2Y1 purinergic receptors and enhancing cell adhesion

Neuroblasts migrate as directed chains of cells during development and following brain damage. A fuller understanding of the mechanisms driving this will help define its developmental significance and in the refinement of strategies for brain repair using transplanted stem cells. Recently, we reported that in adult mouse there are ionic gradients within the extracellular spaces that create an electrical field (EF) within the rostral migratory stream (RMS), and that this acts as a guidance cue for neuroblast migration. Here, we demonstrate an endogenous EF in brain slices and show that mimicking this by applying an EF of physiological strength, switches on chain migration in mouse neurospheres and in the SH-SY5Y neuroblastoma cell line. Firstly, we detected a substantial endogenous EF of 31.8 ± 4.5 mV/mm using microelectrode recordings from explants of the subventricular zone (SVZ). Pharmacological inhibition of this EF, effectively blocked chain migration in 3D cultures of SVZ explants. To mimic this EF, we applied a physiological EF and found that this increased the expression of N-cadherin and β-catenin, both of which promote cell-cell adhesion. Intriguingly, we found that the EF up-regulated P2Y purinoceptor 1 (P2Y1) to contribute to chain migration of neuroblasts through regulating the expression of N-cadherin, β-catenin and the activation of PKC. Our results indicate that the naturally occurring EF in brain serves as a novel stimulant and directional guidance cue for neuronal chain migration, via up-regulation of P2Y1.

Identification and functional studies of regulatory variants responsible for the association of NRG3 with a delusion phenotype in schizophrenia

We previously reported genetic linkage for Schizophrenia (SZ) (NPL of 4.7) at 10q22 in the Ashkenazi Jewish (AJ) population. In follow up fine mapping we found strong evidence of association between three intronic single nucleotide variants (SNVs) in the 5' end of Neuregulin 3 (NRG3) and the delusion factor score of our phenotypic principal component analysis. Two independent groups replicated these findings, indicating that variants in NRG3 confer risk for a delusion-rich SZ subtype. To identify the causative variants, we sequenced the 162 kb linkage disequilibrium (LD) block covering the NRG3 5' end in 47 AJ SZ patients at the extremes of the delusion factor quantitative trait distribution. Among the identified variants we found 5 noncoding SNVs present on the high delusion factor haplotype and significantly overrepresented in high delusion factor subjects. We tested these for regulatory effects and found that risk alleles of rs10883866 and rs60827755 decreased and increased, respectively, the expression of a reporter gene as compared to the reference allele. In post-mortem brain RNA quantification experiments we found the same variants also perturb relative expression of alternative NRG3 isoforms. In summary, we have identified regulatory SNVs contributing to the association of NRG3 with delusion symptoms in SZ.

Hic-5 Mediates TGFβ-Induced Adhesion in Vascular Smooth Muscle Cells by a Nox4-Dependent Mechanism

OBJECTIVE

Focal adhesions (FAs) link the cytoskeleton to the extracellular matrix and as such play important roles in growth, migration, and contractile properties of vascular smooth muscle cells. Recently, it has been shown that downregulation of Nox4, a transforming growth factor (TGF) β-inducible, hydrogen peroxide (H2O2)-producing enzyme, affects the number of FAs. However, the effectors downstream of Nox4 that mediate FA regulation are unknown. The FA resident protein H2O2-inducible clone (Hic)-5 is H2O2 and TGFβ inducible, and a binding partner of the heat shock protein (Hsp) 27. The objective of this study was to elucidate the mechanism, by which Hic-5 and Hsp27 participate in TGFβ-induced, Nox4-mediated vascular smooth muscle cell adhesion and migration.

APPROACH AND RESULTS

Through a combination of molecular biology and biochemistry techniques, we found that TGFβ, by a Nox4-dependent mechanism, induces the expression and interaction of Hic-5 and Hsp27, which is essential for Hic-5 localization to FAs. Importantly, we found that Hic-5 expression is required for the TGFβ-mediated increase in FA number, adhesive forces and migration. Mechanistically, Nox4 downregulation impedes Smad (small body size and mothers against decapentaplegic) signaling by TGFβ, and Hsp27 and Hic-5 upregulation by TGFβ is blocked in small body size and mothers against decapentaplegic 4-deficient cells.

CONCLUSIONS

Hic-5 and Hsp27 are effectors of Nox4 required for TGFβ-stimulated FA formation, adhesion strength and migration in vascular smooth muscle cell.

Genetic labeling reveals novel cellular targets of schizophrenia susceptibility gene: distribution of GABA and non-GABA ErbB4-positive cells in adult mouse brain

Neuregulin 1 (NRG1) and its receptor ErbB4 are schizophrenia risk genes. NRG1-ErbB4 signaling plays a critical role in neural development and regulates neurotransmission and synaptic plasticity. Nevertheless, its cellular targets remain controversial. ErbB4 was thought to express in excitatory neurons, although recent studies disputed this view. Using mice that express a fluorescent protein under the promoter of the ErbB4 gene, we determined in what cells ErbB4 is expressed and their identity. ErbB4 was widely expressed in the mouse brain, being highest in amygdala and cortex. Almost all ErbB4-positive cells were GABAergic in cortex, hippocampus, basal ganglia, and most of amygdala in neonatal and adult mice, suggesting GABAergic transmission as a major target of NRG1-ErbB4 signaling in these regions. Non-GABAergic, ErbB4-positive cells were present in thalamus, hypothalamus, midbrain, and hindbrain. In particular, ErbB4 is expressed in serotoninergic neurons of raphe nuclei but not in norepinephrinergic neurons of the locus ceruleus. In hypothalamus, ErbB4 is present in neurons that express oxytocin. Finally, ErbB4 is expressed in a group of cells in the subcortical areas that are positive for S100 calcium binding protein β. These results identify novel cellular targets of NRG1-ErbB4 signaling.

Level of plasma neuregulin-1 SMDF is reduced in patients with idiopathic Parkinson's disease

Parkinson's disease (PD) is characterised by the progressive loss of dopaminergic neurons, neurons that are regulated by the development, protection and function of neuregulin-1 (NRG1)-ErbB4 signals, in the substantia nigra (SN). NRG1 is a neurotrophic differentiation factor and one of its isoforms is a sensory and motor neuron-derived factor (SMDF), mostly expressed in neurons. To examine the relationship between NRG1 SMDF and PD, we tested whether NRG1 SMDF can be detected and measured in plasma and whether their level in plasma correlates with the clinical severity of PD. We detected NRG1 SMDF to be immunoreactive in plasma. Using an ELISA method specific for NRG1 SMDF, we found that NRG1 SMDF levels were significantly reduced in sporadic PD as compared to controls. However, levels of plasma NRG1 SMDF showed no correlation with the clinical severity of PD. Additionally, we found that there was a correlation of NRG1 SMDF levels in CSF with that in plasma where levels in plasma were significantly higher, at approximately ten times that in CSF. Finally, we also examined the expression of NRG1 SMDF in the post-mortem brain using immunohistochemistry and showed that Lewy bodies in the SN of patients with PD were immunoreactive for NRG1 SMDF. In summary, we found that the reduction of plasma NRG1 SMDF is specifically associated with PD, but has no correlation with the clinical severity of PD. These findings of NRG1 SMDF may provide important complementary information for diagnosing the onset of PD.

Elevated ErbB4 mRNA is related to interneuron deficit in prefrontal cortex in schizophrenia

Neuregulin 1 and its receptor ErbB4 are confirmed risk genes for schizophrenia, but the neuropathological alterations in NRG1-ErbB4 in schizophrenia are unclear. The present investigations therefore focused on determining lamina specific (ErbB4-pan) and quantitative (pan, JMa, JMb, CYT1 and CYT2) ErbB4 mRNA changes in the dorsolateral prefrontal cortex (DLPFC) in schizophrenia. We also determined which neuronal profiles are ErbB4 mRNA+ in the human DLPFC and the relationship between ErbB4 and interneuron marker mRNAs. In situ hybridisation and quantitative PCR measurements were performed to determine changes in ErbB4 splice variant mRNA levels in the DLPFC in schizophrenia (n = 37) compared to control (n = 37) subjects. Cortical neurons expressing ErbB4-pan were labelled with silver grain clusters. Correlations were performed between ErbB4 and interneuron mRNA levels. ErbB4-pan mRNA was significantly increased (layers I, II and V) in the DLPFC in schizophrenia. Silver grain clusters for ErbB4-pan were detected predominantly over small-medium neurons with low-no expression in the larger, paler, more triangular neuronal profiles. ErbB4-JMa mRNA expression was increased in schizophrenia. Somatostatin, neuropeptide Y and vasoactive intestinal peptide mRNAs negatively correlated with ErbB4-JMa mRNA in people with schizophrenia. Our findings demonstrate that ErbB4-pan laminar mRNA expression is elevated (layers I, II, V) in schizophrenia. At the cellular level, ErbB4-pan mRNA+ signal was detected predominantly in interneuron-like neurons. We provide evidence from this independent Australian postmortem cohort that ErbB4-JMa expression is elevated in schizophrenia and is linked to deficits in dendrite-targeting somatostatin, neuropeptide Y and vasoactive intestinal peptide interneurons.

Cdk5 phosphorylation of ErbB4 is required for tangential migration of cortical interneurons

Interneuron dysfunction in humans is often associated with neurological and psychiatric disorders, such as epilepsy, schizophrenia, and autism. Some of these disorders are believed to emerge during brain formation, at the time of interneuron specification, migration, and synapse formation. Here, using a mouse model and a host of histological and molecular biological techniques, we report that the signaling molecule cyclin-dependent kinase 5 (Cdk5), and its activator p35, control the tangential migration of interneurons toward and within the cerebral cortex by modulating the critical neurodevelopmental signaling pathway, ErbB4/phosphatidylinositol 3-kinase, that has been repeatedly linked to schizophrenia. This finding identifies Cdk5 as a crucial signaling factor in cortical interneuron development in mammals.

Fusion of large-scale genomic knowledge and frequency data computationally prioritizes variants in epilepsy

Curation and interpretation of copy number variants identified by genome-wide testing is challenged by the large number of events harbored in each personal genome. Conventional determination of phenotypic relevance relies on patterns of higher frequency in affected individuals versus controls; however, an increasing amount of ascertained variation is rare or private to clans. Consequently, frequency data have less utility to resolve pathogenic from benign. One solution is disease-specific algorithms that leverage gene knowledge together with variant frequency to aid prioritization. We used large-scale resources including Gene Ontology, protein-protein interactions and other annotation systems together with a broad set of 83 genes with known associations to epilepsy to construct a pathogenicity score for the phenotype. We evaluated the score for all annotated human genes and applied Bayesian methods to combine the derived pathogenicity score with frequency information from our diagnostic laboratory. Analysis determined Bayes factors and posterior distributions for each gene. We applied our method to subjects with abnormal chromosomal microarray results and confirmed epilepsy diagnoses gathered by electronic medical record review. Genes deleted in our subjects with epilepsy had significantly higher pathogenicity scores and Bayes factors compared to subjects referred for non-neurologic indications. We also applied our scores to identify a recently validated epilepsy gene in a complex genomic region and to reveal candidate genes for epilepsy. We propose a potential use in clinical decision support for our results in the context of genome-wide screening. Our approach demonstrates the utility of integrative data in medical genomics.

Radixin inhibition decreases adult neural progenitor cell migration and proliferation in vitro and in vivo

Neuronal progenitors capable of long distance migration are produced throughout life in the subventricular zone (SVZ). Migration from the SVZ is carried out along a well-defined pathway called the rostral migratory stream (RMS). Our recent finding of the specific expression of the cytoskeleton linker protein radixin in neuroblasts suggests a functional role for radixin in RMS migration. The ezrin-radixin-moesin (ERM) family of proteins is capable of regulating migration through interaction with the actin cytoskeleton and transmembrane proteins. The ERM proteins are differentially expressed in the RMS with radixin and moesin localized to neuroblasts, and ezrin expression confined to astrocytes of the glial tubes. Here, we inhibited radixin function using the quinocarmycin analog DX52-1 which resulted in reduced neuroblast migration in vitro, while glial migration remained unaltered. Furthermore, the morphology of neuroblasts was distorted resulting in a rounded shape with no or short polysialylated neural cell adhesion molecule positive processes. Intracerebroventricular infusion of the radixin inhibitor resulted in accumulation of neuroblasts in the anterior SVZ. Neuroblast chains were short and intermittently interrupted in the SVZ and considerably disorganized in the RMS. Moreover, we studied the proliferation activity in the RMS after radixin inhibition, since concentrated radixin expression has been demonstrated in the cleavage furrow of dividing cells, which indicates a role of radixin in cell division. Radixin inhibition decreased neuroblast proliferation, whereas the proliferation of other cells in the RMS was not affected. Our results demonstrate a significant role for radixin in neuroblast proliferation and migration.

NRG3 gene is associated with the risk and age at onset of Alzheimer disease

The Neuregulin 3 (NRG3) gene at 10q22-q24 has been implicated in multiple psychiatric traits such as cognitive impairment. We therefore hypothesized that NRG3 gene polymorphisms may play a role in Alzheimer disease (AD). This present study explored the association of NRG3 with the age at onset (AAO) of AD and the risk of developing AD. Secondary data analysis of 257 single-nucleotide polymorphisms (SNPs) in NRG3 gene was performed in 806 Alzheimer's disease patients and 782 controls using logistic regression and linear regression analyses. Eight SNPs were associated with the risk of AD (p < 0.05), while linear regression analysis showed 33 SNPs associated with the AAO of AD (p < 0.05). Two-SNP haplotype analyses based on UNPHASED revealed that the G-C haplotype from rs17685233 and rs17101017 was significantly associated with AD (p = 0.0031) and the A-G haplotype from rs504522 and rs474018 as well as the A-G haplotype from rs504522 and rs2483295 were more significantly associated with the AAO of AD (p = 6.72 × 10(-5)). Using an independent family-based sample, we found one SNP rs11192423 associated with AAO both in the case-control sample (p = 0.0155) and in the family sample (p = 0.0166). In addition, we observed nominally significant associations with AD and AAO for several flanking SNPs (p < 0.05). This is the first study demonstrating that genetic variants in the NRG3 gene play a role in AD. Our results also revealed that SNPs in the NRG3 genes were more strongly associated with AAO of AD.

Integrative mechanisms of oriented neuronal migration in the developing brain

The emergence of functional neuronal connectivity in the developing cerebral cortex depends on neuronal migration. This process enables appropriate positioning of neurons and the emergence of neuronal identity so that the correct patterns of functional synaptic connectivity between the right types and numbers of neurons can emerge. Delineating the complexities of neuronal migration is critical to our understanding of normal cerebral cortical formation and neurodevelopmental disorders resulting from neuronal migration defects. For the most part, the integrated cell biological basis of the complex behavior of oriented neuronal migration within the developing mammalian cerebral cortex remains an enigma. This review aims to analyze the integrative mechanisms that enable neurons to sense environmental guidance cues and translate them into oriented patterns of migration toward defined areas of the cerebral cortex. We discuss how signals emanating from different domains of neurons get integrated to control distinct aspects of migratory behavior and how different types of cortical neurons coordinate their migratory activities within the developing cerebral cortex to produce functionally critical laminar organization.

Neuregulin-1/ErbB4 signaling regulates Kv4.2-mediated transient outward K+ current through the Akt/mTOR pathway

Neuregulin-1 (NRG-1) is a member of a family of neurotrophic factors that is required for the differentiation, migration, and development of neurons. NRG-1 signaling is thought to contribute to both neuronal development and the neuropathology of schizophrenia, which is believed to be a neurodevelopmental disorder. However, few studies have investigated the role of NRG-1 on voltage-gated ion channels. In this study, we report that NRG-1 specifically increases the density of transient outward K(+) currents (IA) in rat cerebellar granule neurons (CGNs) in a time-dependent manner without modifying the activation or inactivation properties of IA channels. The increase in IA density is mediated by increased protein expression of Kv4.2, the main α-subunit of the IA channel, most likely by upregulation of translation. The effect of NRG-1 on IA density and Kv4.2 expression was only significant in immature neurons. Mechanistically, both Akt and mammalian target of rapamycin (mTOR) signaling pathways are required for the increased NRG-1-induced IA density and expression of Kv4.2. Moreover, pharmacological blockade of the ErbB4 receptor reduced the effect of NRG-1 on IA density and Kv4.2 induction. Our data reveal, for the first time, that stimulation of ErbB4 signaling by NRG-1 upregulates the expression of K(+) channel proteins via activation of the Akt/mTOR signaling pathway and plays an important role in neuronal development and maturation. NRG1 does not acutely change IA and delayed-rectifier outward (IK) of rat CGNs, suggesting that it may not alter excitability of immature neurons by altering potassium channel property.

Comprehensive genomic characterization of cutaneous malignant melanoma cell lines derived from metastatic lesions by whole-exome sequencing and SNP array profiling

Cutaneous malignant melanoma is the most fatal skin cancer and although improved comprehension of its pathogenic pathways allowed to realize some effective molecular targeted therapies, novel targets and drugs are still needed. Aiming to add genetic information potentially useful for novel targets discovery, we performed an extensive genomic characterization by whole-exome sequencing and SNP array profiling of six cutaneous melanoma cell lines derived from metastatic patients. We obtained a total of 3,325 novel coding single nucleotide variants, including 2,172 non-synonymous variants. We catalogued the coding mutations according to Sanger COSMIC database and to a manually curated list including genes involved in melanoma pathways identified by mining recent literature. Besides confirming the presence of known melanoma driver mutations (BRAF(V600E), NRAS(Q61R) ), we identified novel mutated genes involved in signalling pathways crucial for melanoma pathogenesis and already addressed by current targeted therapies (such as MAPK and glutamate pathways). We also identified mutations in four genes (MUC19, PAICS, RBMXL1, KIF23) never reported in melanoma, which might deserve further investigations. All data are available to the entire research community in our Melanoma Exome Database (at https://155.253.6.64/MExDB/). In summary, these cell lines are valuable biological tools to improve the genetic comprehension of this complex cancer disease and to study functional relevance of individual mutational events, and these findings could provide insights potentially useful for identification of novel therapeutic targets for cutaneous malignant melanoma.

Targeted deletion of the ERK5 MAP kinase impairs neuronal differentiation, migration, and survival during adult neurogenesis in the olfactory bulb

Recent studies have led to the exciting idea that adult-born neurons in the olfactory bulb (OB) may be critical for complex forms of olfactory behavior in mice. However, signaling mechanisms regulating adult OB neurogenesis are not well defined. We recently reported that extracellular signal-regulated kinase (ERK) 5, a MAP kinase, is specifically expressed in neurogenic regions within the adult brain. This pattern of expression suggests a role for ERK5 in the regulation of adult OB neurogenesis. Indeed, we previously reported that conditional deletion of erk5 in adult neurogenic regions impairs several forms of olfactory behavior in mice. Thus, it is important to understand how ERK5 regulates adult neurogenesis in the OB. Here we present evidence that shRNA suppression of ERK5 in adult neural stem/progenitor cells isolated from the subventricular zone (SVZ) reduces neurogenesis in culture. By contrast, ectopic activation of endogenous ERK5 signaling via expression of constitutive active MEK5, an upstream activating kinase for ERK5, stimulates neurogenesis. Furthermore, inducible and conditional deletion of erk5 specifically in the neurogenic regions of the adult mouse brain interferes with cell cycle exit of neuroblasts, impairs chain migration along the rostral migratory stream and radial migration into the OB. It also inhibits neuronal differentiation and survival. These data suggest that ERK5 regulates multiple aspects of adult OB neurogenesis and provide new insights concerning signaling mechanisms governing adult neurogenesis in the SVZ-OB axis.

Waking up the sleepers: shared transcriptional pathways in axonal regeneration and neurogenesis

In the last several years, relevant progress has been made in our understanding of the transcriptional machinery regulating CNS repair after acute injury, such as following trauma or stroke. In order to survive and functionally reconnect to the synaptic network, injured neurons activate an intrinsic rescue program aimed to increase their plasticity. Perhaps, in the attempt to switch back to a plastic and growth-competent state, post-mitotic neurons wake up and re-express a set of transcription factors that are also critical for the regulation of their younger brothers, the neural stem cells. Here, we review and discuss the transcriptional pathways regulating both axonal regeneration and neurogenesis highlighting the connection between the two. Clarification of their common molecular substrate may help simultaneous targeting of both neurogenesis and axonal regeneration with the hope to enhance functional recovery following CNS injury.

Synapse-specific contributions in the cortical pathology of schizophrenia

Schizophrenia (SZ) is often described as a disease of neuronal connectivity. Cognitive processes such as working memory, which are particularly dependent on the proper functioning of complex cortical circuitry, are disturbed in the disease. Reciprocal connections between pyramidal neurons and interneurons, as well as dopaminergic innervations, form the basis for higher cognition in the cortex. Nonetheless, only a few review articles are available which address how each synapse operates, and is possibly disturbed in SZ, at least in part by the mechanisms involving genetic susceptibility factors for SZ. In this review, we provide an overview of cortical glutamatergic, GABAergic, and dopaminergic circuitry, review SZ-associated deficits at each of these synapses, and discuss how genetic factors for SZ may contribute to SZ-related phenotype deficits in a synapse-specific manner. Pinpointing the spatially and temporally distinct sites of action of putative SZ susceptibility factors may help us better understand the pathological mechanisms of SZ, especially those associated with synaptic functioning and neuronal connectivity.

Time course and progression of wild type α-synuclein accumulation in a transgenic mouse model

Background

Progressive accumulation of α-synuclein (α-Syn) protein in different brain regions is a hallmark of synucleinopathic diseases, such as Parkinson’s disease, dementia with Lewy bodies and multiple system atrophy. α-Syn transgenic mouse models have been developed to investigate the effects of α-Syn accumulation on behavioral deficits and neuropathology. However, the onset and progression of pathology in α-Syn transgenic mice have not been fully characterized. For this purpose we investigated the time course of behavioral deficits and neuropathology in PDGF-β human wild type α-Syn transgenic mice (D-Line) between 3 and 12 months of age.

Results

These mice showed progressive impairment of motor coordination of the limbs that resulted in significant differences compared to non-transgenic littermates at 9 and 12 months of age. Biochemical and immunohistological analyses revealed constantly increasing levels of human α-Syn in different brain areas. Human α-Syn was expressed particularly in somata and neurites of a subset of neocortical and limbic system neurons. Most of these neurons showed immunoreactivity for phosphorylated human α-Syn confined to nuclei and perinuclear cytoplasm. Analyses of the phenotype of α-Syn expressing cells revealed strong expression in dopaminergic olfactory bulb neurons, subsets of GABAergic interneurons and glutamatergic principal cells throughout the telencephalon. We also found human α-Syn expression in immature neurons of both the ventricular zone and the rostral migratory stream, but not in the dentate gyrus.

Conclusion

The present study demonstrates that the PDGF-β α-Syn transgenic mouse model presents with early and progressive accumulation of human α-Syn that is accompanied by motor deficits. This information is essential for the design of therapeutical studies of synucleinopathies.

Discovery, validation and characterization of Erbb4 and Nrg1 haplotypes using data from three genome-wide association studies of schizophrenia

Schizophrenia is one of the most common and complex neuropsychiatric disorders, which is contributed both by genetic and environmental exposures. Recently, it is shown that NRG1-mediated ErbB4 signalling regulates many important cellular and molecular processes such as cellular growth, differentiation and death, particularly in myelin-producing cells, glia and neurons. Recent association studies have revealed genomic regions of NRG1 and ERBB4, which are significantly associated with risk of developing schizophrenia; however, inconsistencies exist in terms of validation of findings between distinct populations. In this study, we aim to validate the previously identified regions and to discover novel haplotypes of NRG1 and ERBB4 using logistic regression models and Haploview analyses in three independent datasets from GWAS conducted on European subjects, namely, CATIE, GAIN and nonGAIN. We identified a significant 6-kb block in ERBB4 between chromosome locations 212,156,823 and 212,162,848 in CATIE and GAIN datasets (p = 0.0206 and 0.0095, respectively). In NRG1, a significant 25-kb block, between 32,291,552 and 32,317,192, was associated with risk of schizophrenia in all CATIE, GAIN, and nonGAIN datasets (p = 0.0005, 0.0589, and 0.0143, respectively). Fine mapping and FastSNP analysis of genetic variation located within significantly associated regions proved the presence of binding sites for several transcription factors such as SRY, SOX5, CEPB, and ETS1. In this study, we have discovered and validated haplotypes of ERBB4 and NRG1 in three independent European populations. These findings suggest that these haplotypes play an important role in the development of schizophrenia by affecting transcription factor binding affinity.

Dynamic changes in the transcriptional profile of subventricular zone-derived postnatally born neuroblasts

The subventricular zone (SVZ) of the lateral ventricles is a major neurogenic region in the postnatal mammalian brain. Thousands of neuroblasts are generated daily throughout the life of an animal. Newly born neuroblasts migrate via the rostral migratory stream (RMS) into the olfactory bulb where they mature into distinct neuronal subtypes. Neuroblasts exiting the SVZ retain the ability to proliferate, however, proliferation declines in the course of migration to the olfactory bulb. While migrating in the RMS, neuroblasts receive a plethora of stimuli that modify transcription according to the local microenvironment, and eventually modulate neuroblast migration. In the target area, the olfactory bulb, neuroblasts develop into mature neurons. In this review, we discuss dynamic changes of the transcriptome that occur during the "lifetime" of a neuroblast, thereby governing the activation or inhibition of distinct genes/pathways that are responsible for proliferation, migration and differentiation.

Pten deletion causes mTorc1-dependent ectopic neuroblast differentiation without causing uniform migration defects

Neuronal precursors, generated throughout life in the subventricular zone, migrate through the rostral migratory stream to the olfactory bulb where they differentiate into interneurons. We found that the PI3K-Akt-mTorc1 pathway is selectively inactivated in migrating neuroblasts in the subventricular zone and rostral migratory stream, and activated when these cells reach the olfactory bulb. Postnatal deletion of Pten caused aberrant activation of the PI3K-Akt-mTorc1 pathway and an enlarged subventricular zone and rostral migratory stream. This expansion was caused by premature termination of migration and differentiation of neuroblasts and was rescued by inhibition of mTorc1. This phenotype is reminiscent of lamination defects caused by Pten deletion in developing brain that were previously described as defective migration. However, live imaging in acute slices showed that Pten deletion did not cause a uniform defect in the mechanics of directional neuroblast migration. Instead, a subpopulation of Pten-null neuroblasts showed minimal movement and altered morphology associated with differentiation, whereas the remainder showed unimpeded directional migration towards the olfactory bulb. Therefore, migration defects of Pten-null neurons might be secondary to ectopic differentiation.

Regional differences in human ependymal and subventricular zone cytoarchitecture are unchanged in neuropsychiatric disease

Much work has focused on the possible contribution of adult hippocampal neurogenesis to neuropsychiatric diseases. The hippocampal subgranular zone and the other stem cell-containing neurogenic niche, the subventricular zone (SVZ), share several cytological features and are regulated by some of the same molecular mechanisms. However, very little is known about the SVZ in neuropsychiatric disorders. This is important since it surrounds the lateral ventricles and in schizophrenia ventricular enlargement frequently follows forebrain nuclei shrinkage. Also, adult neurogenesis has been implicated in pharmacotherapy for affective disorders and many of the molecules associated with neuropsychiatric disorders affect SVZ biology. To assess the neurogenic niche, we examined material from 60 humans (Stanley Collection) and characterized the cytoarchitecture of the SVZ and ependymal layer in age-, sex- and post mortem interval-matched controls, and patients diagnosed with schizophrenia, bipolar illness, and depression (n = 15 each). There is a paucity of post mortem brains available for study in these diseases, so to maximize the number of possible parameters examined here, we quantified individual sections rather than a large series. Previous work showed that multiple sclerosis is associated with increased width of the hypocellular gap, a cell-sparse region that typifies the human SVZ. Statistically there were no differences between disease groups and controls in the width of the hypocellular gap or in the density of cells in the hypocellular gap. Because ventricular enlargement in schizophrenia may disrupt ependymal cells, we quantified them, but observed no difference between diagnostic groups and controls. There are significant differences in the prevalence of neuropsychiatric illness between the sexes. Therefore, we looked for male versus female differences, but did not observe any in the parameters quantified. We next turned to a finer spatial resolution and asked if there were differences amongst the disease groups in dorsal ventral subdivisions of the SVZ. Similar to when we treated the SVZ as a whole, we did not find such differences. However, compared to the dorsal SVZ, the ventral SVZ had a wider hypocellular gap and more ependymal cells in all four groups. In contrast, cell density was similar in dorsal ventral subregions of the SVZ hypocellular gap. These results show that though there are regional differences in the SVZ in humans, neuropsychiatric disorders do not seem to alter several fundamental histological features of this adult neurogenic zone.

Postnatal subventricular zone of the neocortex contributes GFAP+ cells to the rostral migratory stream under the control of Sip1

The rostral migratory stream (RMS) is composed of neuroblasts migrating from the striatal SVZ to the olfactory bulb through a meshwork of GFAP- expressing astrocytes called the glial tube. So far, the origin of the glial tube astrocytes was attributed to differentiation of Type-B stem cells of the striatal SVZ. The true identity of these cells (Type-B stem cells versus immature/mature astrocytes) is also unclear. By analyzing a neocortex-specific conditional knockout of the transcriptional repressor Sip1 (Smad-interacting protein 1), we have now identified a novel pool of progenitors located within the dorsal SVZ (dSVZ) at early postnatal stages that differentiate into GFAP+ cells of the glial tube. We show that Sip1, expressed in postmitotic cortical neurons, controls the size of this dorsal progenitor pool possibly through cell-extrinsic mechanisms. Lack of Sip1 in the neocortex causes an expansion of this population leading to an increased production of GFAP+ astrocytes/Type-B stem cells in the glial tube, and a denser intercalation of these cells with Dcx+ neuroblasts of the RMS, the consequence of which is not yet clear. Neocortex-specific Sip1 deletion also led to an expansion of Dcx+ and Tbr2+ progenitor populations in the dSVZ. We show that the dSVZ progenitors (possibly remnants of embryonic radial glia) differentiate exclusively into BLBP+ cells which migrate into the RMS and mature into GFAP+ astrocytes/Type-B stem cells at around two weeks of postnatal development. In summary, our work shows that Sip1 controls the generation of GFAP+ cells of the RMS by regulating the size of a novel progenitor pool located in the postnatal dSVZ.

The importance of the NRG-1/ErbB4 pathway for synaptic plasticity and behaviors associated with psychiatric disorders

Neuregulin 1 (NRG-1) and its receptor ErbB4 have emerged as biologically plausible schizophrenia risk factors, modulators of GABAergic and dopaminergic neurotransmission, and as potent regulators of glutamatergic synaptic plasticity. NRG-1 acutely depotentiates LTP in hippocampal slices, and blocking ErbB kinase activity inhibits LTP reversal by theta-pulse stimuli (TPS), an activity-dependent reversal paradigm. NRG-1/ErbB4 signaling in parvalbumin (PV) interneurons has been implicated in inhibitory transmission onto pyramidal neurons. However, the role of ErbB4, in particular in PV interneurons, for LTP reversal has not been investigated. Here we show that ErbB4-null (ErbB4(-/-)) and PV interneuron-restricted mutant (PV-Cre;ErbB4) mice, as well as NRG-1 hypomorphic mice, exhibit increased hippocampal LTP. Moreover, both ErbB4(-/-) and PV-Cre;ErbB4 mice lack TPS-mediated LTP reversal. A comparative behavioral analysis of full and conditional ErbB4 mutant mice revealed that both exhibit hyperactivity in a novel environment and deficits in prepulse inhibition of the startle response. Strikingly, however, only ErbB4(-/-) mice exhibit reduced anxiety-like behaviors in the elevated plus maze task and deficits in cued and contextual fear conditioning. These results suggest that aberrant NRG-1/ErbB4 signaling in PV interneurons accounts for some but not all behavioral abnormalities observed in ErbB4(-/-) mice. Consistent with the observation that PV-Cre;ErbB4 mice exhibit normal fear conditioning, we find that ErbB4 is broadly expressed in the amygdala, largely by cells negative for PV. These findings are important to better understand ErbB4's role in complex behaviors and warrant further analysis of ErbB4 mutant mice lacking the receptor in distinct neuron types.

Schizophrenia-associated HapICE haplotype is associated with increased NRG1 type III expression and high nucleotide diversity

Excitement and controversy have followed neuregulin (NRG1) since its discovery as a putative schizophrenia susceptibility gene; however, the mechanism of action of the associated risk haplotype (HapICE) has not been identified, and specific genetic variations, which may increase risk to schizophrenia have remained elusive. Using a postmortem brain cohort from 37 schizophrenia cases and 37 controls, we resequenced upstream of the type I-IV promoters, and the HapICE repeat regions in intron 1. Relative abundance of seven NRG1 mRNA transcripts in the prefrontal cortex were determined and compared across diagnostic and genotypic groups. We identified 26 novel DNA variants and showed an increased novel variant load in cases compared with controls (χ(2)=7.815; P=0.05). The average nucleotide diversity (θ = 10.0 × 10(-4)) was approximately twofold higher than that previously reported for BDNF, indicating that NRG1 may be particularly prone to genetic change. A greater nucleotide diversity was observed in the HapICE linkage disequilibrium block in schizophrenia cases (θ((case)) = 13.2 × 10(-4); θ((control)) = 10.0 × 10(-4)). The specific HapICE risk haplotype was associated with increased type III mRNA (F = 3.76, P = 0.028), which in turn, was correlated with an earlier age of onset (r = -0.343, P = 0.038). We found a novel intronic five-SNP haplotype ~730 kb upstream of the type I promoter and determined that this region functions as transcriptional enhancer that is suppressed by SRY. We propose that the HapICE risk haplotype increases expression of the most brain-abundant form of NRG1, which in turn, elicits an earlier clinical presentation, thus providing a novel mechanism through which this genetic association may increase risk of schizophrenia.

Astrocytes control the development of the migration-promoting vasculature scaffold in the postnatal brain via VEGF signaling

New neurons are constantly being generated in the postnatal subventricular zone. They have to migrate long distances via the rostral migratory stream (RMS) to reach their final destination in the olfactory bulb (OB). In adults, these neuronal precursors migrate in chains, ensheathed by astrocytic processes, and travel toward the OB along blood vessels (BVs) that topographically outline the RMS. The molecular and cellular mechanisms leading to the development of the RMS and the formation of the migration-promoting vasculature scaffold in the adult mice remain unclear. We now reveal that astrocytes orchestrate the formation and structural reorganization of the vasculature scaffold in the RMS and, during early developmental stages, the RMS contains only a few BVs oriented randomly with respect to the migrating neuroblasts. The first parallel BVs appeared at the outer border of the RMS, where vascular endothelial growth factor (VEGF)-expressing astrocytes are located. Gain-of-function and loss-of-function experiments revealed that astrocyte-derived VEGF plays a crucial role in the formation and growth of new BVs. Real-time videoimaging also showed that the migration of neuronal precursors in the developing RMS differs substantially from neuronal displacement in the adult migratory stream partially because of not yet fully developed vasculature scaffold. The downregulation of VEGF in vivo, specifically in the astrocytes of the developing RMS, affected the development of the vasculature scaffold and led to alterations in neuroblast migration. Altogether, our results demonstrate that astrocytes orchestrate the formation and growth of parallel BVs, crucial migration-promoting scaffolds in the adult migratory stream, via VEGF signaling.

Ependymal ciliary dysfunction and reactive astrocytosis in a reorganized subventricular zone after stroke

Subventricular zone (SVZ) astrocytes and ependymal cells are both derived from radial glia and may have similar gliotic reactions after stroke. Diminishing SVZ neurogenesis worsens outcomes in mice, yet the effects of stroke on SVZ astrocytes and ependymal cells are poorly understood. We used mouse experimental stroke to determine if SVZ astrocytes and ependymal cells assume similar phenotypes and if stroke impacts their functions. Using lateral ventricular wall whole mount preparations, we show that stroke caused SVZ reactive astrocytosis, disrupting the neuroblast migratory scaffold. Also, SVZ vascular density and neural proliferation increased but apoptosis did not. In contrast to other reports, ependymal denudation and cell division was never observed. Remarkably, however, ependymal cells assumed features of reactive astrocytes post stroke, robustly expressing de novo glial fibrillary acidic protein, enlargening and extending long processes. Unexpectedly, stroke disrupted motile cilia planar cell polarity in ependymal cells. This suggested ciliary function was affected and indeed ventricular surface flow was slower and more turbulent post stroke. Together, these results demonstrate that in response to stroke there is significant SVZ reorganization with implications for both pathophysiology and therapeutic strategies.

Delving into somatic variation in sporadic melanoma

Melanoma, the most aggressive form of skin cancer, has increased in incidence more rapidly than any other cancer. The completion of the human genome project and advancements in genomics technologies has allowed us to investigate genetic alterations of melanoma at a scale and depth that is unprecedented. Here, we survey the history of the different approaches taken to understand the genomics of melanoma - from early candidate genes, to gene families, to genome-wide studies. The new era of whole-exome and whole-genome sequencing has paved the way for an in-depth understanding of melanoma biology, identification of new therapeutic targets, and development of novel personalized therapies for melanoma.

Neuregulin repellent signaling via ErbB4 restricts GABAergic interneurons to migratory paths from ganglionic eminence to cortical destinations

Background

Cortical GABAergic interneurons (INs) are generated in the medial ganglionic eminence (MGE) and migrate tangentially into cortex. Because most, if not all, migrating MGE-derived INs express the neuregulin (NRG) receptor, ErbB4, we investigated influences of Nrg1 isoforms and Nrg3 on IN migration through ventral telencephalon (vTel) and within cortex.

Results

During IN migration, NRG expression domains and distributions of ErbB4-expressing, MGE-derived INs are complementary with minimal overlap, both in vTel and cortex. In wild-type mice, within fields of NRG expression, these INs are focused at positions of low or absent NRG expression. However, in ErbB4-/- HER4^heart mutant mice in which INs lack ErbB4, these complementary patterns are degraded with considerable overlap evident between IN distribution and NRG expression domains. These findings suggest that NRGs are repellents for migrating ErbB4-expressing INs, a function supported by in vitro and in vivo experiments. First, in collagen co-cultures, MGE-derived cells preferentially migrate away from a source of secreted NRGs. Second, cells migrating from wild-type MGE explants on living forebrain slices from wild-type embryonic mice tend to avoid endogenous NRG expression domains, whereas this avoidance behavior is not exhibited by ErbB4-deficient cells migrating from MGE explants and instead they have a radial pattern with a more uniform distribution. Third, ectopic NRG expression in the IN migration pathway produced by in utero electroporation blocks IN migration and results in cortex distal to the blockade being largely devoid of INs. Finally, fewer INs reach cortex in ErbB4 mutants, indicating that NRG-ErbB4 signaling is required for directing IN migration from the MGE to cortex.

Conclusions

Our results show that NRGs act as repellents for migrating ErbB4-expressing, MGE-derived GABAergic INs and that the patterned expression of NRGs funnels INs as they migrate from the MGE to their cortical destinations.

Morphological and behavioral changes in the pathogenesis of a novel mouse model of communicating hydrocephalus

The Ro1 model of hydrocephalus represents an excellent model for studying the pathogenesis of hydrocephalus due to its complete penetrance and inducibility, enabling the investigation of the earliest cellular and histological changes in hydrocephalus prior to overt pathology. Hematoxylin and eosin staining, immunofluorescence and electron microscopy were used to characterize the histopathological events of hydrocephalus in this model. Additionally, a broad battery of behavioral tests was used to investigate behavioral changes in the Ro1 model of hydrocephalus. The earliest histological changes observed in this model were ventriculomegaly and disorganization of the ependymal lining of the aqueduct of Sylvius, which occurred concomitantly. Ventriculomegaly led to thinning of the ependyma, which was associated with periventricular edema and areas of the ventricular wall void of cilia and microvilli. Ependymal denudation was subsequent to severe ventriculomegaly, suggesting that it is an effect, rather than a cause, of hydrocephalus in the Ro1 model. Additionally, there was no closure of the aqueduct of Sylvius or any blockages within the ventricular system, even with severe ventriculomegaly, suggesting that the Ro1 model represents a model of communicating hydrocephalus. Interestingly, even with severe ventriculomegaly, there were no behavioral changes, suggesting that the brain is able to compensate for the structural changes that occur in the pathogenesis of hydrocephalus if the disorder progresses at a sufficiently slow rate.

Expression of the neuregulin receptor ErbB4 in the brain of the rhesus monkey (Macaca mulatta)

We demonstrated recently that frontal cortical expression of the Neuregulin (NRG) receptor ErbB4 is restricted to interneurons in rodents, macaques, and humans. However, little is known about protein expression patterns in other areas of the brain. In situ hybridization studies have shown high ErbB4 mRNA levels in various subcortical areas, suggesting that ErbB4 is also expressed in cell types other than cortical interneurons. Here, using highly-specific monoclonal antibodies, we provide the first extensive report of ErbB4 protein expression throughout the cerebrum of primates. We show that ErbB4 immunoreactivity is high in association cortices, intermediate in sensory cortices, and relatively low in motor cortices. The overall immunoreactivity in the hippocampal formation is intermediate, but is high in a subset of interneurons. We detected the highest overall immunoreactivity in distinct locations of the ventral hypothalamus, medial habenula, intercalated nuclei of the amygdala and structures of the ventral forebrain, such as the islands of Calleja, olfactory tubercle and ventral pallidum, and medium expression in the reticular thalamic nucleus. While this pattern is generally consistent with ErbB4 mRNA expression data, further investigations are needed to identify the exact cellular and subcellular sources of mRNA and protein expression in these areas. In contrast to in situ hybridization in rodents, we detected only low levels of ErbB4-immunoreactivity in mesencephalic dopaminergic nuclei but a diffuse pattern of immunofluorescence that was medium in the dorsal striatum and high in the ventral forebrain, suggesting that most ErbB4 protein in dopaminergic neurons could be transported to axons. We conclude that the NRG-ErbB4 signaling pathway can potentially influence many functional systems throughout the brain of primates, and suggest that major sites of action are areas of the “corticolimbic” network. This interpretation is functionally consistent with the genetic association of NRG1 and ERBB4 with schizophrenia.

Neuregulin1/ErbB4-induced migration in ST14A striatal progenitors: calcium-dependent mechanisms and modulation by NMDA receptor activation

Background

A number of studies have separately shown that the neuregulin1 (NRG1)/ErbB4 system and NMDA-type glutamate receptors (NMDARs) are involved in several aspects of neuronal migration. In addition, intracellular calcium fluctuations play central roles in neuronal motility. Stable expression of the tyrosine kinase receptor ErbB4 promotes migratory activity in the neural progenitor cell line ST14A upon NRG1 stimulation. In this work we analyzed the potential interactions between the NRG1/ErbB4 system and NMDARs in the ST14A migratory process as well as its calcium dependence.

Results

RT-PCR studies have shown that both native ST14A cells (non-expressing ErbB4), as well as ErbB4-transfected cells express low levels of a restricted number of NMDAR subunits: NR1, NR2C, NR2D and NR3B. The resulting NMDAR would form Ca²⁺ channels characterized by low Mg²⁺-sensitivity and low Ca²⁺-permeability, generating small, long-lasting currents. Ca²⁺-imaging experiments showed slow [Ca²⁺]_i increases in 45% of the cells following 8 μM NMDA stimulation. Basal migration of ErbB4-transfected ST14A cells was unaffected by 18 hrs NMDA incubation. However, over the same incubation time, NMDA was able to significantly enhance NRG1-induced migration. Pre-incubation with the intracellular calcium chelator BAPTA-AM reduced both NRG1- and NRG1/NMDA-stimulated migration, suggesting the involvement of Ca²⁺ in these processes. NRG1 stimulation of ErbB4-transfected ST14A cells induced a sustained, long-lasting increase in [Ca²⁺]_i, in 99% of the cells. These intracellular Ca²⁺ signals could be ascribed to both release from intracellular stores and influx from the extracellular medium trough a mechanism of store-operated calcium entry (SOCE). Short-time co-incubation of NMDA and NRG1 did not substantially modify the NRG1-induced intracellular calcium signals.

Conclusions

In summary, NRG1 stimulation of the ErbB4 receptor exerts a sustained [Ca²⁺]_i increase in ST14A neural progenitors; NRG1-induced migration is Ca²⁺-dependent and can be positively modulated by activation of the NMDA receptor.

Conserved interneuron-specific ErbB4 expression in frontal cortex of rodents, monkeys, and humans: implications for schizophrenia

BACKGROUND

Neuregulin-1 and ErbB4 are genetically associated with schizophrenia, and detailed knowledge of the cellular and subcellular localization of ErbB4 is important for understanding how neuregulin-1 regulates neuronal network activity and behavior. Expression of ErbB4 is restricted to interneurons in the rodent hippocampus and cortex. However, controversy remains about the cellular expression pattern in primate brain and its subcellular distribution in postsynaptic somatodendritic locations versus presynaptic terminals.

METHODS

ErbB4 expression was analyzed in pyramidal cells and interneurons in the frontal cortex of five species: C57BL6 mice (n = 3), ErbB4⁻/⁻ mice (n = 2), Sprague-Dawley rats (n = 3), two macaque species (n = 3 + 2), and humans (normal control subjects, n = 2). We investigated 1) messenger RNA in mice, macaques, and humans; 2) protein expression in all species using highly specific monoclonal antibodies; and 3) specificity tests of several ErbB4 antibodies on brain samples (mouse, macaque, human).

RESULTS

ErbB4 RNA is restricted to interneurons in the frontal cortex of mice. ErbB4 protein is undetectable in pyramidal cells of rodents, macaques, and human frontal cortex, whereas most interneurons positive for parvalbumin, calretinin, or cholecystokinin, but only a minority of calbindin-positive cells, co-express ErbB4 in macaques. Importantly, no presynaptic ErbB4 expression was detected in any species.

CONCLUSIONS

The interneuron-selective somatodendritic expression of ErbB4 is consistent with a primary role of neuregulin-ErbB4 signaling in the postsynaptic modulation of gamma-aminobutyric acidergic function in rodents and primates. Our data validate the use of rodents to analyze effects of abnormal ErbB4 function as a means to model endophenotypes of psychiatric disorders.

Analysis of 94 candidate genes and 12 endophenotypes for schizophrenia from the Consortium on the Genetics of Schizophrenia

OBJECTIVE

The authors used a custom array of 1,536 single-nucleotide polymorphisms (SNPs) to interrogate 94 functionally relevant candidate genes for schizophrenia and identify associations with 12 heritable neurophysiological and neurocognitive endophenotypes in data collected by the Consortium on the Genetics of Schizophrenia.

METHOD

Variance-component association analyses of 534 genotyped subjects from 130 families were conducted by using Merlin software. A novel bootstrap total significance test was also developed to overcome the limitations of existing genomic multiple testing methods and robustly demonstrate significant associations in the context of complex family data and possible population stratification effects.

RESULTS

Associations with endophenotypes were observed for 46 genes of potential functional significance, with three SNPs at p<10(-4), 27 SNPs at p<10(-3), and 147 SNPs at p<0.01. The bootstrap analyses confirmed that the 47 SNP-endophenotype combinations with the strongest evidence of association significantly exceeded that expected by chance alone, with 93% of these findings expected to be true. Many of the genes interact on a molecular level, and eight genes (e.g., NRG1 and ERBB4) displayed evidence for pleiotropy, revealing associations with four or more endophenotypes. The results collectively support a strong role for genes related to glutamate signaling in mediating schizophrenia susceptibility.

CONCLUSIONS

This study supports use of relevant endophenotypes and the bootstrap total significance test for identifying genetic variation underlying the etiology of schizophrenia. In addition, the observation of extensive pleiotropy for some genes and singular associations for others suggests alternative, independent pathways mediating pathogenesis in the "group of schizophrenias."

Girdin is an intrinsic regulator of neuroblast chain migration in the rostral migratory stream of the postnatal brain

In postnatally developing and adult brains, interneurons of the olfactory bulb (OB) are continuously generated at the subventricular zone of the forebrain. The newborn neuroblasts migrate tangentially to the OB through a well defined pathway, the rostral migratory stream (RMS), where the neuroblasts undergo collective migration termed "chain migration." The cell-intrinsic regulatory mechanism of neuroblast chain migration, however, has not been uncovered. Here we show that mice lacking the actin-binding Akt substrate Girdin (a protein that interacts with Disrupted-In-Schizophrenia 1 to regulate neurogenesis in the dentate gyrus) have profound defects in neuroblast chain migration along the RMS. Analysis of two gene knock-in mice harboring Girdin mutants identified unique amino acid residues in Girdin's C-terminal domain that are responsible for the regulation of neuroblast chain migration but revealed no apparent requirement of Girdin phosphorylation by Akt. Electron microscopic analyses demonstrated the involvement of Girdin in neuroblast cell-cell interactions. These findings suggest that Girdin is an important intrinsic factor that specifically governs neuroblast chain migration along the RMS.

Direct visualization of microtubules using a genetic tool to analyse radial progenitor-astrocyte continuum in brain

Microtubule cytoskeletal dynamics of cortical progenitors and astroglial cells play critical roles in the emergence of normal functional organization of cerebral cortex and in disease processes such as tumorigenesis. However, tools to efficiently visualize these events are lacking. Here we describe a mouse genetic model to efficiently visualize and analyze radial progenitors, their astroglial progeny, and the microtubule cytoskeleton of these cells in the developing and adult brain. Using this tool, we demonstrate altered microtubule organization and capture dynamics in adenomatous polyposis coli deficient radial progenitors. Further, using multiphoton microscopy, we show the utility of this tool in real-time imaging of astrocytes in living mouse brain and the short- term stable nature of astrocytes in cerebral cortex. Thus, this model will help explore the dynamics of radial progenitor/astrocyte development or dysfunction and the influence of microtubule functions during these events.

Regional expression of ADAM19 during chicken embryonic development

ADAM19 (also named meltrin β) is a member of the ADAM (a disintegrin and metalloprotease) family of metalloproteases and is involved in morphogenesis and tissue formation during embryonic development. In the present study, chicken ADAM19 is cloned by reverse transcription-polymerase chain reaction and identified by sequencing. Its expression patterns in different parts of the developing chicken embryo are investigated by Western blot analysis and immunohistochemistry. Results show that ADAM19 protein is widely expressed in chicken embryos. It is detectable in the central nervous system, including the brain, spinal cord, cochlea, and retina. Furthermore, ADAM19 protein is also found in other tissues and organs such as digestive organs, the thymus, the lung bud, the dorsal aorta, the kidney, the gonad, muscles, and in the feather buds. All these data suggest that ADAM19 plays an important role in the embryonic development of chicken.

Neuregulin links dopaminergic and glutamatergic neurotransmission to control hippocampal synaptic plasticity

Neuregulin-1 (NRG-1) and its receptor ErbB4 are genetically associated with schizophrenia, a complex developmental disorder of high heritability but unknown etiology that has been proposed to result from deficits in functional connectivity and synaptic plasticity. Based on pharmacological evidence, imbalances in dopaminergic and glutamatergic transmission systems are believed to contribute to its pathophysiology, but genetic data supporting a causative role for either are sparse. Stimulation of NRG-1/ErbB4 signaling inhibits or reverts hippocampal long-term potentiation (LTP) at glutamatergic synapses between Schaeffer collateral afferents and CA1 pyramidal neurons (SC-->CA1). We have recently demonstrated that NRG-1 regulates glutamatergic plasticity by rapidly increasing extracellular hippocampal dopamine levels and activation of D4 dopamine receptors.7 These new findings position the NRG-1/ErbB4 signaling pathway at the crossroads between dopaminergic and glutamatergic neurotransmission and offer novel ways to consolidate genetic, functional and pharmacological data toward a better understanding of the etiological processes underlying schizophrenia, and the role of NRG-1 for normal synaptic function and plasticity. The currently available data suggest that hippocampal interneurons might play a crucial role in mediating NRG-1 induced depotentiation. This interpretation is in line with other evidence pointing towards an involvement of GABAergic cells in the etiology of schizophrenia.

Endocannabinoids regulate the migration of subventricular zone-derived neuroblasts in the postnatal brain

In the adult brain, neural stem cells proliferate within the subventricular zone before differentiating into migratory neuroblasts that travel along the rostral migratory stream (RMS) to populate the olfactory bulb with new neurons. Because neuroblasts have been shown to migrate to areas of brain injury, understanding the cues regulating this migration could be important for brain repair. Recent studies have highlighted an important role for endocannabinoid (eCB) signaling in the proliferation of the stem cell population, but it remained to be determined whether this pathway also played a role in cell migration. We now show that mouse migratory neuroblasts express cannabinoid receptors, diacylglycerol lipase α (DAGLα), the enzyme that synthesizes the endocannabinoid 2-arachidonoylglycerol (2-AG), and monoacylglycerol lipase, the enzyme responsible for its degradation. Using a scratch wound assay for a neural stem cell line and RMS explant cultures, we show that inhibition of DAGL activity or CB(1)/CB(2) receptors substantially decreases migration. In contrast, direct activation of cannabinoid receptors or preventing the breakdown of 2-AG increases migration. Detailed analysis of primary neuroblast migration by time-lapse imaging reveals that nucleokinesis, as well as the length and branching of the migratory processes are under dynamic control of the eCB system. Finally, similar effects are observed in vivo by analyzing the morphology of green fluorescent protein-labeled neuroblasts in brain slices from mice treated with CB(1) or CB(2) antagonists. These results describe a novel role for the endocannabinoid system in neuroblast migration in vivo, highlighting its importance in regulating an additional essential step in adult neurogenesis.

Hepatocyte growth factor acts as a mitogen and chemoattractant for postnatal subventricular zone-olfactory bulb neurogenesis

Neural progenitor cells persist throughout life in the forebrain subventricular zone (SVZ). They generate neuroblasts that migrate to the olfactory bulb and differentiate into interneurons, but mechanisms underlying these processes are poorly understood. Hepatocyte growth factor/scatter factor (HGF/SF) is a pleiotropic factor that influences cell motility, proliferation and morphogenesis in neural and non-neural tissues. HGF and its receptor, c-Met, are present in the rodent SVZ-olfactory bulb pathway. Using in vitro neurogenesis assays and in vivo studies of partially HGF-deficient mice, we find that HGF promotes SVZ cell proliferation and progenitor cell maintenance, while slowing differentiation and possibly altering cell fate choices. HGF also acts as a chemoattractant for SVZ neuroblasts in co-culture assays. Decreased HGF signaling induces ectopic SVZ neuroblast migration and alters the timing of migration to the olfactory bulb. These results suggest that HGF influences multiple steps in postnatal forebrain neurogenesis. HGF is a mitogen for SVZ neural progenitors, and regulates their differentiation and olfactory bulb migration.