Reelin signals survival through Src-family kinases that inactivate BAD activity

Intravenous Reelin Treatment Rescues Atrophy of Spleen White Pulp and Correlates to Rescue of Forced Swim Test Immobility and Neurochemical Alterations Induced by Chronic Stress

Reelin, an extracellular matrix protein with putative antidepressant-like properties, becomes dysregulated by chronic stress. Improvement in cognitive dysfunction and depression-like behavior induced by chronic stress has been reported with both intrahippocampal and intravenous Reelin treatment but the mechanisms responsible are not clear. To determine if treatment with Reelin modifies chronic stress-induced dysfunction in immune organs and whether this relates to behavioral and/or neurochemical outcomes, spleens were collected from both male (n = 62) and female (n = 53) rats treated with daily corticosterone injections for three weeks that received Reelin or vehicle. Reelin was intravenously administered once on the final day of chronic stress, or repeatedly, with weekly treatments throughout chronic stress. Behavior was assessed during the forced swim test and the object-in-place test. Chronic corticosterone caused significant atrophy of the spleen white pulp, but treatment with a single shot of Reelin restored white pulp in both males and females. Repeated Reelin injections also resolved atrophy in females. Correlations were observed between recovery of white pulp atrophy and recovery of behavioral deficits and expression of both Reelin and glutamate receptor 1 in the hippocampus, supporting a role of the peripheral immune system in the recovery of chronic stress-induced behaviors following treatment with Reelin. Our data adds to research indicating Reelin could be a valuable therapeutic target for chronic stress-related disorders including major depression.

Prenatal exposure to valproic acid alters Reelin, NGF expressing neuron architecture and impairs social interaction in their autistic-like phenotype male offspring

Maternal exposure to anti-epileptic drug Valproic acid (VPA) during pregnancy increases the risk for the development of autism spectrum disorders (ASD). In this study, we have examined whether prenatal exposure to VPA will alter expression of key genes, synaptic morphology of nerve growth factor (NGF) and Reelin expressing neurons in the cortex of male offspring. To characterize in animal models, rat fetuses were exposed to VPA on 12.5 gestational day. The offspring of the VPA-exposed individuals (42%) resembles ASD-related phenotype (facial malformation, crooked-like tail, flattened paw, toenails and in-turning-ankles). Furthermore, we have observed deficit in social interaction accompanied by deregulation in expression of genes such as Caspase-3, focal adhesion kinase (FAK), Reelin, glial fibrillary acidic protein (GFAP), proliferating cell nuclear antigen (PCNA) and NGF. Subsequently, immunohistochemistry analysis revealed that exposure to VPA alters the cytoarchitecture (area, diameter) and reduced the dendritic arborization of Reelin, NGF expressing neurons in cortex. The compromised neurodevelopment by altered expression of Caspase-3, FAK, Reelin, GFAP, PCNA and NGF may cause defects in neuronal architecture, synaptic formation, synaptic plasticity and neuronal communication which could be linked with observed ASD-like phenotype and deficit social interaction.

Enhancement of angiogenesis and neurogenesis by intracerebroventricular injection of secretome from human embryonic stem cell-derived mesenchymal stem cells in ischemic stroke model

It is well accepted that the success of mesenchymal stem cells (MSCs) therapy against experimental stroke is mainly due to cellular paracrine manners rather than to replace lost tissue per se. Given such "bystander" effects, cell-free therapeutics manifest as a promising approach in regenerative medicine. Here we aimed at evaluating the effect of conditioned medium (CM) derived from human embryonic MSCs (hESC-MSC) on the neurological deficit, neurogenesis, and angiogenesis in experimental stroke. Adult male Wistar rats subjected to middle cerebral artery occlusion (MCAO), were treated with intracerebroventricular CM either one time (1 h post MCAO) or three times (1, 24, and 48 h post MCAO). Motor performance was assessed by the cylinder test on days 3 and 7. Cerebral samples were obtained for infarct size and molecular analysis on day 7 post-injury. Neurogenesis was evaluated by probing Nestin, Ki67, DCX, and Reelin transcripts and protein levels in the striatum, cortex, subventricular zone, and corpus callosum. The mRNA and protein expression of CD31 were also assessed in the striatum and cortical region to estimate angiogenesis post MCAO. Our findings demonstrate that CM treatment could significantly ameliorate neurological deficits and infarct volume in MCAO rats. Furthermore, ischemic stroke was associated with higher levels of neurogenesis and angiogenesis markers. Following treatment with CM, these markers were further potentiated in the brain regions. This study suggests that the therapeutic benefits of CM obtained from hESC-MSCs at least partly are mediated through improved neurogenesis and angiogenesis to accelerate the recovery of cerebral ischemia insult.

Evidence of Reelin Signaling in GBM and Its Derived Cancer Stem Cells

Glioblastoma (GBM) is the most aggressive and malignant form of primary brain cancer, characterized by an overall survival time ranging from 12 to 18 months. Despite the progress in the clinical treatment and the growing number of experimental data aimed at investigating the molecular bases of GBM development, the disease remains characterized by a poor prognosis. Recent studies have proposed the existence of a population of GBM cancer stem cells (CSCs) endowed with self-renewal capability and a high tumorigenic potential that are believed to be responsible for the resistance against common chemotherapy and radiotherapy treatments. Reelin is a large secreted extracellular matrix glycoprotein, which contributes to positioning, migration, and laminar organization of several central nervous system structures during brain development. Mutations of the reelin gene have been linked to disorganization of brain structures during development and behavioral anomalies. In this study, we explored the expression of reelin in GBM and its related peritumoral tissue and performed the same analysis in CSCs isolated from both GBM (GCSCs) and peritumoral tissue (PCSCs) of human patients. Our findings reveal (i) the higher expression of reelin in GBM compared to the peritumoral tissue by immunohistochemical analysis, (ii) the mRNA expression of both reelin and its adaptor molecule Dab1 in either CSC subtypes, although at a different extent; and (iii) the contribution of CSCs-derived reelin in the migration of human primary GBM cell line U87MG. Taken together, our data indicate that the expression of reelin in GBM may represent a potential contribution to the regulation of GBM cancer stem cells behavior, further stimulating the interest on the reelin pathway as a potential target for GBM treatment.

β-1, 3-galactosyltransferase 2 deficiency exacerbates brain injury after transient focal cerebral ischemia in mice

Glycosyltransferases are enzymes that catalyze the formation of a variety of glycoconjugates. Glycoconjugates play vital roles in the nervous system. β-1, 3-Galactosyltransferase 2 (B3galt2) is one of the major types of glycosyltransferases, which has not been reported in ischemia induced-brain injury. The purpose of this study was to explore the role of B3galt2 exerts and its underlying mechanism in cerebral ischemia in mice. Wild-type (WT) and heterozygous B3galt2 knockout (B3galt2^-/+) mice were subjected to 90 min transient focal cerebral ischemia by middle cerebral artery occlusion (MCAO). The brain samples were analyzed at 24 h after reperfusion. The B3galt2 level in the peri-infarct penumbra was quantified. The cerebral infarct volume, neurological deficits, apoptosis and the levels of Reelin and Dab1 were assessed. Compared with control mice, B3galt2^-/+ mice not only showed severe brain damage, neurologic functional deficits, but also showed severe neuronal apoptosis in the cortical penumbra after ischemia/reperfusion (I/R). The Caspase-3 activity was increased and the levels of Reelin and Dab1 were decreased in B3galt2^-/+ mice. Recombinant human Reelin (rh-Reelin) administered intracerebroventricularly before MCAO significantly reduced infarct volume, and prevented neuronal loss in B3galt2^-/+ mice after I/R. Our results suggest B3galt2 deficiency exacerbates ischemic brain damage in acute ischemic stroke in mice, and this was reversed by giving rh-Reelin. B3galt2 might play a beneficial role for neurons survival in the penumbra through modulation of Reelin pathway.

Reelin Functions, Mechanisms of Action and Signaling Pathways During Brain Development and Maturation

During embryonic development and adulthood, Reelin exerts several important functions in the brain including the regulation of neuronal migration, dendritic growth and branching, dendritic spine formation, synaptogenesis and synaptic plasticity. As a consequence, the Reelin signaling pathway has been associated with several human brain disorders such as lissencephaly, autism, schizophrenia, bipolar disorder, depression, mental retardation, Alzheimer’s disease and epilepsy. Several elements of the signaling pathway are known. Core components, such as the Reelin receptors very low-density lipoprotein receptor (VLDLR) and Apolipoprotein E receptor 2 (ApoER2), Src family kinases Src and Fyn, and the intracellular adaptor Disabled-1 (Dab1), are common to most but not all Reelin functions. Other downstream effectors are, on the other hand, more specific to defined tasks. Reelin is a large extracellular protein, and some aspects of the signal are regulated by its processing into smaller fragments. Rather than being inhibitory, the processing at two major sites seems to be fulfilling important physiological functions. In this review, I describe the various cellular events regulated by Reelin and attempt to explain the current knowledge on the mechanisms of action. After discussing the shared and distinct elements of the Reelin signaling pathway involved in neuronal migration, dendritic growth, spine development and synaptic plasticity, I briefly outline the data revealing the importance of Reelin in human brain disorders.

Fetal exposure to high levels of maternal glucocorticoids alters reelin signaling in the prefrontal cortex of rat pups

Maternal stress (MS) is associated with various neuropsychiatric disorders and cognitive impairment in the offspring. However, it is unclear how early life stress alters the pup's brain development and how it contributes to the pathology of neuropsychiatric disorders later in life. Reelin is a large extracellular matrix glycoprotein that plays essential roles in early brain development such as neural migration, synaptic development, and maturation. Dysregulation of reelin and its signaling proteins is associated with the emergence of neuropsychiatric disorders in adulthood. This study examined the effect of repeated maternal Carbenoxolone (CBX) injection during late gestation on reelin signaling in the prefrontal cortex (PFC) of rat pups. CBX is a selective 11β-HSD2 enzyme inhibitor that promotes the direct transfer of maternal corticosteroids (CORT) to the fetus. Therefore, treatment with CBX can mimic the animal model of early life exposure to high levels of maternal stress hormone. In this study, pregnant rats were injected daily with either saline or CBX during gestation day (GD) 14-21, and the levels of reelin and its signaling proteins were examined in the PFC of rat pups at different postnatal age from P0-P21. The main result of this study is the repeated maternal CBX injections during GD14-21 acutely increase reln mRNA and protein expression in the PFC of rat pups at birth (P0) and follow by a significant decrease during P7-P14. The treatment also causes long term decreases in the amount of VLDLR and Dab1 which are the downstream signaling proteins for the reelin pathway, at least until P21. Our results indicated that fetal exposure to high levels of maternal CORT interferes with reelin signaling which might have profound effects on cortical development associated with neuropsychiatric disorders later in life.

Integrity of Cajal-Retzius cells in the reeler-mouse hippocampus

Cajal-Retzius (CR) cells are early-born glutamatergic neurons that are primarily known as the early main source of the signal protein Reelin. In the reeler mutant, the absence of Reelin causes severe defects in the radial migration of neurons, resulting in abnormal cortical layering. To date, the exact morphological properties of CR-cells independent of Reelin are unknown. With this in view, we studied the ontogenesis, density, and distribution of CR-cells in reeler mice that were cross-bred with a CXCR4-EGFP reporter mouse line, thus enabling us to clearly identify CR-cells positions in the disorganized hippocampus of the reeler mouse. As evidenced by morphological analysis, differences were found regarding CR-cell distribution and density: generally, we found fewer CR-cells in the developing and adult reeler hippocampus as compared to the hippocampus of wild-type animals (WT); however, in reeler mice, CR-cells were much more closely associated to the hippocampal fissure (HF), resulting in relatively higher local CR-cell densities. This higher local cell density was accompanied by stronger immunoreactivity of the CXCR4 ligand, stroma-derived factor-1 (SDF-1) that is known to regulate CR-cell positioning. Importantly, confocal microscopy indicates an integration of CR-cells into the developing and adult hippocampal network in reeler mice, raising evidence that network integration of CR-cells might be independent of Reelin.

The Reelin Receptors Apolipoprotein E receptor 2 (ApoER2) and VLDL Receptor

Apolipoprotein E receptor 2 (ApoER2) and VLDL receptor belong to the low density lipoprotein receptor family and bind apolipoprotein E. These receptors interact with the clathrin machinery to mediate endocytosis of macromolecules but also interact with other adapter proteins to perform as signal transduction receptors. The best characterized signaling pathway in which ApoER2 and VLDL receptor (VLDLR) are involved is the Reelin pathway. This pathway plays a pivotal role in the development of laminated structures of the brain and in synaptic plasticity of the adult brain. Since Reelin and apolipoprotein E, are ligands of ApoER2 and VLDLR, these receptors are of interest with respect to Alzheimer’s disease. We will focus this review on the complex structure of ApoER2 and VLDLR and a recently characterized ligand, namely clusterin.

Reelin Expression in Creutzfeldt-Jakob Disease and Experimental Models of Transmissible Spongiform Encephalopathies

Reelin is an extracellular glycoprotein involved in key cellular processes in developing and adult nervous system, including regulation of neuronal migration, synapse formation, and plasticity. Most of these roles are mediated by the intracellular phosphorylation of disabled-1 (Dab1), an intracellular adaptor molecule, in turn mediated by binding Reelin to its receptors. Altered expression and glycosylation patterns of Reelin in cerebrospinal and cortical extracts have been reported in Alzheimer's disease. However, putative changes in Reelin are not described in natural prionopathies or experimental models of prion infection or toxicity. With this is mind, in the present study, we determined that Reelin protein and mRNA levels increased in CJD human samples and in mouse models of human prion disease in contrast to murine models of prion infection. However, changes in Reelin expression appeared only at late terminal stages of the disease, which prevent their use as an efficient diagnostic biomarker. In addition, increased Reelin in CJD and in in vitro models does not correlate with Dab1 phosphorylation, indicating failure in its intracellular signaling. Overall, these findings widen our understanding of the putative changes of Reelin in neurodegeneration.

Alterations of Cell Proliferation and Apoptosis in the Hypoplastic Reeler Cerebellum

A mutation of the reln gene gives rise to the Reeler mouse (reln^−∕−) displaying an ataxic phenotype and cerebellar hypoplasia. We have characterized the neurochemistry of postnatal (P0–P60) reln^−∕− mouse cerebella with specific attention to the intervention of cell proliferation and apoptosis in the P0–P25 interval. Homozygous reln^−∕− mice and age-matched controls were analyzed by immunofluorescence using primary antibodies against NeuN, calbindin, GFAP, vimentin, SMI32, and GAD67. Proliferation and apoptosis were detected after a single intraperitoneal BrdU injection and by the TUNEL assay with anti-digoxigenin rhodamine-conjugated antibodies. Quantitative analysis with descriptive and predictive statistics was used to calculate cell densities (number/mm²) after fluorescent nuclear stain (TCD, total cell density), labeling with BrdU (PrCD, proliferating cell density), or TUNEL (ApoCD, apoptotic cell density). By this approach we first have shown that the temporal pattern of expression of neuronal/glial markers in postnatal cerebellum is not affected by the Reeler mutation. Then, we have demonstrated that the hypoplasia in the Reeler mouse cerebellum is consequent to reduction of cortical size and cellularity (TCD), and that TCD is, in turn, linked to quantitative differences in the extent of cell proliferation and apoptosis, as well as derangements in their temporal trends during postnatal maturation. Finally, we have calculated that PrCD is the most important predictive factor to determine TCD in the cerebellar cortex of the mutants. These results support the notion that, beside the well-known consequences onto the migration of the cerebellar neurons, the lack of Reelin results in a measurable deficit in neural proliferation.

Bcl-2 associated with severity of manic symptoms in bipolar patients in a manic phase

B cell lymphoma protein-2 (Bcl-2) may contribute to the pathophysiology of bipolar disorder, and may be involved in the therapeutic action of anti-manic drugs. The aim of this study was to investigate serum levels of Bcl-2 in bipolar patients in a manic phase, and evaluate the Bcl-2 changes after treatment. We consecutively enrolled 23 bipolar inpatients in a manic phase and 40 healthy subjects; 20 bipolar patients were followed up with treatment. Serum Bcl-2 levels were measured with assay kits. All 20 patients were evaluated by examining the correlation between Bcl-2 levels and Young Mania Rating Scale (YMRS) scores, using Spearman׳s correlation coefficients. The serum Bcl-2 levels in bipolar patients in a manic phase were higher than in healthy subjects, but without a significant difference. The YMRS scores were significantly negatively associated with serum Bcl-2 levels (p=0.042). Bcl-2 levels of the 20 bipolar patients were measured at the end of treatment. Using the Wilcoxon Signed Rank test, we found no significant difference in the Bcl-2 levels of bipolar patients after treatment. Our results suggest that Bcl-2 levels might be an indicator of severity of manic symptoms in bipolar patients in a manic phase.

MicroRNA-200c contributes to injury from transient focal cerebral ischemia by targeting Reelin

BACKGROUND AND PURPOSE

MicroRNA (miR)-200c increases rapidly in the brain after transient cerebral ischemia but its role in poststroke brain injury is unclear. Reelin, a regulator of neuronal migration and synaptogenesis, is a predicted target of miR-200c. We hypothesized that miR-200c contributes to injury from transient cerebral ischemia by targeting reelin.

METHODS

Brain infarct volume, neurological score and levels of miR-200c, reelin mRNA, and reelin protein were assessed in mice subjected to 1 hour of middle cerebral artery occlusion with or without intracerebroventricular infusion of miR-200c antagomir, mimic, or mismatch control. Direct targeting of reelin by miR-200c was assessed in vitro by dual luciferase assay and immunoblot.

RESULTS

Pretreatment with miR-200c antagomir decreased post-middle cerebral artery occlusion brain levels of miR-200c, resulting in a significant reduction in infarct volume and neurological deficit. Changes in brain levels of miR-200c inversely correlated with reelin protein expression. Direct targeting of the Reln 3' untranslated region by miR-200c was verified with dual luciferase assay. Inhibition of miR-200c resulted in an increase in cell survival subsequent to in vitro oxidative injury. This effect was blocked by knockdown of reelin mRNA, whereas application of reelin protein afforded protection.

CONCLUSIONS

These findings suggest that the poststroke increase in miR-200c contributes to brain cell death by inhibiting reelin expression, and that reducing poststroke miR-200c is a potential target to mitigate stroke-induced brain injury.

Neurotrophins regulate ApoER2 proteolysis through activation of the Trk signaling pathway

Background

ApoER2 and the neurotrophin receptors Trk and p75^NTR are expressed in the CNS and regulate key functional aspects of neurons, including development, survival, and neuronal function. It is known that both ApoER2 and p75^NTR are processed by metalloproteinases, followed by regulated intramembrane proteolysis. TrkA activation by nerve growth factor (NGF) increases the proteolytic processing of p75^NTR mediated by ADAM17. Reelin induces the sheeding of ApoER2 ectodomain depending on metalloproteinase activity. However, it is not known if there is a common regulation mechanism for processing these receptors.

Results

We found that TrkA activation by NGF in PC12 cells induced ApoER2 processing, which was dependent on TrkA activation and metalloproteinases. NGF-induced ApoER2 proteolysis was independent of mitogen activated protein kinase activity and of phosphatidylinositol-3 kinase activity. In contrast, the basal proteolysis of ApoER2 increased when both kinases were pharmacologically inhibited. The ApoER2 ligand reelin regulated the proteolytic processing of its own receptor but not of p75^NTR. Finally, in primary cortical neurons, which express both ApoER2 and TrkB, we found that the proteolysis of ApoER2 was also regulated by brain-derived growth factor (BDNF).

Conclusions

Our results highlight a novel relationship between neurotrophins and the reelin-ApoER2 system, suggesting that these two pathways might be linked to regulate brain development, neuronal survival, and some pathological conditions.

Abnormal behaviors and developmental disorder of hippocampus in zinc finger protein 521 (ZFP521) mutant mice

Zinc finger protein 521 (ZFP521) regulates a number of cellular processes in a wide range of tissues, such as osteoblast formation and adipose commitment and differentiation. In the field of neurobiology, it is reported to be an essential factor for transition of epiblast stem cells into neural progenitors in vitro. However, the role of ZFP521 in the brain in vivo still remains elusive. To elucidate the role of ZFP521 in the mouse brain, we generated mice lacking exon 4 of the ZFP521 gene. The birth ratio of our ZFP521Δ/Δ mice was consistent with Mendel's laws. Although ZFP521Δ/Δ pups had no apparent defect in the body and were indistinguishable from ZFP521+/+ and ZFP521+/Δ littermates at the time of birth, ZFP521Δ/Δ mice displayed significant weight reduction as they grew, and most of them died before 10 weeks of age. They displayed abnormal behavior, such as hyper-locomotion, lower anxiety and impaired learning, which correspond to the symptoms of schizophrenia. The border of the granular cell layer of the dentate gyrus in the hippocampus of the mice was indistinct and granular neurons were reduced in number. Furthermore, Sox1-positive neural progenitor cells in the dentate gyrus and cerebellum were significantly reduced in number. Taken together, these findings indicate that ZFP521 directly or indirectly affects the formation of the neuronal cell layers of the dentate gyrus in the hippocampus, and thus ZFP521Δ/Δ mice displayed schizophrenia-relevant symptoms. ZFP521Δ/Δ mice may be a useful research tool as an animal model of schizophrenia.

Interdigital cell death in the embryonic limb is associated with depletion of Reelin in the extracellular matrix

Interdigital cell death is a physiological regression process responsible for sculpturing the digits in the embryonic vertebrate limb. Changes in the intensity of this degenerative process account for the different patterns of interdigital webbing among vertebrate species. Here, we show that Reelin is present in the extracellular matrix of the interdigital mesoderm of chick and mouse embryos during the developmental stages of digit formation. Reelin is a large extracellular glycoprotein which has important functions in the developing nervous system, including neuronal survival; however, the significance of Reelin in other systems has received very little attention. We show that reelin expression becomes intensely downregulated in both the chick and mouse interdigits preceding the establishment of the areas of interdigital cell death. Furthermore, fibroblast growth factors, which are cell survival signals for the interdigital mesoderm, intensely upregulated reelin expression, while BMPs, which are proapototic signals, downregulate its expression in the interdigit. Gene silencing experiments of reelin gene or its intracellular effector Dab-1 confirmed the implication of Reelin signaling as a survival factor for the limb undifferentiated mesoderm. We found that Reelin activates canonical survival pathways in the limb mesoderm involving protein kinase B and focal adhesion kinase. Our findings support that Reelin plays a role in interdigital cell death, and suggests that anoikis (apoptosis secondary to loss of cell adhesion) may be involved in this process.

Cell-autonomous inactivation of the reelin pathway impairs adult neurogenesis in the hippocampus

Adult hippocampal neurogenesis is thought to be essential for learning and memory, and has been implicated in the pathogenesis of several disorders. Although recent studies have identified key factors regulating neuroprogenitor proliferation in the adult hippocampus, the mechanisms that control the migration and integration of adult-born neurons into circuits are largely unknown. Reelin is an extracellular matrix protein that is vital for neuronal development. Activation of the Reelin cascade leads to phosphorylation of Disabled-1, an adaptor protein required for Reelin signaling. Here we used transgenic mouse and retroviral reporters along with Reelin signaling gain-of-function and loss-of-function studies to show that the Reelin pathway regulates migration and dendritic development of adult-generated hippocampal neurons. Whereas overexpression of Reelin accelerated dendritic maturation, inactivation of the Reelin signaling pathway specifically in adult neuroprogenitor cells resulted in aberrant migration, decreased dendrite development, formation of ectopic dendrites in the hilus, and the establishment of aberrant circuits. Our findings support a cell-autonomous and critical role for the Reelin pathway in regulating dendritic development and the integration of adult-generated granule cells and point to this pathway as a key regulator of adult neurogenesis. Moreover, our data reveal a novel role of the Reelin cascade in adult brain function with potential implications for the pathogenesis of several neurological and psychiatric disorders.

Reelin is involved in the crypt-villus unit homeostasis

Intestinal myofibroblasts secrete substances that control organogenesis and wound repair of the intestine. The myofibroblasts of the rat small intestine express reelin and the present work explores whether reelin regulates crypt-villus unit homeostasis using normal mice and mice with the reelin gene disrupted (reeler). The results reveal that mouse small intestine expresses reelin, its receptors apolipoprotein E receptor 2 (ApoER2) and very low-density lipoprotein receptor (VldlR) and the reelin effector protein Disabled-1 (Dab1) and that reelin expression is restricted to myofibroblasts. The absence of reelin significantly reduces epithelial cell proliferation, migration, and apoptosis and the number of Paneth cells. These effects are observed during the suckling, weaning, and adult periods. The number of Goblet cells is increased in the 2-month-old reeler mice. The absence of reelin also expands the extracellular space of the adherens junctions and desmosomes without significantly affecting either the tight-junction structure or the epithelial paracellular permeability. In conclusion, this is the first in vivo work showing that the absence of reelin alters intestinal epithelium homeostasis.

The neurodevelopmental implications of PI3K signaling

Our understanding of the mechanisms involved in the formation of the complex arrangement of neurons and their interconnections within the brain has made significant progress in recent years. Current research has uncovered a network of intracellular signaling events that provide precise coordination of a diverse array of cellular responses, including trafficking events, cytoskeletal remodeling, gene transcription, and protein ubiquitination and translation. This chapter considers the specific cellular responses controlled by the phosphatidylinositol 3-kinase (PI3K) signaling pathway, which is instructive with regard to a number of important steps involved in the development of the brain. These range from the mediation of extrinsic signals - such as growth factors, axon guidance cues, and extracellular matrix components - to intrinsic effectors, such as downstream signaling components that act, for example, at the translation level. PI3K signaling is, consequently, at the heart of controlling neuronal migration and neuronal morphogenesis, as well as dendrite and synapse development. Many neurobehavioral disorders arise as a consequence of subtle developmental abnormalities. Unsurprisingly, therefore, aberrant PI3K signaling has been indicated by many studies to be a contributing factor to the pathophysiology of disorders such as schizophrenia and autism. In this chapter, we will focus on the specific, yet divergent, cellular processes that are achieved through PI3K signaling in neurons and are key to brain development.

A genome-wide analysis identifies genetic variants in the RELN gene associated with otosclerosis

Otosclerosis is a common form of progressive hearing loss, characterized by abnormal bone remodeling in the otic capsule. The etiology of the disease is largely unknown, and both environmental and genetic factors have been implicated. To identify genetic factors involved in otosclerosis, we used a case-control discovery group to complete a genome-wide association (GWA) study with 555,000 single-nucleotide polymorphisms (SNPs), utilizing pooled DNA samples. By individual genotyping of the top 250 SNPs in a stepwise strategy, we were able to identify two highly associated SNPs that replicated in two additional independent populations. We then genotyped 79 tagSNPs to fine map the two genomic regions defined by the associated SNPs. The region with the strongest association signal, p(combined) = 6.23 x 10(-10), is on chromosome 7q22.1 and spans intron 1 to intron 4 of reelin (RELN), a gene known for its role in neuronal migration. Evidence for allelic heterogeneity was found in this region. Consistent with the GWA data, expression of RELN was confirmed in the inner ear and in stapes footplate specimens. In conclusion, we provide evidence that implicates RELN in the pathogenesis of otosclerosis.

Genome-wide association analysis of susceptibility and clinical phenotype in multiple sclerosis

Multiple sclerosis (MS), a chronic disorder of the central nervous system and common cause of neurological disability in young adults, is characterized by moderate but complex risk heritability. Here we report the results of a genome-wide association study performed in a 1000 prospective case series of well-characterized individuals with MS and group-matched controls using the Sentrix HumanHap550 BeadChip platform from Illumina. After stringent quality control data filtering, we compared allele frequencies for 551 642 SNPs in 978 cases and 883 controls and assessed genotypic influences on susceptibility, age of onset, disease severity, as well as brain lesion load and normalized brain volume from magnetic resonance imaging exams. A multi-analytical strategy identified 242 susceptibility SNPs exceeding established thresholds of significance, including 65 within the MHC locus in chromosome 6p21.3. Independent replication confirms a role for GPC5, a heparan sulfate proteoglycan, in disease risk. Gene ontology-based analysis shows a functional dichotomy between genes involved in the susceptibility pathway and those affecting the clinical phenotype.