Interaction of reelin signaling and Lis1 in brain development

LRP8 promotes tumorigenesis in ovarian cancer through inhibiting p53 signaling

Ovarian cancer (OC) is the most lethal gynecological malignancy with a high mortality rate. Low-density lipoprotein (LDL) receptor-related protein 8 (LRP8) is a cell membrane receptor belonging LDL receptor family and is involved in several tumor progressions. However, there is limited understanding of how LRP8 mediates OC development. LRP8 expression level was identified in human OC tissues and cells using immunohistochemical staining and quantitative polymerase chain reaction assays, respectively. Functions of LRP8 in OC progression were evaluated by Celigo cell counting, wound healing, transwell and flow cytometry assays, and the xenograft models. The human phospho-kinase array analysis was used for screening potential signaling involved in OC development. We observed that LRP8 was overexpressed in OC tissues, and high expression of LRP8 was associated with poor prognosis of OC patients. Functionally, LRP8 knockdown remarkably reduced proliferation and migration of OC cells, and induced apoptosis and S phase cycle arrest. LRP8 deficiency attenuated in vivo tumor growth of OC cells. Moreover, the addition of p53 inhibitor partially reversed the effects of LRP8 knockdown on OC cell proliferation and apoptosis, indicating the involvement of p53 signaling in LRP8-mediated OC progression. This study confirmed that LRP8/p53 axis contributed to OC progression, which might serve as a novel potential therapeutic target for OC patients.

DISC1 and reelin interact to alter cognition, inhibition, and neurogenesis in a novel mouse model of schizophrenia

The etiology of schizophrenia (SCZ) is multifactorial, and depending on a host of genetic and environmental factors. Two putative SCZ susceptibility genes, Disrupted-in-Schizophrenia-1 (DISC1) and reelin (RELN), interact at a molecular level, suggesting that combined disruption of both may lead to an intensified SCZ phenotype. To examine this gene-gene interaction, we produced a double mutant mouse line. Mice with heterozygous RELN haploinsufficiency were crossed with mice expressing dominant-negative c-terminal truncated human DISC1 to produce offspring with both mutations (HRM/DISC1 mice). We used an array of behavioral tests to generate a behavioral phenotype for these mice, then examined the prefrontal cortex and hippocampus using western blotting and immunohistochemistry to probe for SCZ-relevant molecular and cellular alterations. Compared to wild-type controls, HRM/DISC1 mice demonstrated impaired pre-pulse inhibition, altered cognition, and decreased activity. Diazepam failed to rescue anxiety-like behaviors, paradoxically increasing activity in HRM/DISC1 mice. At a cellular level, we found increased α1-subunit containing GABA receptors in the prefrontal cortex, and a reduction in fast-spiking parvalbumin positive neurons. Maturation of adult-born neurons in the hippocampus was also altered in HRM/DISC1 mice. While there was no difference in the total number proliferating cells, more of these cells were in immature stages of development. Homozygous DISC1 mutation combined with RELN haploinsufficiency produces a complex phenotype with neuropsychiatric characteristics relevant to SCZ and related disorders, expanding our understanding of how multiple genetic susceptibility factors might interact to influence the variable presentation of these disorders.

Reelin Signaling in Neurodevelopmental Disorders and Neurodegenerative Diseases

Reelin is an extracellular matrix glycoprotein involved in neuronal migration during embryonic brain development and synaptic plasticity in the adult brain. The role of Reelin in the developing central nervous system has been extensively characterized. Indeed, a loss of Reelin or a disruption in its signaling cascade leads to neurodevelopmental defects and is associated with ataxia, intellectual disability, autism, and several psychiatric disorders. In the adult brain, Reelin is critically involved in neurogenesis and synaptic plasticity. Reelin's signaling potentiates glutamatergic and GABAergic neurotransmission, induces synaptic maturation, and increases AMPA and NMDA receptor subunits' expression and activity. As a result, there is a growing literature reporting that a loss of function and/or reduction of Reelin is implicated in numerous neurodegenerative diseases. The present review summarizes the current state of the literature regarding the implication of Reelin and Reelin-mediated signaling during aging and neurodegenerative disorders, highlighting Reelin as a possible target in the prevention or treatment of progressive neurodegeneration.

In silico analysis of the possible crosstalk between O-linked β-GlcNAcylation and phosphorylation sites of Disabled 1 adaptor protein in vertebrates

Disabled 1 (Dab1) is an adaptor protein with essential functions regulated by reelin signaling and affects many biological processes in the nervous system, including cell motility, adhesion, cortical development, maturation, and synaptic plasticity. Posttranslational modifications directly guide the fates of cytoplasmic proteins to complete their functions correctly. Reciprocal crosstalk between O-GlcNAcylation and phosphorylation is a dynamic modification in cytoplasmic proteins. It modulates the functions of the proteins by regulating their interactions with other molecules in response to the continuously changeable cell microenvironment. Although Dab1 contains conserved recognition sites for phosphorylation in their N-terminal protein interaction domain, the O-β-GlcNAcylation and phosphorylation sites of human Dab1 sequence, their reciprocal crosstalk, and potential kinases catalyzing the phosphorylation remain unknown. In this study, we determined potential thirty-seven O-β-GlcNAcylation and sixty-seven phosphorylation sites. Conserved twenty-one residues of these glycosylated sites were also phosphorylated with various kinases, including ATM, CKI, DNAPK, GSK3, PKC, PKG, RSK, cdc2, cdk5, and p38MAPK. In addition, we analyzed these conserved sites at our constructed two- and three-dimensional structures of human Dab1 protein. Dab1 protein models were frequently composed of coil structures as well as α-helix and β-strands. Many of these conserved crosstalk sites between O-β-GlcNAcylation and phosphorylation were localized at the coil region of the protein model. These findings may guide biochemical, genetic, and glyco-biology based on further experiments about the Dab1 signaling process. Understanding these modifications might change the point of view of the Dab1 signaling process and treatment for pathological conditions in neurodegenerative diseases such as Alzheimer's disease.

The Neuron Navigators: Structure, function, and evolutionary history

Neuron navigators (Navigators) are cytoskeletal-associated proteins important for neuron migration, neurite growth, and axon guidance, but they also function more widely in other tissues. Recent studies have revealed novel cellular functions of Navigators such as macropinocytosis, and have implicated Navigators in human disorders of axon growth. Navigators are present in most or all bilaterian animals: vertebrates have three Navigators (NAV1-3), Drosophila has one (Sickie), and Caenorhabditis elegans has one (Unc-53). Structurally, Navigators have conserved N- and C-terminal regions each containing specific domains. The N-terminal region contains a calponin homology (CH) domain and one or more SxIP motifs, thought to interact with the actin cytoskeleton and mediate localization to microtubule plus-end binding proteins, respectively. The C-terminal region contains two coiled-coil domains, followed by a AAA+ family nucleoside triphosphatase domain of unknown activity. The Navigators appear to have evolved by fusion of N- and C-terminal region homologs present in simpler organisms. Overall, Navigators participate in the cytoskeletal response to extracellular cues via microtubules and actin filaments, in conjunction with membrane trafficking. We propose that uptake of fluid-phase cues and nutrients and/or downregulation of cell surface receptors could represent general mechanisms that explain Navigator functions. Future studies developing new models, such as conditional knockout mice or human cerebral organoids may reveal new insights into Navigator function. Importantly, further biochemical studies are needed to define the activities of the Navigator AAA+ domain, and to study potential interactions among different Navigators and their binding partners.

Thyroid hormones regulate reelin expression in neuropsychiatric disorders

The incidence and prevalence of hypothyroidism in pregnancy have increased over the past two decades, leading to the occurrence of neuropsychiatric disorders. However, the underlying mechanisms of thyroid hormone (TH)-regulated gene expression and neuropsychiatric development during the postnatal period remain unknown. Recent achievements have shown that reelin, a large extracellular glycoprotein, plays a crucial role in neuronal migration and localization during the development of neocortex and cerebellar cortex, thereby participating in the development of neuropsychiatric diseases. Reelin-induced neuronal migration requires triiodothyronine (T3) from the deiodination of thyroxine (T4) by fetal brain deiodinases. Previous studies have reported decreased reelin levels and abnormal gene expression, which are the same as the pathological alternations in reelin-induced neuropsychiatric disorders including schizophrenia and autism. Low T3 in the fetal brain due to hypothyroxinemia during pregnancy may be detrimental to neuronal migration, leading to neuropsychiatric disorders. In this review, we focus on the reelin expression between hypothyroidism and neuropsychiatric disorders.

LRP8, modulated by miR-1262, promotes tumour progression and forecasts the prognosis of patients in breast cancer

This research was designed to detect the function of low-density lipoprotein receptor (LDLR)-related protein 8 (LRP8) in breast cancer (BC). Our results revealed that LRP8 was highly expressed in BC tissues and cell lines compared with human normal breast tissues. The poor prognosis of patients with BC was associated with the up-regulation of LRP8 while inversely connected with overexpression of miR-1262. Functionally, LRP8 depletion in BC cells impaired the proliferative, clonogenic, invasive, and migratory capabilities, which was consistent with the effects of upregulated miR-1262. Bioinformatics prediction and luciferase reporter assay confirmed that miR-1262 was an upstream factor for LRP8 and negatively regulated the expression of LRP8. Further experiments illustrated that the co-transfection of miR-1262 antamir and si-LRP8 could significantly suppress the promoting impacts caused by the transfection of miR-1262 antamir alone. These findings highlighted that LRP8 accelerated the BC development by contributing cellular aggressiveness, which was modulated by miR-1262.

Genome-wide CNV investigation suggests a role for cadherin, Wnt, and p53 pathways in primary open-angle glaucoma

BACKGROUND

To investigate whether copy number variations (CNVs) are implicated in molecular mechanisms underlying primary open-angle glaucoma (POAG), we used genotype data of POAG individuals and healthy controls from two case-control studies, AGS (n = 278) and GLGS-UGLI (n = 1292). PennCNV, QuantiSNP, and cnvPartition programs were used to detect CNV. Stringent quality controls at both sample and marker levels were applied. The identified CNVs were intersected in CNV region (CNVR). After, we performed burden analysis, CNV-genome-wide association analysis, gene set overrepresentation and pathway analysis. In addition, in human eye tissues we assessed the expression of the genes lying within significant CNVRs.

RESULTS

We reported a statistically significant greater burden of CNVs in POAG cases compared to controls (p-value = 0,007). In common between the two cohorts, CNV-association analysis identified statistically significant CNVRs associated with POAG that span 11 genes (APC, BRCA2, COL3A1, HLA-DRB1, HLA-DRB5, HLA-DRB6, MFSD8, NIPBL, SCN1A, SDHB, and ZDHHC11). Functional annotation and pathway analysis suggested the involvement of cadherin, Wnt signalling, and p53 pathways.

CONCLUSIONS

Our data suggest that CNVs may have a role in the susceptibility of POAG and they can reveal more information on the mechanism behind this disease. Additional genetic and functional studies are warranted to ascertain the contribution of CNVs in POAG.

Potential roles of natural products in the targeting of proteinopathic neurodegenerative diseases

Defective proteostasis is associated with the gradual accumulations of misfolded proteins and is a hallmark of many age-associated neurodegenerative diseases. In the aged brain, maintenance of the proteostasis network presents a substantial challenge, and its loss contributes to the onset and progression of neurological diseases associated with cognitive decline due to the generation of toxic protein aggregates, a process termed 'proteinopathy'. Emerging evidence suggests that reversing proteinopathies by boosting proteostasis might provide an effective means of preventing neurodegeneration. From this perspective, phytochemicals may play significant roles as potent modulators of the proteostasis network, as previous reports have suggested they can interact with various network components to modify pathologies and confer neuroprotection. This review focuses on some potent phytochemicals that directly or indirectly modulate the proteostasis network and on their possible molecular targets. In addition, we propose strategies for the natural product-based modulation of proteostasis machinery that target proteinopathies.

Rare single-nucleotide DAB1 variants and their contribution to Schizophrenia and autism spectrum disorder susceptibility

Disabled 1 (DAB1) is an intracellular adaptor protein in the Reelin signaling pathway and plays an essential role in correct neuronal migration and layer formation in the developing brain. DAB1 has been repeatedly reported to be associated with neurodevelopmental disorders including schizophrenia (SCZ) and autism spectrum disorders (ASD) in genetic, animal, and postmortem studies. Recently, increasing attention has been given to rare single-nucleotide variants (SNVs) found by deep sequencing of candidate genes. In this study, we performed exon-targeted resequencing of DAB1 in 370 SCZ and 192 ASD patients using next-generation sequencing technology to identify rare SNVs with a minor allele frequency <1%. We detected two rare missense mutations (G382C, V129I) and then performed a genetic association study in a sample comprising 1763 SCZ, 380 ASD, and 2190 healthy control subjects. Although no statistically significant association with the detected mutations was observed for either SCZ or ASD, G382C was found only in the case group, and in silico analyses and in vitro functional assays suggested that G382C alters the function of the DAB1 protein. The rare variants of DAB1 found in the present study should be studied further to elucidate their potential functional relevance to the pathophysiology of SCZ and ASD.

Emergence of non-canonical parvalbumin-containing interneurons in hippocampus of a murine model of type I lissencephaly

Type I lissencephaly is a neuronal migration disorder caused by haploinsuffiency of the PAFAH1B1 (mouse: Pafah1b1) gene and is characterized by brain malformation, developmental delays, and epilepsy. Here, we investigate the impact of Pafah1b1 mutation on the cellular migration, morphophysiology, microcircuitry, and transcriptomics of mouse hippocampal CA1 parvalbumin-containing inhibitory interneurons (PV+INTs). We find that WT PV+INTs consist of two physiological subtypes (80% fast-spiking (FS), 20% non-fast-spiking (NFS)) and four morphological subtypes. We find that cell-autonomous mutations within interneurons disrupts morphophysiological development of PV+INTs and results in the emergence of a non-canonical 'intermediate spiking (IS)' subset of PV+INTs. We also find that now dominant IS/NFS cells are prone to entering depolarization block, causing them to temporarily lose the ability to initiate action potentials and control network excitation, potentially promoting seizures. Finally, single-cell nuclear RNAsequencing of PV+INTs revealed several misregulated genes related to morphogenesis, cellular excitability, and synapse formation.

Purification of an Intact Human Protein Overexpressed from Its Endogenous Locus via Direct Genome Engineering

The overproduction and purification of human proteins is a requisite of both basic and medical research. Although many recombinant human proteins have been purified, current protein production methods have several limitations; recombinant proteins are frequently truncated, fail to fold properly, and/or lack appropriate post-translational modifications. In addition, such methods require subcloning of the target gene into relevant plasmids, which can be difficult for long proteins with repeated domains. Here we devised a novel method for target protein production by introduction of a strong promoter for overexpression and an epitope tag for purification in front of the endogenous human gene, in a sense performing molecular cloning directly in the human genome, which does not require cloning of the target gene. As a proof of concept, we successfully purified intact human Reelin protein, which is lengthy (3460 amino acids) and contains repeating domains, and confirmed that it was biologically functional.

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.

Quantitative Three-Dimensional Reconstructions of Excitatory Synaptic Boutons in the "Barrel Field" of the Adult "Reeler" Mouse Somatosensory Neocortex: A Comparative Fine-Scale Electron Microscopic Analysis with the Wild Type Mouse

Synapses are key structural determinants for information processing and computations in the normal and pathologically altered brain. Here, the quantitative morphology of excitatory synaptic boutons in the "reeler" mutant, a model system for various neurological disorders, was investigated and compared with wild-type (WT) mice using high-resolution, fine-scale electron microscopy (EM) and quantitative three-dimensional (3D) models of synaptic boutons. Beside their overall geometry, the shape and size of presynaptic active zones (PreAZs) and postsynaptic densities (PSDs) forming the active zones and the three pools of synaptic vesicles (SVs), namely the readily releasable pool (RRP), the recycling pool (RP), and the resting pool, were quantified. Although the reeler mouse neocortex is severely disturbed, no significant differences were found in most of the structural parameters investigated: the size of boutons (~3 μm2), size of the PreAZs and PSDs (~0.17 μm2), total number of SVs, and SVs within a perimeter (p) of 10 nm and p20 nm RRP; the p60 nm, p100 nm, and p60-p200 nm RP; and the resting pool, except the synaptic cleft width. Taken together, the synaptic organization and structural composition of synaptic boutons in the reeler neocortex remain comparably "normal" and may thus contribute to a "correct" wiring of neurons within the reeler cortical network.

Disrupted in Schizophrenia 1 regulates the processing of reelin in the perinatal cortex

Disrupted in Schizophrenia 1 (DISC1) is a prominent gene in mental illness research, encoding a scaffold protein known to be of importance in the developing cerebral cortex. Reelin is a critical extracellular protein for development and lamination of the prenatal cortex and which has also been independently implicated in mental illness. Regulation of reelin activity occurs through processing by the metalloproteinases ADAMTS-4 and ADAMTS-5. Through cross-breeding of heterozygous transgenic DISC1 mice with heterozygous reeler mice, which have reduced reelin, pups heterozygous for both phenotypes were generated. From these, we determine that transgenic DISC1 leads to a reduction in the processing of reelin, with implications for its downstream signalling element Dab1. An effect of DISC1 on reelin processing was confirmed in vitro, and revealed that intracellular DISC1 affects ADAMTS-4 protein, which in turn is exported and affects processing of extracellular reelin. In transgenic rat cortical cultures, an effect of DISC1 on reelin processing could also be seen specifically in early, immature neurons, but was lost in calretinin and reelin-positive mature neurons, suggesting cell-type specificity. DISC1 therefore acts upstream of reelin in the perinatal cerebral cortex in a cell type/time specific manner, leading to regulation of its activity through altered proteolytic cleavage. Thus a functional link is demonstrated between two proteins, each of independent importance for both cortical development and associated cognitive functions leading to behavioural maladaptation and mental illness.

Intra-day variations of blood reelin levels in healthy individuals

INTRODUCTION

Reelin (RELN) is an extracellular glycoprotein best known to be crucial for neuronal migration during the embryonic period and regulation of synaptic plasticity in the adult brain, with recent studies pointing to reelin playing an important part in the organization of peripheral organs as well. Abnormalities in RELN function are associated with a variety of medical conditions in human beings. These alterations partly also reflect in RELN's blood levels, which gives it a clinical relevance as a potential biomarker. Requirement for a possible clinical use is a profound understanding of RELN's physiology. We hypothesized blood RELN levels could underlie time-dependent variations and therefore examined individuals' serum reelin concentrations in the course of one day.

MATERIAL AND METHODS

We obtained blood samples from healthy individuals (n = 10) at several times of measurement over a time period of 24 h. We subsequently determined the respective serum RELN concentrations utilizing an enzyme-linked immunosorbent assay and tested for intra- and interindividual variations in serum RELN concentrations over time.

RESULTS

All tested individuals' serum RELN levels displayed significant intraindividual variations in the course of 24 h. Test subjects' reelin day profiles showed substantial divergence among each other.

CONCLUSIONS

Our findings point to short-term fluctuations in blood RELN levels being part of physiological RELN homeostasis. This is of special interest with regard to a potential clinical use of RELN as a biomarker.

The Reeler Mouse: A Translational Model of Human Neurological Conditions, or Simply a Good Tool for Better Understanding Neurodevelopment?

The first description of the Reeler mutation in mouse dates to more than fifty years ago, and later, its causative gene (reln) was discovered in mouse, and its human orthologue (RELN) was demonstrated to be causative of lissencephaly 2 (LIS2) and about 20% of the cases of autosomal-dominant lateral temporal epilepsy (ADLTE). In both human and mice, the gene encodes for a glycoprotein referred to as reelin (Reln) that plays a primary function in neuronal migration during development and synaptic stabilization in adulthood. Besides LIS2 and ADLTE, RELN and/or other genes coding for the proteins of the Reln intracellular cascade have been associated substantially to other conditions such as spinocerebellar ataxia type 7 and 37, VLDLR-associated cerebellar hypoplasia, PAFAH1B1-associated lissencephaly, autism, and schizophrenia. According to their modalities of inheritances and with significant differences among each other, these neuropsychiatric disorders can be modeled in the homozygous (reln^−/−) or heterozygous (reln^+/−) Reeler mouse. The worth of these mice as translational models is discussed, with focus on their construct and face validity. Description of face validity, i.e., the resemblance of phenotypes between the two species, centers onto the histological, neurochemical, and functional observations in the cerebral cortex, hippocampus, and cerebellum of Reeler mice and their human counterparts.

Platelet-activating factor acetylhydrolase 1B3 (PAFAH1B3) is required for the formation of the meiotic spindle during in vitro oocyte maturation

Platelet-activating factor (PAF) is a well-described autocrine growth factor involved in several reproductive processes and is tightly regulated by its hydrolysing enzyme, PAF acetylhydrolase 1B (PAFAH1B). This intracellular enzyme consists of three subunits: one regulatory, 1B1, and two catalytic, 1B2 and 1B3. PAFAH1B3 has remained uncharacterised until now. Here, we report that PAFAH1B3 is present during the different stages of the first meiotic division in bovine, murine and human oocytes. In these species, the PAFAH1B3 subunit was clearly present in the germinal vesicle, while at metaphase I and II, it localised primarily at the meiotic spindle structure. In cattle, manipulation of the microtubules of the spindle by nocodazole, taxol or cryopreservation revealed a close association with PAFAH1B3. On the other hand, disruption of the enzyme activity either by P11, a selective inhibitor of PAFAH1B3, or by PAFAH1B3 antibody microinjection, caused arrest at the MI stage with defective spindle morphology and consequent failure of first polar body extrusion. In conclusion, our results show that one of the catalytic subunits of PAFAH1B, namely PAFAH1B3, is present in bovine, murine and human oocytes and that it plays a functional role in spindle formation and meiotic progression during bovine oocyte maturation.

LRP8 is overexpressed in estrogen-negative breast cancers and a potential target for these tumors

Triple‐negative breast cancer (TNBC) is the breast cancer subtype with the worst prognosis. New treatments improving the survival of TNBC patients are, therefore, urgently required. We performed a transcriptome microarray analysis to identify new treatment targets for TNBC. We found that low‐density lipoprotein receptor‐related protein 8 (LRP8) was more strongly expressed in estrogen receptor‐negative breast tumors, including TNBCs and those overexpressing HER2, than in luminal breast tumors and normal breast tissues. LRP8 depletion decreased cell proliferation more efficiently in estrogen receptor‐negative breast cancer cell lines: TNBC and HER2 overexpressing cell lines. We next focused on TNBC cells for which targeted therapies are not available. LRP8 depletion induced an arrest of the cell cycle progression in G1 phase and programmed cell death. We also found that LRP8 is required for anchorage‐independent growth in vitro, and that its depletion in vivo slowed tumor growth in a xenograft model. Our findings suggest that new approaches targeting LRP8 may constitute promising treatments for hormone‐negative breast cancers, those overexpressing HER2 and TNBCs.

The functions of Reelin in membrane trafficking and cytoskeletal dynamics: implications for neuronal migration, polarization and differentiation

Reelin is a large extracellular matrix protein with relevant roles in mammalian central nervous system including neurogenesis, neuronal polarization and migration during development; and synaptic plasticity with its implications in learning and memory, in the adult. Dysfunctions in reelin signaling are associated with brain lamination defects such as lissencephaly, but also with neuropsychiatric diseases like autism, schizophrenia and depression as well with neurodegeneration. Reelin signaling involves a core pathway that activates upon reelin binding to its receptors, particularly ApoER2 (apolipoprotein E receptor 2)/LRP8 (low-density lipoprotein receptor-related protein 8) and very low-density lipoprotein receptor, followed by Src/Fyn-mediated phosphorylation of the adaptor protein Dab1 (Disabled-1). Phosphorylated Dab1 (pDab1) is a hub in the signaling cascade, from which several other downstream pathways diverge reflecting the different roles of reelin. Many of these pathways affect the dynamics of the actin and microtubular cytoskeleton, as well as membrane trafficking through the regulation of the activity of small GTPases, including the Rho and Rap families and molecules involved in cell polarity. The complexity of reelin functions is reflected by the fact that, even now, the precise mode of action of this signaling cascade in vivo at the cellular and molecular levels remains unclear. This review addresses and discusses in detail the participation of reelin in the processes underlying neurogenesis, neuronal migration in the cerebral cortex and the hippocampus; and the polarization, differentiation and maturation processes that neurons experiment in order to be functional in the adult brain. In vivo and in vitro evidence is presented in order to facilitate a better understanding of this fascinating system.

Low-Density Lipoprotein Receptor-Related Proteins in Skeletal Development and Disease

The identification of the low-density lipoprotein receptor (LDLR) provided a foundation for subsequent studies in lipoprotein metabolism, receptor-mediated endocytosis, and many other fundamental biological functions. The importance of the LDLR led to numerous studies that identified homologous molecules and ultimately resulted in the description of the LDL-receptor superfamily, a group of proteins that contain domains also found in the LDLR. Subsequent studies have revealed that members of the LDLR-related protein family play roles in regulating many aspects of signal transduction. This review is focused on the roles of selected members of this protein family in skeletal development and disease. We present background on the identification of this subgroup of receptors, discuss the phenotypes associated with alterations in their function in human patients and mouse models, and describe the current efforts to therapeutically target these proteins to treat human skeletal disease.

Control of Neuronal Migration and Aggregation by Reelin Signaling in the Developing Cerebral Cortex

The mammalian cerebral neocortex has a well-organized laminar structure, achieved by the highly coordinated control of neuronal migration. During cortical development, excitatory neurons born near the lateral ventricle migrate radially to reach their final positions to form the cortical plate. During this process, dynamic changes are observed in the morphologies and migration modes, including multipolar migration, locomotion, and terminal translocation, of the newborn neurons. Disruption of these migration processes can result in neuronal disorders such as lissencephaly and periventricular heterotopia. The extracellular protein, Reelin, mainly secreted by the Cajal-Retzius neurons in the marginal zone during development, plays a crucial role in the neuronal migration and neocortical lamination. Reelin signaling, which exerts essential roles in the formation of the layered neocortex, is triggered by the binding of Reelin to its receptors, ApoER2 and VLDLR, followed by phosphorylation of the Dab1 adaptor protein. Accumulating evidence suggests that Reelin signaling controls multiple steps of neuronal migration, including the transition from multipolar to bipolar neurons, terminal translocation, and termination of migration beneath the marginal zone. In addition, it has been shown that ectopically expressed Reelin can cause neuronal aggregation via an N-cadherin-mediated manner. This review attempts to summarize our knowledge of the roles played by Reelin in neuronal migration and the underlying mechanisms.

Evidence of early defects in Cajal-Retzius cell localization during brain development in a mouse model of dystroglycanopathy

AIMS

The secondary dystroglycanopathies represent a heterogeneous group of congenital muscular dystrophies characterized by the defective glycosylation of alpha dystroglycan. These disorders are associated with mutations in at least 17 genes, including Fukutin-related protein (FKRP). At the severe end of the clinical spectrum there is substantial brain involvement, and cobblestone lissencephaly is highly suggestive of these disorders. The precise pathogenesis of this phenotype has, however, remained unclear with most attention focused on the disruption to the radial glial scaffold. Here, we set out to investigate whether lesions are apparent prior to the differentiation of the radial glia.

METHODS

A detailed investigation of the structural brain defects from embryonic day 10.5 (E10.5) up until the time of birth (P0) was undertaken in the Fkrp-deficient mice (FKRP^KD ). Reelin, and downstream PI3K/Akt signalling pathways were analysed using Western blot.

RESULTS

We show that early basement membrane defects and neuroglial ectopia precede radial glial cell differentiation. Furthermore, we identify mislocalization of Cajal-Retzius cells which nonetheless is not associated with any apparent disruption to the reelin, and downstream PI3K/Akt signalling pathways.

CONCLUSIONS

These observations identify Cajal-Retzius cell mislocalization as an early event during the development of cortical defects thereby identifying an earlier onset and more complex pathogenesis than originally reported for the secondary dystroglycanopathies. Overall this study provides new insight into central nervous system involvement in this group of diseases.

Functional Roles of the Interaction of APP and Lipoprotein Receptors

The biological fates of the key initiator of Alzheimer’s disease (AD), the amyloid precursor protein (APP), and a family of lipoprotein receptors, the low-density lipoprotein (LDL) receptor-related proteins (LRPs) and their molecular roles in the neurodegenerative disease process are inseparably interwoven. Not only does APP bind tightly to the extracellular domains (ECDs) of several members of the LRP group, their intracellular portions are also connected through scaffolds like the one established by FE65 proteins and through interactions with adaptor proteins such as X11/Mint and Dab1. Moreover, the ECDs of APP and LRPs share common ligands, most notably Reelin, a regulator of neuronal migration during embryonic development and modulator of synaptic transmission in the adult brain, and Agrin, another signaling protein which is essential for the formation and maintenance of the neuromuscular junction (NMJ) and which likely also has critical, though at this time less well defined, roles for the regulation of central synapses. Furthermore, the major independent risk factors for AD, Apolipoprotein (Apo) E and ApoJ/Clusterin, are lipoprotein ligands for LRPs. Receptors and ligands mutually influence their intracellular trafficking and thereby the functions and abilities of neurons and the blood-brain-barrier to turn over and remove the pathological product of APP, the amyloid-β peptide. This article will review and summarize the molecular mechanisms that are shared by APP and LRPs and discuss their relative contributions to AD.

How does Reelin signaling regulate the neuronal cytoskeleton during migration?

Neuronal migration is an essential step in the formation of laminated brain structures. In the developing cerebral cortex, pyramidal neurons migrate toward the Reelin-containing marginal zone. Reelin is an extracellular matrix protein synthesized by Cajal-Retzius cells. In this review, we summarize our recent results and hypotheses on how Reelin might regulate neuronal migration by acting on the actin and microtubule cytoskeleton. By binding to ApoER2 receptors on the migrating neurons, Reelin induces stabilization of the leading processes extending toward the marginal zone, which involves Dab1 phosphorylation, adhesion molecule expression, cofilin phosphorylation and inhibition of tau phosphorylation. By binding to VLDLR and integrin receptors, Reelin interacts with Lis1 and induces nuclear translocation, accompanied by the ubiquitination of phosphorylated Dab1. Eventually Reelin induces clustering of its receptors resulting in the endocytosis of a Reelin/receptor complex (particularly VLDLR). The resulting decrease in Reelin contributes to neuronal arrest at the marginal zone.

Canonical and Non-canonical Reelin Signaling

Reelin is a large secreted glycoprotein that is essential for correct neuronal positioning during neurodevelopment and is important for synaptic plasticity in the mature brain. Moreover, Reelin is expressed in many extraneuronal tissues; yet the roles of peripheral Reelin are largely unknown. In the brain, many of Reelin's functions are mediated by a molecular signaling cascade that involves two lipoprotein receptors, apolipoprotein E receptor-2 (Apoer2) and very low density-lipoprotein receptor (Vldlr), the neuronal phosphoprotein Disabled-1 (Dab1), and members of the Src family of protein tyrosine kinases as crucial elements. This core signaling pathway in turn modulates the activity of adaptor proteins and downstream protein kinase cascades, many of which target the neuronal cytoskeleton. However, additional Reelin-binding receptors have been postulated or described, either as coreceptors that are essential for the activation of the "canonical" Reelin signaling cascade involving Apoer2/Vldlr and Dab1, or as receptors that activate alternative or additional signaling pathways. Here we will give an overview of canonical and alternative Reelin signaling pathways, molecular mechanisms involved, and their potential physiological roles in the context of different biological settings.

New Insights into Reelin-Mediated Signaling Pathways

Reelin, a multifunctional extracellular protein that is important for mammalian brain development and function, is secreted by different cell types in the prenatal or postnatal brain. The spatiotemporal regulation of Reelin expression and distribution during development relates to its multifaceted function in the brain. Prenatally Reelin controls neuronal radial migration and proper positioning in cortical layers, whereas postnatally Reelin promotes neuronal maturation, synaptic formation and plasticity. The molecular mechanisms underlying the distinct biological functions of Reelin during and after brain development involve unique and overlapping signaling pathways that are activated following Reelin binding to its cell surface receptors. Distinct Reelin ligand isoforms, such as the full-length protein or fragments generated by proteolytic cleavage differentially affect the activity of downstream signaling pathways. In this review, we discuss recent advances in our understanding of the signaling transduction pathways activated by Reelin that regulate different aspects of brain development and function. A core signaling machinery, including ApoER2/VLDLR receptors, Src/Fyn kinases, and the adaptor protein Dab1, participates in all known aspects of Reelin biology. However, distinct downstream mechanisms, such as the Crk/Rap1 pathway and cell adhesion molecules, play crucial roles in the control of neuronal migration, whereas the PI3K/Akt/mTOR pathway appears to be more important for dendrite and spine development. Finally, the NMDA receptor (NMDAR) and an unidentified receptor contribute to the activation of the MEK/Erk1/2 pathway leading to the upregulation of genes involved in synaptic plasticity and learning. This knowledge may provide new insight into neurodevelopmental or neurodegenerative disorders that are associated with Reelin dysfunction.

The microtubule-associated molecular pathways may be genetically disrupted in patients with Bipolar Disorder. Insights from the molecular cascades

Bipolar Disorder is a severe disease characterized by pathological mood swings from major depressive episodes to manic ones and vice versa. The biological underpinnings of Bipolar Disorder have yet to be defined. As a consequence, pharmacological treatments are suboptimal. In the present paper we test the hypothesis that the molecular pathways involved with the direct targets of lithium, hold significantly more genetic variations associated with BD. A molecular pathway approach finds its rationale in the polygenic nature of the disease. The pathways were tested in a sample of ∼ 7,000 patients and controls. Data are available from the public NIMH database. The definition of the pathways was conducted according to the National Cancer Institute (http://pid.nci.nih.gov/). As a result, 3 out of the 18 tested pathways related to lithium action resisted the permutation analysis and were found to be associated with BD. These pathways were related to Reelin, Integrins and Aurora. A pool of genes selected from the ones linked with the above pathways was further investigated in order to identify the fine molecular mechanics shared by our significant pathways and also their link with lithium mechanism of action. The data obtained point out to a possible involvement of microtubule-related mechanics.

Platelet-Activating Factor Acetylhydrolase and Brain Development

The heterotrimeric brain platelet-activating factor acetylhydrolase (PAFAH1B1) contains two catalytic subunits and a regulatory subunit. This complex plays important, surprising roles in brain development and in spermatogenesis. The regulatory subunit, PAFAH1B1 (LIS1 protein), is critically regulated and when deficient leads to the devastating human neurological disorder Lissencephaly, or smooth brain. The role of the protein in brain development is not the catalysis of platelet-activating factor, rather the entire brain platelet-activating factor acetylhydrolase complex serves a signaling role, coordinating important pathways in brain development. The role of this complex in spermatogenesis was not foreseen, but appears to function to regulate a critical level of the PAFAH1B1 protein, such that too much of this protein or too little of this protein can lead to a disruption of spermatogenesis. Brain platelet-activating factor is thus a signaling complex, important for brain development and for spermatogenesis.

Intracellular PAF-Acetylhydrolase Type I

Platelet-activating factor (PAF) is a phospholipid mediator whose synthesis and degradation depend on specific sets of enzymes. PAF-acetylhydrolase (PAF-AH) hydrolyzes the acetyl moiety of PAF at its sn-2 position and thereby inactivates it. PAF-AH Ib, originally identified in brain, exists in the cytoplasm of many (probably all) types of mammalian cells and tissues. PAF-AH Ib consists of three subunits (α1, α2, and β), in which the α subunits provide the catalytic activity. The finding that the β subunit is the product of the causative gene for Miller-Dieker lissencephaly led to extensive analyses of PAF-AH Ib subunits in the field of cell biology and neurobiology. More than 20 molecules are known to bind to PAF-AH Ib subunits, and PAF-AH Ib has been implicated in neuronal development, neuronal functions, Alzheimer's disease, bipolar disorder, cancer, spermatogenesis, and tolerance to hypoxia. However, in almost all of these cases, how the catalytic activity is involved and the identity of the most important substrate of this enzyme are unclear. In this chapter, the structure and functions of PAF-AH Ib and its subunit proteins are summarized and their contributions to human diseases are discussed.

Cellular dynamics of neuronal migration in the hippocampus

A fine structure of the hippocampus is required for proper functions, and disruption of this formation by neuronal migration defects during development may play a role in some psychiatric illnesses. During hippocampal development in rodents, pyramidal neurons in the Ammon's horn are mostly generated in the ventricular zone (VZ), spent as multipolar cells just above the VZ, and then migrate radially toward the pial surface, ultimately settling into the hippocampal plate. Although this process is similar to that of neocortical projection neurons, these are not identical. In addition to numerous histological studies, the development of novel techniques gives a clear picture of the cellular dynamics of hippocampal neurons, as well as neocortical neurons. In this article, we provide an overview of the cellular mechanisms of rodent hippocampal neuronal migration including those of dentate granule cells, especially focusing on the differences of migration modes between hippocampal neurons and neocortical neurons. The unique migration mode of hippocampal pyramidal neurons might enable clonally related cells in the Ammon's horn to distribute in a horizontal fashion.

A temporary compendium of thyroid hormone target genes in brain

BACKGROUND

Thyroid hormone controls a number of developmental and physiological processes in the brain by directly acting on gene expression. Transcriptome analyses in rodent identified a number of thyroid hormone regulated genes in several brain areas at different stages. Genome wide analysis of chromatin occupancy in a neural cell line also identified a subset of genes which transcription is likely to be directly regulated by thyroid hormone receptors in neurons. However, the abundance of these data and apparent discrepancies between studies brought some confusion.

RESULTS

We present here a meta-analysis of available data to identify recurrent themes in thyroid hormone action in brain cells. This provides a curated list of 734 regulated genes in rodent brain, and highlights a small number of likely direct target genes. Some of these genes are also regulated in amphibians during metamorphosis. This article is part of a Special Issue entitled: Nuclear receptors in animal development.

Reelin, neuronal polarity and process orientation of cortical neurons

Deficient reelin signaling leads to characteristic layering malformations in the cerebral cortex and causes polarity defects of cortical neurons. Since the discovery of reelin much has been learned about the molecular mechanisms that underlie the characteristic defects of layering defects in the reeler mutant. More recent studies provided insights in the crosstalk between reelin signaling and molecular pathways that control polarity development of radially migrating neurons. The present review summarizes and discusses recent findings on the role of reelin in modulating polarization and process orientation of neurons in the neocortex and hippocampus.

Cytoskeleton in action: lissencephaly, a neuronal migration disorder

During neocortical development, the extensive migratory movements of neurons from their place of birth to their final location are essential for the coordinated wiring of synaptic circuits and proper neurological function. Failure or delay in neuronal migration causes severe abnormalities in cortical layering, which consequently results in human lissencephaly ('smooth brain'), a neuronal migration disorder. The brains of lissencephaly patients have less-convoluted gyri in the cerebral cortex with impaired cortical lamination of neurons. Since microtubule (MT) and actin-associated proteins play important functions in regulating the dynamics of MT and actin cytoskeletons during neuronal migration, genetic mutations or deletions of crucial genes involved in cytoskeletal processes lead to lissencephaly in human and neuronal migration defects in mouse. During neuronal migration, MT organization and transport are controlled by platelet-activating factor acetylhydrolase isoform 1b regulatory subunit 1 (PAFAH1B1, formerly known as LIS1, Lissencephaly-1), doublecortin (DCX), YWHAE, and tubulin. Actin stress fibers are modulated by PAFAH1B1 (LIS1), DCX, RELN, and VLDLR (very low-density lipoprotein receptor)/LRP8 (low-density lipoprotein-related receptor 8, formerly known as APOER2). There are several important levels of crosstalk between these two cytoskeletal systems to establish accurate cortical patterning in development. The recent understanding of the protein networks that govern neuronal migration by regulating cytoskeletal dynamics, from human and mouse genetics as well as molecular and cellular analyses, provides new insights on neuronal migration disorders and may help us devise novel therapeutic strategies for such brain malformations.

Neuronal migration and its disorders affecting the CA3 region

In this review, we focus on CA3 neuronal migration disorders in the rodent. We begin by introducing the main steps of hippocampal development, and we summarize characteristic hippocampal malformations in human. We then describe various mouse mutants showing structural hippocampal defects. Notably, genes identified in human cortical neuronal migration disorders consistently give rise to a CA3 phenotype when mutated in the mouse. We successively describe their molecular, physiological and behavioral phenotypes that together contribute to a better understanding of CA3-dependent functions. We finally discuss potential factors underlying the CA3 vulnerability revealed by these mouse mutants and that may also contribute to other human neurological and psychiatric disorders.

Reelin in the Years: Controlling Neuronal Migration and Maturation in the Mammalian Brain

The extracellular protein Reelin was initially identified as an essential factor in the control of neuronal migration and layer formation in the developing mammalian brain. In the years following its discovery, however, it became clear that Reelin is a multifunctional protein that controls not only the positioning of neurons in the developing brain, but also their growth, maturation, and synaptic activity in the adult brain. In this review, we will highlight the major discoveries of the biological activities of Reelin and the underlying molecular mechanisms that affect the development and function of the mammalian brain, from embryonic ages to adulthood.

Molecular pathways controlling the sequential steps of cortical projection neuron migration

Coordinated migration of newly-born neurons to their target territories is essential for correct neuronal circuit assembly in the developing brain. Although a cohort of signaling pathways has been implicated in the regulation of cortical projection neuron migration, the precise molecular mechanisms and how a balanced interplay of cell-autonomous and non-autonomous functions of candidate signaling molecules controls the discrete steps in the migration process, are just being revealed. In this chapter, I will focally review recent advances that improved our understanding of the cell-autonomous and possible cell-nonautonomous functions of the evolutionarily conserved LIS1/NDEL1-complex in regulating the sequential steps of cortical projection neuron migration. I will then elaborate on the emerging concept that the Reelin signaling pathway, acts exactly at precise stages in the course of cortical projection neuron migration. Lastly, I will discuss how finely tuned transcriptional programs and downstream effectors govern particular aspects in driving radial migration at discrete stages and how they regulate the precise positioning of cortical projection neurons in the developing cerebral cortex.

The development of hippocampal cellular assemblies

The proper assembly of a cohort of distinct cell types is a prerequisite for building a functional hippocampus. In this review, we describe the major molecular events of the developmental program leading to the cellular construction of the hippocampus. Data from rodent studies are used here to elaborate on our understanding of these processes.

Apolipoprotein E and apolipoprotein E receptors: normal biology and roles in Alzheimer disease

Apolipoprotein E (APOE) genotype is the major genetic risk factor for Alzheimer disease (AD); the ε4 allele increases risk and the ε2 allele is protective. In the central nervous system (CNS), apoE is produced by glial cells, is present in high-density-like lipoproteins, interacts with several receptors that are members of the low-density lipoprotein receptor (LDLR) family, and is a protein that binds to the amyloid-β (Aβ) peptide. There are a variety of mechanisms by which apoE isoform may influence risk for AD. There is substantial evidence that differential effects of apoE isoform on AD risk are influenced by the ability of apoE to affect Aβ aggregation and clearance in the brain. Other mechanisms are also likely to play a role in the ability of apoE to influence CNS function as well as AD, including effects on synaptic plasticity, cell signaling, lipid transport and metabolism, and neuroinflammation. ApoE receptors, including LDLRs, Apoer2, very low-density lipoprotein receptors (VLDLRs), and lipoprotein receptor-related protein 1 (LRP1) appear to influence both the CNS effects of apoE as well as Aβ metabolism and toxicity. Therapeutic strategies based on apoE and apoE receptors may include influencing apoE/Aβ interactions, apoE structure, apoE lipidation, LDLR receptor family member function, and signaling. Understanding the normal and disease-related biology connecting apoE, apoE receptors, and AD is likely to provide novel insights into AD pathogenesis and treatment.

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.

Association study between genes in Reelin signaling pathway and autism identifies DAB1 as a susceptibility gene in a Chinese Han population

Autism is a pervasive neurodevelopmental disorder diagnosed in early childhood. The genetic factors might play an important role in its pathogenesis. Previous studies revealed that Reelin (RELN) polymorphisms were associated with autism. However, the roles of genes in Reelin signaling pathway for autism are largely unknown. As several knockout mice models in which the Reelin pathway genes (i.e. DAB1, VLDLR/APOER2, FYN/SRC and CRK/CRKL) are deficient have the similar phenotype as the reeler mice (Reelin(-/-)), we hypothesized that the Reelin signaling pathway genes might play roles in the etiology of autism. Therefore, we conducted a family-based association study. Sixty-two tagged single nucleotide polymorphisms (SNPs) covering 15 genes in Reelin pathway were genotyped in 239 trios, and 14 significant SNPs were further investigated in the additional 188 trios. In the total 427 trios, we found significant genetic association between autism and four SNPs in DAB1 (rs12035887 G: p=0.0006; rs3738556 G: p=0.0044; rs1202773 A: p=0.0048; rs12740765 T: p=0.0196). After the Bonferroni correction, SNP rs12035887 remained significant. Furthermore, the haplotype constructed with rs1202773 and rs12023109 in DAB1 showed significant excess transmission in both individual and global haplotype analyses (p=0.0052 and 0.0279, respectively). Our findings suggested that variations in DAB1 involved in the Reelin signaling pathway might contribute to genetic susceptibility to autism with Chinese Han decent, supporting the defect in the Reelin signaling pathway as a predisposition factor for autism.

The involvement of Reelin in neurodevelopmental disorders

Reelin is a glycoprotein that serves important roles both during development (regulation of neuronal migration and brain lamination) and in adulthood (maintenance of synaptic function). A number of neuropsychiatric disorders including autism, schizophrenia, bipolar disorder, major depression, Alzheimer's disease and lissencephaly share a common feature of abnormal Reelin expression in the brain. Altered Reelin expression has been hypothesized to impair neuronal connectivity and synaptic plasticity, leading ultimately to the cognitive deficits present in these disorders. The mechanisms for abnormal Reelin expression in some of these disorders are currently unknown although possible explanations include early developmental insults, mutations, hypermethylation of the promoter for the Reelin gene (RELN), miRNA silencing of Reelin mRNA, FMRP underexpression and Reelin processing abnormalities. Increasing Reelin expression through pharmacological therapies may help ameliorate symptoms resulting from Reelin deficits. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

Developmental dynamics of PAFAH1B subunits during mouse brain development

Platelet-activating factor (PAF) mediates an array of biological processes in the mammalian central nervous system as a bioactive lipid messenger in synaptic function and dysfunction (plasticity, memory, and neurodegeneration). The intracellular enzyme that deacetylates the PAF (PAFAH1B) is composed of a tetramer of two catalytic subunits, ALPHA1 (PAFAH1B3) and ALPHA2 (PAFAH1B2), and a regulatory dimer of LIS1 (PAFAH1B1). We have investigated the mouse PAFAH1B subunit genes during brain development in normal mice and in mice with a hypomorphic allele for Lis1 (Lis1/sLis1; Cahana et al. [2001] Proc Natl Acad Sci U S A 98:6429-6434). We have analyzed quantitatively (by means of real-time polymerase chain reaction) and qualitatively (by in situ hybridization techniques) the amounts and expression patterns of their transcription in developing and postnatal brain, focusing mainly on differences in two laminated encephalic regions, the forebrain (telencephalon) and hindbrain (cerebellum) separately. The results revealed significant differences in cDNA content between these two brain subdivisions but, more importantly, between the LIS1 complex subunits. In addition, we found significant spatial differences in gene expression patterns. Comparison of results obtained with Lis1/sLis1 analysis also revealed significant temporal and spatial differences in Alpha1 and Lis1 expression levels. Thus, small changes in the amount of the Lis1 gene may differentially regulate expression of Alpha1 and Alpha2, depending on the brain region, which suggests different roles for each LIS1 complex subunit during neural differentiation and neural migration.

Transcription factor Sox11 is essential for both embryonic and adult neurogenesis

BACKGROUND

Neurogenesis requires neural progenitor cell (NPC) proliferation, neuronal migration, and differentiation. During embryonic development, neurons are generated in specific areas of the developing neuroepithelium and migrate to their appropriate positions. In the adult brain, neurogenesis continues in the subgranular zone (SGZ) of the hippocampal dentate gyrus and the subventricular zone (SVZ) of the lateral ventricle. Although neurogenesis is fundamental to brain development and function, our understanding of the molecular mechanisms that regulate neurogenesis is still limited.

RESULTS

In this study, we generated a Sox11 floxed allele and a Sox11 null allele in mice using the Cre-loxP technology. We first analyzed the role of the transcription factor Sox11 in embryonic neurogenesis using Sox11 null embryos. We also examined the role of Sox11 in adult hippocampal neurogenesis using Sox11 conditional knockout mice in which Sox11 is specifically deleted in adult NPCs. Sox11 null embryos developed small and disorganized brains, accompanied by transient proliferation deficits in NPCs. Deletion of Sox11 in adult NPCs blunted proliferation in the SGZ. Using functional genomics, we identified potential downstream target genes of Sox11.

CONCLUSIONS

Taken together, our work provides evidence that Sox11 is required for both embryonic and adult neurogenesis, and identifies potential downstream target genes.