Role In Neuronal Migration Research Articles

Nesprin-2 Recruitment of BicD2 to the Nuclear Envelope Controls Dynein/Kinesin-Mediated Neuronal Migration In Vivo

Vertebrate brain development depends on a complex program of cell proliferation and migration. Post-mitotic neuronal migration in the developing cerebral cortex involves Nesprin-2, which recruits cytoplasmic dynein, kinesin, and actin to the nuclear envelope (NE) in other cell types. However, the relative importance of these interactions in neurons has remained poorly understood. To address these issues, we performed in utero electroporation into the developing rat brain to interfere with Nesprin-2 function. We find that an ∼100-kDa "mini" form of the ∼800-kDa Nesprin-2 protein, which binds dynein and kinesin, is sufficient, remarkably, to support neuronal migration. In contrast to dynein's role in forward nuclear migration in these cells, we find that kinesin-1 inhibition accelerates neuronal migration, suggesting a novel role for the opposite-directed motor proteins in regulating migration velocity. In contrast to studies in fibroblasts, the actin-binding domain of Nesprin-2 was dispensable for neuronal migration. We find further that, surprisingly, the motor proteins interact with Nesprin-2 through the dynein/kinesin "adaptor" BicD2, both in neurons and in non-mitotic fibroblasts. Furthermore, mutation of the Nesprin-2 LEWD sequence, implicated in nuclear envelope kinesin recruitment in other systems, interferes with BicD2 binding. Although disruption of the Nesprin-2/BicD2 interaction severely inhibited nuclear movement, centrosome advance proceeded unimpeded, supporting an independent mechanism for centrosome advance. Our data together implicate Nesprin-2 as a novel and fundamentally important form of BicD2 cargo and help explain BicD2's role in neuronal migration and human disease.

Afadin Signaling at the Spinal Neuroepithelium Regulates Central Canal Formation and Gait Selection

Afadin, a scaffold protein controlling the activity of the nectin family of cell adhesion molecules, regulates important morphogenetic processes during development. In the central nervous system, afadin has critical roles in neuronal migration, axonal elongation, and synapse formation. Here we examine the role of afadin in development of spinal motor circuits. Afadin elimination in motor neuron progenitors results in striking locomotor behavior: left-right limb alternation is substituted by synchronous activation, characteristic of bound gait. We find that afadin function at the neuroepithelium is required for structural organization of the spinal midline and central canal morphogenesis. Perturbation of afadin results in formation of two central canals, aberrant contralateral wiring of different classes of spinal premotor interneurons, and loss of left-right limb alternation, highlighting important developmental principles controlling the assembly of spinal motor circuits.

Hippocampal CCR5/RANTES Elevations in a Rodent Model of Post-Traumatic Stress Disorder: Maraviroc (a CCR5 Antagonist) Increases Corticosterone Levels and Enhances Fear Memory Consolidation.

Background: Contextual fear conditioning (CFC) is a rodent model that induces a high and long-lasting level of conditioning associated with traumatic memory formation; this behavioral paradigm resembles many characteristics of posttraumatic stress disorder (PSTD). Chemokines (chemotactic cytokines) play a known role in neuronal migration and neurodegeneration but their role in cognition is not totally elucidated. Aim: We ascertain whether CCR5/RANTES beta chemokines (hippocampus/prefrontal cortex) could play a role in fear memory consolidation (CFC paradigm). We also evaluated whether chronic stress restraint (21 days of restraint, 6-h/day) could regulate levels of these beta chemokines in CFC-trained rats; fear memory retention was determined taking the level of freezing (context and tone) by the animals as an index of fear memory consolidation 24 h after CFC training session; these chemokines (CCR5/RANTES) and IL-6 levels were measured in the hippocampus and prefrontal cortex of chronically stressed rats, 24 h after CFC post-training, and compared with undisturbed CFC-trained rats (Experiment 1). In Experiment 2, rats received 1 mA of footshock during the CFC training session and fear memory consolidation was evaluated at 12 and 24 h after CFC training sessions. We evaluated whether RANTES levels could be differentially regulated at 12 and 24 h after CFC training; in Experiment 3, maraviroc was administered to rats (i.m: 100 mg/Kg, a CCR5 antagonist) before CFC training. These rats were not subjected to chronic stress restraint. We evaluated whether CCR5 blockade before CFC training could increase corticosterone, RANTES, or IL-6 levels and affects fear memory consolidation in the rats 24-h post-testing compared with vehicle CFC-trained rats. Results: Elevations of CCR5/RANTES chemokine levels in the hippocampus could have contributed to fear memory consolidation (24 h post-training) and chronic stress restraint did not affect these chemokines in the hippocampus; there were no significant differences in CCR5/RANTES levels between stressed and control rats in the prefrontal cortex (Experiment 1). In Experiment 2, hippocampal CCR5/RANTES levels increased and enhanced fear memory consolidation was observed 12 and 24 h after CFC training sessions with 1 mA of footshock. Increased corticosterone and CCR5/RANTES levels, as well as a higher freezing percentage to the context, were found at 24 h CFC post-testing in maraviroc-treated rats as compared to vehicle-treated animals (experiment-3). Conversely, IL-6 is not affected by maraviroc treatment in CFC training. Conclusion. Our findings suggest a role for a hippocampal CCR5/RANTES axis in contextual fear memory consolidation; in fact, RANTES levels increased at 12 and 24 h after CFC training. When CCR5 was blocked by maraviroc before CFC training, RANTES (hippocampus), corticosterone levels, and fear memory consolidation were greater than in vehicle CFC-trained rats 24 h after the CFC session.

Selective Inactivation of Reelin in Inhibitory Interneurons Leads to Subtle Changes in the Dentate Gyrus But Leaves Cortical Layering and Behavior Unaffected.

Reelin is an extracellular matrix protein, known for its dual role in neuronal migration during brain development and in synaptic plasticity at adult stages. During the perinatal phase, Reelin expression switches from Cajal-Retzius (CR) cells, its main source before birth, to inhibitory interneurons (IN), the main source of Reelin in the adult forebrain. IN-derived Reelin has been associated with schizophrenia and temporal lobe epilepsy; however, the functional role of Reelin from INs is presently unclear. In this study, we used conditional knockout mice, which lack Reelin expression specifically in inhibitory INs, leading to a substantial reduction in total Reelin expression in the neocortex and dentate gyrus. Our results show that IN-specific Reelin knockout mice exhibit normal neuronal layering and normal behavior, including spatial reference memory. Although INs are the major source of Reelin within the adult stem cell niche, Reelin from INs does not contribute substantially to normal adult neurogenesis. While a closer look at the dentate gyrus revealed some unexpected alterations at the cellular level, including an increase in the number of Reelin expressing CR cells, overall our data suggest that Reelin derived from INs is less critical for cortex development and function than Reelin expressed by CR cells.

A role for gangliosides and β1-integrin in the motility of olfactory ensheathing glia.

Olfactory ensheathing glia (OEG) are found in the olfactory mucosa, nerve and bulb, and provide in vivo ensheathment for the unmyelinated olfactory axons within the central and peripheral nervous system domains. OEG cells are able to migrate long distances within the neuropil of the central nervous system. Because gangliosides such as 9-O-acetyl GD3 have crucial regulatory roles in neuronal migration during development, we analyzed whether OEG in organotypical cultures are revealed by anti-9-O-acetyl GD3 and/or gangliosides are recognized by the A2B5 antibody (G-A2B5), and whether these gangliosides are involved in OEG migration. Our results showed that all OEG migrating out of a section of olfactory bulb onto a laminin substrate bound to the 9-O-acetyl GD3 and A2B5 antibodies, and that 2',3'-cyclic nucleotide phosphodiesterase (CNPase) colocalized with 9-O-acetyl GD3 and with G-A2B5. Additionally, we showed that the immune blockade of 9-O-acetyl GD3 or G-A2B5 reduced the migration of OEG on laminin, and that 9-O-acetyl GD3 and G-A2B5 colocalized with the β1-integrin subunit. We also confirmed the phenotype of in-vitro-grown OEG cells derived from adult rats, showing that they express CNPase, and also α-smooth muscle actin, which is not expressed by Schwann cells. Our data showed that the gangliosides 9-O-acetyl GD3 and G-A2B5 participate in the migratory activity of OEG cells, and that the β1-integrin subunit colocalizes with these gangliosides. These results suggest a new role for β1-integrin and gangliosides in the polarized migration of OEG cells, and provide new information on the molecules controlling OEG motility and behavior.

Spatiotemporal Regulation of Rho GTPases in Neuronal Migration.

Neuronal migration is essential for the orchestration of brain development and involves several contiguous steps: interkinetic nuclear movement (INM), multipolar–bipolar transition, locomotion, and translocation. Growing evidence suggests that Rho GTPases, including RhoA, Rac, Cdc42, and the atypical Rnd members, play critical roles in neuronal migration by regulating both actin and microtubule cytoskeletal components. This review focuses on the spatiotemporal-specific regulation of Rho GTPases as well as their regulators and effectors in distinct steps during the neuronal migration process. Their roles in bridging extracellular signals and cytoskeletal dynamics to provide optimal structural support to the migrating neurons will also be discussed.

Growth Arrest Triggers Extra-Cell Cycle Regulatory Function in Neurons: Possible Involvement of p27kip1 in Membrane Trafficking as Well as Cytoskeletal Regulation.

Cell cycle regulation is essential for the development of multicellular organisms, but many cells in adulthood, including neurons, exit from cell cycle. Although cell cycle-related proteins are suppressed after cell cycle exit in general, recent studies have revealed that growth arrest triggers extra-cell cycle regulatory function (EXCERF) in some cell cycle proteins, such as p27(kip1), p57(kip2), anaphase-promoting complex/cyclosome (APC/C), and cyclin E. While p27 is known to control G1 length and cell cycle exit via inhibition of cyclin-dependent kinase (CDK) activities, p27 acquires additional cytoplasmic functions in growth-arrested neurons. Here, we introduce the EXCERFs of p27 in post-mitotic neurons, mainly focusing on its actin and microtubule regulatory functions. We also show that a small amount of p27 is associated with the Golgi apparatus positive for Rab6, p115, and GM130, but not endosomes positive for Rab5, Rab7, Rab8, Rab11, SNX6, or LAMTOR1. p27 is also colocalized with Dcx, a microtubule-associated protein. Based on these results, we discuss here the possible role of p27 in membrane trafficking and microtubule-dependent transport in post-mitotic cortical neurons. Collectively, we propose that growth arrest leads to two different fates in cell cycle proteins; either suppressing their expression or activating their EXCERFs. The latter group of proteins, including p27, play various roles in neuronal migration, morphological changes and axonal transport, whereas the re-activation of the former group of proteins in post-mitotic neurons primes for cell death.

The dyslexia susceptibility KIAA0319 gene shows a specific expression pattern during zebrafish development supporting a role beyond neuronal migration.

Dyslexia is a common neurodevelopmental disorder caused by a significant genetic component. The KIAA0319 gene is one of the most robust dyslexia susceptibility factors but its function remains poorly understood. Initial RNA‐interference studies in rats suggested a role in neuronal migration whereas subsequent work with double knock‐out mouse models for both Kiaa0319 and its paralogue Kiaa0319‐like reported effects in the auditory system but not in neuronal migration. To further understand the role of KIAA0319 during neurodevelopment, we carried out an expression study of its zebrafish orthologue at different embryonic stages. We used different approaches including RNAscope in situ hybridization combined with light‐sheet microscopy. The results show particularly high expression during the first few hours of development. Later, expression becomes localized in well‐defined structures. In addition to high expression in the brain, we report for the first time expression in the eyes and the notochord. Surprisingly, kiaa0319‐like, which generally shows a similar expression pattern to kiaa0319, was not expressed in the notochord suggesting a distinct role for kiaa0319 in this structure. This observation was supported by the identification of notochord enhancers enriched upstream of the KIAA0319 transcription start site, in both zebrafish and humans. This study supports a developmental role for KIAA0319 in the brain as well as in other developing structures, particularly in the notochord which, is key for establishing body patterning in vertebrates.

Dissociation of impulsivity and aggression in mice deficient for the ADHD risk gene Adgrl3: Evidence for dopamine transporter dysregulation

Adhesion G protein-coupled receptor L3 (ADGRL3, LPHN3) has putative roles in neuronal migration and synapse function. Various polymorphisms in ADGRL3 have been linked with an increased risk of attention deficit/hyperactivity disorder (ADHD). In this study, we examined the characteristics of Adgrl3-deficient mice in multiple behavioural domains related to ADHD: locomotive activity, impulsivity, gait, visuospatial and recognition memory, sociability, anxiety-like behaviour and aggression. Additionally, we investigated the effect of Adgrl3-depletion at the transcriptomic level by RNA-sequencing three ADHD-relevant brain regions: prefrontal cortex (PFC), hippocampus and striatum.Adgrl3−/− mice show increased locomotive activity across all tests and subtle gait abnormalities. These mice also show impairments across spatial memory and learning domains, alongside increased levels of impulsivity and sociability with decreased aggression. However, these alterations were absent in Adgrl3+/− mice. Across all brain regions tested, the numbers of genes found to exhibit differential expression was relatively small, indicating a specific pathway of action, rather than a broad neurobiological perturbation. Gene-set analysis of differential expression in the PFC detected a number of ADHD-relevant pathways including dopaminergic synapses as well as cocaine and amphetamine addiction. The Slc6a3 gene coding for the dopamine transporter was the most dysregulated gene in the PFC. Unexpectedly, several neurohormone/peptides which are typically only expressed in the hypothamalus were found to be dysregulated in the striatum. Our study further validates Adgrl3 constitutive knockout mice as an experimental model of ADHD while providing neuroanatomical targets for future studies involving ADGRL3 modified models.This article is part of the Special Issue entitled ‘Current status of the neurobiology of aggression and impulsivity’.

The catalytic activity and secretion of zebrafish RNases are essential for their in vivo function in motor neurons and vasculature

Angiogenin (hANG), a member of the Ribonuclease A superfamily has angiogenic, neurotrophic and neuroprotective activities. Mutations in hANG have been found in patients with Amyotrophic lateral sclerosis (ALS). The zebrafish (Danio rerio) rnasel-1, 2 and 3 are orthologues of hANG and of these only Rnasel-1 and Rnasel-2 have been shown to be angiogenic. Herein we show that NCI-65828, a potent and specific small molecule inhibitor of hANG inhibits Rnasel-1 to a similar extent. Treatment of early zebrafish embryos with NCI-65828, or with terrein, a fungal metabolite which prevents the secretion of hANG, resulted in spinal neuron aberrations as well defects in trunk vasculature. Our detailed expression analysis and inhibitor studies suggest that Rnasel-1 plays important roles in neuronal migration and pathfinding as well as in angiogenesis in zebrafish. Our studies suggest the usefulness of the zebrafish as a model to dissect the molecular consequences of the ANG ALS variants.

Alterations in reelin and reelin receptors in Down syndrome.

Reelin is an extracellular matrix glycoprotein that modulates synaptic function and plasticity, with a crucial role in neuronal migration. Changes in the expression of this protein have been reported in neurodegenerative diseases, such as Alzheimer's disease (AD). This molecule is produced by Cajal-Retzius neurons during development and by inhibitory neurons in the adult nervous system. Individuals with Down syndrome (DS) present an early development of AD; therefore, we analyzed the alterations in this molecule and its receptors in the murine model for DS Ts65Dn as well as in human with DS. We performed immunofluorescence analysis for reelin and its receptors very-low-density lipoprotein receptor and apolipoprotein R receptor 2 in the temporal cortex of mice and humans and have quantified the density of reelin-expressing neurons and the intensity of expression of both receptors. We have observed an increment in the density of reelin immunoreactive neurons in both the temporal cortex of adult Ts65Dn mice and humans with DS. Moreover, these reelin immunoreactive neurons displayed a disorganized distribution when compared with wild-type mice. Regarding reelin receptors, very-low-density lipoprotein receptor expression remained unaltered in both Ts65Dn and humans with DS, whereas apolipoprotein R receptor 2 decreased in both individuals with DS and Ts65Dn mice. These alterations are similar to those observed in individuals with AD.

Drebrin-like (Dbnl) Controls Neuronal Migration via Regulating N-Cadherin Expression in the Developing Cerebral Cortex.

The actin cytoskeleton is crucial for neuronal migration in the mammalian developing cerebral cortex. The adaptor protein Drebrin-like (Dbnl) plays important roles in reorganization of the actin cytoskeleton, dendrite formation, and endocytosis by interacting with F-actin, cobl, and dynamin. Although Dbnl is known to be expressed in the brain, the functions of this molecule during brain development are largely unknown. In this study, to examine the roles of Dbnl in the developing cerebral cortex, we conducted experiments using mice of both sexes with knockdown of Dbnl, effected by in utero electroporation, in the migrating neurons of the embryonic cortex. Time-lapse imaging of the Dbnl-knockdown neurons revealed that the presence of Dbnl is a prerequisite for appropriate formation of processes in the multipolar neurons in the multipolar cell accumulation zone or the deep part of the subventricular zone, and for neuronal polarization and entry into the cortical plate. We found that Dbnl knockdown decreased the amount of N-cadherin protein expressed on the plasma membrane of the cortical neurons. The defect in neuronal migration caused by Dbnl knockdown was rescued by moderate overexpression of N-cadherin and αN-catenin or by transfection of the phospho-mimic form (Y337E, Y347E), but not the phospho-resistant form (Y337F, Y347F), of Dbnl. These results suggest that Dbnl controls neuronal migration, neuronal multipolar morphology, and cell polarity in the developing cerebral cortex via regulating N-cadherin expression.SIGNIFICANCE STATEMENT Disruption of neuronal migration can cause neuronal disorders, such as lissencephaly and subcortical band heterotopia. During cerebral cortical development, the actin cytoskeleton plays a key role in neuronal migration; however, the mechanisms of regulation of neuronal migration by the actin cytoskeleton still remain unclear. Herein, we report that the novel protein Dbnl, an actin-binding protein, controls multiple events during neuronal migration in the developing mouse cerebral cortex. We also showed that this regulation is mediated by phosphorylation of Dbnl at tyrosine residues 337 and 347 and αN-catenin/N-cadherin, suggesting that the Dbnl-αN-catenin/N-cadherin pathway is important for neuronal migration in the developing cortex.

FIP4/Arfophilin-2 plays overlapping but distinct roles from FIP3/Arfophilin-1 in neuronal migration during cortical layer formation.

The class II Rab11 family-interacting proteins, FIP3 and FIP4, also termed Arfophilin-1 and Arfophilin-2, respectively, are endosomal proteins that function as dual effector proteins for Rab11 and ADP ribosylation factor (Arf) small GTPases. In the present study, we examined the expression and role of FIP4 in neuronal migration during cerebral layer formation. FIP4 mRNA was first weakly detected in post-mitotic migrating neurons in the upper intermediate zone, and expression was markedly increased in the cortical layer. Exogenously expressed FIP4 protein was localized to subpopulations of EEA1- and syntaxin 12-positive endosomes in migrating neurons, and was partially colocalized with FIP3. Knockdown of FIP4 by in utero electroporation significantly stalled transfected neurons in the lower cortical layer and decreased the speed of neuronal migration in the upper intermediate zone and in the cortical plate compared with control small hairpin RNA (shRNA)-transfected neurons. Furthermore, co-transfection of shRNA-resistant wild-type FIP4, but not wild type FIP3 or FIP4 mutants lacking the binding region for Rab11 or Arf, significantly improved the disturbed cortical layer formation caused by FIP4 knockdown. Collectively, our findings suggest that FIP4 and FIP3 play overlapping but distinct roles in neuronal migration downstream of Arf and Rab11 during cortical layer formation.

A pilot Indian family-based association study between dyslexia and Reelin pathway genes, DCDC2 and ROBO1, identifies modest association with a triallelic unit TAT in the gene RELN.

Dyslexia is a neurodevelopmental disorder that manifests as a reading disability despite normal intelligence and adequate educational opportunity. Twin and family studies have indicated a genetic component, while genome-wide studies have implicated a number of susceptibility genes, most of which have direct or indirect roles in neuronal migration. Reelin (RELN) has important biological functions facilitating migration of neurons. Polymorphisms in RELN have been implicated in related disorders like autism and schizophrenia but have not been examined in dyslexia. We hypothesized that not only RELN, but its interactors in the neuronal migration pathway may play roles in the etiology of dyslexia. Twenty two functional variants across six RELN signalling genes (RELN, VLDLR, APOER2, DAB1, LIS1 and NDEL1) and two dyslexia candidate genes (DCDC2 and ROBO1) were analyzed for association in twenty six nuclear and three extended families with individuals affected with dyslexia. Univariate association analysis was suggestive of association (puncorrected = 0.01) with rs362746 in RELN which however did not withstand Bonferroni corrections (pcorrected = 0.21). Multimarker tests indicated significant association (p = 0.037), based on which we tested for haplotype associations. Although there were no significant haplotypic associations, we found that a three marker unit with rs3808039 and rs2072403 flanking and independently in linkage disequilibrium with rs362746 was significantly overtransmitted (risk allelic combination - TAT) to dyslexia affected individuals in the sample (p = 0.002). Our results suggest preliminary evidence for a new potential risk variant in the RELN locus for dyslexia.

RBM4 Modulates Radial Migration via Alternative Splicing of Dab1 during Cortex Development.

The RNA-binding motif 4 (RBM4) protein participates in cell differentiation via its role in regulating the expression of tissue-specific or developmentally regulated mRNA splice isoforms. RBM4 is expressed in embryonic brain during development; it is initially enriched in the ventricular zone/subventricular zone and subsequently distributed throughout the cerebral cortex. Rbm4a knockout brain exhibited delayed migration of late-born neurons. Using in utero electroporation, we confirmed that knockdown of RBM4 impaired cortical neuronal migration. RNA immunoprecipitation with high-throughput sequencing identified Disabled-1 (Dab1), which encodes a critical reelin signaling adaptor, as a potential target of RBM4. Rbm4a knockout embryonic brain showed altered Dab1 isoform ratios. Overexpression of RBM4 promoted the inclusion of Dab1 exons 7 and 8 (7/8), whereas its antagonist polypyrimidine tract-binding protein 1 (PTBP1) acted in an opposite manner. RBM4 directly counteracted the effect of PTBP1 on exon 7/8 selection. Finally, we showed that the full-length Dab1, but not exon 7/8-truncated Dab1, rescued neuronal migration defects in RBM4-depleted neurons, indicating that RBM4 plays a role in neuronal migration via modulating the expression of Dab1 splice isoforms. Our findings imply that RBM4 is necessary during brain development and that its deficiency may lead to developmental brain abnormality.

Distinct roles for the cell adhesion molecule Contactin2 in the development and function of neural circuits in zebrafish

Contactin2 (Cntn2)/Transient Axonal Glycoprotein 1 (Tag1), a neural cell adhesion molecule, has established roles in neuronal migration and axon fasciculation in chick and mouse. In zebrafish, antisense morpholino-based studies have indicated roles for cntn2 in the migration of facial branchiomotor (FBM) neurons, the guidance of the axons of the nucleus of the medial longitudinal fascicle (nucMLF), and the outgrowth of Rohon-Beard (RB) central axons. To study functions of Cntn2 in later stages of neuronal development, we generated cntn2 mutant zebrafish using CRISPR-Cas9. Using a null mutant allele, we detected genetic interactions between cntn2 and the planar cell polarity gene vangl2, as shown previously with cntn2 morphants, demonstrating a function for cntn2 during FBM neuron migration in a sensitized background of reduced planar cell polarity signaling. In addition, maternal-zygotic (MZ) cntn2 mutant larvae exhibited aberrant touch responses and swimming, suggestive of defects in sensorimotor circuits, consistent with studies in mice. However, the nucMLF axon convergence, FBM neuron migration, and RB outgrowth defects seen in morphants were not seen in the mutants, and we show here that they are likely off-target effects of morpholinos. However, MLF axons exhibited local defasciculation in MZcntn2 mutants, consistent with a role for Cntn2 in axon fasciculation. These data demonstrate distinct roles for zebrafish cntn2 in neuronal migration and axon fasciculation, and in the function of sensorimotor circuits.

Evaluation of visual motion perception ability in mice with knockout of the dyslexia candidate susceptibility gene Dcdc2.

Developmental dyslexia is a heritable disability characterized by difficulties in learning to read and write. The neurobiological and genetic mechanisms underlying dyslexia remain poorly understood; however, several dyslexia candidate risk genes have been identified. One of these candidate risk genes-doublecortin domain containing 2 (DCDC2)-has been shown to play a role in neuronal migration and cilia function. At a behavioral level, variants of DCDC2 have been associated with impairments in phonological processing, working memory and reading speed. Additionally, a specific mutation in DCDC2 has been strongly linked to deficits in motion perception-a skill subserving reading abilities. To further explore the relationship between DCDC2 and dyslexia, a genetic knockout (KO) of the rodent homolog of DCDC2 (Dcdc2) was created. Initial studies showed that Dcdc2 KOs display deficits in auditory processing and working memory. The current study was designed to evaluate the association between DCDC2 and motion perception, as these skills have not yet been assessed in the Dcdc2 KO mouse model. We developed a novel motion perception task, utilizing touchscreen technology and operant conditioning. Dcdc2 KOs displayed deficits on the Pairwise Discrimination task specifically as motion was added to visual stimuli. Following behavioral assessment, brains were histologically prepared for neuroanatomical analysis of the lateral geniculate nucleus (LGN). The cumulative distribution showed that Dcdc2 KOs exhibited more small neurons and fewer larger neurons in the LGN. Results compliment findings that DCDC2 genetic alteration results in anomalies in visual motion pathways in a subpopulation of dyslexic patients.

P85 regulates neuronal migration through affecting neuronal morphology during mouse corticogenesis.

In mammalian developing embryonic cortex, projection neurons migrate from the ventricular zone to the cortical plate, guided by radial glial cells with a transformation between bipolar and multipolar morphology. Previous studies have demonstrated that the PI3K-Akt-mTOR signal plays a critical role in brain development. However, the function of P85 in cortical development is still unclear. In the present study, we found that overexpression of P85 impaired cortical neuronal migration. Using in utero electroporation, we revealed that the length of the leading process in P85 overexpressed neurons became shorter than that in the control group but with more branches. Using markers for new-born neurons, we further found that overexpression of P85 did not affect the ultimate fate of these cortical neurons. These findings indicated that the P85 subunit plays an essential role in neuronal migration and neuronal morphology during mouse corticogenesis.

Knockout Mice for Dyslexia Susceptibility Gene Homologs KIAA0319 and KIAA0319L have Unaffected Neuronal Migration but Display Abnormal Auditory Processing.

Developmental dyslexia is a neurodevelopmental disorder that affects reading ability caused by genetic and non-genetic factors. Amongst the susceptibility genes identified to date, KIAA0319 is a prime candidate. RNA-interference experiments in rats suggested its involvement in cortical migration but we could not confirm these findings in Kiaa0319-mutant mice. Given its homologous gene Kiaa0319L (AU040320) has also been proposed to play a role in neuronal migration, we interrogated whether absence of AU040320 alone or together with KIAA0319 affects migration in the developing brain. Analyses of AU040320 and double Kiaa0319;AU040320 knockouts (dKO) revealed no evidence for impaired cortical lamination, neuronal migration, neurogenesis or other anatomical abnormalities. However, dKO mice displayed an auditory deficit in a behavioral gap-in-noise detection task. In addition, recordings of click-evoked auditory brainstem responses revealed suprathreshold deficits in wave III amplitude in AU040320-KO mice, and more general deficits in dKOs. These findings suggest that absence of AU040320 disrupts firing and/or synchrony of activity in the auditory brainstem, while loss of both proteins might affect both peripheral and central auditory function. Overall, these results stand against the proposed role of KIAA0319 and AU040320 in neuronal migration and outline their relationship with deficits in the auditory system.

Characterisation of spinophilin immunoreactivity in postmortem human brain homogenates

Spinophilin is a multifunctional scaffold protein that regulates the formation and function of dendritic spines and plays a role in neuronal migration. The distinct roles of spinophilin depend on its localization and the direct interaction with other proteins, which may target spinophilin to specific locations within the cell. Several studies suggest a role of spinophilin in the pathophysiology of neurological or psychiatric diseases. However, the majority have been performed in animals or cultured cells. Thus, the aim of the present study was to characterise the regional and subcellular expression of spinophilin immunoreactivity by western blot in postmortem human brain. Two specific immunoreactive bands for spinophilin were observed: an intense band migrating at around 120kDa, which seems to correspond to the apparent molecular weight of spinophilin described by other authors, and a less intense band of around 95kDa. This second form seems to be a proteolysis or cleavage product of the ~120kDa spinophilin. Interestingly, the subcellular distribution of both bands was different. In membrane fraction, the ~120kDa spinophilin band was the most abundant, whereas in cytosol it was the ~95kDa form. Furthermore, a different regional distribution for ~120kDa spinophilin band was observed, with the highest expression in prefrontal cortex, followed by hippocampus and cerebellum, and the lowest in caudate nucleus. Altogether, these results constitute a useful reference for future studies of spinophilin in pathological and non-pathological human brain tissues.