Migration Of Interneurons Research Articles

In utero alcohol exposure exacerbates endothelial protease activity from pial microvessels and impairs GABA interneuron positioning

In utero alcohol exposure can induce severe neurodevelopmental disabilities leading to long-term behavioral deficits. Because alcohol induces brain defects, many studies have focused on nervous cells. However, recent reports have shown that alcohol markedly affects cortical angiogenesis in both animal models and infants with fetal alcohol spectrum disorder (FASD). In addition, the vascular system is known to contribute to controlling gamma-aminobutyric acid (GABA)ergic interneuron migration in the developing neocortex. Thus, alcohol-induced vascular dysfunction may contribute to the neurodevelopmental defects in FASD. The present study aimed at investigating the effects of alcohol on endothelial activity of pial microvessels. Ex vivo experiments on cortical slices from mouse neonates revealed that in endothelial cells from pial microvessels acute alcohol exposure inhibits both glutamate-induced calcium mobilization and activities of matrix metalloproteinase-9 (MMP-9) and tissue plasminogen activator (tPA). The inhibitory effect of alcohol on glutamate-induced MMP-9 activity was abrogated in tPA-knockout and Grin1flox/VeCadcre mice suggesting that alcohol interacts through the endothelial NMDAR/tPA/MMP-9 vascular pathway. Contrasting with the effects from acute alcohol exposure, in mouse neonates exposed to alcohol in utero during the last gestational week, glutamate exacerbated both calcium mobilization and endothelial protease activities from pial microvessels. This alcohol-induced vascular dysfunction was associated with strong overexpression of the N-methyl-d-aspartate receptor subunit GluN1 and mispositioning of the Gad67-GFP interneurons that normally populate the superficial cortical layers. By comparing several human control fetuses with a fetus chronically exposed to alcohol revealed that alcohol exposure led to mispositioning of the calretinin-positive interneurons, whose density was decreased in the superficial cortical layers II-III and increased in deepest layers. This study provides the first mechanistic and functional evidence that alcohol impairs glutamate-regulated activity of pial microvessels. Endothelial dysfunction is characterized by altered metalloproteinase activity and interneuron mispositioning, which was also observed in a fetus with fetal alcohol syndrome. These data suggest that alcohol-induced endothelial dysfunction may contribute in ectopic cortical GABAergic interneurons, that has previously been described in infants with FASD.

Human forebrain endothelial cell therapy for psychiatric disorders

Abnormalities of or reductions in GABAergic interneurons are implicated in the pathology of severe neuropsychiatric disorders, for which effective treatments are still elusive. Transplantation of human stem cell-derived interneurons is a promising cell-based therapy for treatment of these disorders. In mouse xenograft studies, human stem cell-derived-interneuron precursors could differentiate in vivo, but required a prolonged time of four to seven months to migrate from the graft site and integrate with the host tissue. This poses a serious roadblock for clinical translation of this approach. For transplantation to be effective, grafted neurons should migrate to affected areas at a faster rate. We have previously shown that endothelial cells of the periventricular vascular network are the natural substrates for GABAergic interneurons in the developing mouse forebrain, and provide valuable guidance cues for their long-distance migration. In addition, periventricular endothelial cells house a GABA signaling pathway with direct implications for psychiatric disease origin. In this study we translated this discovery into human, with significant therapeutic implications. We generated human periventricular endothelial cells, using human pluripotent stem cell technology, and extensively characterized its molecular, cellular, and functional properties. Co-culture of human periventricular endothelial cells with human interneurons significantly accelerated interneuron migration in vitro and led to faster migration and wider distribution of grafted interneurons in vivo, compared to neuron-only transplants. Furthermore, the co-transplantation strategy was able to rescue abnormal behavioral symptoms in a pre-clinical model of psychiatric disorder, within 1 month after transplantation. We anticipate this strategy to open new doors and facilitate exciting advances in angiogenesis-mediated treatment of psychiatric disorders.

JNK Signaling Regulates Cellular Mechanics of Cortical Interneuron Migration.

Aberrant migration of inhibitory interneurons can alter the formation of cortical circuitry and lead to severe neurologic disorders including epilepsy, autism, and schizophrenia. However, mechanisms involved in directing the migration of interneurons remain incompletely understood. Using a mouse model, we performed live-cell confocal microscopy to explore the mechanisms by which the c-Jun NH2-terminal kinase (JNK) pathway coordinates leading process branching and nucleokinesis, two cell biological processes that are essential for the guided migration of cortical interneurons. Pharmacological inhibition of JNK signaling disrupts the kinetics of leading process branching, rate and amplitude of nucleokinesis, and leads to the rearward mislocalization of the centrosome and primary cilium to the trailing process. Genetic loss of Jnk from interneurons also impairs leading process branching and nucleokinesis, suggesting that important mechanics of interneuron migration depend on the intrinsic activity of JNK. These findings highlight key roles for JNK signaling in leading process branching, nucleokinesis, and the trafficking of centrosomes and cilia during interneuron migration, and further implicates JNK signaling as an important mediator of cortical development.

Differentiation and localization of interneurons in the developing spinal cord depends on DOT1L expression

Genetic and epigenetic factors contribute to the development of the spinal cord. Failure in correct exertion of the developmental programs, including neurulation, neural tube closure and neurogenesis of the diverse spinal cord neuronal subtypes results in defects of variable severity. We here report on the histone methyltransferase Disruptor of Telomeric 1 Like (DOT1L), which mediates histone H3 lysine 79 (H3K79) methylation. Conditional inactivation of DOT1L using Wnt1-cre as driver (Dot1l-cKO) showed that DOT1L expression is essential for spinal cord neurogenesis and localization of diverse neuronal subtypes, similar to its function in the development of the cerebral cortex and cerebellum. Transcriptome analysis revealed that DOT1L deficiency favored differentiation over progenitor proliferation. Dot1l-cKO mainly decreased the numbers of dI1 interneurons expressing Lhx2. In contrast, Lhx9 expressing dI1 interneurons did not change in numbers but localized differently upon Dot1l-cKO. Similarly, loss of DOT1L affected localization but not generation of dI2, dI3, dI5, V0 and V1 interneurons. The resulting derailed interneuron patterns might be responsible for increased cell death, occurrence of which was restricted to the late developmental stage E18.5. Together our data indicate that DOT1L is essential for subtype-specific neurogenesis, migration and localization of dorsal and ventral interneurons in the developing spinal cord, in part by regulating transcriptional activation of Lhx2.

M174. REDUCED CHEMOKINE SIGNALLING CAPACITY IS ASSOCIATED WITH INHIBITORY INTERNEURON DYSFUNCTION IN SUBCORTICAL BRAIN REGIONS IN SCHIZOPHRENIA AND BIPOLAR DISORDER

BackgroundThe subependymal zone (SEZ) adjacent to the lateral ventricles represents the largest reservoir of postnatally-generated cortical and striatal inhibitory interneurons in the human brain. Expression of markers representing the generation of neuronal progenitors from neural stem cells is reduced in the adult SEZ in schizophrenia and bipolar disorder; however, underlying mechanisms and relationships to inhibitory interneuron dysfunction remain unknown. Stem cell maintenance, neuronal migration and cell survival are regulated by signaling of the CXC motif chemokine 12 (CXCL12) through CXC motif chemokine receptors 4 (CXCR4) and 7 (CXCR7), which are increasingly implicated in the pathophysiology of psychiatric disorders.MethodsPost-mortem tissue was obtained from 33 schizophrenia, 32 bipolar disorder and 33 control cases from the Stanley Medical Research Institute. SEZ and caudate nucleus tissue was dissected from 60 µm sections for RNA isolation and cDNA synthesis. Gene expression of CXCL12, CXCR4 and CXCR7 were determined by quantitative polymerase chain reactions. Semi-partial correlations were performed to assess whether CXC chemokine family member mRNAs may correlate with markers of neural stem cells (PROM1, GFAPD), neuronal progenitors (SOX2, ASCL1) and inhibitory interneurons (CALB2, NPY) in the SEZ and caudate nucleus.ResultsIn the SEZ, CXCL12 mRNA was decreased in schizophrenia compared to controls and bipolar disorder (14–24%, all p≤0.03). CXCR4 and CXCR7 mRNAs were both decreased in schizophrenia and bipolar disorder compared to controls (9–33%, all p≤0.05). CXCL12, CXCR4 and CXCR7 expression positively correlated with PROM1, GFAPD, SOX2 and ASCL1 mRNAs (0.28≥sr≤0.61). In the caudate nucleus, CXCL12 mRNA was decreased in schizophrenia and bipolar disorder compared to controls (19–26%, all p≤0.05). CXCR4 mRNA was decreased in schizophrenia compared to controls (20%, p=0.01), while CXCR7 expression did not significantly differ across diagnostic groups. CALB2 and NPY mRNAs were increased in bipolar disorder compared to controls (13–27%, all p≤0.05). CXCR4 expression positively correlated with CALB2 mRNA (sr=0.26), while CXCR7 expression negatively correlated with NPY mRNA (sr=0.26).DiscussionThese findings provide the first molecular evidence of decreased CXC chemokine family member expression in the SEZ and caudate nucleus in psychiatric disorders, with exacerbated deficits in schizophrenia compared to bipolar disorder. Dysregulated CXC chemokine family member expression may hamper neural stem cell maintenance and neuronal differentiation, which may contribute to inhibitory interneuron dysfunction in psychiatric disorders. Future work will determine the cellular localisation of CXCR4 and CXCR7 expression in the SEZ and caudate nucleus to disentangle the regulatory role of CXCL12 signalling in the generation, migration and survival of inhibitory interneurons in the human brain.

Application of Fused Organoid Models to Study Human Brain Development and Neural Disorders.

Human brain organoids cultured from human pluripotent stem cells provide a promising platform to recapitulate histological features of the human brain and model neural disorders. However, unlike animal models, brain organoids lack a reproducible topographic organization, which limits their application in modeling intricate biology, such as the interaction between different brain regions. To overcome these drawbacks, brain organoids have been pre-patterned into specific brain regions and fused to form an assembloid that represents reproducible models recapitulating more complex biological processes of human brain development and neurological diseases. This approach has been applied to model interneuron migration, neuronal projections, tumor invasion, oligodendrogenesis, forebrain axis establishment, and brain vascularization. In this review article, we will summarize the usage of this technology to understand the fundamental biology underpinning human brain development and disorders.

Cystatin B is essential for proliferation and interneuron migration in individuals with EPM1 epilepsy

Progressive myoclonus epilepsy (PME) of Unverricht–Lundborg type (EPM1) is an autosomal recessive neurodegenerative disorder with the highest incidence of PME worldwide. Mutations in the gene encoding cystatin B (CSTB) are the primary genetic cause of EPM1. Here, we investigate the role of CSTB during neurogenesis in vivo in the developing mouse brain and in vitro in human cerebral organoids (hCOs) derived from EPM1 patients. We find that CSTB (but not one of its pathological variants) is secreted into the mouse cerebral spinal fluid and the conditioned media from hCOs. In embryonic mouse brain, we find that functional CSTB influences progenitors’ proliferation and modulates neuronal distribution by attracting interneurons to the site of secretion via cell‐non‐autonomous mechanisms. Similarly, in patient‐derived hCOs, low levels of functional CSTB result in an alteration of progenitor's proliferation, premature differentiation, and changes in interneurons migration. Secretion and extracellular matrix organization are the biological processes particularly affected as suggested by a proteomic analysis in patients’ hCOs. Overall, our study sheds new light on the cellular mechanisms underlying the development of EPM1.

Developmental characterization of Zswim5 expression in the progenitor domains and tangential migration pathways of cortical interneurons in the mouse forebrain.

GABAergic interneurons play an essential role in modulating cortical networks. The progenitor domains of cortical interneurons are localized in developing ventral forebrain, including the medial ganglionic eminence (MGE), caudal ganglionic eminence (CGE), preoptic area (POA), and preoptic hypothalamic border domain (POH). Here, we characterized the expression pattern of Zswim5, an MGE-enriched gene in the mouse forebrain. At E11.5-E13.5, prominent Zswim5 expression was detected in the subventricular zone (SVZ) of MGE, POA, and POH, but not CGE of ventral telencephalon where progenitors of cortical interneurons resided. At E15.5 and E17.5, Zswim5 expression remained in the MGE/pallidum primordium and ventral germinal zone. Zswim5 mRNA was markedly decreased after birth and was absent in the adult forebrain. Interestingly, the Zswim5 expression pattern resembled the tangential migration pathways of cortical interneurons. Zswim5-positive cells in the MGE appeared to migrate from the MGE through the SVZ of LGE to overlying neocortex. Indeed, Zswim5 was co-localized with Nkx2.1 and Lhx6, markers of progenitors and migratory cortical interneurons. Double labeling showed that Ascl1/Mash1-positive cells co-expressed Zswim5. Zswim5 expressing cells contained none or at most low levels of Ki67 but co-expressed Tuj1 in the SVZ of MGE. These results suggest that Zswim5 is immediately upregulated as progenitors exiting cell cycle become postmitotic. Given that recent studies have elucidated that the cell fate of cortical interneurons is determined shortly after becoming postmitotic, the timing of Zswim5 expression in early postmitotic interneurons suggests a potential role of Zswim5 in regulation of neurogenesis and tangential migration of cortical interneurons.

Migration, Chemo-Attraction, and Co-Culture Assays for Human Stem Cell-Derived Endothelial Cells and GABAergic Neurons.

Role of brain vasculature in nervous system development and etiology of brain disorders is increasingly gaining attention. Our recent studies have identified a special population of vascular cells, the periventricular endothelial cells, that play a critical role in the migration and distribution of forebrain GABAergic interneurons during embryonic development. This, coupled with their cell-autonomous functions, alludes to novel roles of periventricular endothelial cells in the pathology of neuropsychiatric disorders like schizophrenia, epilepsy, and autism. Here, we have described three different in vitro assays that collectively evaluate the functions of periventricular endothelial cells and their interaction with GABAergic interneurons. Use of these assays, particularly in a human context, will allow us to identify the link between periventricular endothelial cells and brain disorders. These assays are simple, low cost, and reproducible, and can be easily adapted to any adherent cell type.

Onecut-dependent Nkx6.2 transcription factor expression is required for proper formation and activity of spinal locomotor circuits

In the developing spinal cord, Onecut transcription factors control the diversification of motor neurons into distinct neuronal subsets by ensuring the maintenance of Isl1 expression during differentiation. However, other genes downstream of the Onecut proteins and involved in motor neuron diversification have remained unidentified. In the present study, we generated conditional mutant embryos carrying specific inactivation of Onecut genes in the developing motor neurons, performed RNA-sequencing to identify factors downstream of Onecut proteins in this neuron population, and employed additional transgenic mouse models to assess the role of one specific Onecut-downstream target, the transcription factor Nkx6.2. Nkx6.2 expression was up-regulated in Onecut-deficient motor neurons, but strongly downregulated in Onecut-deficient V2a interneurons, indicating an opposite regulation of Nkx6.2 by Onecut factors in distinct spinal neuron populations. Nkx6.2-null embryos, neonates and adult mice exhibited alterations of locomotor pattern and spinal locomotor network activity, likely resulting from defective survival of a subset of limb-innervating motor neurons and abnormal migration of V2a interneurons. Taken together, our results indicate that Nkx6.2 regulates the development of spinal neuronal populations and the formation of the spinal locomotor circuits downstream of the Onecut transcription factors.

JNK signaling is required for proper tangential migration and laminar allocation of cortical interneurons.

The precise migration of cortical interneurons is essential for the formation and function of cortical circuits, and disruptions to this key developmental process are implicated in the etiology of complex neurodevelopmental disorders, including schizophrenia, autism and epilepsy. We have recently identified the Jun N-terminal kinase (JNK) pathway as an important mediator of cortical interneuron migration in mice, regulating the proper timing of interneuron arrival into the cortical rudiment. In the current study, we demonstrate a vital role for JNK signaling at later stages of corticogenesis, when interneurons transition from tangential to radial modes of migration. Pharmacological inhibition of JNK signaling in ex vivo slice cultures caused cortical interneurons to rapidly depart from migratory streams and prematurely enter the cortical plate. Similarly, genetic loss of JNK function led to precocious stream departure ex vivo, and stream disruption, morphological changes and abnormal allocation of cortical interneurons in vivo These data suggest that JNK signaling facilitates the tangential migration and laminar deposition of cortical interneurons, and further implicates the JNK pathway as an important regulator of cortical development.

Cell-autonomous impact of polysialic acid-producing enzyme ST8SIA2 on developmental migration and distribution of cortical interneurons.

In humans, variations in the polysialic acid-producing enzyme ST8SIA2 and disturbances in the cortical inhibitory system are associated with neurodevelopmental psychiatric disorders such as schizophrenia and autism. In mice, the ST8SIA2-dependent formation of polysialic acid during embryonic development is crucial for the establishment of interneuron populations of the medial prefrontal cortex. However, the spatial pattern and the neurodevelopmental mechanisms of interneuron changes caused by loss of ST8SIA2 function have not been fully characterized. Here, we use immunohistochemical analysis to demonstrate that densities of parvalbumin-positive interneurons are not only reduced in the medial prefrontal cortex, but also in the adjacent motor and somatosensory cortices of St8sia2-deficient male mice. These reductions, however, were confined to the rostral parts of the analyzed region. Mice with conditional knockout of St8sia2 under the interneuron-specific Lhx6 promoter, but not mice with a deletion under the Emx1 promoter that targets cortical excitatory neurons and glia, largely recapitulated the area-specific changes of parvalbumin-positive interneurons in the anterior cortex of St8sia2-/- mice. Live imaging of interneuron migration in slice cultures of the developing cortex revealed a comparable reduction of directional persistence accompanied by increased branching of leading processes in slice cultures obtained from St8sia2-/- embryos or from embryos with interneuron-specific ablation of St8sia2. Together, the data demonstrate a cell-autonomous impact of ST8SIA2 on cortical interneuron migration and the distribution of parvalbumin-positive interneurons in the anterior cortex. This provides a neurodevelopmental mechanism for how dysregulation of ST8SIA2 may lead to disturbed inhibitory balance as observed in schizophrenia and autism.

Pou2f2 Regulates the Distribution of Dorsal Interneurons in the Mouse Developing Spinal Cord.

Spinal dorsal interneurons, which are generated during embryonic development, relay and process sensory inputs from the periphery to the central nervous system. Proper integration of these cells into neuronal circuitry depends on their correct positioning within the spinal parenchyma. Molecular cues that control neuronal migration have been extensively characterized but the genetic programs that regulate their production remain poorly investigated. Onecut (OC) transcription factors have been shown to control the migration of the dorsal interneurons (dINs) during spinal cord development. Here, we report that the OC factors moderate the expression of Pou2f2, a transcription factor essential for B-cell differentiation, in spinal dINs. Overexpression or inactivation of Pou2f2 leads to alterations in the differentiation of dI2, dI3 and Phox2a-positive dI5 populations and to defects in the distribution of dI2-dI6 interneurons. Thus, an OC-Pou2f2 genetic cascade regulates adequate diversification and distribution of dINs during embryonic development.

The NKCC1 antagonist bumetanide mitigates interneuronopathy associated with ethanol exposure in utero.

Prenatal exposure to ethanol induces aberrant tangential migration of corticopetal GABAergic interneurons, and long-term alterations in the form and function of the prefrontal cortex. We have hypothesized that interneuronopathy contributes significantly to the pathoetiology of fetal alcohol spectrum disorders (FASD). Activity-dependent tangential migration of GABAergic cortical neurons is driven by depolarizing responses to ambient GABA present in the cortical enclave. We found that ethanol exposure potentiates the depolarizing action of GABA in GABAergic cortical interneurons of the embryonic mouse brain. Pharmacological antagonism of the cotransporter NKCC1 mitigated ethanol-induced potentiation of GABA depolarization and prevented aberrant patterns of tangential migration induced by ethanol in vitro. In a model of FASD, maternal bumetanide treatment prevented interneuronopathy in the prefrontal cortex of ethanol exposed offspring, including deficits in behavioral flexibility. These findings position interneuronopathy as a mechanism of FASD symptomatology, and posit NKCC1 as a pharmacological target for the management of FASD.

JAK3 modulates the migration of gabaergic interneurons during development of murine cortex

JAK3 modulates the migration of gabaergic interneurons during development of murine cortex

A Brief Boost of Positive Energy When Young Makes for a Healthy Adult Interneuron.

Tonic Activation of GluN2C/GluN2D-Containing NMDA Receptors by Ambient Glutamate Facilitates Cortical Interneuron Maturation Hanson E, Armbruster M, Lau LA, Sommer ME, Klaft ZJ, Swanger SA, Traynelis SF, Moss SJ, Noubary F, Chadchankar J, Dulla CG. J Neurosci. 2019;39(19):3611-3626. doi:10.1523/JNEUROSCI.1392-18.2019. PMID: 30846615. Epub Mar 7, 2019.Developing cortical GABAergic interneurons rely on genetic programs, neuronal activity, and environmental cues to construct inhibitory circuits during early postnatal development. Disruption of these events can cause long-term changes in cortical inhibition and may be involved in neurological disorders associated with inhibitory circuit dysfunction. We hypothesized that tonic glutamate signaling in the neonatal cortex contributes to, and is necessary for, the maturation of cortical interneurons. To test this hypothesis, we used mice of both sexes to quantify extracellular glutamate concentrations in the cortex during development, measure ambient glutamate-mediated activation of developing cortical interneurons, and manipulate tonic glutamate signaling using subtype-specific N-methyl-d-aspartic acid (NMDA) receptor antagonists in vitro and in vivo. We report that ambient glutamate levels are high (≈100 nm) in the neonatal cortex and decrease (to ≈50 nm) during the first weeks of life, coincident with increases in astrocytic glutamate uptake. Consistent with elevated ambient glutamate, putative parvalbumin-positive interneurons in the cortex (identified using G42: GAD1-eGFP reporter mice) exhibit a transient, tonic NMDA current at the end of the first postnatal week. GluN2C/GluN2D-containing NMDA receptors mediate the majority of this current and contribute to the resting membrane potential and intrinsic properties of developing putative parvalbumin interneurons. Pharmacological blockade of GluN2C/GluN2D-containing NMDA receptors in vivo during the period of tonic interneuron activation, but not later, leads to lasting decreases in interneuron morphological complexity and causes deficits in cortical inhibition later in life. These results demonstrate that dynamic ambient glutamate signaling contributes to cortical interneuron maturation via tonic activation of GluN2C/GluN2D-containing NMDA receptors. Significance statement: Inhibitory GABAergic interneurons make up 20% of cortical neurons and are critical to controlling cortical network activity. Dysfunction of cortical inhibition is associated with multiple neurological disorders, including epilepsy. Establishing inhibitory cortical networks requires in utero proliferation, differentiation, and migration of immature GABAergic interneurons and subsequent postnatal morphological maturation and circuit integration. Here, we demonstrate that ambient glutamate provides tonic activation of immature, putative parvalbumin-positive GABAergic interneurons in the neonatal cortex via high-affinity NMDA receptors. When this activation is blocked, GABAergic interneuron maturation is disrupted, and cortical networks exhibit lasting abnormal hyperexcitability. We conclude that temporally precise activation of developing cortical interneurons by ambient glutamate is critically important for establishing normal cortical inhibition.

Inhibitory neurons in the right place

Neurodevelopment Disruption of γ-aminobutyric acid–mediated (GABAergic) interneuron migration is implicated in neurodevelopmental disorders such as autism spectrum disorder and schizophrenia. Su et al. found that dopamine induced the association of the dopamine receptor D1R with the guanosine triphosphatase–activating protein SynGAP. During embryonic and early postnatal development in mice, this complex promoted dopamine-induced migration of GABAergic interneurons but not glutamatergic interneurons. These findings may explain why mutations in SYNGAP1 give rise to neurodevelopmental disorders. Sci. Signal. 12 , eaau9122 (2019).

Glutamate controls vessel-associated migration of GABA interneurons from the pial migratory route via NMDA receptors and endothelial protease activation

During cortex development, fine interactions between pyramidal cells and migrating GABA neurons are required to orchestrate correct positioning of interneurons, but cellular and molecular mechanisms are not yet clearly understood. Functional and age-specific expression of NMDA receptors by neonate endothelial cells suggests a vascular contribution to the trophic role of glutamate during cortical development. Associating functional and loss-of-function approaches, we found that glutamate stimulates activity of the endothelial proteases MMP-9 and t-PA along the pial migratory route (PMR) and radial cortical microvessels. Activation of MMP-9 was NMDAR-dependent and abrogated in t-PA−/− mice. Time-lapse recordings revealed that glutamate stimulated migration of GABA interneurons along vessels through an NMDAR-dependent mechanism. In Gad67-GFP mice, t-PA invalidation and in vivo administration of an MMP inhibitor impaired positioning of GABA interneurons in superficial cortical layers, whereas Grin1 endothelial invalidation resulted in a strong reduction of the thickness of the pial migratory route, a marked decrease of the glutamate-induced MMP-9-like activity along the PMR and a depopulation of interneurons in superficial cortical layers. This study supports that glutamate controls the vessel-associated migration of GABA interneurons by regulating the activity of endothelial proteases. This effect requires endothelial NMDAR and is t-PA-dependent. These neurodevelopmental data reinforce the debate regarding safety of molecules with NMDA-antagonist properties administered to preterm and term neonates.

Disruption of SynGAP-dopamine D1 receptor complexes alters actin and microtubule dynamics and impairs GABAergic interneuron migration.

Disruption of γ-aminobutyric acid (GABA)-ergic interneuron migration is implicated in various neurodevelopmental disorders, including autism spectrum disorder and schizophrenia. The dopamine D1 receptor (D1R) promotes GABAergic interneuron migration, which is disrupted in various neurological disorders, some of which are also associated with mutations in the gene encoding synaptic Ras-guanosine triphosphatase-activating protein (SynGAP). Here, we explored the mechanisms underlying these associations and their possible connection. In prenatal mouse brain tissue, we found a previously unknown interaction between the D1R and SynGAP. This D1R-SynGAP interaction facilitated D1R localization to the plasma membrane and promoted D1R-mediated downstream signaling pathways, including phosphorylation of protein kinase A and p38 mitogen-activated protein kinase. These effects were blocked by a peptide (TAT-D1Rpep) that disrupted the D1R-SynGAP interaction. Furthermore, disrupting this complex in mice during embryonic development resulted in pronounced and selective deficits in the tangential migration of GABAergic interneurons, possibly due to altered actin and microtubule dynamics. Our results provide insights into the molecular mechanisms regulating interneuron development and suggest that disruption of the D1R-SynGAP interaction may underlie SYNGAP1 mutation-related neurodevelopmental disorders.

The PROK2/PROKR2 signaling pathway is required for the migration of most olfactory bulb interneurons.

Neural stem cells in the subventricular zone (SVZ) of the lateral ventricle generate new interneurons, which migrate tangentially through the rostral migratory stream (RMS) to the olfactory bulb (OB). The PROK2 (prokineticin 2) and PROKR2 (prokineticin receptor 2) signaling pathway has been identified to cause human Kallmann syndrome, a developmental disease that associates hypogonadism with anosmia (OB developmental defects). However, the identities and properties of PROK2+ and PROKR2+ cells in the SVZ-RMS-OB remain largely unknown. Here we examine the expression patterns of Prok2 and Prokr2 in the SVZ-RMS-OB using Prok2EGFP transgenic and Prokr2LacZ/+ knockin mice. Our results show that Prokr2 is expressed in postmitotic immature interneurons in the SVZ-RMS-OB. Prok2 is not expressed in the SVZ, but a few PROK2+ cells are found in the medial part of the RMS; they are not neural progenitors or migrating neuroblasts. In the OB, Prok2 is expressed in a subset of granule cells and tufted cells, but no coexpression of Prok2 and Prokr2 in the OB cells is observed. In Prok2 and Prokr2 mutant mice, severe tangential and radial migration defects of neuroblasts in the SVZ-RMS-OB result in loss of ~75% of GABAergic interneurons in the OB. These analyses demonstrate that PROK2/PROKR2 signaling is crucial for the tangential and radial migration of OB interneurons.