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Although the Na-K-Cl cotransporter (NKCC1) inhibitor bumetanide has prominent positive effects on the pathophysiology of many neurological disorders, the mechanism of action is obscure. Attention for elucidating the role of Nkcc1 has been mainly focused on neurons. Recent single cell mRNA sequencing analysis has demonstrated that the major cellular populations expressing NKCC1 in the cortex are non-neuronal. We used a combination of conditional transgenic animals, in vivo electrophysiology, two-photon imaging, cognitive behavioral tests and flow cytometry to investigate the role of Nkcc1 inhibition by bumetanide in a mouse model of controlled cortical impact (CCI). Here, we found that bumetanide rescues parvalbumin-positive interneurons by increasing interneuron-microglia contacts shortly after injury. The longitudinal phenotypic changes of microglia were significantly modified by bumetanide, including an increase in the expression of microglial-derived Bdnf. These effects were accompanied by the prevention of CCI-induced decrease in hippocampal neurogenesis. Treatment with bumetanide during the first week post-CCI resulted in significant recovery of working and episodic memory as well as changes in theta band oscillations one month later. These results disclose a novel mechanism for the neuroprotective action of bumetanide mediated by an acceleration of microglial activation dynamics that leads to an increase of parvalbumin interneuron survival following CCI, possibly resulting from increased microglial Bdnf expression and contact with interneurons. Salvage of interneurons may normalize ambient gamma-aminobutyric acid (GABA), resulting in the preservation of adult neurogenesis processes as well as contributing to bumetanide-mediated improvement of cognitive performance.

Pioneer transcription factors are thought to play pivotal roles in developmental processes by binding nucleosomal DNA to activate gene expression, though mechanisms through which pioneer transcription factors remodel chromatin remain unclear. Here, using single-cell transcriptomics, we show that endogenous expression of neurogenic transcription factor ASCL1, considered a classical pioneer factor, defines a transient population of progenitors in human neural differentiation. Testing ASCL1's pioneer function using a knockout model to define the unbound state, we found that endogenous expression of ASCL1 drives progenitor differentiation bycis-regulation both as a classical pioneer factor and as a nonpioneer remodeler, where ASCL1 binds permissive chromatin to induce chromatin conformation changes. ASCL1 interacts with BAF SWI/SNF chromatin remodeling complexes, primarily at targets where it acts as a nonpioneer factor, and we provide evidence for codependent DNA binding and remodeling at a subset of ASCL1 and SWI/SNF cotargets. Our findings provide new insights into ASCL1 function regulating activation of long-range regulatory elements in human neurogenesis and uncover a novel mechanism of its chromatin remodeling function codependent on partner ATPase activity.

Pioneer transcription factors are thought to play pivotal roles in developmental processes by binding nucleosomal DNA to activate gene expression. The role of neurogenic pioneer factor ASCL1 in shaping chromatin landscape in human neurogenesis remains unclear. Here we show that ASCL1 acts as a pioneer transcription factor in a transient population of progenitors. Using anin vitroASCL1 knockout model we show it drives progenitor differentiation by cis-regulation both as a classical pioneer factor and as a non-pioneer remodeler, where ASCL1 binds permissive chromatin to induce chromatin conformation changes. We find ASCL1 directly interacts with mammalian BAF SWI/SNF chromatin remodeling complexes, essential for neurogenesis and involved in multiple neurodevelopmental disorders. ASCL1 acts as a non-pioneer chromatin remodeler to regulate gene expression at a subset of loci, requiring mBAF SWI/SNF’s ATPase activity for cis-regulation of gene expression. Our findings demonstrate that ASCL1 is a key chromatin remodeler in human neurogenesis, uncovering an alternative mechanism of remodeling function dependent on partner ATPase activity.

Dossier thématique sous la direction de Naomi Davidson et Capucine Boidin; International audience; Dans l’historiographie vietnamienne des années 1990, apparaît le terme « nữ », désignant le genre féminin pour souligner l’engagement spécifique des femmes dans la guerre, à l’égale de celui des hommes, voire au-delà de celui des hommes dans une facture d’héroïsation. À partir de nouveaux corpus d’histoire orale des combattantes et combattants clandestins dits des « Commandos de Saigon », l’article interroge les tensions de l’écriture d’une histoire des femmes en temps de guerre. En effet, penser le genre de l’indépendance, attentif aux mécanismes des dominations masculines, aide à construire une histoire de la guerre plus proche des réalités sociales, moins hagiographique.

Aims We understand little of the pathogenesis of developmental cortical lesions, because we understand little of the diversity of the cell types that contribute to the diseases or how those cells interact. We tested the hypothesis that cellular diversity and cell-cell interactions play an important role in these disorders by investigating the signalling molecules in the commonest cortical malformations that lead to childhood epilepsy, focal cortical dysplasia (FCD) and tuberous sclerosis (TS). Methods Transcriptional profiling clustered cases into molecularly distinct groups. Using gene expression data, we identified the secretory signalling molecules in FCD/TS and characterised the cell types expressing these molecules. We developed a functional model using organotypic cultures. Results We identified 113 up-regulated secretory molecules in FCDIIB/TS. The top 12 differentially expressed genes (DEGs) were validated by immunohistochemistry. This highlighted two molecules, Chitinase 3-like protein 1 (CHI3L1) and C-C motif chemokine ligand 2 (CCL2) (MCP1) that were expressed in a unique population of small cells in close proximity to balloon cells (BC). We then characterised these cells and developed a functional model in organotypic slice cultures. We found that the number of CHI3L1 and CCL2 expressing cells decreased following inhibition of mTOR, the main aberrant signalling pathway in TS and FCD. Conclusions Our findings highlight previously uncharacterised small cell populations in FCD and TS which express specific signalling molecules. These findings indicate a new level of diversity and cellular interactions in cortical malformations and provide a generalisable approach to understanding cell-cell interactions and cellular heterogeneity in developmental neuropathology.

ObjectiveThe Na-K-Cl cotransporter (NKCC1) inhibitor bumetanide has prominent positive effects on the pathophysiology of many neurological disorders. Here we studied whether bumetanide could influence post-traumatic cognitive decline and inflammatory processes by regulating astrocyte and microglia activation.MethodControlled cortical impacted (CCI) animals were treated with bumetanide during the first post-CCI week. Immunochemistry, flow cytometry, immunoassay, and in vivo imaging were used to study astrocytic and microglial morphology and phenotype as well as adult neurogenesis. Telemetric electroencephalograms and cognitive behavioral test were performed at one-month post CCI.ResultsBumetanide prevented CCI-induced decrease in hippocampal neurogenesis and parvalbumin positive interneuron loss. Deletion of NKCC1 in astrocytes neither rescued interneurons nor promote neurogenesis. Interestingly, bumetanide had a strong effect on microglial activation by inducing polarization towards the M1-like phenotype 3 days post-CCI and the M2-like phenotype 7 days post-CCI. Bumetanide increased microglial Brain-derived neurotrophic factor (BDNF) expression and interaction with parvalbumin interneurons. The early treatment with bumetanide resulted in improvements in working and episodic memory, one-month post-CCI, as well as the normalization of theta band oscillations.InterpretationHere, we disclose a novel mechanism for the neuroprotective action of bumetanide mediated by an acceleration of microglial activation dynamics that leads to an increase of parvalbumin interneuron survival following CCI, possibly resulting from increased microglial BDNF expression and contact with interneurons. Salvage of interneurons may normalize ambient gamma-aminobutyric acid (GABA) resulting in the preservation of adult neurogenesis processes as well as contributing to bumetanide-mediated improvement of cognitive performance.

Despite the central role of Rho GTPases in neuronal development, their functions in adult hippocampal neurogenesis remain poorly explored. Here, by using a retrovirus-based loss-of-function approach in vivo, we show that the atypical Rho GTPase Rnd2 is crucial for survival, positioning, somatodendritic morphogenesis, and functional maturation of adult-born dentate granule neurons. Interestingly, most of these functions are specific to granule neurons generated during adulthood since the deletion of Rnd2 in neonatally-born granule neurons only affects dendritogenesis. In addition, suppression of Rnd2 in adult-born dentate granule neurons increases anxiety-like behavior whereas its deletion in pups has no such effect, a finding supporting the adult neurogenesis hypothesis of anxiety disorders. Thus, our results are in line with the view that adult neurogenesis is not a simple continuation of earlier processes from development, and establish a causal relationship between Rnd2 expression and anxiety.

Adult mouse hippocampal neural stem cells (NSCs) generate new neurons that integrate into existing hippocampal networks and modulate mood and memory. These NSCs are largely quiescent and are stimulated by niche signals to activate and produce neurons. Wnt/β-catenin signalling acts at different steps along the hippocampal neurogenic lineage, but whether it has a direct role in the regulation of NSCs remains unclear. Here, we used Wnt/β-catenin reporters and transcriptomic data from in vivo and in vitro models to show that adult NSCs respond to Wnt/β-catenin signalling. Wnt/β-catenin stimulation instructed the neuronal differentiation of proliferating NSCs and promoted the activation or differentiation of quiescent NSCs in a dose-dependent manner. However, deletion of β-catenin in NSCs did not affect either their activation or maintenance of their stem cell characteristics. Together, these results indicate that, although NSCs do respond to Wnt/β-catenin stimulation in a dose-dependent and state-specific manner, Wnt/β-catenin signalling is not cell-autonomously required to maintain NSC homeostasis, which reconciles some of the contradictions in the literature as to the role of Wnt/β-catenin signalling in adult hippocampal NSCs., Summary: Wnt/β-catenin signalling stimulation promotes the exit from quiescence and differentiation of adult hippocampal neural stem cells but is dispensable for homeostatic neurogenesis in the dentate gyrus of young mice.

PurposeHeterozygous variants in BCL11A underlie an intellectual developmental disorder with persistence of fetal hemoglobin (BCL11A-IDD, a.k.a. Dias-Logan syndrome). We sought to delineate the genotypic and phenotypic spectrum of BCL11A-IDD.MethodsWe performed an in-depth analysis of 42 patients with BCL11A-IDD ascertained through a collaborative network of clinical and research colleagues. We also reviewed 33 additional affected individuals previously reported in the literature or available through public repositories with clinical information.ResultsMolecular and clinical data analysis of 75 patients with BCL11A-IDD identified 60 unique variants (30 frameshift, 7 missense, 6 splice-site, 17 stop-gain) and 8 unique CNVs (microdeletions involving BCL11A only). We redefined the most frequent manifestations of the condition: intellectual disability, hypotonia, behavioral abnormalities, postnatal microcephaly and autism spectrum disorder. Two thirds of patients have brain MRI abnormalities, and we identified a recurrent posterior fossa phenotype of vermian hypoplasia and/or small brainstem. Truncating BCL11A variants, particularly those affecting the long (BCL11A-L) and extra-long (-XL) isoforms, sparing the short (-S) isoform, were associated with increased severity.ConclusionsWe expand the clinical delineation of BCL11A-IDD and identify a potential isoform-specific genotype-phenotype correlation. We show that BCL11A-IDD is associated with posterior fossa anomalies and highlight the differences between BCL11A-IDD and 2p16.1p15 microdeletion syndrome.

To fully understand the complexity of ideological commitments in Vietnam between 1945 and 1975, it is useful to return to the 1930s, when the attraction of the Vietnamese nationalists for the Fascist European regimes led a number of them to publicly celebrate the figure of Adolf Hitler. Within the context of the Popular Front in France and a certain political openness in Indochina, the intellectual and organizational turmoil of the nationalist parties gave substance to a doctrine nourished by Western models but that nevertheless remained uniquely Vietnamese. This article addresses the question of the “fascist temptation” of the prewar nationalist Đại Việt parties, which is rarely addressed by historiography.

Cells with latent stem ability can contribute to mammalian tissue regeneration after damage. Whether the central nervous system (CNS) harbors such cells remains controversial. Here, we report that DNGR-1 lineage tracing in mice identifies an ependymal cell subset, wherein resides latent regenerative potential. We demonstrate that DNGR-1-lineage-traced ependymal cells arise early in embryogenesis (E11.5) and subsequently spread across the lining of cerebrospinal fluid (CSF)-filled compartments to form a contiguous sheet from the brain to the end of the spinal cord. In the steady state, these DNGR-1-traced cells are quiescent, committed to their ependymal cell fate, and do not contribute to neuronal or glial lineages. However, trans-differentiation can be induced in adult mice by CNS injury or in vitro by culture with suitable factors. Our findings highlight previously unappreciated ependymal cell heterogeneity and identify across the entire CNS an ependymal cell subset wherein resides damage-responsive neural stem cell potential.

Germline missense mutations in the BAF swi/snf chromatin remodeling subunit SMARCA4 are associated with neurodevelopmental disorders, including Coffin Siris Syndrome (CSS). Here, we generated an induced pluripotent stem cell line from a male patient with atypical CSS features and a de novo heterozygous missense mutation in the SMARCA4 gene (c.3607C>T, p.(Arg1203Cys)). Hair root derived keratinocytes were reprogrammed using non-integrative Sendai virus vector delivery of pluripotency factors. iPSCs generated display normal morphology and molecular karyotype, express pluripotency markers and are able to differentiate into the three germ layers.

Quiescence is a cellular state characterised by reversible cell-cycle arrest and diminished biosynthetic activity that protects against environmental insults, replicative exhaustion and proliferation-induced mutations1. Entry into and exit from this state controls development, maintenance and repair of tissues plus, in the adult central nervous system, generation of new neurons and thus cognition and mood2–4. Cancer stem cells too can undergo quiescence, which confers them resistance to current therapies5, 6. Despite clinical relevance, quiescence is poorly understood and is defined functionally given lack of molecular markers. Decrease of the most resource-intensive cellular process of protein synthesis is a feature of quiescence, controlled across species and cell types by inhibition of the Target of Rapamycin (TOR) pathway1, 7. Here, we combine Drosophila genetics and a mammalian model to show that altered nucleocytoplasmic partitioning and nuclear accumulation of polyadenylated RNAs are novel evolutionarily conserved hallmarks of quiescence regulation. Furthermore, nuclear accumulation of messenger RNA (mRNA) in quiescent NSCs (qNSCs) largely predicts protein downregulation, accounting for uncoupling between transcriptome and proteome in quiescence. These mechanisms provide a previously unappreciated regulatory layer to reducing protein synthesis in quiescent cells, whilst priming them for reactivation in response to appropriate cues.

The lateral ventricle (LV) is flanked by the subventricular zone (SVZ), a neural stem cell (NSC) niche rich in extrinsic growth factors regulating NSC maintenance, proliferation, and neuronal differentiation. Dysregulation of the SVZ niche causes LV expansion, a condition known as hydrocephalus; however, the underlying pathological mechanisms are unclear. We show that deficiency of the proteoglycan Tsukushi (TSK) in ependymal cells at the LV surface and in the cerebrospinal fluid results in hydrocephalus with neurodevelopmental disorder-like symptoms in mice. These symptoms are accompanied by altered differentiation and survival of the NSC lineage, disrupted ependymal structure, and dysregulated Wnt signaling. Multiple TSK variants found in patients with hydrocephalus exhibit reduced physiological activity in mice in vivo and in vitro. Administration of wild-type TSK protein or Wnt antagonists, but not of hydrocephalus-related TSK variants, in the LV of TSK knockout mice prevented hydrocephalus and preserved SVZ neurogenesis. These observations suggest that TSK plays a crucial role as a niche molecule modulating the fate of SVZ NSCs and point to TSK as a candidate for the diagnosis and therapy of hydrocephalus.

Adult mouse hippocampal neural stem cells (NSCs) generate new neurons that integrate into existing hippocampal networks and modulate mood and memory. These NSCs are largely quiescent and are stimulated by niche signals to activate and produce neurons. Wnt/β-catenin signalling acts at different steps along the hippocampal neurogenic lineage and has been shown to promote the proliferation of intermediate progenitor cells. However, whether it has a direct role in the regulation of NSCs still remains unclear. Here we used Wnt/β-catenin reporters and transcriptomic data fromin vivoandin vitromodels to show that both active and quiescent adult NSCs respond to Wnt/β-catenin signalling. Wnt/β-catenin stimulation instructed neuronal differentiation of active NSCs and promoted the activation or differentiation of quiescent NSCs in a dose-dependent manner. However, we found that inhibiting NSCs response to Wnt, by conditionally deleting β-catenin, did not affect their activation or maintenance of their stem cell characteristics. Together, our results indicate that whilst NSCs do respond to Wnt/β-catenin stimulation in a dose-dependent and state-specific manner, Wnt/β-catenin signalling is not cell-autonomously required to maintain NSC homeostasis, which could reconcile some of the contradictions in the literature as to the role of Wnt/β-catenin signalling in adult hippocampal NSCs.

Summary Cortical GABAergic interneurons are generated in large numbers in the ganglionic eminences and migrate into the cerebral cortex during embryogenesis. At early postnatal stages, during neuronal circuit maturation, autonomous and activity-dependent mechanisms operate within the cortex to adjust cell numbers by eliminating naturally occurring neuron excess. Here, we show that when cortical interneurons are generated in aberrantly high numbers—due to a defect in precursor cell proliferation during embryogenesis—extra parvalbumin interneurons persist in the postnatal mouse cortex during critical periods of cortical network maturation. Even though cell numbers are subsequently normalized, behavioral abnormalities remain in adulthood. This suggests that timely clearance of excess cortical interneurons is critical for correct functional maturation of circuits that drive adult behavior., Graphical abstract, Highlights • CUX2 regulates cortical parvalbumin interneuron number generation in the MGE • Excess parvalbumin (PV) interneuron integrates into the early postnatal cortex • Excess PV interneuron is eliminated through PTEN-dependent mechanisms • Behavioral abnormalities persist long after abnormal interneuron excess is cleared, Cortical interneurons are generated in excess during embryogenesis, and numbers are trimmed soon after birth for optimal inhibition. Magno et al. demonstrate that aberrant parvalbumin interneuron excess persists in the postnatal cortex, spanning critical periods of cortical network maturation. Cell numbers are eventually normalized, but behavioral abnormalities remain in adulthood.

Despite the central role of Rho GTPases in neuronal development, their functions in adult hippocampal neurogenesis remain poorly explored. Here, by using a retrovirus-based loss-of-function approach in vivo, we show that the atypical Rho GTPase Rnd2 is crucial for the survival, positioning, somatodendritic morphogenesis and functional maturation of adult-born dentate granule neurons. Interestingly, most of these functions are specific to granule neurons generated during adulthood since the deletion of Rnd2 in neonatally-born granule neurons only affects dendritogenesis. In addition, suppression of Rnd2 in adult-born dentate granule neurons increases anxiety-like behaviour whereas its deletion in pups has no such effect, a finding supporting the adult neurogenesis hypothesis of anxiety disorders. Thus, our results provide mechanistic insight into the differential regulation of hippocampal neurogenesis during development and adulthood, and establishes a causal relationship between Rnd2 expression and anxiety.

Thymus function depends on the epithelial compartment of the thymic stroma. Cortical thymic epithelial cells (cTECs) regulate T cell lineage commitment and positive selection, while medullary (m) TECs impose central tolerance on the T cell repertoire. During thymus organogenesis, these functionally distinct sub-lineages are thought to arise from a common thymic epithelial progenitor cell (TEPC). However, the mechanisms controlling cTEC and mTEC production from the common TEPC are not understood. Here, we show that emergence of the earliest mTEC lineage-restricted progenitors requires active NOTCH signaling in progenitor TEC and that, once specified, further mTEC development is NOTCH independent. In addition, we demonstrate that persistent NOTCH activity favors maintenance of undifferentiated TEPCs at the expense of cTEC differentiation. Finally, we uncover a cross-regulatory relationship between NOTCH and FOXN1, a master regulator of TEC differentiation. These data establish NOTCH as a potent regulator of TEPC and mTEC fate during fetal thymus development, and are thus of high relevance to strategies aimed at generating/regenerating functional thymic tissue in vitro and in vivo., Summary: Notch signaling regulates the initial emergence of medullary thymic epithelial sublineage, implicating Notch in the maintenance of primitive thymic epithelial progenitors and uncovering its cross-interaction with Foxn1.

Astrocytes have essential functions in brain homeostasis that are established late in differentiation, but the mechanisms underlying the functional maturation of astrocytes are not well understood. Here we identify extensive transcriptional changes that occur during murine astrocyte maturation in vivo that are accompanied by chromatin remodelling at enhancer elements. Investigating astrocyte maturation in a cell culture model revealed that in vitro-differentiated astrocytes lack expression of many mature astrocyte-specific genes, including genes for the transcription factors Rorb, Dbx2, Lhx2 and Fezf2. Forced expression of these factors in vitro induces distinct sets of mature astrocyte-specific transcripts. Culturing astrocytes in a three-dimensional matrix containing FGF2 induces expression of Rorb, Dbx2 and Lhx2 and improves astrocyte maturity based on transcriptional and chromatin profiles. Therefore, extrinsic signals orchestrate the expression of multiple intrinsic regulators, which in turn induce in a modular manner the transcriptional and chromatin changes underlying astrocyte maturation., Astrocytes have functions crucial for brain homeostasis, which are disrupted in many neurological disorders, but how these functions are established during astrocyte maturation is largely unknown. Here the authors show transcriptional and chromatin changes underlying astrocyte maturation in mice and identify transcription factors regulating maturation of cultured astrocytes.

SUMMARYNeural stem cell numbers fall rapidly in the hippocampus of juvenile mice but stabilise during adulthood, ensuring lifelong hippocampal neurogenesis. We show that this reduction in stem cell depletion rate is the result of multiple coordinated changes in stem cell behaviour. In particular, while active neural stem cells divide only once or twice before differentiating rapidly in juveniles, they increasingly return to a resting state of shallow quiescence and progress through additional self-renewing divisions in adulthood. Single-cell transcriptomic, mathematical modelling and label-retention analyses indicate that resting cells have a higher activation rate and greater contribution to neurogenesis than dormant cells, which have not left quiescence. These progressive changes in stem cell behaviour result from reduced expression of the pro-activation protein ASCL1 due to increased post-translational degradation. These mechanisms help reconcile current contradictory models of hippocampal NSC dynamics and may contribute to the different rates of decline of hippocampal neurogenesis in mammalian species including humans.

Neural stem cell numbers fall rapidly in the hippocampus of juvenile mice but stabilize during adulthood, ensuring lifelong hippocampal neurogenesis. We show that this stabilization of stem cell numbers in young adults is the result of coordinated changes in stem cell behavior. Although proliferating neural stem cells in juveniles differentiate rapidly, they increasingly return to a resting state of shallow quiescence and progress through additional self-renewing divisions in adulthood. Single-cell transcriptomics, modeling, and label retention analyses indicate that resting cells have a higher activation rate and greater contribution to neurogenesis than dormant cells, which have not left quiescence. These changes in stem cell behavior result from a progressive reduction in expression of the pro-activation protein ASCL1 because of increased post-translational degradation. These cellular mechanisms help reconcile current contradictory models of hippocampal neural stem cell (NSC) dynamics and may contribute to the different rates of decline of hippocampal neurogenesis in mammalian species, including humans.

Perturbation of CaMKIIβ expression has been associated with multiple neuropsychiatric diseases, highlighting CaMKIIβ as a gene of interest. Yet, in contrast to CaMKIIα, the specific functions of CaMKIIβ in the brain remain poorly explored. Here, we reveal a novel function for this CaMKII isoform in vivo during neuronal development. By using in utero electroporation, we show that CaMKIIβ is an important regulator of radial migration of projection neurons during cerebral cortex development. Knockdown of CaMKIIβ causes accelerated migration of nascent pyramidal neurons, whereas overexpression of CaMKIIβ inhibits migration, demonstrating that precise regulation of CaMKIIβ expression is required for correct neuronal migration. More precisely, CaMKIIβ controls the multipolar-bipolar transition in the intermediate zone and locomotion in the cortical plate through its actin-binding and -bundling activities. In addition, our data indicate that a fine-tuned balance between CaMKIIβ and cofilin activities is necessary to ensure proper migration of cortical neurons. Thus, our findings define a novel isoform-specific function for CaMKIIβ, demonstrating that CaMKIIβ has a major biological function in the developing brain.

Somatic stem/progenitor cells are active in embryonic tissues but quiescent in many adult tissues. The detailed mechanisms that regulate active versus quiescent stem cell states are largely unknown. In active neural stem cells, Hes1 expression oscillates and drives cyclic expression of the proneural gene Ascl1, which activates cell proliferation. Here, we found that in quiescent neural stem cells in the adult mouse brain, Hes1 levels are oscillatory, although the peaks and troughs are higher than those in active neural stem cells, causing Ascl1 expression to be continuously suppressed. Inactivation of Hes1 and its related genes up-regulates Ascl1 expression and increases neurogenesis. This causes rapid depletion of neural stem cells and premature termination of neurogenesis. Conversely, sustained Hes1 expression represses Ascl1, inhibits neurogenesis, and maintains quiescent neural stem cells. In contrast, induction of Ascl1 oscillations activates neural stem cells and increases neurogenesis in the adult mouse brain. Thus, Ascl1 oscillations, which normally depend on Hes1 oscillations, regulate the active state, while high Hes1 expression and resultant Ascl1 suppression promote quiescence in neural stem cells.

Silicon nitride is used for many technological applications, but a quantitative knowledge of its surface chemistry is still lacking. Native oxynitride at the surface is generally removed using fluorinated etchants, but the chemical composition of surfaces still needs to be determined. In this work, the thinning (etching efficiency) of the layers after treatments in HF and NH4F solutions has been followed by using spectroscopic ellipsometry. A quantitative estimation of the chemical bonds found on the surface is obtained by a combination of infrared absorption spectroscopy in ATR mode, X-ray photoelectron spectroscopy, and colorimetry. Si–F bonds are the majority species present at the surface after silicon nitride etching; some Si–OH and a few Si–NHx bonds are also present. No Si–H bonds are present, an unfavorable feature for surface functionalization in view of the interest of such mildly reactive groups for achieving stable covalent grafting. Mechanisms are described to support the experimental results...

Summary Mutations in NIPBL are the most frequent cause of Cornelia de Lange syndrome (CdLS), a developmental disorder encompassing several neurological defects, including intellectual disability and seizures. How NIPBL mutations affect brain development is not understood. Here we identify Nipbl as a functional interaction partner of the neural transcription factor Zfp609 in brain development. Depletion of Zfp609 or Nipbl from cortical neural progenitors in vivo is detrimental to neuronal migration. Zfp609 and Nipbl overlap at genomic binding sites independently of cohesin and regulate genes that control cortical neuron migration. We find that Zfp609 and Nipbl interact with the Integrator complex, which functions in RNA polymerase 2 pause release. Indeed, Zfp609 and Nipbl co-localize at gene promoters containing paused RNA polymerase 2, and Integrator similarly regulates neuronal migration. Our data provide a rationale and mechanistic insights for the role of Nipbl in the neurological defects associated with CdLS., Highlights • Nipbl interacts with the transcription factor Zfp609 and the Integrator complex • Nipbl, Zfp609, and Integrator are required for cortical neuron migration • Nipbl, Zfp609, and Integrator co-occupy genomic binding sites independently of cohesin • Nipbl, Zfp609, and Integrator directly regulate neuronal migration genes, NIPBL mutations cause Cornelia de Lange syndrome, but Nipbl function in brain development is not well understood. Van den Berg et al. show that Nipbl interacts with Zfp609 and the Integrator complex to transcriptionally regulate cortical neuron migration.

Midbrain dopaminergic neurons are highly heterogeneous. They differ in their connectivity and firing patterns and, therefore, in their functional properties. The molecular underpinnings of this heterogeneity are largely unknown, and there is a paucity of markers that distinguish these functional subsets. In this paper, we report the identification and characterization of a novel subset of midbrain dopaminergic neurons located in the ventral tegmental area that expresses the basic helix-loop-helix transcription factor, Neurogenic Differentiation Factor-6 (NEUROD6). Retrograde fluorogold tracing experiments demonstrate thatNeurod6+midbrain dopaminergic neurons neurons project to two distinct septal regions: the dorsal and intermediate region of the lateral septum. Loss-of-function studies in mice demonstrate thatNeurod6and the closely related family memberNeurod1are both specifically required for the survival of this lateral-septum projecting neuronal subset during development. Our findings underscore the complex organization of midbrain dopaminergic neurons and provide an entry point for future studies of the functions of theNeurod6+subset of midbrain dopaminergic neurons.SIGNIFICANCE STATEMENTMidbrain dopaminergic neurons regulate diverse brain functions, including voluntary movement and cognitive and emotive behaviors. These neurons are heterogeneous, and distinct subsets are thought to regulate different behaviors. However, we currently lack the means to identify and modify gene function in specific subsets of midbrain dopaminergic neurons. In this study, we identify the transcription factor NEUROD6 as a specific marker for a novel subset of midbrain dopaminergic neurons in the ventral midbrain that project to the lateral septum, and we reveal essential roles forNeurod1andNeurod6in the survival of these neurons during development. Our findings highlight the molecular and anatomical heterogeneity of midbrain dopaminergic neurons and contribute to a better understanding of this functionally complex group of neurons.

In utero electroporation is a rapid and powerful technique to study the development of many brain regions. This approach presents several advantages over other methods to study specific steps of brain development in vivo, from proliferation to synaptic integration. Here, we describe in detail the individual steps necessary to carry out the technique. We also highlight the variations that can be implemented to target different cerebral structures and to study specific steps of development.

Summary During neurogenesis, progenitors switch from self-renewal to differentiation through the interplay of intrinsic and extrinsic cues, but how these are integrated remains poorly understood. Here, we combine whole-genome transcriptional and epigenetic analyses with in vivo functional studies to demonstrate that Bcl6, a transcriptional repressor previously reported to promote cortical neurogenesis, acts as a driver of the neurogenic transition through direct silencing of a selective repertoire of genes belonging to multiple extrinsic pathways promoting self-renewal, most strikingly the Wnt pathway. At the molecular level, Bcl6 represses its targets through Sirt1 recruitment followed by histone deacetylation. Our data identify a molecular logic by which a single cell-intrinsic factor represses multiple extrinsic pathways that favor self-renewal, thereby ensuring robustness of neuronal fate transition., Graphical Abstract, Highlights • Bcl6 ensures robust neurogenesis by repressing major extrinsic self-renewal pathways • Bcl6 inhibits the Notch, Wnt, SHH, and FGF signaling pathways at multiple levels • Bcl6 represses transcription through Sirt1 recruitment and histone deacetylation, Bonnefont et al. show that Bcl6 promotes neurogenesis by directly repressing genes belonging to the major signaling pathways promoting cortical progenitor self-renewal. These data indicate that a single cell-intrinsic factor represses multiple extrinsic signaling pathways to ensure irreversible neurogenic commitment.

Neural stem cells in the adult mammalian brain are the source of new neurons that contribute to complex sensory and cognitive functions. Most adult neural stem cells are maintained in a state of reversible cell cycle arrest, also called quiescence. Quiescent neural stem cells present a low rate of metabolic activity and a high sensitivity to their local signaling environment, and they can be activated by diverse physiological stimuli. The balance between stem cell quiescence and activity determines not only the rate of neurogenesis but also the long-term maintenance of the stem cell pool and the neurogenic capacity of the aging brain. In recent years, significant progress has been made in characterizing quiescent stem cells thanks to the introduction of new genomic and imaging techniques. We discuss in this review our current understanding of neural stem cell quiescence and its regulation by intrinsic and systemic factors.

Significance Midbrain dopamine neurons play a role in motivational and cognitive control of behavior. In addition, they regulate motor functions. Dysregulation of dopamine neurons has been linked to depression, schizophrenia, and addiction and their degeneration is causal to Parkinson’s disease. Peripheral hormones have been shown to regulate dopamine neurons functions. Insulin-like growth factor 1 (IGF-1) is a hormone mainly produced in the liver. With this study we discovered that midbrain dopamine neurons synthesize and release IGF-1 in an activity dependent manner. In addition, dopamine neuron-derived IGF-1 modulates dopamine synthesis and dopamine neuron firing and ultimately it controls dopamine-dependent behaviors. This study highlights the neuromodulatory role of neuron-derived IGF-1 and its role in shaping dopamine transmission in the brain., Midbrain dopamine neurons, which can be regulated by neuropeptides and hormones, play a fundamental role in controlling cognitive processes, reward mechanisms, and motor functions. The hormonal actions of insulin-like growth factor 1 (IGF-1) produced by the liver have been well described, but the role of neuronally derived IGF-1 remains largely unexplored. We discovered that dopamine neurons secrete IGF-1 from the cell bodies following depolarization, and that IGF-1 controls release of dopamine in the ventral midbrain. In addition, conditional deletion of dopamine neuron-derived IGF-1 in adult mice leads to decrease of dopamine content in the striatum and deficits in dopamine neuron firing and causes reduced spontaneous locomotion and impairments in explorative and learning behaviors. These data identify that dopamine neuron-derived IGF-1 acts as a regulator of dopamine neurons and regulates dopamine-mediated behaviors.

Quiescence is essential for the long-term maintenance of adult stem cells but how stem cells maintain quiescence is poorly understood. Here, we show that neural stem cells (NSCs) in the adult mouse hippocampus actively transcribe the pro-activation factor Ascl1 regardless of their activated or quiescent states. We found that the inhibitor of DNA binding protein Id4 is enriched in quiescent NSCs and that elimination of Id4 results in abnormal accumulation of Ascl1 protein and premature stem cell activation. Accordingly, Id4 and other Id proteins promote elimination of Ascl1 protein in NSC cultures. Id4 sequesters Ascl1 heterodimerization partner E47, promoting Ascl1 protein degradation and stem cell quiescence. Our results highlight the importance of non-transcriptional mechanisms for the maintenance of NSC quiescence and reveal a role for Id4 as a quiescence-inducing factor, in contrast with its role of promoting the proliferation of embryonic neural progenitors., eLife digest Stem cells in embryos give rise to all the tissues in the body. Adults also have stem cells, but they are fewer in number and they are usually dedicated to repairing and regenerating specific tissues. A region of the brain called the hippocampus, which is involved in learning, memory and mood, has a pool of neural stem cells. These cells can produce new brain cells long into adulthood, but maintaining their regenerative potential is a balancing act. Enough new brain cells need to be made to keep up with the brain’s demands, but if every stem cell matured into a brain cell, the brain’s capacity for repair would be lost. So, some neural stem cells hit a metaphorical snooze button to enter a resting state known as quiescence. Stem cells in the hippocampus make a protein called Ascl1 that interacts with DNA to switch on quiescent cells so they will divide and mature. Left unchecked, Ascl1 could deplete the stem cell supply, so resting stem cells must have a way to turn Ascl1 off, but it was previously unknown how. Clues point to the E proteins, which interact with Ascl1 to allow it to bind to DNA. If the E proteins are not present, Ascl1 cannot work as a genetic switch. E proteins can also interact with inhibitor of DNA binding/differentiation proteins, known as Id proteins for short. To find out whether Id proteins affect Ascl1 activity, Blomfield et al. looked at stem cells in the hippocampus of adult mice, and at quiescent stem cells grown in the laboratory. Blomfield et al. showed that all stem cells in the hippocampus make Ascl1, but its levels are much lower when stem cells are resting. This difference was down to an Id protein called Id4. In resting stem cells, Id4 interacted with E proteins, preventing them from binding to Ascl1, and stopping Ascl1 from ‘waking up’ the cells. This not only left Ascl1 unable to activate its target genes, it also made it vulnerable to destruction by the cell's protein recycling system. Mice with no Id4 in their hippocampus stem cells had higher levels of Ascl1, and their stem cells were more active. The number of stem cells in a resting state increases as we age, and in illnesses like depression, limiting brain cell replacement. Uncovering the signals that switch Id4 on or off could reveal why stem cells rest more with age and illness. This could help us find ways to kick-start the production of new brain cells in adulthood.

Summary Throughout life, adult neural stem cells (NSCs) produce new neurons and glia that contribute to crucial brain functions. Quiescence is an essential protective feature of adult NSCs; however, the establishment and maintenance of this state remain poorly understood. We demonstrate that in the adult zebrafish pallium, the brain-enriched miR-9 is expressed exclusively in a subset of quiescent NSCs, highlighting a heterogeneity within these cells, and is necessary to maintain NSC quiescence. Strikingly, miR-9, along with Argonaute proteins (Agos), is localized to the nucleus of quiescent NSCs, and manipulating their nuclear/cytoplasmic ratio impacts quiescence. Mechanistically, miR-9 permits efficient Notch signaling to promote quiescence, and we identify the RISC protein TNRC6 as a mediator of miR-9/Agos nuclear localization in vivo. We propose a conserved non-canonical role for nuclear miR-9/Agos in controlling the balance between NSC quiescence and activation, a key step in maintaining adult germinal pools., Graphical Abstract, Highlights • miR-9 highlights a state heterogeneity among adult quiescent neural stem cells (NSC) • miR-9 maintains NSC quiescence notably through permitting efficient Notch signaling • miR-9, along with Argonaute proteins, is present in the nucleus of adult quiescent NSCs • Active nucleo-cytoplasmic shuttling of miR-9/Ago impacts NSCs quiescence status, An essential protective feature of adult neural stem cells is their relative quiescence. Katz et al. identify microRNA-9 as crucial factor that maintains adult NSCs quiescence and sets a heterogeneity within these cells, through a non-canonical nuclear mode of action.

The development of multicellularity is a key evolutionary transition allowing for differentiation of physiological functions across a cell population that confers survival benefits; among unicellular bacteria, this can lead to complex developmental behaviors and the formation of higher-order community structures. Herein, we demonstrate that in the social δ-proteobacterium Myxococcus xanthus, the secretion of a novel biosurfactant polysaccharide (BPS) is spatially modulated within communities, mediating swarm migration as well as the formation of multicellular swarm biofilms and fruiting bodies. BPS is a type IV pilus (T4P)-inhibited acidic polymer built of randomly acetylated β-linked tetrasaccharide repeats. Both BPS and exopolysaccharide (EPS) are produced by dedicated Wzx/Wzy-dependent polysaccharide-assembly pathways distinct from that responsible for spore-coat assembly. While EPS is preferentially produced at the lower-density swarm periphery, BPS production is favored in the higher-density swarm interior; this is consistent with the former being known to stimulate T4P retraction needed for community expansion and a function for the latter in promoting initial cell dispersal. Together, these data reveal the central role of secreted polysaccharides in the intricate behaviors coordinating bacterial multicellularity., A study of the social bacterium Myxococcus xanthus reveals that the bacteria preferentially secrete specific polysaccharides within distinct zones of a swarm to facilitate spreading across a surface.