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SummaryNeural progenitor cells (NPCs) in the embryonic mammalian neocortex generate different neuronal subtypes sequentially. A long-standing hypothesis to account for this temporal fate specification process is that NPCs change their differentiation potential over time. However, the molecular mechanisms underlying these temporal changes in NPC properties are poorly understood. Here we show that Neurogenin1 and Neurogenin2 (Neurog1/2), two proneural transcription factors expressed in NPCs throughout cortical neurogenesis, specify the identity of one of the first cortical neuron subtypes generated, layer 6 cortico-thalamic neurons (CTNs). We found that Neurog1/2 specify the CTN fate through regulation of the cortical fate determinants Fezf2 and Foxp2 and that this Neurog-induced programme becomes inactive after the period of CTN production. Two independent mechanisms contribute to the arrest of CTN neuron generation at the end of layer 6 neurogenesis, including a reduction in the transcriptional activity of Neurog1/2 and the deposition of epigenetic repressive modifications mediated by Polycomb repressive complexes at the Foxp2 gene. Therefore, the duration of production of a cortical neuron subtype is controlled by multiple locking mechanisms involving both transcriptional and epigenetic processes.

SummaryDuring 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 and show that Bcl6, a transcriptional repressor known to promote neurogenesis, acts as a key 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 acts through both generic and pathway-specific mechanisms. Our data identify a molecular logic by which a single cell-intrinsic factor ensures robustness of neural cell fate transition by decreasing responsiveness to the extrinsic pathways that favor self-renewal.

International audience

We report experiments in which positronium (Ps) atoms were created in thin, porous silica films containing isolated voids with diameters ranging from 5 to 75 nm. Ps lifetimes in the pore structures were measured directly via time-delayed laser excitation of ${1}^{3}{S}_{1}\ensuremath{\rightarrow}{2}^{3}{P}_{J}$ transitions. In a film containing 5-nm pores Ps was predominantly emitted into vacuum, with a small component of confined Ps with a lifetime of 75 ns also observed. In films with larger pores Ps atoms were not emitted into vacuum except from the film surface, and confined Ps lifetimes of $\ensuremath{\approx}90$ ns were measured with no dependence on the pore size. However, for such large pores, extended Tao-Eldrup (ETE)-type models predict Ps lifetimes close to the 142-ns vacuum value. Moreover, ${1}^{3}{S}_{1}\ensuremath{\rightarrow}{2}^{3}{P}_{J}$ excitation of Ps atoms inside the pores was found to result in annihilation and exhibited an extremely broad $(\ensuremath{\approx}10$ THz) linewidth. We attribute these observations to a process in which nonthermal Ps atoms in the isolated voids become temporarily trapped in a series of surface states that dissociate following excitation. The occurrence of this mechanism is not necessarily apparent from ground-state Ps decay rates without some prior knowledge of the sample structure, and it precludes the application of ETE-type models as they do not take into account surface interactions other than pickoff annihilation.

The wavelength used during photochemical grafting of alkene onto silicon related surfaces influences molecular surface coverage. Ultraviolet light leads to apparent highly dense layers on UV absorbing materials due to the side reaction between alkenes resulting in strongly physisorbed dimers whereas higher wavelengths lead to dense and well-controlled layers.

Neural progenitors undergo temporal identity transitions to sequentially generate the neuronal and glial cells that make up the mature brain. Proneural genes have well-characterised roles in promoting neural cell differentiation and subtype specification, but they also regulate the timing of identity transitions through poorly understood mechanisms. Here, we investigated how the highly related proneural genes Neurog1 and Neurog2 interact to control the timing of neocortical neurogenesis. We found that Neurog1 acts in an atypical fashion as it is required to suppress rather than promote neuronal differentiation in early corticogenesis. In Neurog1 −/− neocortices, early born neurons differentiate in excess, whereas, in vitro , Neurog1 −/− progenitors have a decreased propensity to proliferate and form neurospheres . Instead, Neurog1 −/− progenitors preferentially generate neurons, a phenotype restricted to the Neurog2 + progenitor pool. Mechanistically, Neurog1 and Neurog2 heterodimerise, and while Neurog1 and Neurog2 individually promote neurogenesis, misexpression together blocks this effect. Finally, Neurog1 is also required to induce the expression of neurogenic factors ( Dll1 and Hes5 ) and to repress the expression of neuronal differentiation genes ( Fezf2 and Neurod6 ). Neurog1 thus employs different mechanisms to temper the pace of early neocortical neurogenesis.

SUMMARYQuiescence is essential for the long-term maintenance of adult stem cells and tissue homeostasis. However, how stem cells maintain quiescence is still poorly understood. Here we show that stem cells in the dentate gyrus of the adult hippocampus actively transcribe the pro-activation factor Ascl1 regardless of their activation state. We found that the inhibitor of DNA binding protein Id4 suppresses Ascl1 activity in neural stem cell cultures. Id4 sequesters Ascl1 heterodimerisation partner E47, promoting Ascl1 protein degradation and neural stem cell quiescence. Accordingly, elimination of Id4 from stem cells in the adult hippocampus results in abnormal accumulation of Ascl1 protein and premature stem cell activation. We also found that multiple signalling pathways converge on the regulation of Id4 to reduce the activity of hippocampal stem cells. Id4 therefore maintains quiescence of adult neural stem cells, in sharp contrast with its role of promoting the proliferation of embryonic neural progenitors.

Summary Direct lineage reprogramming induces dramatic shifts in cellular identity, employing poorly understood mechanisms. Recently, we demonstrated that expression of Neurog2 or Ascl1 in postnatal mouse astrocytes generates glutamatergic or GABAergic neurons. Here, we take advantage of this model to study dynamics of neuronal cell fate acquisition at the transcriptional level. We found that Neurog2 and Ascl1 rapidly elicited distinct neurogenic programs with only a small subset of shared target genes. Within this subset, only NeuroD4 could by itself induce neuronal reprogramming in both mouse and human astrocytes, while co-expression with Insm1 was required for glutamatergic maturation. Cultured astrocytes gradually became refractory to reprogramming, in part by the repressor REST preventing Neurog2 from binding to the NeuroD4 promoter. Notably, in astrocytes refractory to Neurog2 activation, the underlying neurogenic program remained amenable to reprogramming by exogenous NeuroD4. Our findings support a model of temporal hierarchy for cell fate change during neuronal reprogramming., Graphical Abstract, Highlights • Neurog2 and Ascl1 regulate largely non-overlapping neurogenic targets • A subset of genes is required and sufficient to convert astrocytes and fibroblasts • Neurog2 and REST compete for binding to the NeuroD4 promoter • REST deletion enhances Neurog2-mediated reprogramming in vitro, Masserdotti et al. analyzed early transcriptional changes mediated by Neurog2 and Ascl1 during direct reprogramming of murine postnatal astrocytes into distinct neuronal subtypes in vitro. This led to the identification of shared downstream targets, including NeuroD4, capable of neuronal reprogramming of fibroblasts and human astrocytes, as well as mechanistic insight into how the repressor REST functions as a barrier in direct neuronal reprogramming.

The gene regulatory network (GRN) that supports neural stem cell (NS cell) self-renewal has so far been poorly characterized. Knowledge of the central transcription factors (TFs), the noncoding gene regulatory regions that they bind to, and the genes whose expression they modulate will be crucial in unlocking the full therapeutic potential of these cells. Here, we use DNase-seq in combination with analysis of histone modifications to identify multiple classes of epigenetically and functionally distinct cis-regulatory elements (CREs). Through motif analysis and ChIP-seq, we identify several of the crucial TF regulators of NS cells. At the core of the network are TFs of the basic helix-loop-helix (bHLH), nuclear factor I (NFI), SOX, and FOX families, with CREs often densely bound by several of these different TFs. We use machine learning to highlight several crucial regulatory features of the network that underpin NS cell self-renewal and multipotency. We validate our predictions by functional analysis of the bHLH TF OLIG2. This TF makes an important contribution to NS cell self-renewal by concurrently activating pro-proliferation genes and preventing the untimely activation of genes promoting neuronal differentiation and stem cell quiescence.

A transparent glass or ceramic or glass-ceramic substrate, coated with a functional layer or with a stack of at least two functional layers, the functional layer or at least one of the functional layers of the stack being porous and made of an inorganic material M1, wherein the or at least one of the porous functional layer(s) of inorganic material M1 has, at the surface of at least one portion of the pores thereof, at least one inorganic material M2 different from M1.

Neural progenitors undergo temporal identity transitions to sequentially generate the neuronal and glial cells that make up the mature brain. Proneural genes have well-characterised roles in promoting neural cell differentiation and subtype specification, but they also regulate the timing of identity transitions through poorly understood mechanisms. Here, we investigated how the highly related proneural genes Neurog1 and Neurog2 interact to control the timing of neocortical neurogenesis. We found that Neurog1 acts in an atypical fashion as it is required to suppress rather than promote neuronal differentiation in early corticogenesis. In Neurog1−/− neocortices, early born neurons differentiate in excess, whereas, in vitro, Neurog1−/− progenitors have a decreased propensity to proliferate and form neurospheres. Instead, Neurog1−/− progenitors preferentially generate neurons, a phenotype restricted to the Neurog2+ progenitor pool. Mechanistically, Neurog1 and Neurog2 heterodimerise, and while Neurog1 and Neurog2 individually promote neurogenesis, misexpression together blocks this effect. Finally, Neurog1 is also required to induce the expression of neurogenic factors (Dll1 and Hes5) and to repress the expression of neuronal differentiation genes (Fezf2 and Neurod6). Neurog1 thus employs different mechanisms to temper the pace of early neocortical neurogenesis., Summary: Proneural genes are well known inducers of neurogenesis; however, Neurog1 induces the expression of Notch pathway genes and represses the expression of neuronal differentiation genes.

International audience; Proneural proteins, which include Ascl1, Atoh1 and Neurogenins e ´ piniè re in vertebrates and Achaete-Scute proteins and Atonal in Drosophila, are expressed in the developing nervous system throughout the animal kingdom and have an essential and well-characterised role in specifying the neural identity of progenitors. New properties and additional roles of these factors have emerged in recent years, including the regulation of stem cell proliferation and the capacity to reprogram many types of cells into neurons. This review will focus on these recent findings. The review will also discuss the mechanisms that allow proneural proteins to induce the transcription of their target genes in different chromatin contexts and the phosphorylation events and other post-transcriptional mechanisms that regulate the proneural proteins themselves.

Cet ouvrage de 71 pages est grand par la question qu’il pose en son titre « Les femmes peuvent-elles etre de Grands Hommes ? » et a laquelle il tente de repondre. Il est important dans ce qu’il enseigne « sur l’effacement des femmes de l’histoire, des arts et des sciences » comme l’indique son sous-titre. Il fait figure de livre manifeste. En cinq chapitres, la sociologue Christine Detrez nous convie a faire le point par un etat des lieux rude et sec, deconcertant, et nous invite a une prise...

Glia constitute the majority of cells in the mammalian central nervous system and are crucial for neurological function. However, there is an incomplete understanding of the molecular control of glial cell development. We find that the transcription factor Ascl1 (Mash1), which is best known for its role in neurogenesis, also functions in both astrocyte and oligodendrocyte lineages arising in the mouse spinal cord at late embryonic stages. Clonal fate mapping in vivo reveals heterogeneity in Ascl1-expressing glial progenitors and shows that Ascl1 defines cells that are restricted to either gray matter (GM) or white matter (WM) as astrocytes or oligodendrocytes. Conditional deletion of Ascl1 post-neurogenesis shows that Ascl1 is required during oligodendrogenesis for generating the correct numbers of WM but not GM oligodendrocyte precursor cells, whereas during astrocytogenesis Ascl1 functions in balancing the number of dorsal GM protoplasmic astrocytes with dorsal WM fibrous astrocytes. Thus, in addition to its function in neurogenesis, Ascl1 marks glial progenitors and controls the number and distribution of astrocytes and oligodendrocytes in the GM and WM of the spinal cord.

We recently investigated the prognostic impact of a Chronic Care Model (CCM)-based healthcare program applied in primary care in Tuscany Region mainly run by multidisciplinary teams composed of general practitioners (GPs) and nurses. The project included proactively planned follow-up visits for each patient, individualized counselling to optimize lifestyle modifications and adherence to appropriate diagnostic and therapeutic pathways. 1761 patients with Chronic heart failure (CHF) directly enrolled by the GPs were matched with 3522 CHF controls not involved in the project. Over a 4-year follow-up in the CCM group a higher CHF hospitalization rate was found (12.1 vs 10.3 events/100 patient-years; incidence rate ratio [IRR] 1.15, p=0.0030), whereas mortality was lower (10.8 vs 12.6 events/100 patient-years; IRR 0.82, p0.0001). The CCM status was independently associated with a 34% increase in the risk of CHF hospitalization and a 18% reduction in the risk of death (p0.0001 for both). The CCM status was associated with a 50% increase in the rate of planned Heart failure (HF) hospitalizations whereas the rate of 1-month CHF readmissions showed no differences. Such a divergent trend could be explained by the direct involvement of GPs in the CCM program, leading them to a better awareness of patients' clinical status, and then to a more frequent use of clinical pathways and facilities, including hospitalization. It is reasonable to argue that not all hospitalizations must necessarily be considered as a poor outcome, as they often provide additional opportunities to improve therapies, optimize patient education, or define follow-up strategies. The evidence of a divergent trend between mortality and hospitalization in our population might support the clinical importance of a multidisciplinary approach for the management of patients with HF.

SummaryDirect lineage reprogramming is a promising approach for human disease modeling and regenerative medicine, with poorly understood mechanisms. Here, we reveal a hierarchical mechanism in the direct conversion of fibroblasts into induced neuronal (iN) cells mediated by the transcription factors Ascl1, Brn2, and Myt1l. Ascl1 acts as an “on-target” pioneer factor by immediately occupying most cognate genomic sites in fibroblasts. In contrast, Brn2 and Myt1l do not access fibroblast chromatin productively on their own; instead, Ascl1 recruits Brn2 to Ascl1 sites genome wide. A unique trivalent chromatin signature in the host cells predicts the permissiveness for Ascl1 pioneering activity among different cell types. Finally, we identified Zfp238 as a key Ascl1 target gene that can partially substitute for Ascl1 during iN cell reprogramming. Thus, a precise match between pioneer factors and the chromatin context at key target genes is determinative for transdifferentiation to neurons and likely other cell types.

SummaryFOXO transcription factors are central regulators of longevity from worms to humans. FOXO3, the FOXO isoform associated with exceptional human longevity, preserves adult neural stem cell pools. Here, we identify FOXO3 direct targets genome-wide in primary cultures of adult neural progenitor cells (NPCs). Interestingly, FOXO3-bound sites are enriched for motifs for bHLH transcription factors, and FOXO3 shares common targets with the proneuronal bHLH transcription factor ASCL1/MASH1 in NPCs. Analysis of the chromatin landscape reveals that FOXO3 and ASCL1 are particularly enriched at the enhancers of genes involved in neurogenic pathways. Intriguingly, FOXO3 inhibits ASCL1-dependent neurogenesis in NPCs and direct neuronal conversion in fibroblasts. FOXO3 also restrains neurogenesis in vivo. Our study identifies a genome-wide interaction between the prolongevity transcription factor FOXO3 and the cell-fate determinant ASCL1 and raises the possibility that FOXO3’s ability to restrain ASCL1-dependent neurogenesis may help preserve the neural stem cell pool.

International audience; Porous sol-gel silica monoliths are prepared using PMMA nanoparticles, 60 nm in diameter, as sacrificial templates. The pore-structure of the calcined pellets is investigated through nitrogen adsorption to assess the evolution of the porosity when varying the amount of porogen. The latex templated monoliths present a well defined spherical extrinsic porosity and an intrinsic microporosity due to preparation process. As a result of a careful analysis of the adsorption hysteresis, we identify a percolation threshold of the spherical porosity around 30% volume fraction. This phenomenon, similar to the percolation previously observed in latex-templated silica films, opens the way to the use of latex-templated porous silica monoliths with a tailorable and reliable pore structure.

A travers un exercice périlleux d’égo-histoire, cette contribution sur le groupe Bérurier Noir s’attache à présenter des aspects culturels et politiques de la genèse du groupe alternatif des années 1980. L’auteur a privilégié une perspective culturelle qui permet de mieux comprendre les sources d’inspiration des chansons et des thématiques portées par ce groupe musical entre 1983 et 1989. Au fil de quatre temps forts, les lecteurs sont plongés dans un tourbillon d’actions débutant au lycée Paul Valéry (Paris 12e), se poursuivant dans la rue sur le Parvis Beaubourg, les squatts et l’Usine Pali-Kao, pour investir le Zénith de Paris en mars 1988, le Québec et finalement l’Olympia les 9, 10 et 11 novembre 1989 alors que le mur de Berlin tombe. Sur le plan culturel, l’imaginaire élaboré par Bérurier Noir au fil de son existence est dévoilé : du cinéma d’avant-garde japonais aux films politiques européens, de la bande à Baader-Meinhof à l’association Actes Energie Perdue, de la boutique Harry Cover (aux Halles) aux dojos de Karaté, du « No future » au « Yes future », du noir & blanc à la couleur. En outre, l’Asie apparaît comme le fil conducteur invisible d’une expérience plus personnelle. Cette contribution peut se concevoir comme un essai d’interprétation d’une histoire culturelle en construction. Through a perilous exercise of ego-history, this contribution seeks to present cultural and political aspects of the genesis of Bérurier Noir, the famous French alternative musical band of the 1980s. In order to better understanding the sources of inspiration of songs and themes carried by this group between 1983 and 1989, the author have privileged a cultural perspective. By four highlights, readers are immersed in a whirlwind of actions debuting at lycée Paul Valéry (Paris 12th district), continuing in the streets of Paris in alternative and artistic places, in the Zenith in March 1988, in Quebec (Canada) and finally at the Olympia concert hall on the 9, 10 and 11 November 1989 when the Berlin Wall fell. Culturally, the imaginary developed by Bérurier Noir throughout its existence is unveiled: Japanese avant-garde cinema and European political films, the Baader-Meinhof group influence and the artistic association Actes Energie Perdue, from the Harry Cover shop (Les Halles in the centre of Paris) to Karate dojos, from "No future" to "future Yes", from black & white to color. In addition, Asia emerges as the invisible thread of a more personal experience. This contribution can be seen as a tentative interpretation of a cultural history in progress.

Neuronal migration is a fundamental process of brain development, and its disruption underlies devastating neurodevelopmental disorders. The transcriptional programs governing this process are relatively well characterized. However, how environmental cues instruct neuronal migration remains poorly understood. Here, we demonstrate that the cannabinoid CB1 receptor is strictly required for appropriate pyramidal neuron migration in the developing cortex. Acute silencing of the CB1 receptor alters neuronal morphology and impairs radial migration. Consequently, CB1 siRNA-electroporated mice display cortical malformations mimicking subcortical band heterotopias and increased seizure susceptibility in adulthood. Importantly, rescuing the CB1 deficiency-induced radial migration arrest by knockdown of the GTPase protein RhoA restored the hyperexcitable neuronal network and seizure susceptibility. Our findings show that CB1 receptor/RhoA signaling regulates pyramidal neuron migration, and that deficient CB1 receptor signaling may contribute to cortical development malformations leading to refractory epilepsy independently of its canonical neuromodulatory role in the adult brain.

Brain electroporation is a rapid and powerful approach to study neuronal development. In particular, this technique has become a method of choice for studying the process of radial migration of projection neurons in the embryonic cerebral cortex. This method has considerably helped to describe in detail the different steps of radial migration and to characterize the molecular mechanisms controlling this process. Delineating the complexities of neuronal migration is critical to our understanding not only of normal cerebral cortex formation but also of neurodevelopmental disorders resulting from neuronal migration defects. Here, we describe in detail the protocols to perform in utero or ex vivo electroporation of progenitor cells in the ventricular zone of the cerebral cortex with the aim of studying the process of radial migration of projection neurons during embryonic development. © 2016 by John Wiley & Sons, Inc.

The T-box containing Tbr2 gene encodes for a transcription factor essential for the specification of the intermediate neural progenitors (INPs) originating the excitatory neurons of the cerebral cortex. However, its overall mechanism of action, direct target genes and cofactors remain unknown. Herein, we carried out global gene expression profiling combined with genome-wide binding site identification to determine the molecular pathways regulated by TBR2 in INPs. This analysis led to the identification of novel protein-protein interactions that control multiple features of INPs including cell-type identity, morphology, proliferation and migration dynamics. In particular, NEUROG2 and JMJD3 were found to associate with TBR2 revealing unexplored TBR2-dependent mechanisms. These interactions can explain, at least in part, the role of this transcription factor in the implementation of the molecular program controlling developmental milestones during corticogenesis. These data identify TBR2 as a major determinant of the INP-specific traits by regulating both genetic and epigenetic pathways.

International audience; Evidence before this study We searched PubMed on June 30, 2016, for English-language cohort studies published since Jan 1, 1980, of patients with invasive listeriosis worldwide with the keywords " listeria " , " listeriosis " , " maternal " , and " neurolisteriosis ". Studies had to include epidemiological or clinical data on listeriosis. All clinical forms of infection were included (bacteraemia, neurolisteriosis, and maternal–neonatal infection). Host risk factors for listeriosis have been well identified, but the clinical features and prognostic factors of the disease are based on retrospective studies compiling heterogeneous data or random collected cases. Furthermore, no clinical trial has ever been done and medical management is not evidence based. Added value of the study Our study is the first prospective clinical study focusing on all forms of invasive listeriosis. The study is based on a national mandatory system that allowed the nearly complete capture of microbiologically proven cases. The study shows a higher burden of listeriosis than reported before: more than 80% of infected mothers experienced major fetal or neonatal complications (fetal loss, very high prematurity, early or late onset disease); only 39% of patients with neurolisteriosis survived and fully recovered. The study provides important new data to improve management and predict outcome in listeriosis, such as determination of the time window for fetal losses (

The enteric nervous system (ENS) is organized into neural circuits within the gastrointestinal wall where it controls the peristaltic movements, secretion, and blood flow. Although proper gut function relies on the complex neuronal composition of the ENS, little is known about the transcriptional networks that regulate the diversification into different classes of enteric neurons and glia during development. Here we redefine the role of Ascl1 (Mash1), one of the few regulatory transcription factors described during ENS development. We show that enteric glia and all enteric neuronal subtypes appear to be derived from Ascl1-expressing progenitor cells. In the gut ofAscl1−/−mutant mice, neurogenesis is delayed and reduced, and posterior gliogenesis impaired. The ratio of neurons expressing Calbindin, TH, and VIP is selectively decreased while, for instance, 5-HT+neurons, which previously were believed to be Ascl1-dependent, are formed in normal numbers. Essentially the same differentiation defects are observed inAscl1KINgn2transgenic mutants, where the proneural activity of Ngn2 replaces Ascl1, demonstrating that Ascl1 is required for the acquisition of specific enteric neuronal subtype features independent of its role in neurogenesis. In this study, we provide novel insights into the expression and function of Ascl1 in the differentiation process of specific neuronal subtypes during ENS development.SIGNIFICANCE STATEMENTThe molecular mechanisms underlying the generation of different neuronal subtypes during development of the enteric nervous system are poorly understood despite its pivotal function in gut motility and involvement in gastrointestinal pathology. This report identifies novel roles for the transcription factor Ascl1 in enteric gliogenesis and neurogenesis. Moreover, independent of its proneurogenic activity, Ascl1 is required for the normal expression of specific enteric neuronal subtype characteristics. Distinct enteric neuronal subtypes are formed in a temporally defined order, and we observe that the early-born 5-HT+neurons are generated inAscl1−/−mutants, despite the delayed neurogenesis. Enteric nervous system progenitor cells may therefore possess strong intrinsic control over their specification at the initial waves of neurogenesis.

The generation and specification of pyramidal neuron subpopulations during development relies on a complex network of transcription factors. The CB1cannabinoid receptor is the major molecular target of endocannabinoids and marijuana active compounds. This receptor has been shown to influence neural progenitor proliferation and axonal growth, but its involvement in neuronal differentiation and the functional impact in the adulthood caused by altering its signaling during brain development are not known. Here we show that the CB1receptor, by preventing Satb2 (special AT-rich binding protein 2)-mediated repression, increased Ctip2 (COUP-TF interacting protein 2) promoter activity, and Ctip2-positive neuron generation. Unbalanced neurogenic fate determination found in completeCB1−/−mice and in glutamatergic neuron-specificNex–CB1−/−mice induced overt alterations in corticospinal motor neuron generation and subcerebral connectivity, thereby resulting in an impairment of skilled motor function in adult mice. Likewise, genetic deletion of CB1receptors inThy1–YFP–Hmice elicited alterations in corticospinal tract development. Altogether, these data demonstrate that the CB1receptor contributes to the generation of deep-layer cortical neurons by coupling endocannabinoid signals from the neurogenic niche to the intrinsic proneurogenic Ctip2/Satb2 axis, thus influencing appropriate subcerebral projection neuron specification and corticospinal motor function in the adulthood.

International audience; From its creation with the strong support of General de Lattre until the end of the Indochina War in 1954, the National Army of Vietnam ('Quan doi quoc gia Viet Nam') underwent impressive development. This 'new unified army' (entitled Forces Armées du Viet Nam, FAVN) was present in all the battles from 1951, especially in the North in operations against the main Viet-Minh divisions. Its five Vietnamese paratrooper battalions, known as the 'Bawouan', distinguished themselves in major military operations in the Red River delta as well as the historic battle of Dien Bien Phu. Other military formations, such as the capital battalions in the North or the local armies in the South (Binh Xuyen, Cao Dai, Hoa Hao, and UMDC) played important roles in the pacification of the two deltas. This article explores the emergence, development, and transformation of this defeated army and considers what the experience of war might have been from the point of view of its soldiers, offering a glimpse into a neglected social dimension of this conflict for the decolonization of Vietnam.

By serving as the sole output of the cerebellar cortex, integrating a myriad of afferent stimuli, Purkinje cells (PCs) constitute the principal neuron in cerebellar circuits. Several neurodegenerative cerebellar ataxias feature a selective cell-autonomous loss of PCs, warranting the development of regenerative strategies. To date, very little is known as to the regulatory cascades controlling PC development. During central nervous system development, the proneural gene neurogenin 2 (Neurog2) contributes to many distinct neuronal types by specifying their fate and/or dictating development of their morphological features. By analyzing a mouse knock-in line expressing Cre recombinase under the control of Neurog2 cis-acting sequences we show that, in the cerebellar primordium, Neurog2 is expressed by cycling progenitors cell-autonomously fated to become PCs, even when transplanted heterochronically. During cerebellar development, Neurog2 is expressed in G1 phase by progenitors poised to exit the cell cycle. We demonstrate that, in the absence of Neurog2, both cell-cycle progression and neuronal output are significantly affected, leading to an overall reduction of the mature cerebellar volume. Although PC fate identity is correctly specified, the maturation of their dendritic arbor is severely affected in the absence of Neurog2, as null PCs develop stunted and poorly branched dendrites, a defect evident from the early stages of dendritogenesis. Thus, Neurog2 represents a key regulator of PC development and maturation.

Neurogenin 2 (Ngn2) controls neuronal differentiation cell-autonomously by transcriptional activation of targets such as NeuroD, while simultaneously controlling progenitor maintenance non-cell-autonomously by upregulating Delta expression and Notch signalling. Reduction in Cdk-dependent multisite phosphorylation of Ngn2 enhances its promoter binding affinity. This leads specifically to an increase in neuronal differentiation without an apparent increase in progenitor maintenance via Delta-Notch signalling, although the mechanism underlying this imbalance remains unclear. Here we show in Xenopus embryos and mouse P19 cells that the NeuroD promoter is substantially more sensitive to the phosphorylation status of Ngn2 than the Delta promoter, and that this can be attributed to differences in the ease of promoter activation. In addition, we also show that the phosphorylation status of Ngn2 regulates sensitivity to Notch signalling. These observations explain how Ngn2 post-translational modification in response to changes in the cell cycle kinase environment results in enhanced neuronal differentiation upon cell cycle lengthening.

During development of the central nervous system, the transition from progenitor maintenance to differentiation is directly triggered by a lengthening of the cell cycle that occurs as development progresses. However, the mechanistic basis of this regulation is unknown. The proneural transcription factor Neurogenin 2 (Ngn2) acts as a master regulator of neuronal differentiation. Here, we demonstrate that Ngn2 is phosphorylated on multiple serine-proline sites in response to rising cyclin-dependent kinase (cdk) levels. This multi-site phosphorylation results in quantitative inhibition of the ability of Ngn2 to induce neurogenesis in vivo and in vitro. Mechanistically, multi-site phosphorylation inhibits binding of Ngn2 to E box DNA, and inhibition of DNA binding depends on the number of phosphorylation sites available, quantitatively controlling promoter occupancy in a rheostat-like manner. Neuronal differentiation driven by a mutant of Ngn2 that cannot be phosphorylated by cdks is no longer inhibited by elevated cdk kinase levels. Additionally, phosphomutant Ngn2-driven neuronal differentiation shows a reduced requirement for the presence of cdk inhibitors. From these results, we propose a model whereby multi-site cdk-dependent phosphorylation of Ngn2 interprets cdk levels to control neuronal differentiation in response to cell cycle lengthening during development.

The generation of a functional nervous system involves a multitude of steps that are controlled by just a few families of extracellular signaling molecules. Among these, the fibroblast growth factor (FGF) family is particularly prominent for the remarkable diversity of its functions. FGFs are best known for their roles in the early steps of patterning of the neural primordium and proliferation of neural progenitors. However, other equally important functions have emerged more recently, including in the later steps of neuronal migration, axon navigation, and synaptogenesis. We review here these diverse functions and discuss the mechanisms that account for this unusual range of activities. FGFs are essential components of most protocols devised to generate therapeutically important neuronal populations in vitro or to stimulate neuronal repair in vivo. How FGFs promote the development of the nervous system and maintain its integrity will thus remain an important focus of research in the future.

Two recently generated targeted mouse alleles of the neurogenic gene Ascl1 were used to characterize cerebellum circuit formation. First, genetic inducible fate mapping (GIFM) with an Ascl1(CreER) allele was found to specifically mark all glial and neuron cell types that arise from the ventricular zone (vz). Moreover, each cell type has a unique temporal profile of marking with Ascl1(CreER) GIFM. Of great utility, Purkinje cells (Pcs), an early cohort of Bergmann glia, and four classes of GABAergic interneurons can be genetically birth dated during embryogenesis using Ascl1(CreER) GIFM. Astrocytes and oligodendrocytes, in contrast, express Ascl1(CreER) throughout their proliferative phase in the white matter. Interestingly, the final position each neuron type acquires differs depending on when it expresses Ascl1. Interneurons (including candelabrum) attain a more outside position the later they express Ascl1, whereas Pcs have distinct settling patterns each day they express Ascl1. Second, using a conditional Ascl1 allele, we discovered that Ascl1 is differentially required for generation of most vz-derived cells. Mice lacking Ascl1 in the cerebellum have a major decrease in three types of interneurons with a tendency toward a loss of later-born interneurons, as well as an imbalance of oligodendrocytes and astrocytes. Double-mutant analysis indicates that a related helix-loop-helix protein, Ptf1a, functions with Ascl1 in generating interneurons and Pcs. By fate mapping vz-derived cells in Ascl1 mutants, we further discovered that Ascl1 plays a specific role during the time period when Pcs are generated in restricting vz progenitors from becoming rhombic lip progenitors.

12 p., 8 figures and references., The decision of a neural precursor to stop dividing and begin its terminal differentiation at the correct place, and at the right time, is a crucial step in the generation of cell diversity in the nervous system. Here, we show that the Down’s syndrome candidate gene (Mnb/Dyrk1a) is transiently expressed in prospective neurons of vertebrate CNS neuroepithelia. The gain of function (GoF) of Mnb/Dyrk1a induced proliferation arrest. Conversely, its loss of function (LoF) caused over proliferation and cell death. We found that MNB/DYRK1A is both necessary and sufficient to upregulate, at transcriptional level, the expression of the cyclin-dependent kinase inhibitor p27KIP1 in the embryonic chick spinal cord and mouse telencephalon, supporting a regulatory role for MNB/DYRK1A in cell cycle exit of vertebrate CNS neurons. All these actions required the kinase activity of MNB/DYRK1A. We also observed that MNB/DYRK1A is co-expressed with the NOTCH ligand Delta1 in single neuronal precursors. Furthermore, we found that MNB/DYRK1A suppressed NOTCH signaling, counteracted the pro-proliferative action of the NOTCH intracellular domain (NICD), stimulated Delta1 expression and was required for the neuronal differentiation induced by the decrease in NOTCH signaling. Nevertheless, although Mnb/Dyrk1a GoF led to extensive withdrawal of neuronal precursors from the cell cycle, it was insufficient to elicit their differentiation. Remarkably, a transient (ON/OFF) Mnb/Dyrk1a GoF efficiently induced neuronal differentiation. We propose that the transient expression of MNB/DYRK1A in neuronal precursors acts as a binary switch, coupling the end of proliferation and the initiation of neuronal differentiation by upregulating p27KIP1 expression and suppressing NOTCH signaling., This work was supported by Deutsche Forschungsgemeinschaft grants (BE 1967/2-1) to W.B. and (SFB-870) J.G., by a grant in aid from the Medical Research Council (U117570528) to F.G., by grants from the Spanish Ministry of Science and Innovation, the Generalitat Valenciana and the Fundación Inocente Inocente to F.J.T., and by a join grant from the Fondation Jerôme Lejeune to W.B. and F.J.T. B.H. was recipient of two Travel-Fellowships of the Generalitat Valenciana.

BackgroundWhile the diversity and spatio-temporal origin of olfactory bulb (OB) GABAergic interneurons has been studied in detail, much less is known about the subtypes of glutamatergic OB interneurons.ResultsWe studied the temporal generation and diversity of Neurog2-positive precursor progeny using an inducible genetic fate mapping approach. We show that all subtypes of glutamatergic neurons derive from Neurog2 positive progenitors during development of the OB. Projection neurons, that is, mitral and tufted cells, are produced at early embryonic stages, while a heterogeneous population of glutamatergic juxtaglomerular neurons are generated at later embryonic as well as at perinatal stages. While most juxtaglomerular neurons express the T-Box protein Tbr2, those generated later also express Tbr1. Based on morphological features, these juxtaglomerular cells can be identified as tufted interneurons and short axon cells, respectively. Finally, targeted electroporation experiments provide evidence that while the majority of OB glutamatergic neurons are generated from intrabulbar progenitors, a small portion of them originate from extrabulbar regions at perinatal ages.ConclusionsWe provide the first comprehensive analysis of the temporal and spatial generation of OB glutamatergic neurons and identify distinct populations of juxtaglomerular interneurons that differ in their antigenic properties and time of origin.

International audience; Vascular-specific growth factor angiopoietin-2 (Ang2) is mainly involved during vascular network setup. Recently, Ang2 was suggested to play a role in adult neurogenesis, affecting migration and differentiation of adult neuroblasts in vitro. However, to date, no data have reported an effect of Ang2 on neurogenesis during embryonic development. As we detected Ang2 expression in the developing cerebral cortex at embryonic day E14.5 and E16.5, we used in utero electroporation to knock down $Ang2$ expression in neuronal progenitors located in the cortical ventricular zone (VZ) to examine the role of Ang2 in cortical embryonic neurogenesis. Using this strategy, we showed that radial migration from the VZ toward the cortical plate of $Ang2$-knocked down neurons is altered as well as their morphology. In parallel, we observed a perturbation of intermediate progenitor population and the surrounding vasculature. Taken together, our results show for the first time that, in addition to its role during brain vasculature setup, Ang2 is also involved in embryonic cortical neurogenesis and especially in the radial migration of projection neurons.

The wiring of the nervous system arises from extensive directional migration of neuronal cell bodies and growth of processes that, somehow, end up forming functional circuits. Thus far, this feat of biological engineering appears to rely on sequences of pathfinding decisions upon local cues, each with little relationship to the anatomical and physiological outcome. Here, we uncover a straightforward cellular mechanism for circuit building whereby a neuronal type directs the development of its future partners. We show that visceral afferents of the head (that innervate taste buds) provide a scaffold for the establishment of visceral efferents (that innervate salivatory glands and blood vessels). In embryological terms, sensory neurons derived from an epibranchial placode—that we show to develop largely independently from the neural crest—guide the directional outgrowth of hindbrain visceral motoneurons and control the formation of neural crest–derived parasympathetic ganglia.

International audience; Cajal-Retzius (CR) cells play a key role in the formation of the cerebral cortex. These pioneer neurons are distributed throughout the cortical marginal zone in distinct graded distributions. Fate mapping and cell lineage tracing studies have recently shown that CR cells arise from restricted domains of the pallial ventricular zone, which are associated with signalling centres involved in the early regionalisation of the telencephalic vesicles. In this study, we identified a subpopulation of CR cells in the rostral telencephalon that expresses Er81, a downstream target of Fgf8 signalling. We investigated the role of the rostral telencephalic patterning centre, which secretes FGF molecules, in the specification of these cells. Using pharmacological inhibitors and genetic inactivation of Fgf8, we showed that production of Fgf8 by the rostral telencephalic signalling centre is required for the specification of the Er81+ CR cell population. Moreover, the analysis of Fgf8 gain-of-function in cultivated mouse embryos and of Emx2 and Gli3 mutant embryos revealed that ectopic Fgf8 signalling promotes the generation of CR cells with a rostral phenotype from the dorsal pallium. These data showed that Fgf8 signalling is both required and sufficient to induce rostral CR cells. Together, our results shed light on the mechanisms specifying rostral CR cells and further emphasise the crucial role of telencephalic signalling centres in the generation of distinct CR cell populations.

This paper examines the history of an unknown “mass murder” perpetrated in 1947 in Southern Vietnam by the Viet Minh forces. It was organized in the outskirts of Saigon, mainly against Cao Dai and Hoa Hao religious forces that were portrayed as “reactionary” during their political revolutionary trials. Before presenting and analyzing the data of nearly 900 victims, the paper briefly presents the social, political and military conquest and context of French Cochinchina, as well as explains the political and military ambitions of the Viet Minh forces after the advent of the Democratic Republic of Vietnam in Hanoi on September 2, 1945. The focal point of this article is the review of the data related to the massacre and its uses, i.e.what they can reveal about the course of the massacre, its actors and victims. Finally, the paper's last section assesses the official historiography of the massacre, which has been recognized by the current regime in a 'soft' mea culpa. In conclusion, this article discusses the issue of violence in Southern Vietnam and its consequences for the Socialist Republic of Vietnam in a more long term perspective.

An important feature of the cerebral cortex is its layered organization, which is modulated in an area-specific manner. We found that the transcription factor AP2gamma regulates laminar fate in a region-specific manner. Deletion of AP2gamma (also known as Tcfap2c) during development resulted in a specific reduction of upper layer neurons in the occipital cortex, leading to impaired function and enhanced plasticity of the adult visual cortex. AP2gamma functions in apical progenitors, and its absence resulted in mis-specification of basal progenitors in the occipital cortex at the time at which upper layer neurons were generated. AP2gamma directly regulated the basal progenitor fate determinants Math3 (also known as Neurod4) and Tbr2, and its overexpression promoted the generation of layer II/III neurons in a time- and region-specific manner. Thus, AP2gamma acts as a regulator of basal progenitor fate, linking regional and laminar specification in the mouse developing cerebral cortex.

Extracellular stimuli regulate neuronal differentiation and subtype specification during brain development, although the intracellular signaling pathways that mediate these processes remain largely unclear. We now show that the PDK1-Akt pathway regulates differentiation of telencephalic neural precursor cells (NPCs). Active Akt promotes differentiation of NPC into γ-aminobutyric acid-containing (GABAergic) but not glutamatergic neurons. Disruption of the Pdk1 gene or expression of dominant-negative forms of Akt suppresses insulin-like growth factor (IGF)-1 enhancement of NPC differentiation into neurons in vitro and production of neocortical GABAergic neurons in vivo. Furthermore, active Akt increased the protein levels and transactivation activity of Mash1, a proneural basic helix-loop-helix protein required for the generation of neocortical GABAergic neurons, and Mash1 was required for Akt-induced neuronal differentiation. These results have unveiled an unexpected role of the PDK1-Akt pathway: a key mediator of extracellular signals regulating the production of neocortical GABAergic neurons.

Self-renewal and proliferation of neural stem cells and the decision to initiate neurogenesis are the crucial events directing brain development. Here we show that the ubiquitin ligase Huwe1 operates upstream of the N-Myc-DLL3-Notch pathway to control neural stem cell activity and promote neurogenesis. Conditional inactivation of the Huwe1 gene in the mouse brain caused neonatal lethality associated with disorganization of the laminar patterning of the cortex. These defects stemmed from severe impairment of neurogenesis associated with uncontrolled expansion of the neural stem cell compartment. Loss and gain of function experiments for Huwe1 in the mouse cortex demonstrated that Huwe1 restrains proliferation and enables neuronal differentiation by suppressing the N-Myc-DLL3 cascade. Notably, human high-grade gliomas carry focal hemizygous deletions of the X-linked Huwe1 gene in association with amplification of the N-myc locus. Our results indicate that Huwe1 is a master regulator of the balance between proliferation and neurogenesis in the developing brain and this pathway is subverted in malignant brain tumors.

International audience; A central issue during embryonic development is to define how different signals cooperate in generating unique cell types. To address this issue, we focused on the function and the regulation of the proneural gene Neurogenin2 (Neurog2) during early mouse spinal neurogenesis. We showed that Neurog2 is first expressed in cells within the neural plate anterior to the node from the 5 somite-stage. The analysis of Neurog2 mutants established a role for this gene in triggering neural differentiation during spinal cord elongation. We identified a 798 base pair enhancer element (Neurog2-798) upstream of the Neurog2 coding sequence that directs the early caudal expression of Neurog2. Embryo culture experiments showed that Retinoic Acid (RA), Sonic hedgehog (Shh) and Fibroblast Growth Factor signals act in concert on this enhancer to control the spatial and temporal induction of Neurog2. We further demonstrated by transgenesis that two RA response elements and a Gli binding site within the Neurog2-798 element are absolutely required for its activity, strongly suggesting that the regulation of Neurog2 early expression by RA and Shh signals is direct. Our data thus support a model where signal integration at the level of a single enhancer constitutes a key mechanism to control the onset of neurogenesis.

Motility is a universal property of newly generated neurons. How cell migration is coordinately regulated with other aspects of neuron production is not well understood. Here we show that the proneural protein neurogenin 2 (Neurog2), which controls neurogenesis in the embryonic cerebral cortex1,2, directly induces the expression of the small GTP-binding protein Rnd2 (ref. 3) in newly generated mouse cortical neurons before they initiate migration. Rnd2 silencing leads to a defect in radial migration of cortical neurons similar to that observed when the Neurog2 gene is deleted. Remarkably, restoring Rnd2 expression in Neurog2-mutant neurons is sufficient to rescue their ability to migrate. Our results identify Rnd2 as a novel essential regulator of neuronal migration in the cerebral cortex and demonstrate that Rnd2 is a major effector of Neurog2 function in the promotion of migration. Thus, a proneural protein controls the complex cellular behaviour of cell migration through a remarkably direct pathway involving the transcriptional activation of a small GTP-binding protein.

Endocannabinoids (eCBs) have recently been identified as axon guidance cues shaping the connectivity of local GABAergic interneurons in the developing cerebrum. However, eCB functions during pyramidal cell specification and establishment of long-range axonal connections are unknown. Here, we show that eCB signaling is operational in subcortical proliferative zones from embryonic day 12 in the mouse telencephalon and controls the proliferation of pyramidal cell progenitors and radial migration of immature pyramidal cells. When layer patterning is accomplished, developing pyramidal cells rely on eCB signaling to initiate the elongation and fasciculation of their long-range axons. Accordingly, CB 1 cannabinoid receptor (CB 1 R) null and pyramidal cell-specific conditional mutant (CB 1 R f/f,NEX-Cre ) mice develop deficits in neuronal progenitor proliferation and axon fasciculation. Likewise, axonal pathfinding becomes impaired after in utero pharmacological blockade of CB 1 Rs. Overall, eCBs are fundamental developmental cues controlling pyramidal cell development during corticogenesis.

The dentate gyrus (DG) of the hippocampus has a central role in learning and memory in adult rodents. The DG is generated soon after birth, although new neurons continue to be generated in the DG throughout life. The proneural factors Mash1 (Ascl1) and neurogenin 2 (Ngn2) are expressed during formation of the DG but their role in the development of this structure has not yet been addressed. Here, we show that Ngn2 is essential for the development of the DG. Ngn2 mutant mice have fewer DG progenitors and these cells present defects in neuronal differentiation. By contrast, the DG is normal in Mash1 mutant mice at birth, and loss of both Mash1 and Ngn2 does not aggravate the defect observed in Ngn2 single mutants. These data establish a unique role of Ngn2 in DG neurogenesis during development and raise the possibility that Ngn2has a similar function in adult neurogenesis.

Development of the nervous system requires that timely withdrawal from the cell cycle be coupled with initiation of differentiation. Ubiquitin-mediated degradation of the N-Myc oncoprotein in neural stem/progenitor cells is thought to trigger the arrest of proliferation and begin differentiation. Here we report that the HECT-domain ubiquitin ligase Huwe1 ubiquitinates the N-Myc oncoprotein through Lys 48-mediated linkages and targets it for destruction by the proteasome. This process is physiologically implemented by embryonic stem (ES) cells differentiating along the neuronal lineage and in the mouse brain during development. Genetic and RNA interference-mediated inactivation of the Huwe1 gene impedes N-Myc degradation, prevents exit from the cell cycle by opposing the expression of Cdk inhibitors and blocks differentiation through persistent inhibition of early and late markers of neuronal differentiation. Silencing of N-myc in cells lacking Huwe1 restores neural differentiation of ES cells and rescues cell-cycle exit and differentiation of the mouse cortex, demonstrating that Huwe1 restrains proliferation and enables neuronal differentiation by mediating the degradation of N-Myc. These findings indicate that Huwe1 links destruction of N-Myc to the quiescent state that complements differentiation in the neural tissue.

Development of oligodendrocytes, myelin-forming glia in the central nervous system (CNS), proceeds on a protracted schedule. Specification of oligodendrocyte progenitors (OLPs) begins early in development, whereas their terminal differentiation occurs at late embryonic and postnatal periods. How these distinct steps are controlled remains unclear. Our previous study demonstrated an important role of the helix-loop-helix (HLH) transcription factor Ascl1 in early generation of OLPs in the developing spinal cord. Here,we show that Ascl1 is also involved in terminal differentiation of oligodendrocytes late in development. Ascl1-/- mutant mice showed a deficiency in differentiation of myelin-expressing oligodendrocytes at birth. In vitro culture studies demonstrate that the induction and maintenance of co-expression of Olig2 and Nkx2-2 in OLPs, and thyroid hormone-responsive induction of myelin proteins are impaired in Ascl1-/- mutants. Gain-of-function studies further showed that Ascl1 collaborates with Olig2 and Nkx2-2 in promoting differentiation of OLPs into oligodendrocytes in vitro. Overexpression of Ascl1, Olig2 and Nkx2-2 alone stimulated the specification of OLPs, but the combinatorial action of Ascl1 and Olig2 or Nkx2-2 was required for further promoting their differentiation into oligodendrocytes. Thus, Ascl1 regulates multiple aspects of oligodendrocyte development in the spinal cord.