Dynamic interplay between thalamic activity and Cajal-Retzius cells regulates the wiring of cortical layer 1

Cortical wiring relies on guidepost cells and activity-dependent processes that are thought to act sequentially. Here, we show that the construction of layer 1 (L1), a main site of top-down integration, is regulated by crosstalk between transient Cajal-Retzius cells (CRc) and spontaneous activity of the thalamus, a main driver of bottom-up information. While activity was known to regulate CRc migration and elimination, we found that prenatal spontaneous thalamic activity and NMDA receptors selectively control CRc early density, without affecting their demise. CRc density, in turn, regulates the distribution of upper layer interneurons and excitatory synapses, thereby drastically impairing the apical dendrite activity of output pyramidal neurons. In contrast, postnatal sensory-evoked activity had a limited impact on L1 and selectively perturbed basal dendrites synaptogenesis. Collectively, our study highlights a remarkable interplay between thalamic activity and CRc in L1 functional wiring, with major implications for our understanding of cortical development.We thank the IBENS Imaging Facility (France BioImaging, supported by ANR-10-INBS-04, ANR-10-LABX-54 MEMO LIFE, and ANR-11-IDEX-000-02 PSL∗ Research University, “Investments for the Future”). This work was supported by grants from the Spanish Ministry of Science, Innovation, and Universities (PGC2018-096631-B-I00) and the European Research Council (ERC-2014-CoG-647012) to G.L.-B. N.C. received funding from the Marie Skłodowska-Curie individual fellowship under the European Union’s Horizon 2020 research and innovation program (AXO-MATH, grant agreement no. 798326). F.G. received funding from the Agence Nationale de la Recherche (SyTune, ANR-21-CE37-0010), the European Research Council under the European Union’s Horizon 2020 research and innovation program (NEUROGOAL, grant agreement no.677878), the Region Nouvelle-Aquitaine, and the University of Bordeaux. The Garel laboratory is supported by INSERM, CNRS, ANR-15-CE16-0003, ANR-19-CE16-0017-02, Investissements d’Avenir implemented by ANR-10-LABX-54 MEMO LIFE, ANR-11-IDEX-0001-02 PSL∗ Research University, and the European Research Council (ERC-2013-CoG-616080, NImO). I.G. is a recipient of a fellowship from the French Ministry of Research and postdoctoral funding from Labex MemoLife, and S.G. is part of the Ecole des Neurosciences de Paris Ile-de-France network.Peer reviewe

Microglia maintain structural integrity during fetal brain morphogenesis

Microglia (MG), the brain-resident macrophages, play major roles in health and disease via a diversity of cellular states. While embryonic MG display a large heterogeneity of cellular distribution and transcriptomic states, their functions remain poorly characterized. Here, we uncovered a role for MG in the maintenance of structural integrity at two fetal cortical boundaries. At these boundaries between structures that grow in distinct directions, embryonic MG accumulate, display a state resembling post-natal axon-tract-associated microglia (ATM) and prevent the progression of microcavities into large cavitary lesions, in part via a mechanism involving the ATM-factor Spp1. MG and Spp1 furthermore contribute to the rapid repair of lesions, collectively highlighting protective functions that preserve the fetal brain from physiological morphogenetic stress and injury. Our study thus highlights key major roles for embryonic MG and Spp1 in maintaining structural integrity during morphogenesis, with major implications for our understanding of MG functions and brain development.</p

Développement précoce hépatique et rénal chez la souris (implication du facteur de transcription vHNF1/HNF1b/TCF2)

Chez la souris, le facteur de transcription variant Hepatocyte Nuclear Factor vHNF1/HNF1 /TCF2 possède un profil d expression large et précoce au cours du développement. Son invalidation provoque une létalité embryonnaire précoce, pouvant être sauvée par apport d annexes extra-embryonnaires tétraploïdes sauvages. Cette technique permet d obtenir des embryons vHnf1-/- présentant plusieurs phénotypes dont une hypoplasie hépatique sévère et un défaut d arborisation du bourgeon urétéral. L analyse du phénotype hépatique révèle que les embryons vHnf1-/- ne forment pas de bourgeon hépatique et n expriment pas plusieurs facteurs clés du développement hépatique. Des analyses complémentaires ont permis de mettre en évidence un défaut de compétence de l endoderme ventral à répondre aux signaux inducteurs. Ainsi, vHNF1 est nécessaire pour une spécification correcte de l endoderme ventral en endoderme pré-hépatique, son invalidation conduisant à une absence de développement du foie. De plus, j ai caractérisé le rôle de vHNF1 lors du développement du métanéphros, rein définitif des mammifères. Ces analyses ont mis en évidence un délai de mise en place du métanéphros associé à un défaut sévère du développement conduisant à une agénésie précoce. Ainsi, vHNF1 jouerait un rôle dans le maintien de l épithélium du canal néphrique ainsi que dans le processus de condensation du mésenchyme métanéphrique nécessaire pour l arborisation élaborée du bourgeon urétéral et la néphrogenèse.Ainsi, l ensemble du travail présenté dans cette thèse contribue à une meilleure connaissance du rôle de vHNF1 dans les cascades complexes de régulation contrôlant des phases précoces du développement.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Subrepellent doses of Slit1 promote Netrin-1 chemotactic responses in subsets of axons

International audienceBackground: Axon pathfinding is controlled by guidance cues that elicit specific attractive or repulsive responses in growth cones. It has now become clear that some cues such as Netrin-1 can trigger either attraction or repulsion in a context-dependent manner. In particular, it was recently found that the repellent Slit1 enables the attractive response of rostral thalamic axons to Netrin-1. This finding raised the intriguing possibility that Netrin-1 and Slit1, two essential guidance cues, may act more generally in an unexpected combinatorial manner to orient specific axonal populations. To address this major issue, we have used an innovative microfluidic device compatible not only with dissociated neuronal cultures but also with explant cultures to systematically and quantitatively characterize the combinatorial activity of Slit1 and Netrin-1 on rostral thalamic axons as well as on hippocampal neurons. Results: We found that on rostral thalamic axons, only a subthreshold concentration of the repellent Slit1 triggered an attractive response to a gradient of Netrin-1. On hippocampal neurons, we similarly found that Slit1 alone is repulsive and a subthreshold concentration of Slit1 triggered a potent attractive or repulsive behavioral response to a gradient of Netrin-1, depending on the nature of the substrate. Conclusions: Our study reveals that at subthreshold repulsive levels, Slit1 acts as a potent promoter of both Netrin-1 attractive and repulsive activities on distinct neuronal cell types, thereby opening novel perspectives on the role of combinations of cues in brain wiring

Trio GEF mediates RhoA activation downstream of Slit2 and coordinates telencephalic wiring

International audienceTrio, a member of the Dbl family of guanine nucleotide exchange factors, activates Rac1 downstream of netrin 1/DCC signalling in axon outgrowth and guidance. Although it has been proposed that Trio also activates RhoA, the putative upstream factors remain unknown. Here, we show that Slit2 induces Trio-dependent RhoA activation, revealing a crosstalk between Slit and Trio/RhoA signalling. Consistently, we found that RhoA activity is hindered in vivo in T rio mutant mouse embryos. We next studied the development of the ventral telencephalon and thalamocortical axons, which have been previously shown to be controlled by Slit2. Remarkably, this analysis revealed that Trio knockout (KO) mice show phenotypes that bear strong similarities to the ones that have been reported in Slit2 KO mice in both guidepost corridor cells and thalamocortical axon pathfinding in the ventral telencephalon. Taken together, our results show that Trio induces RhoA activation downstream of Slit2, and support a functional role in ensuring the proper positioning of both guidepost cells and a major axonal tract. Our study indicates a novel role for Trio in Slit2 signalling and forebrain wiring, highlighting its role in multiple guidance pathways as well as in biological functions of importance for a factor involved in human brain disorders

Local glycolysis fuels actomyosin contraction during axonal retraction

International audiencegeneration of ATP by glycolysis, as shown by chemical inhibition and genetic knock-down of GAPDH. Co-immunoprecipitation and proximal-ligation assay showed that actomyosin associates with ATP-generating glycolytic enzymes and that this association is strongly enhanced during retraction. Using microfluidics, we confirmed that the energetic coupling between glycolysis and actomyosin necessary for axonal retraction is localized to the growth cone and near axonal shaft. These results indicate a tight coupling between on-demand energy production by glycolysis and energy consumption by actomyosin contraction suggesting a function of glycolysis in axonal guidance

Tangential migration of corridor guidepost neurons contributes to anxiety circuits

International audienceIn mammals, thalamic axons are guided internally toward their neocortical target by corridor (Co) neurons that act as axonal guideposts. The existence of Co-like neurons in non-mammalian species, in which thalamic axons do not grow internally, raised the possibility that Co cells might have an ancestral role. Here, we investigated the contribution of corridor (Co) cells to mature brain circuits using a combination of genetic fate-mapping and assays in mice. We unexpectedly found that Co neurons contribute to striatal-like projection neurons in the central extended amygdala. In particular, Co-like neurons participate in specific nuclei of the bed nucleus of the stria terminalis, which plays essential roles in anxiety circuits. Our study shows that Co neurons possess an evolutionary conserved role in anxiety circuits independently from an acquired guidepost function. It furthermore highlights that neurons can have multiple sequential functions during brain wiring and supports a general role of tangential migration in the building of subpallial circuits

A vHNF1/TCF2-HNF6 cascade regulates the transcription factor network that controls generation of pancreatic precursor cells

Generation of pancreatic precursor cells in the endoderm is controlled by a network of transcription factors. Hepatocyte nuclear factor-6 (HNF6) is a key player in this network, because it controls the initiation of the expression of pancreatic and duodenal homeobox 1 (Pdx1), the earliest marker of pancreatic precursor cells. To further characterize this network, we have investigated how the expression of HNF6 is controlled in mouse endoderm, by using in vitro and in vivo protein-DNA interaction techniques combined with endoderm electroporation, transgenesis, and gene inactivation in embryos. We delineated Hnf6 regulatory regions that confer expression of a reporter gene in the embryonic endoderm but not in extraembryonic visceral endoderm. HNF6 expression in the embryonic endoderm was found to depend on an intronic enhancer. This enhancer contains functional binding sites for the tissue-specific factors of the forkhead box A and HNF1 families. Among the latter, variant HNF1 (vHNF1)/TCF2, which is expressed before HNF6 in the endoderm, was found to be critical for HNF6 expression. Therefore, the sequential activation of vHNF1, HNF6, and Pdx1 in the endoderm appears to control the generation of pancreatic precursors. This cascade may be used to benchmark in vitro differentiation of pancreatic precursor cells from embryonic stem cells, for cell therapy of diabetes

Screening for genes that wire the cerebral cortex

<p>Abstract</p> <p>Thalamocortical projections convey visual, somatosensory and auditory information to the cerebral cortex. A recent report in <it>Neural Development </it>shows how a forward genetic screen has enabled the identification of novel mutations affecting specific decision points of thalamocortical axon pathfinding.</p> <p>See research article: <url>http://www.neuraldevelopment.com/content/6/1/3/abstract</url></p