RESUMO
Cerebral cortex size differs dramatically between reptiles, birds, and mammals, owing to developmental differences in neuron production. In mammals, signaling pathways regulating neurogenesis have been identified, but genetic differences behind their evolution across amniotes remain unknown. We show that direct neurogenesis from radial glia cells, with limited neuron production, dominates the avian, reptilian, and mammalian paleocortex, whereas in the evolutionarily recent mammalian neocortex, most neurogenesis is indirect via basal progenitors. Gain- and loss-of-function experiments in mouse, chick, and snake embryos and in human cerebral organoids demonstrate that high Slit/Robo and low Dll1 signaling, via Jag1 and Jag2, are necessary and sufficient to drive direct neurogenesis. Attenuating Robo signaling and enhancing Dll1 in snakes and birds recapitulates the formation of basal progenitors and promotes indirect neurogenesis. Our study identifies modulation in activity levels of conserved signaling pathways as a primary mechanism driving the expansion and increased complexity of the mammalian neocortex during amniote evolution.
Assuntos
Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Proteínas do Tecido Nervoso/genética , Proteínas do Tecido Nervoso/metabolismo , Neurogênese/genética , Receptores Imunológicos/genética , Receptores Imunológicos/metabolismo , Animais , Proteínas de Ligação ao Cálcio , Córtex Cerebral/metabolismo , Embrião de Galinha , Regulação da Expressão Gênica no Desenvolvimento/genética , Proteínas de Homeodomínio , Humanos , Peptídeos e Proteínas de Sinalização Intercelular/genética , Proteína Jagged-1 , Proteína Jagged-2 , Mamíferos/embriologia , Camundongos , Camundongos Endogâmicos C57BL , Neocórtex/fisiologia , Células-Tronco Neurais , Neurogênese/fisiologia , Neuroglia/fisiologia , Neurônios , Fator de Transcrição PAX6/metabolismo , Proteínas Repressoras , Transdução de Sinais , Serpentes/embriologia , Proteínas RoundaboutRESUMO
NR3A is the only NMDA receptor (NMDAR) subunit that downregulates sharply prior to the onset of sensitive periods for plasticity, yet the functional importance of this transient expression remains unknown. To investigate whether removal/replacement of juvenile NR3A-containing NMDARs is involved in experience-driven synapse maturation, we used a reversible transgenic system that prolonged NR3A expression in the forebrain. We found that removal of NR3A is required to develop strong NMDAR currents, full expression of long-term synaptic plasticity, a mature synaptic organization characterized by more synapses and larger postsynaptic densities, and the ability to form long-term memories. Deficits associated with prolonged NR3A were reversible, as late-onset suppression of transgene expression rescued both synaptic and memory impairments. Our results suggest that NR3A behaves as a molecular brake to prevent the premature strengthening and stabilization of excitatory synapses and that NR3A removal might thereby initiate critical stages of synapse maturation during early postnatal neural development.
Assuntos
Regulação para Baixo/fisiologia , Memória/fisiologia , Neurônios/citologia , Receptores de N-Metil-D-Aspartato/metabolismo , Sinapses/fisiologia , Animais , Animais Recém-Nascidos , Biofísica , Proteína 4 Homóloga a Disks-Large , Estimulação Elétrica/métodos , Preferências Alimentares/fisiologia , Proteínas de Fluorescência Verde/genética , Guanilato Quinases , Hipocampo/citologia , Imunoprecipitação/métodos , Técnicas In Vitro , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Aprendizagem em Labirinto/fisiologia , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Microscopia Eletrônica de Transmissão/métodos , Plasticidade Neuronal/genética , Plasticidade Neuronal/fisiologia , Neurônios/ultraestrutura , Técnicas de Patch-Clamp/métodos , Receptores de N-Metil-D-Aspartato/genética , Reconhecimento Psicológico/fisiologia , Coloração pela Prata/métodos , Comportamento Social , Potenciais Sinápticos/genética , Potenciais Sinápticos/fisiologiaRESUMO
Regulation of surface insertion and internalization of AMPA and NMDA receptors has emerged as a key mechanism for the control of synaptic strength. Regulatory elements for synaptic kainate receptors (KARs) are, however, largely undetermined. We have found that SNAP25 is critical for the synaptic removal of KARs, acting via GluK5 (i.e., KA2) subunits. SNAP25 coimmunoprecipitates with protein complexes containing PICK1, GRIP1, and GluK5 and colocalizes with GluK5 in both hippocampal neurons and transfected HEK293 cells. In hippocampal slices, purified SNAP25 antibodies and blocking peptides caused a GluK5-dependent run-up of KARs-mediated EPSC (EPSC(KAR)) recorded from CA3 pyramidal neurons when included in the patch pipette and prevented activity-dependent long-term depression of EPSC(KAR). As EPSC(KAR) LTD, SNAP25/PICK1/GluK5 interactions are dynamically regulated by PKC.
Assuntos
Plasticidade Neuronal/fisiologia , Neurônios/metabolismo , Receptores de Ácido Caínico/metabolismo , Sinapses/metabolismo , Proteína 25 Associada a Sinaptossoma/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Animais Recém-Nascidos , Cálcio/metabolismo , Proteínas de Transporte/metabolismo , Proteínas de Ciclo Celular , Linhagem Celular Transformada , Linhagem Celular Tumoral , Estimulação Elétrica , Inibidores Enzimáticos/farmacologia , Antagonistas de Aminoácidos Excitatórios/farmacologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/genética , Hipocampo/citologia , Hipocampo/ultraestrutura , Humanos , Imunoprecipitação/métodos , Proteínas Luminescentes/genética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Naftalenos/farmacologia , Proteínas do Tecido Nervoso/metabolismo , Vias Neurais/fisiologia , Neuroblastoma , Plasticidade Neuronal/efeitos dos fármacos , Neurônios/citologia , Neurotoxinas/farmacologia , Proteínas Nucleares/metabolismo , Técnicas de Patch-Clamp/métodos , Transporte Proteico/genética , Transporte Proteico/fisiologia , Piridinas/farmacologia , Ratos , Receptores de Ácido Caínico/deficiência , Proteína 25 Associada a Sinaptossoma/genética , Transfecção , Proteína 2 Associada à Membrana da Vesícula/metabolismoRESUMO
Functioning of the cerebral cortex requires the coordinated assembly of circuits involving glutamatergic projection neurons and GABAergic interneurons. Although much is known about the migration of interneurons from the subpallium to the cortex, our understanding of the mechanisms controlling their precise integration within the cortex is still limited. Here, we have investigated in detail the behavior of GABAergic interneurons as they first enter the developing cortex by using time-lapse videomicroscopy, slice culture, and in utero experimental manipulations and analysis of mouse mutants. We found that interneurons actively avoid the cortical plate for a period of approximately 48 h after reaching the pallium; during this time, interneurons disperse tangentially through the marginal and subventricular zones. Perturbation of CXCL12/CXCR4 signaling causes premature cortical plate invasion by cortical interneurons and, in the long term, disrupts their laminar and regional distribution. These results suggest that regulation of cortical plate invasion by GABAergic interneurons is a key event in cortical development, because it directly influences the coordinated formation of appropriate glutamatergic and GABAergic neuronal assemblies.
