Temporally-Divergent Regulatory Mechanisms Govern Neuronal Diversification and Maturation in the Neocortex [RNA-seq]
Ontology highlight
ABSTRACT: Mammalian neocortical neurons span one of the most diverse cell type spectra of any tissue. The regulatory strategies that neurons use during progressive development and maturation remain unclear. We present an integrated single-cell epigenomic and transcriptional analysis of individual classes of neurons from both mouse and marmoset neocortex, sampled during both early postmitotic stages of identity acquisition and later stages of neuronal plasticity and circuit integration. We find that in both species, the regulatory strategies controlling early and late stages of pan-neuronal development diverge. Early postmitotic neurons use molecular regulatory programs with broader tissue distribution and greater evolutionary conservation. In contrast, programs that are active during later neuronal maturation implement more brain- and neuron-specific mechanisms showing greater evolutionary divergence. Our work uncovers a temporally-regulated shift in regulatory choices, likely reflecting unique evolutionary constraints on distinct events of neuronal development in the neocortex.
Project description:Mammalian neocortical neurons span one of the most diverse cell type spectra of any tissue. The regulatory strategies that neurons use during progressive development and maturation remain unclear. We present an integrated single-cell epigenomic and transcriptional analysis of individual classes of neurons from both mouse and marmoset neocortex, sampled during both early postmitotic stages of identity acquisition and later stages of neuronal plasticity and circuit integration. We find that in both species, the regulatory strategies controlling early and late stages of pan-neuronal development diverge. Early postmitotic neurons use molecular regulatory programs with broader tissue distribution and greater evolutionary conservation. In contrast, programs that are active during later neuronal maturation implement more brain- and neuron-specific mechanisms showing greater evolutionary divergence. Our work uncovers a temporally-regulated shift in regulatory choices, likely reflecting unique evolutionary constraints on distinct events of neuronal development in the neocortex.
Project description:Mammalian neocortical neurons span one of the most diverse cell type spectra of any tissue. The regulatory strategies that neurons use during progressive development and maturation remain unclear. We present an integrated single-cell epigenomic and transcriptional analysis of individual classes of neurons from both mouse and marmoset neocortex, sampled during both early postmitotic stages of identity acquisition and later stages of neuronal plasticity and circuit integration. We find that in both species, the regulatory strategies controlling early and late stages of pan-neuronal development diverge. Early postmitotic neurons use molecular regulatory programs with broader tissue distribution and greater evolutionary conservation. In contrast, programs that are active during later neuronal maturation implement more brain- and neuron-specific mechanisms showing greater evolutionary divergence. Our work uncovers a temporally-regulated shift in regulatory choices, likely reflecting unique evolutionary constraints on distinct events of neuronal development in the neocortex.
Project description:Mammalian neocortical neurons span one of the most diverse cell type spectra of any tissue. The regulatory strategies that neurons use during progressive development and maturation remain unclear. We present an integrated single-cell epigenomic and transcriptional analysis of individual classes of neurons from both mouse and marmoset neocortex, sampled during both early postmitotic stages of identity acquisition and later stages of neuronal plasticity and circuit integration. We find that in both species, the regulatory strategies controlling early and late stages of pan-neuronal development diverge. Early postmitotic neurons use molecular regulatory programs with broader tissue distribution and greater evolutionary conservation. In contrast, programs that are active during later neuronal maturation implement more brain- and neuron-specific mechanisms showing greater evolutionary divergence. Our work uncovers a temporally-regulated shift in regulatory choices, likely reflecting unique evolutionary constraints on distinct events of neuronal development in the neocortex.
Project description:Mammalian neocortical neurons span one of the most diverse cell type spectra of any tissue. The regulatory strategies that neurons use during progressive development and maturation remain unclear. We present an integrated single-cell epigenomic and transcriptional analysis of individual classes of neurons from both mouse and marmoset neocortex, sampled during both early postmitotic stages of identity acquisition and later stages of neuronal plasticity and circuit integration. We find that in both species, the regulatory strategies controlling early and late stages of pan-neuronal development diverge. Early postmitotic neurons use molecular regulatory programs with broader tissue distribution and greater evolutionary conservation. In contrast, programs that are active during later neuronal maturation implement more brain- and neuron-specific mechanisms showing greater evolutionary divergence. Our work uncovers a temporally-regulated shift in regulatory choices, likely reflecting unique evolutionary constraints on distinct events of neuronal development in the neocortex.
Project description:Mammalian neocortical neurons span one of the most diverse cell type spectra of any tissue. The regulatory strategies that neurons use during progressive development and maturation remain unclear. We present an integrated single-cell epigenomic and transcriptional analysis of individual classes of neurons from both mouse and marmoset neocortex, sampled during both early postmitotic stages of identity acquisition and later stages of neuronal plasticity and circuit integration. We find that in both species, the regulatory strategies controlling early and late stages of pan-neuronal development diverge. Early postmitotic neurons use molecular regulatory programs with broader tissue distribution and greater evolutionary conservation. In contrast, programs that are active during later neuronal maturation implement more brain- and neuron-specific mechanisms showing greater evolutionary divergence. Our work uncovers a temporally-regulated shift in regulatory choices, likely reflecting unique evolutionary constraints on distinct events of neuronal development in the neocortex.
Project description:Assembly of transcriptomes encoding unique neuronal identities requires selective accessibility of transcription factors to cis-regulatory sequences in nucleosome-embedded postmitotic chromatin. Yet, the mechanisms controlling postmitotic neuronal chromatin accessibility are poorly understood. Here, we show that unique distal enhancers define the Pet1 neuron lineage that generates serotonin (5-HT) neurons. Heterogeneous single cell chromatin landscapes are established early in postmitotic Pet1 neurons and reveal the putative regulatory programs driving Pet1 neuron subtype identities. Distal enhancer accessibility is highly dynamic as Pet1 neurons mature, suggesting the existence of regulatory factors that reorganize postmitotic neuronal chromatin. We find that Pet1 and Lmx1b control chromatin accessibility to select Pet1-lineage specific enhancers for 5-HT neurotransmission. Additionally, these factors are required to maintain chromatin accessibility during early maturation suggesting that postmitotic neuronal open chromatin is unstable and requires continuous regulatory input. Together our findings reveal postmitotic transcription factors that reorganize accessible chromatin for neuron specialization.
Project description:Necdin, a pleiotropic protein expressed predominantly in postmitotic neurons of mammals, regulates neuronal development and survival by interacting with various regulatory proteins. To understand a novel function of necdin, we analyzed gene expression profile of primary cortical neurons prepared from necdin-null mice at embryonic day 14.5. Wild-type and necdin-null cortical cells were prepared from mice at embryonic day 14.5. These cells were incubated in Neurobasal medium supplemented with B27 and differentiated into neurons for 4 days (>97% MAP2-positive postmitotic neurons). Three mice per genotype were used for analysis.
Project description:Neocortical excitatory neurons belong to diverse cell types, which can be distinguished by their dates of birth, laminar location, connectivity and molecular identities. During embryogenesis, apical progenitors (APs) located in the ventricular zone first give birth to deep-layer neurons, and next to superficial-layer neurons. While the overall sequential construction of neocortical layers is well-established, whether multiple neuron types are produced by APs at single time points of corticogenesis is unknown. To address this question, here we used FlashTag to fate-map simultaneously-born (i.e. isochronic) cohorts of AP-born neurons at successive stages of corticogenesis. We reveal that early in corticogenesis, isochronic neurons differentiate into heterogeneous laminar, hodological and molecular cell types. Later on, instead, simultaneously-born neurons have more homogeneous fates. Using single-cell gene expression analyses, we identify an early postmitotic surge in the molecular heterogeneity of nascent neurons during which some early-born neurons initiate and partially execute late-born neuron transcriptional programs. Together, these findings suggest that as corticogenesis unfolds, mechanisms allowing increased homogeneity in neuronal output are progressively implemented, resulting in progressively more predictable neuronal identities.
Project description:Radial glial progenitor cells (RGCs) in the dorsal forebrain directly or indirectly produce excitatory projection neurons and macroglia of the neocortex. Recent evidence shows that the pool of RGCs is more heterogeneous than originally thought and that progenitor subpopulations can generate particular neuronal cell types. Using single cell RNA sequencing, we have studied gene expression patterns of two subtypes of RGCs that differ in their neurogenic behavior. One progenitor type rapidly produces postmitotic neurons, whereas the second progenitor remains relatively quiescence before generating neurons. We have identified candidate genes that are differentially expressed between these RGCs progenitor subtypes, including the transcription factor Sox9. Using in utero electroporation, we demonstrate that elevated Sox9 expression in progenitors prevents RGC division and leads to the generation of upper-layer cortical neurons from these progenitors at later ages. Our data thus reveal molecular differences between cortical progenitors with different neurogenic behavior and indicates that Sox9 is critical for the maintenance of RGCs to regulate the generation of upper layer neurons.
Project description:Understanding evolutionary mechanisms underlying expansion and reorganization of the human brain represents an important aspect in analyzing the emergence of cognitive abilities typical of our species. Comparative analyses of neuronal phenotypes in closest living relatives (Pan troglodytes; the common chimpanzee) can shed the light into changes in neuronal morphology compared to the last common ancestor (LCA), opening possibilities for analyses of the timing of their appearance, and the role of evolutionary mechanisms favoring a particular type of information processing in humans. Here, we use induced pluripotent stem cell (iPSC) technology to model neural progenitor cell migration and early development of cortical pyramidal neurons in humans and chimpanzees. In addition, we provide morphological characterization of the early stages of neuronal development in human and chimpanzee transplanted cells, and examine the role of developmental mechanisms previously proposed for the evolutionary expansions of the human brain on the early development of pyramidal neurons in the two species. The strategy proposed here lay down the basis for further comparative analysis between human and non-human primates and opens new avenues for understanding cognitive capability and neurological disease susceptibility differences between species. PolyA RNA-Seq profiling of neural progenitor cells (NPCs) and neurons differentiated from human and chimpanzee iPSCs.