Project description:The evolutionary expansion of the human neocortex reflects increased amplification of basal progenitors in the subventricular zone, producing more neurons during fetal corticogenesis. Here, we analyze the transcriptomes of distinct progenitor subpopulations isolated by a novel approach from developing mouse and human neocortex. We identify 56 genes preferentially expressed in human apical and basal radial glia that lack mouse orthologs. Among these, ARHGAP11B has the highest degree of radial glia-specific expression. ARHGAP11B arose from partial duplication of the Rho GTPase-activating-protein–encoding ARHGAP11A on the human lineage after separation from the chimpanzee lineage. Expression of ARHGAP11B in embryonic mouse neocortex promotes basal progenitor generation and self-renewal, and can increase cortical plate area and induce gyrification. Hence, ARHGAP11B may have contributed to evolutionary expansion of human neocortex. Gene expression profiles of mouse and human purified neocortical progenitor types and neurons were generated by RNA-seq and analyzed including inter- and intra-species comparison.
Project description:The evolutionary expansion of the human neocortex reflects increased amplification of basal progenitors in the subventricular zone, producing more neurons during fetal corticogenesis. Here, we analyze the transcriptomes of distinct progenitor subpopulations isolated by a novel approach from developing mouse and human neocortex. We identify 56 genes preferentially expressed in human apical and basal radial glia that lack mouse orthologs. Among these, ARHGAP11B has the highest degree of radial glia-specific expression. ARHGAP11B arose from partial duplication of the Rho GTPase-activating-protein–encoding ARHGAP11A on the human lineage after separation from the chimpanzee lineage. Expression of ARHGAP11B in embryonic mouse neocortex promotes basal progenitor generation and self-renewal, and can increase cortical plate area and induce gyrification. Hence, ARHGAP11B may have contributed to evolutionary expansion of human neocortex.
Project description:Neocortex expansion during evolution is linked to higher numbers of neurons thought to result from increased proliferative capacity and neurogenic potential of basal progenitors during development. Here, we show that EREG, encoding the growth factor EPIREGULIN, is expressed in the human developing neocortex, but not in the mouse neocortex. Addition of EPIREGULIN to the mouse neocortex increases proliferation of both major basal progenitor types, intermediate basal progenitors and basal radial glia, whereas ablation of EPIREGULIN in human cortical organoids reduces basal progenitor proliferation. Here, we analyzed gene expression changes upon addition of EPIREGULIN to the mouse neocortex for 24 hours using hemisphere rotation culture. We performed fluorescent activated cell sorting to isolate radial glia (RG), intermediate progenitor (IP) cells and neurons (N) based on the nuclear markers Sox2 and Tbr2, and expression of GFP in neurons isolated from a Tubb3::GFP mouse reporter line.
Project description:Lysosomes are cellular recycling stations and metabolic signaling hubs. Whether lysosome dynamics regulate mammalian brain development is unknown. We found that radial glia cells possess a large number of endolysosomes and that asymmetric inheritance of lysosomes in daughters of radial glia cells can predict fate and cell cycle length. To determine the lysosomal regulation of translation initiation by mTORC1/eIF4E axis, we performed RNA immunoprecipitation sequencing (RIP-seq) with antibody against eIF4E in E13.5 neocortex.
Project description:A specific subpopulation of neural progenitor cells, the basal radial glia cells (bRGCs) of the outer subventricular zone (OSVZ), are thought to have a key role in the evolutionary expansion of mammalian neocortex. In the developing lissencephalic mouse neocortex, bRGCs exist at low abundance and show significant molecular differences from bRGCs in developing gyrencephalic species. Here, we demonstrate that developing mouse medial neocortex, in contrast to the canonically studied lateral neocortex, exhibits an OSVZ and an abundance of bRGCs similar to that in developing gyrencephalic neocortex. Unlike bRGCs in developing mouse lateral neocortex, the bRGCs in medial neocortex exhibit human bRGC-like gene expression, including expression of Hopx, a human bRGC marker. Disruption of Hopx expression in mouse embryonic medial neocortex and forced Hopx expression in mouse embryonic lateral neocortex demonstrate that Hopx is required and sufficient, respectively, for a bRGC abundance as found in developing gyrencephalic neocortex. Taken together, our data identify a novel bRGC subpopulation in developing mouse medial neocortex that is highly related to bRGCs of developing gyrencephalic neocortex.
Project description:Genetic changes causing brain size expansion in human evolution have remained elusive. Notch signaling is essential for radial glia stem cell proliferation and a determinant of neuronal number in the mammalian cortex. We find three paralogs of human-specific NOTCH2NL are highly expressed in radial glia. Functional analysis reveals different alleles of NOTCH2NL have varying potencies to enhance Notch signaling by interacting directly with NOTCH receptors. Consistent with a role in Notch signaling, NOTCH2NL ectopic expression delays differentiation of neuronal progenitors, while deletion accelerates differentiation. Furthermore, NOTCH2NL genes provide the breakpoints in typical cases of 1q21.1 distal deletion/duplication syndrome, where duplications are associated with macrocephaly and autism, and deletions with microcephaly and schizophrenia. Thus, the emergence of hominin-specific NOTCH2NL genes may have contributed to the rapid evolution of the larger hominin neocortex accompanied by loss of genomic stability at the 1q21.1 locus and a resulting recurrent neurodevelopmental disorder.
Project description:A massively expanded outer subventricular zone (OSVZ) in the primate and human has been proposed for generating majority of neocortical neurons, which consists of basally located radial glia cells. Previous studies with various strategies have tried to recognize genes specifically expressed in those cells; however, the molecular and cellular features of these cells still remain uncertain. By profiling gene expression across single cells isolated from cellular anatomy location and subtype sorting, we identified a primate-specific gene TMEM14B as a novel marker for basally located radial glia. Expression of TMEM14B induced dramatic increase in the number of radial glial and OSVZ region. Finally, we found that OSVZ progenitor’s extensive proliferative potential was up regulated through IQGAP1 phosphorylation and nuclear translocation, and remarkably, led to the gyrification in postnatal mouse. These results highlight that evolutionary expansion promoted by primate-specific genes enabling the evolutionary expansion and folding of the human neocortex.
Project description:The unique mental abilities of humans are rooted in the immensely expanded and folded neocortex, which reflects the expansion of neural progenitors, especially basal progenitors including basalradial glia (bRGs, also called outer RGs) and intermediate progenitor cells (IPCs). Here, we show that constitutively active Shh signaling expanded basal progenitors and induced folding in the otherwise smooth mouse neocortex, whereas the loss of Shh signaling decreased the number of basal progenitors and the size of the neocortex. SHH signaling was strongly active in the human fetal neocortex but not in the mouse embryonic neocortex, and blocking SHH signaling in humancerebral organoids decreased the number of bRGs. Mechanistically, Shh signaling increased theinitial generation and self-renewal of bRGs as well as increasing IPC proliferation. Thus, robust SHH signaling in the human fetal neocortex may contribute to basal progenitor expansion and neocortical growth and folding.
Project description:The neocortex, the center for higher brain function, first emerged in mammals and has become massively expanded and folded in humans, constituting almost half the volume of the human brain. Primary microcephaly, a developmental disorder in which the brain is smaller than normal at birth, mainly results from there being fewer neurons in the neocortex because of defects in neural progenitor cells (NPCs). Outer radial glia (oRGs), NPCs that are abundant in gyrencephalic species but rare in lisencephalic species, are thought to play key roles in the expansion and folding of the neocortex. However, how oRGs expand, whether they are necessary for neocortical folding, and whether defects in oRGs cause microcephaly remain important questions in the study of brain development, evolution, and disease. Here, we show that oRG expansion in mice, ferrets, and human cerebral organoids requires cyclin-dependent kinase 6 (CDK6), the mutation of which causes primary microcephaly via an unknown mechanism. In a mouse model in which increased Hedgehog signaling expands oRGs and intermediate progenitor cells and induces neocortical folding, CDK6 loss selectively decreased oRGs and abolished neocortical folding. Remarkably, this function of CDK6 in oRG expansion did not require its kinase activity, was not shared by the highly similar CDK4 and CDK2, and was disrupted by the mutation causing microcephaly. Therefore, our results indicate that CDK6 is conserved to promote oRG expansion; that oRGs are necessary for neocortical folding; and that defects in oRG expansion may cause primary microcephaly.
Project description:<p>We sought to characterize cellular heterogeneity in the human cerebral cortex at a molecular level during cortical neurogenesis. We captured single cells and generated sequencing libraries using the C1TM Single-Cell Auto Prep System (Fluidigm), the SMARTer Ultra Low RNA Kit (Clontech), and the Nextera XT DNA Sample Preparation Kit (Illumina). We performed unbiased clustering of the single cells and further examined transcriptional variation among cell groups interpreted as radial glia. Within this population, the major sources of variation related to cell cycle progression and the stem cell niche from which radial glia were captured. We found that outer subventricular zone radial glia (oRG cells) preferentially express genes related to extracellular matrix formation, migration, and stemness, including <i>TNC</i>, <i>PTPRZ1</i>, <i>FAM107A</i>, <i>HOPX</i>, and <i>LIFR</i> and related this transcriptional state to the position, morphology, and cell behaviors previously used to classify the cell type. Our results suggest that oRG cells maintain the subventricular niche through local production of growth factors, potentiation of growth factor signals by extracellular matrix proteins, and activation of self-renewal pathways, thereby contributing to the developmental and evolutionary expansion of the human neocortex.</p> <p>For <b>study version 2</b>, we have updated this data set to include additional primary cells that we infer to represent microglia, endothelial cells, and immature astrocytes, as well as additional cells from the developing neural retina, and from iPS-cell derived cerebral organoids. The genes distinguishing these cell populations may reveal biological processes supporting the diverse functions of these cell types as well as vulnerabilities of specific cell types in human genetic diseases and in viral infections.</p> <p>For <b>study version 3</b>, we have updated the data set to include additional primary cells, including those published in Nowakowski, et al., Science 2017: "Spatiotemporal Gene Expression Trajectories Reveal Developmental Hierarchies of the Human Cortex" (<i>in press</i>)</p>