Project description:The mammalian cerebral cortex contains an extraordinary diversity of cell types that emerge through the implementation of different developmental programs. Delineating when and how cellular diversification occurs is particularly challenging for cortical inhibitory neurons, as they represent a relatively small proportion of all cortical cells, migrate tangentially from their embryonic origin to the cerebral cortex, and have a protracted development. Here we combine single-cell RNA sequencing and spatial transcriptomics to characterize the emergence of neuronal diversity among somatostatin-expressing (SST+) cells, the most diverse subclass of inhibitory neurons in the mouse cerebral cortex. We found that SST+ inhibitory neurons segregate during embryonic stages into long-range projection (LRP) neurons and two types of interneurons, Martinotti cells and non-Martinotti cells, following distinct developmental trajectories. Two main subtypes of LRP neurons and several subtypes of interneurons are readily distinguishable in the embryo, although interneuron diversity is further refined during early postanal life. Our results suggest that the timing for cellular diversification is unique for different subtypes of SST+ neurons and particularly divergent for LRP neurons and interneurons. Thus, the diversification of SST+ inhibitory neurons involves a temporal cascade of unique molecular programs driving their divergent developmental trajectories.
Project description:We applied massively parallel single-cell RNA-seq to profile a developmental time course of interneuron development, measuring the transcriptomes of over 60,000 progenitors during their maturation in the ganglionic eminences and embryonic migration into the cortex.
Project description:ChIP-seq was carried out by high throughput sequencing in human developmental cortical interneurons derived from healthy control vs schizophrenia iPSCs
Project description:The cerebral cortex is a cellularly-complex structure comprised of a rich diversity of neuronal and glial cell types. Cortical neurons can be broadly categorized into two classes—glutamatergic excitatory neurons and GABAergic inhibitory interneurons. Previous developmental studies in rodents have led to the prevailing model that while excitatory neurons are born from progenitors located in the cortex, cortical interneurons are born from a separate population of progenitors located outside of the developing cortex in the ganglionic eminences1-5. However, the developmental potential of human cortical progenitors has not been thoroughly explored. Here we show that in addition to excitatory neurons and glia, human cortical progenitors are also capable of producing GABAergic neurons with the transcriptional characteristics and morphologies of cortical interneurons. By developing a cellular barcoding tool called “ScRNAseq-compatible Tracer for Identifying Clonal Relationships” (STICR), we were able to perform clonal lineage tracing of 1912 primary human cortical progenitors from six specimens and capture both the transcriptional identities and clonal relationships of their resulting progeny. A subpopulation of cortically-born GABAergic neurons were transcriptionally similar to cortical interneurons born from the caudal ganglionic eminence and these cells were frequently related to excitatory neurons and glia. Thus, our results demonstrate that individual human cortical progenitors can generate both excitatory neurons and cortical interneurons, providing a new framework for understanding the origins of neuronal diversity in the human cortex.
Project description:In the mammalian cerebral cortex, the developmental events governing the allocation of different classes of inhibitory neurons into distinct cortical layers are poorly understood. Here we report that the guidance receptor PlexinA4 is upregulated in serotonin receptor 3a-expressing (HTR3A) cortical interneurons (hINs) as they invade the cortical plate and that it regulates their laminar allocation to superficial cortical layers. We find that the PlexinA4 ligand Semaphorin3A acts as a chemorepulsive factor on hINs migrating into the nascent cortex and demonstrate that Semaphorin3A specifically controls their laminar positioning through PlexinA4. We identify that deep layer interneurons constitute a major source of Semaphorin3A in the developing cortex and demonstrate that cell-type specific genetic deletion of Semaphorin3A in these interneurons specifically affects the laminar allocation of hINs. These data demonstrate that in the neocortex, deep layer interneurons control the laminar allocation of hINs into superficial layers.
Project description:How neuronal connections are established and organized in functional networks determines brain function. In the mouse cerebral cortex, different classes of GABAergic interneurons exhibit specific connectivity patterns that underlie their ability to shape temporal dynamics and information processing. Much progress has been made parsing interneuron diversity, yet the molecular mechanisms by which interneuron subtype-specific connectivity motifs emerge remain unclear. Here we investigate transcriptional dynamics in different classes of interneurons during the formation of cortical inhibitory circuits. We found that whether the interneurons synapse with pyramidal neurons on their dendrites, soma, or axon initial segment is determined by synaptic molecules that are expressed in a subtype-specific manner. Thus cell-specific molecular programs that unfold during early postnatal development underlie the connectivity patterns of cortical interneurons.
Project description:In the cerebral cortex, projection neurons and interneurons work coordinately to establish functional neural networks and to control the balance between excitatory versus inhibitory synaptic activities for normal cortical functions. While the specific mechanisms that control productions of projection neurons and interneurons are beginning to be revealed, a global characterization of the molecular differences between these two groups of neurons is in need for a more comprehensive understanding of their developmental specifications as well as their cortical functions. Previous studies have shown that the majority of cortical projection neurons are produced by radial glial cells (RGCs) through intermediate progenitor cells (IPCs) which can be marked by the expression of transcription factor Tbr2(Eomes). In this study, taking advantage of lineage tracing power of combining Tbr2(Eomes)-GFP and DCX-mRFP transgenic reporter mice, we prospectively separated IPC-derived neurons (IPNs) from non-IPC-derived neurons (non-IPNs) of the embryonic cortex. Molecular characterizations revealed that IPNs and non-IPNs were enriched with projection neurons and interneurons, respectively. Transcriptome analyses documented distinct groups of genes differentially expressed between these two groups of neurons. These data present a useful resource for further investigation of the molecular regulations and functions of projection neurons and interneurons.
Project description:Genome binding/occupancy profiling was carried out by high throughput sequencing in human developmental cortical interneurons and developmental glutamatergic neurons derived from healthy control vs schizophrenia iPSCs
Project description:Our group has reported that the histone methyltransferase DOT1L is necessary for proper cortical plate development and layer distribution of glutamatergic neurons, however, its specific role on cortical interneuron development has not yet been explored. Here, we demonstrate that DOT1L affects interneuron development in a cell-autonomous manner. Deletion of Dot1l in MGE-derived interneuron precursor cells results in an overall reduction and altered distribution of GABAergic interneurons in the cortical plate at postnatal day (P) 0. Furthermore, we observed an altered proportion of GABAergic interneurons in the cortex and striatum at P21 with a significant decrease in Parvalbumin (PVALB)-expressing interneurons. Altogether, our results indicate that reduced numbers of cortical interneurons upon DOT1L deletion results from altered postmitotic differentiation/maturation.