Project description:Traumatic brain injury (TBI) is a risk factor for neurodegeneration, however little is known about how different neuron types respond to this kind of injury. In this study, we follow neuronal populations over several months after a single mild TBI (mTBI) to assess long ranging consequences of injury at the level of single, transcriptionally defined neuronal classes. We find that the stress responsive Activating Transcription Factor 3 (ATF3) defines a population of cortical neurons after mTBI. We show that neurons that activate ATF3 upregulate stress-related genes while repressing many genes, including commonly used markers for these cell types. Using an inducible reporter linked to ATF3, we genetically mark damaged cells to track them over time. Notably, we find that a population in layer V undergoes cell death acutely after injury, while another in layer II/III survives long term and retains the ability to fire action potentials. To investigate the mechanism controlling layer V neuron death, we genetically silenced candidate stress response pathways. We found that the axon injury responsive kinase MAP3K12, also known as dual leucine zipper kinase (DLK), is required for the layer V neuron death. This work provides a rationale for targeting the DLK signaling pathway as a therapeutic intervention for traumatic brain injury. Beyond this, our novel approach to track neurons after a mild, subclinical injury can inform our understanding of neuronal susceptibility to repeated impacts.
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:Traumatic brain injury (TBI) is a risk factor for neurodegeneration, however little is known about how this kind of injury alters neuron subtypes. In this study, we follow neuronal populations over time after a single mild TBI (mTBI) to assess long ranging consequences of injury at the level of single, transcriptionally defined neuronal classes. We find that the stress-responsive Activating Transcription Factor 3 (ATF3) defines a population of cortical neurons after mTBI. Using an inducible reporter linked to ATF3, we genetically mark these damaged cells to track them over time. We find that a population in layer V undergoes cell death acutely after injury, while another in layer II/III survives long term and remains electrically active. To investigate the mechanism controlling layer V neuron death, we genetically silenced candidate stress response pathways. We found that the axon injury responsive dual leucine zipper kinase (DLK) is required for the layer V neuron death. This work provides a rationale for targeting the DLK signaling pathway as a therapeutic intervention for traumatic brain injury. Beyond this, our approach to track neurons after a mild, subclinical injury can inform our understanding of neuronal susceptibility to repeated impacts.
Project description:Recently, direct reprogramming between divergent lineages has been achieved by introducing cell-fate-determining transcription factors. This progress may provide alternative cell resources for drug discovery and regenerative medicine. However, the genetic manipulation may limit the future application of these approaches. In this study, we identified a novel small-molecule cocktail that directly converted fibroblasts into neuronal cell fate with a high yield up after 16-days of induction. After a further maturation stage, these chemically-induced neurons (CiNs) possessed neuron-specific expression patterns, generated action potentials and formed functional synapses. Gene expression profiling revealed the activation of neuronal specific genes in the early stage of small molecule treatment. Overall, our findings prove the principle of chemically-induced direct reprogramming of somatic cell fates across germ layers without genetic manipulation, and show that cell fate can be manipulated through disrupting initial cell program and activating target cell master genes with pure chemicals. Total of 15 samples were analyzed, including mouse fibroblasts, mouse cortical primary neurons and chemically-induced neurons by different duration of chemical induction (Day0, Day4, Day8, Day19) and different small-molecule cocktail (FICB, FICB-1)
Project description:This SuperSeries is composed of the following subset Series: GSE24440: Sprouting transcriptome in cortical neurons: young GSE24441: Sprouting transcriptome in cortical neurons: aged Refer to individual Series
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:TTBK1 and TTBK2 unique substrate identifications in mouse cortical neurons through global phosphoproteomics studies. shRNA for both TTBK1 or TTBK2 was used to treat mouse cortical neurons, to knockdown each kinase.