Project description:The spinal cord receives inputs from the cortex via corticospinal neurons (CSNs). While predominantly a contralateral projection, a less-investigated minority of its axons terminate in the ipsilateral spinal cord. We analyzed the spatial and molecular properties of these ipsilateral axons and their post-synaptic targets in mice and found they project primarily to the ventral horn, including directly to motor neurons. Barcode-based reconstruction of the ipsilateral axons revealed a class of primarily bilaterally-projecting CSNs with a distinct cortical distribution. The molecular properties of these ipsilaterally-projecting CSNs (IP-CSNs) are strikingly similar to the previously described molecular signature of embryonic-like regenerating CSNs. Finally, we show that IP-CSNs are spontaneously regenerative after spinal cord injury. The discovery of a class of spontaneously regenerative CSNs may prove valuable to the study of spinal cord injury. Additionally, this work suggests that the retention of juvenile-like characteristics may be a widespread phenomenon in adult nervous systems. This data set comprises the MPASeq experiment.
Project description:The spinal cord receives inputs from the cortex via corticospinal neurons (CSNs). While predominantly a contralateral projection, a less-investigated minority of its axons terminate in the ipsilateral spinal cord. We analyzed the spatial and molecular properties of these ipsilateral axons and their post-synaptic targets in mice and found they project primarily to the ventral horn, including directly to motor neurons. Barcode-based reconstruction of the ipsilateral axons revealed a class of primarily bilaterally-projecting CSNs with a distinct cortical distribution. The molecular properties of these ipsilaterally-projecting CSNs (IP-CSNs) are strikingly similar to the previously described molecular signature of embryonic-like regenerating CSNs. Finally, we show that IP-CSNs are spontaneously regenerative after spinal cord injury. The discovery of a class of spontaneously regenerative CSNs may prove valuable to the study of spinal cord injury. Additionally, this work suggests that the retention of juvenile-like characteristics may be a widespread phenomenon in adult nervous systems. This data is Smart-seq3 transcriptomic data from single nuclei of the post-synaptic targets of the corticospinal tract, as determined by AAV1-Cre monosynaptic tracing.
Project description:In the present study, we identify transcriptional mechanisms associated with corticospinal regeneration. We took advantage of the ability of NPC grafts to support corticospinal regeneration, together with a genetic mouse model (Glt25d2-GFP-L10a mice, in which a bacterial artificial chromosome (BAC) codes for GFP-tagged polyribosomes in layer 5b cortical neurons) to selectively enrich actively translated mRNA pools from layer Vb cortical projection neurons containing corticospinal neurons (Doyle et al., Cell 2008).
Project description:B-RAF activation in mature corticospinal neurons upregulated a discrete set of transcription factors overlapping with a set induced early in axotomized zebrafish retina ganglion cells which can fully regenerate their axons. Conditional genetic activation of B-RAF promoted robust regeneration and sprouting of corticospinal tract axons after experimental spinal cord injury. Newly sprouting axon collaterals formed synaptic connections, correlating with recovery of skilled motor function. We also found that non-invasive suprathreshold high-frequency repetitive transcranial magnetic stimulation activates the RAF effector MEK and promotes regeneration and sprouting of corticospinal tract axons, dependent on MEK signaling. Our findings demonstrate a central role of neuron-intrinsic RAF–MEK signaling in enhancing the growth capacity of mature corticospinal neurons and propose transcranial magnetic stimulation as a potential therapy for spinal cord injury.
Project description:The cerebral cortical tissue of murine embryo and pluripotent stem cell-derived neurons can survive in adult brain and extend axons to the spinal cord. These features suggest that cell transplantation can be a strategy to reconstruct the corticospinal tract (CST). It is unknown, however, which cell population makes for safe and effective donor cells. To address this issue, we grafted the cerebral cortex of E14.5 mouse to the brain of adult mouse and found that the cells in the graft extending axons along the CST expressed CTIP2. By using CTIP2:GFP knockin mouse embryonic stem cells, we identified L1CAM as a cell surface marker to enrich CTIP2+ cells. We sorted L1CAM+ cells from E14.5 mouse brain and confirmed that they extended a larger number of axons along the CST compared to L1CAM- cells. Our results suggest that sorting L1CAM+ cells from the embryonic cerebral cortex enriches subcortical projection neurons to reconstruct the CST.
Project description:The spinal cord receives inputs from the cortex via corticospinal neurons (CSNs). While predominantly a contralateral projection, a less-investigated minority of its axons terminate in the ipsilateral spinal cord. We analyzed the spatial and molecular properties of these ipsilateral axons and their post-synaptic targets in mice and found they project primarily to the ventral horn, including directly to motor neurons. Barcode-based reconstruction of the ipsilateral axons revealed a class of primarily bilaterally-projecting CSNs with a distinct cortical distribution. The molecular properties of these ipsilaterally-projecting CSNs (IP-CSNs) are strikingly similar to the previously described molecular signature of embryonic-like regenerating CSNs. Finally, we show that IP-CSNs are spontaneously regenerative after spinal cord injury. The discovery of a class of spontaneously regenerative CSNs may prove valuable to the study of spinal cord injury. Additionally, this work suggests that the retention of juvenile-like characteristics may be a widespread phenomenon in adult nervous systems. This TRAP sequencing data was used to determine the molecular similarity to regenerating and embryonic CSNs.
Project description:Molecular mechanisms over differentiation and differential axonal targeting of distinct neuron subtypes in the cerebral cortex are beginning to be elucidated. These studies have focused on controls that specifically distinguish one subtype of neocortical projection neurons, e.g. corticospinal motor neurons (CSMN), from closely related corticothalamic projection neurons (CThPN) or intracortical callosal projection neurons (CPN). CSMN are located in layer V of the neocortex and make synaptic connections to motor output circuitry in the spinal cord and brainstem. CSMN axons form the corticospinal tract (CST), which is the major motor output pathway from the motor cortex and critically controls voluntary movement. CSMN somatotopically and precisely target specific segments along the rostrocaudal axis of the spinal cord, the molecular basis for which remains unknown. We used microarrays to examine gene expression differences between two CSMN subpopulations that target different levels of the spinal cord - CSMN-C (which extend axons to the brainstem and cervical spinal cord) and CSMN-L (which preferrrentially extend axons to the thoracic and lumbar spinal cord). We compared CSMN-C vs CSMN-L gene expression at 3 critical developmental time points (previously described in Arlotta et a., 2005)