Developmental molecular controls over arealization of descending cortical motor pathways [AbeP_GEO]
Ontology highlight
ABSTRACT: Layer 5 extratelencephalic (ET) neurons are a main class of neocortical projection neurons that predominate in the motor cortex and send their axon to multiple proximal and distal targets including the thalamus, pons, medulla and spinal cord1-6. Precise connectivity of ET neurons is critical for fine motor control; they are central to loss of function upon spinal cord injury and specifically degenerate in amyotrophic lateral sclerosis7-10. ET neurons consist of several subtypes of cells with distinct laminar and areal locations, molecular identities, connectivities, and functions11,12. Two cardinal subtypes of ET neurons have been identified: neurons that express Nprs1 or Hpgd and project proximally to the pons and thalamus (ETprox), and neurons that express Slco2a1 and project more distally to the pons, medulla and spinal cord (ETdist)11. Despite their critical function, how these neuronal subtypes emerge during development and acquire their area-specific distributions remains unaddressed. Here, using combinations of anatomical labeling, MAPseq mapping13, and single- nucleus transcriptomics across developing cortical areas, we reveal that these two subtypes of ET neurons are present at birth along opposite antero-posterior cortical gradients. We first characterize area-specific developmental axonal dynamics of ETprox and ETdist neurons and find that the former can emerge by pruning of subsets of ETdist neurons. We next identify area- and ET neuron subtype-specific developmental transcriptional programs to identify key target genes in vivo and predict their gene regulatory networks. Finally, we reprogram ET neuron subtype- specific connectivity from motor to visual-like, by generating more proximal connections through postnatal in vivo knockdown of three subtype-specific transcription factors. Together, these findings delineate the functional transcriptional programs controlling ET neuron diversity across cortical areas and provide a molecular blueprint to investigate and direct the developmental emergence of corticospinal motor function.
Project description:Layer 5 extratelencephalic (ET) neurons are a main class of neocortical projection neurons that predominate in the motor cortex and send their axon to multiple proximal and distal targets including the thalamus, pons, medulla and spinal cord1-6. Precise connectivity of ET neurons is critical for fine motor control; they are central to loss of function upon spinal cord injury and specifically degenerate in amyotrophic lateral sclerosis7-10. ET neurons consist of several subtypes of cells with distinct laminar and areal locations, molecular identities, connectivities, and functions11,12. Two cardinal subtypes of ET neurons have been identified: neurons that express Nprs1 or Hpgd and project proximally to the pons and thalamus (ETprox), and neurons that express Slco2a1 and project more distally to the pons, medulla and spinal cord (ETdist)11. Despite their critical function, how these neuronal subtypes emerge during development and acquire their area-specific distributions remains unaddressed. Here, using combinations of anatomical labeling, MAPseq mapping13, and single- nucleus transcriptomics across developing cortical areas, we reveal that these two subtypes of ET neurons are present at birth along opposite antero-posterior cortical gradients. We first characterize area-specific developmental axonal dynamics of ETprox and ETdist neurons and find that the former can emerge by pruning of subsets of ETdist neurons. We next identify area- and ET neuron subtype-specific developmental transcriptional programs to identify key target genes in vivo and predict their gene regulatory networks. Finally, we reprogram ET neuron subtype- specific connectivity from motor to visual-like, by generating more proximal connections through postnatal in vivo knockdown of three subtype-specific transcription factors. Together, these findings delineate the functional transcriptional programs controlling ET neuron diversity across cortical areas and provide a molecular blueprint to investigate and direct the developmental emergence of corticospinal motor function.
Project description:Human pluripotent stem cells are a promising source of diverse cells for developmental studies, cell transplantation, disease modeling, and drug testing. However, their widespread use even for intensely studied cell types like spinal motor neurons, is hindered by the long duration and low yields of existing protocols for in vitro differentiation and by the molecular heterogeneity of the populations generated. We report a combination of small molecules that induce up to 50% motor neurons within 3 weeks from human pluripotent stem cells with defined subtype identities that are relevant to neurodegenerative diseases. Despite their accelerated differentiation, motor neurons expressed combinations of HB9, ISL1 and column-specific markers that mirror those observed in vivo in human fetal spinal cord. They also exhibited spontaneous and induced activity, and projected axons towards muscles when grafted into developing chick spinal cord. Strikingly, this novel protocol preferentially generates motor neurons expressing markers of limb-innervating lateral motor column motor neurons (FOXP1+/LHX3-). Access to high-yield cultures of human limb-innervating motor neuron subtypes will facilitate in-depth study of motor neuron subtype-specific properties, disease modeling, and development of large-scale cell-based screening assays. We analyze 3 samples including 2 positive samples and 1 negative sample. Descriptions are as follow: a) Positive Sample 1: SHH-derived, day 21 GFP-high FACS purified motor neurons.b) Positive Sample 2: S+P-derived, day 21 GFP-high FACS purified motor neurons. c) Negative: S+P condition, day 21 no GFP FACS purified motor neurons
Project description:Human pluripotent stem cells are a promising source of diverse cells for developmental studies, cell transplantation, disease modeling, and drug testing. However, their widespread use even for intensely studied cell types like spinal motor neurons, is hindered by the long duration and low yields of existing protocols for in vitro differentiation and by the molecular heterogeneity of the populations generated. We report a combination of small molecules that induce up to 50% motor neurons within 3 weeks from human pluripotent stem cells with defined subtype identities that are relevant to neurodegenerative diseases. Despite their accelerated differentiation, motor neurons expressed combinations of HB9, ISL1 and column-specific markers that mirror those observed in vivo in human fetal spinal cord. They also exhibited spontaneous and induced activity, and projected axons towards muscles when grafted into developing chick spinal cord. Strikingly, this novel protocol preferentially generates motor neurons expressing markers of limb-innervating lateral motor column motor neurons (FOXP1+/LHX3-). Access to high-yield cultures of human limb-innervating motor neuron subtypes will facilitate in-depth study of motor neuron subtype-specific properties, disease modeling, and development of large-scale cell-based screening assays.
Project description:We performed RNA-seq experiments on two samples (cortical neurons and spinal motor neurons) from normal induced pluripotent stem cells (iPSCs), and another two samples (cortical neurons and spinal motor neurons) derived from SPG3A (an early onset form of hereditary spastic paraplegia) iPSCs. This initial experiment is to test the system and set up a baseline for future studies. Cortical projection neurons and spinal motor neurons were differentiated from same batch of iPSCs in parallel to minimize variations. The differentiation of cortical neurons and spinal motor neurons are based on protocols well-established in our group.
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)
Project description:3 subtypes of cortical projection neurons were purified by fluorescence-activated cell sorting at 4 different stages of development from mouse cortex. A detailed description of the data set is described in Arlotta, P et al (2005). Keywords = corticospinal motor neuron callosal corticotectal cortex development FACS
Project description:3 subtypes of cortical projection neurons were purified by fluorescence-activated cell sorting (FACS) at 4 different stages of development from mouse cortex. A detailed description of the data set is described in Arlotta, P et al (2005) and Molyneaux, BJ et al (2009). The hybridization cocktails used here were originally applied to the Affymetrix mouse 430A arrays and submitted as GEO accession number GSE2039. The same hybridization cocktails were then applied to the Affymetrix mouse 430 2.0 arrays, and those data are contained in this series. Experiment Overall Design: Three subtypes of cortical neurons were purified by FACS at multiple stages of mouse brain development. The neuron subtypes are: corticospinal motor neurons (CSMN), callosal projection neurons (CPN), and corticotectal projection neurons (CTPN). The stages of development included embryonic day 18 (E18), postnatal day 3 (P3), postnatal day 6 (P6), and postnatal day 14 (P14). CSMN and CPN were analyzed at all four stages, while CTPN were only analyzed at P14. The replicates included in the data set are all true biological replicates with independent sample collection for each.
Project description:Sensorimotor reflex circuits engage distinct neuronal subtypes, defined by precise connectivity, to transform sensation into compensatory behavior. Whether and how motor partner populations shape the subtype fate and connectivity of their pre-motor counterparts remains controversial. Here, we discovered that motor partners are dispensable for proper connectivity across an entire vestibular reflex circuit that stabilizes gaze. We first measured activity following vestibular sensation in pre-motor projection neurons after constitutive loss of their extraocular motor neuron partners.We observed normal responses and topography consistent with unchanged functional connectivity between sensory neurons and projection neurons. Next, we show that projection neurons remain anatomically and molecularly poised to connect appropriately with their motor partners. Lastly, we show that the transcriptional signatures of projection neuron subtypes develop independently of motor partners. Our findings comprehensively overturn a long-standing model: that connectivity in the circuit for gaze stabilization is retrogradely determined by motor partner-derived signals. By defining the contribution of motor neurons to canonical sensorimotor circuit assembly, our work speaks to comparable processes in spinal circuits and advances our understanding of general principles of neural development.
Project description:Egr3 is a zinc-finger transcription factor involved in growth and development. Egr3-deficient mice have severe sensory ataxia due to failed development of muscle spindle stretch receptors. Sensory and motor neurons that normally innervate spindles are absent in Egr3-deficient mice, presumably as a secondary consequence to the loss of trophic signals produced by spindles during development that are required for innervation and neuron survival. The molecular mechanisms involving motor neuron fate specification, target derived growth factor dependencies, and specification of target innervation have been difficult to study since select markers for functionally specific motor neurons are very poorly characterized. A more thorough understanding of the molecular mediators of motor neuron biology will be important to evaluate the efficacy of new strategies devised to thwart neuron death that occurs in a variety of human motor neuronopathies and neuropathies. To identify genes specifically expressed by spinal cord fusimotor neurons: Many motor neuron specific genes have been described over the years. However, none have been described that distinguish fusimotor neurons from skeletomotor neurons despite the fact that they have distinct muscle targets (muscle spindle stretch receptors) and comprise 25-30% of the spinal motor neuron populations. Since these motor neurons have remarkably different target innervation and function, we hypothesize that they express genes that establish their specific phenotypes during development. We hypothesize that fusimotor neurons can be distinguished in the spinal cord by characterizing fusimotor neuron specific gene expression. Once fusimotor neuron specific genes are identified, they will be used as markers to identify fusimotor neurons in complex neuroglial cell populations in vivo and in vitro. We hypothesize that by characterizing fusimotor neuron specific genes, unique marker molecules will be identified for in vivo and in vitro study of this functionally distinct and important motor neuron subtype. Moreover, we hypothesize that many of the genes that are specifically expressed by fusimotor neurons will be involved in mechanisms related to their fate specification, target innervation and growth factor dependent biology. We will use the Affymetrix microarray platform to identify genes that are specifically expressed by fusimotor neurons in mouse spinal cord. The differential expression analysis will be performed on microdissected segments of spinal cord (L3-L5) from wild type and Egr3-deficient mice. Postnatal Egr3-deficient mice lack muscle spindles and fusimotor neurons in their spinal cords. By comparing gene expression from microdissected segments of spinal cord (L3-L5) between wild type and Egr3-deficient mice, we hypothesize that fusimotor neuron selective genes can be identified. We will microdissect L3-L5 segments of spinal cord using precise anatomical landmarks to ensure that comparable spinal cord regions are anlayzed from each animal. For each microarray experiment, total RNA will be extracted from L3-L5 cords (approximately 2 mm length of spinal cord). The integrity of each RNA sample will be verified by gel electrophoresis. The intact RNA samples from mice of similar genotype will be pooled from three (3) 27-day old animals. The intact cord dissection is easier in young animals (eg: 27-day old) and the phenotype is known to exist at this developmental stage. The RNA from each animal of a similar genotype will be pooled into a single sample to minimize false positive gene calls that may represent genes related to the specific state of vigilance of a particular animal at the time of sacrifice (eg: activity dependent genes). Thus, each of the two RNA samples to be analyzed for a particular microarray experiment will represent RNA from three (3) spinal cords of each genotype. RNA amplification for probe synthesis should not be necessary since we will provide 7 ug of intact pooled total RNA for each sample. For statistical analysis, the experiment will be performed twice. Since the RNA samples are precious, they will be provided to the Array Consortium in two shipments with each of the experiments performed independently.
Project description:Neuronal diversification is a fundamental step in the construction of functional neural circuits, yet how neurons generated from single progenitor domains acquire diverse subtype identities remains poorly understood. Here, we developed a stem cell-based system to model subtype diversification of V1 interneurons, a class of spinal neurons comprising four clades, each containing dozens of molecularly distinct neuronal subtypes. We demonstrate that V1 subtype diversity is not hard-wired and can be modified by extrinsic signals. Inhibition of Notch and activation of retinoid signaling results in a switch to MafA clade identity and enriches differentiation of Renshaw cells, a specialized MafA subtype that mediates recurrent inhibition of spinal motor neurons. We show that in vitro-generated Renshaw cells migrate into appropriate spinal laminae upon transplantation and form subtype-specific synapses with motor neurons. Our results demonstrate that stem cell-derived neuronal subtypes can be used to investigate mechanisms underlying neuronal subtype specification and circuit assembly.