Project description:Motor control of the striated esophagus originates in the nucleus ambiguus (nAmb), a vagal motor nucleus which also contains upper airway motor neurons and parasympathetic preganglionic neurons for the heart and lungs. We disambiguate nAmb neurons based on their genome-wide expression profiles, efferent circuitry, and ability to control esophageal muscles. Our single-cell RNA-sequencing analysis predicts three molecularly distinct nAmb neuron subtypes and annotates them by subtype-specific marker genes: Crhr2, Vipr2, and Adcyap1. Mapping the axon projections of the nAmb neuron subtypes reveals that Crhr2nAmb neurons innervate the esophagus, raising the possibility that they control esophageal muscle function. Accordingly, focal optogenetic stimulation of cholinergic Crhr2+ fibers in the esophagus results in contractions. Activating Crhr2nAmb neurons has no effect on heart rate, a key parasympathetic function of the nAmb, whereas activating all nAmb neurons robustly suppresses heart rate. Together these results reveal a genetically defined circuit for motor control of the esophagus.
Project description:We report the characterization of a synthetic genetic circuit using RNA-Seq data. Data is collected for all input inducer combinations and cells harboring the circuit are grown in two conditions (14 ml culture tubes and 250 ml Erlenmeyer flasks).
Project description:The fidelity of motor control requires the precise positional arrangement of motor pools and the establishment of synaptic connections between these pools. In the developing spinal cord, motor nerves project to specific target muscles and receive proprioceptive input from the muscles via the sensorimotor circuit. LIM-homeodomain transcription factors are known to successively restrict specific motor neuronal fates during neural development; however, it remains unclear to what extent they contribute to limb-based motor pools and locomotor circuits. Here, we showed in mice that deletion of Isl2 resulted in scattered motor pools, primarily in the median motor column and lateral LMC (LMCl) populations, and lacked Pea3 expression in the hindlimb motor pools, accompanied by reduced terminal axon branching and disorganized neuromuscular junctions. Transcriptomic analysis of Isl2-deficient spinal cords revealed that a variety of genes involved in motor neuron differentiation, axon development, and synapse organization were downregulated in hindlimb motor pools. Moreover, the loss of Isl2 impaired sensorimotor connectivity and hindlimb locomotion. Together, our studies indicate that Isl2 plays a critical role in organizing motor pool position and sensorimotor circuits in hindlimb motor pools.
Project description:The neurodegenerative disease spinal muscular atrophy (SMA) is a leading genetic cause of infant death caused by deficiency in the survival motor neuron (SMN) protein. Currently approved SMA treatments aim to restore SMN, but the potential for expression of SMN beyond physiological levels is a unique feature of AAV9-SMN gene therapy. Here, we show that long-term AAV9-mediated SMN overexpression in mouse models induces dose-dependent, late-onset motor dysfunction associated with loss of proprioceptive synapses and neurodegeneration. Mechanistically, aggregation of overexpressed SMN in the cytoplasm of motor circuit neurons sequesters components of small nuclear ribonucleoproteins (snRNPs), leading to splicing dysregulation and widespread transcriptome abnormalities with prominent signatures of neuroinflammation and innate immune response. Thus, long-term SMN overexpression can interfere with its normal activity in RNA regulation and trigger SMA-like pathogenic events through toxic gain of function mechanisms. These unanticipated, SMN-dependent and neuron-specific liabilities of AAV9-SMN warrant further evaluation of the long-term safety of gene therapy in SMA.
Project description:Neuronal activity-dependent transcription couples sensory experience to adaptive responses of the brain including learning and memory. Mechanisms of activity-dependent gene expression including alterations of the epigenome have been characterized. However, the fundamental question of whether and how sensory experience remodels chromatin architecture in the adult brain in vivo to induce neural code transformations and learning and memory remains to be addressed. Here, in vivo calcium imaging, optogenetics, and pharmacological approaches reveal that granule neuron activation in the anterior dorsal cerebellar vermis (ADCV) plays a crucial role in a novel delay tactile startle learning paradigm in mice. Strikingly, using large-scale transcriptome and chromatin profiling, we have discovered that activation of the motor learning-linked granule neuron circuit reorganizes neuronal chromatin including through long-distance enhancer-promoter and transcriptionally active compartment interactions to orchestrate distinct granule neuron gene expression modules. Conditional CRISPR knockout of the chromatin architecture regulator Cohesin in ADCV granule neurons in adult mice disrupts activity-dependent transcription and motor learning. These findings define how sensory experience patterns chromatin architecture and neural circuit coding in the brain to drive motor learning.
Project description:When performing a computation, genetic circuits change states through a symphony of genetic parts that turn regulator expression on and off. Debugging is frustrated by an inability to measure part function and identify the origins of failures. Here, we take “snapshots” of a large genetic circuit in different states. RNA-seq is used to visualize circuit function as a changing pattern of RNA polymerase (RNAP) flux along the DNA. Together with ribosome profiling, all 54 genetic parts are parameterized. The circuit behaves as designed; however, it is riddled with errors, including cryptic sense/antisense promoters and translation, attenuation, incorrect start codons and a failed gate. While serendipitously not impacting function, they reduce prediction accuracy and could lead to failures when used in other designs. Finally, the cellular power (RNAPs and ribosomes) required to maintain a circuit state is calculated. This work demonstrates the use of a small number of measurements to fully parameterize a regulatory circuit and quantify its impact on host.
Project description:Astrocytes, the most abundant cells in the central nervous system, promote synapse formation and help refine neural connectivity. Although they are allocated to spatially distinct regional domains during development, it is unknown whether region-restricted astrocytes are functionally heterogeneous. Here we show that postnatal spinal cord astrocytes express several region-specific genes, and that ventral astrocyte-encoded Semaphorin3a (Sema3a) is required for proper motor neuron and sensory neuron circuit organization. Loss of astrocyte-encoded Sema3a led to dysregulated α−motor neuron axon initial segment orientation, markedly abnormal synaptic inputs, and selective death of α−but not of adjacent γ−motor neurons. Additionally, a subset of TrkA+ sensory afferents projected to ectopic ventral positions. These findings demonstrate that stable maintenance of a positional cue by developing astrocytes influences multiple aspects of sensorimotor circuit formation. More generally, they suggest that regional astrocyte heterogeneity may help to coordinate postnatal neural circuit refinement. 12 total samples consisting of three biological replicates each of flow sorted postnatal day 7 dorsal spinal cord astrocytes, ventral spinal cord astrocytes, dorsal SC non astrocytes, and ventral SC non astrocytes
Project description:The flexibility of motor actions is ingrained in the diversity of neurons and how they are organized into functional circuit modules, yet our knowledge of the molecular underpinning of motor circuit modularity remains limited. Locomotion is a motor behavior characterized by sudden changes in speed and strength enabled by the coordinated recruitment of different motoneuron subtypes. Here we use adult zebrafish to link the molecular diversity of motoneurons and the rhythm-generating V2a interneurons with their modular circuit organization that is responsible for changes in locomotor speed. We show that the molecular diversity of motoneurons and V2a interneurons reflects their functional segregation into slow, intermediate or fast subtypes. Furthermore, we reveal shared molecular signatures between V2a interneurons and motoneurons of the three speed circuit modules. Overall, by characterizing how the molecular diversity of motoneurons and V2a interneurons relates to their function, connectivity and behavior, our study provides important insights not only into the molecular mechanisms for neuronal and circuit diversity for locomotor flexibility but also for charting circuits for motor actions in general.
Project description:We report the characterization of the 0x58 circuit, a modified version and wild-type cells not containing any circuit. Data is collected for all input inducer combinations and cells harboring the circuit are grown in culture tubes.