A Population of Navigator Neurons is Essential for Olfactory Map Formation during Critical Period
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ABSTRACT: In the developing brain, heightened plasticity during the critical period enables the proper formation of neural circuits. Here we identify the “navigator” neurons, a group of perinatally born olfactory sensory neurons, as playing an essential role in establishing the olfactory map during the critical period. The navigator axons project circuitously in the olfactory bulb and traverse multiple glomeruli before terminating in perspective glomeruli. These neurons undergo a phase of exuberant axon growth and exhibit a shortened lifespan. Single cell transcriptome analyses reveal distinct molecular signatures for the navigators. Extending their lifespan prolongs the period of exuberant growth and perturbs axon convergence. Conversely, genetic ablation experiment indicates that, despite postnatal neurogenesis, only the navigators are endowed with the ability to establish a convergent map. The presence and the proper removal of the navigator neurons are both required to establish tight axon convergence into the glomeruli.
Project description:Olfactory sensory neurons (OSNs) transform the stochastic choice of one out of >1000 olfactory receptor (OR) genes into precise and stereotyped axon targeting of OR-specific glomeruli in the olfactory bulb. Here, we show that the PERK arm of the unfolded protein response (UPR) regulates both the glomerular coalescence of like axons, and the specificity of their projections. Subtle differences in OR protein sequences lead to distinct patterns of endoplasmic reticulum (ER) stress during OSN development, converting OR identity into distinct gene expression signatures. We identify the transcription factor Ddit3 as a key effector of PERK signaling that maps OR-dependent ER signaling patterns to the transcriptional regulation of axon guidance and cell adhesion genes, instructing targeting precision. Our results extend the known functions of the UPR from a quality control pathway that protects cells from misfolded proteins, to a sensor of cellular identity that interprets physiological states to direct axon wiring.
Project description:We have discovered subsets of axon guidance molecules and transcription factors that are enriched in specific subsets of olfactory sensory neurons. We have demonstrated guidance activity for three of the candidate axon guidance genes we identified, suggesting that this approach is an efficient method for characterizing guidance systems relevant to olfactory axon targeting.
Project description:In the developing brain, axons exhibit remarkable precision in selecting synaptic partners among many non-partner cells. Teneurins are evolutionarily conserved transmembrane proteins that instruct synaptic partner matching via matched expression and homophilic attraction between synaptic partners. Little is known how intracellular signaling pathways execute this and diverse other functions triggered by extracellular interactions of teneurins. Here, we use in situ proximity labeling to identify Ten-ms intracellular interactome in the Drosophila brain. Genetic interaction using quantitative partner matching assays in both olfactory receptor neurons (ORNs) and projection neurons (PNs) suggest a common pathway Ten-m binds to and negatively regulates a RhoGAP, thus activating the Rac1 small GTPases to promote synaptic partner matching. Developmental analyses with single-axon resolution further reveal that ORN axons initially extend exuberant branches along their trajectory, and those that contact partner PN dendrites are selectively stabilized, accompanied by an increase of local F-actin accumulation.
Project description:This experiment studies the gene expression in the mature olfactory sensory neurons and the intermidiate neuronal progenitors in the olfactory epithelia during the critical period. Mature olfactory sensory neurons from OMP-GFP mice and intermediate neuronal progenitors in the olfactory epithelia from Neurog1-GFP mice were FACS purified. PolyA RNA profiles at P2, P3, P7, P9, and P16 were generated by RNA-Seq.
Project description:Dr. Schwarting's research is focused on the analysis of developmentally regulated cell surface molecules and their role in axon guidance and neuronal migration, using the olfactory system as a model. The interaction of cell surface glycans with endogenous lectins in the extracellular matrix provides one mechanism by which axons can utilize specific pathways as they grow towards their targets. We have a mutant mouse (b3GNT2 KO) that up-regulates the expression of lactosamine containing glycans in a subset of olfactory neurons. Gene expression profiling was performed using control and mutant mice that up-regulate the expression of lactosamine containing glycans in a subset of olfactory neurons. Glycosyltransferase expression that differed between control and mutant mice were identified.
Project description:Olfactory dysfunction is an underestimated symptom in multiple sclerosis (MS). Here, we examined the pathogenic mechanisms underlying inflammation-induced dysfunction of the olfactory bulb using the animal model of MS, experimental autoimmune encephalomyelitis (EAE). Reduced olfactory function in EAE was associated with the degeneration of short-axon neurons, immature neurons, and mitral cells, together with their synaptic interactions and axonal repertoire. To dissect the mechanisms underlying the susceptibility of mitral cells, the main projection neurons of the olfactory bulb, we profiled their responses to neuroinflammation by single-nucleus RNA sequencing. Neuroinflammation resulted in the induction of potassium channel transcripts in mitral cells, which was reflected in reduced halothane-induced outward currents of these cells, likely contributing to the impaired olfaction in EAE animals.
Project description:Olfactory sensory neurons (OSNs) express a single abundant olfactory receptor (OR). To assess the differences in gene expression between different OSN sub-types we collected three pools of neurons that express one OR and compared them to three pools of neurons that express another. After extracting RNA from these pools, the samples were multiplexed and sequenced using the Illumina Hiseq2500 platform.This data is part of a pre-publication release. For information on the proper use of pre-publication data shared by the Wellcome Trust Sanger Institute (including details of any publication moratoria), please see http://www.sanger.ac.uk/datasharing/
Project description:The modified DNA base 5-hydroxymethylcytosine (5hmC) is enriched in neurons where it may contribute to gene function and cellular identity. To address this issue in an in vivo neuronal population, we assessed the patterning, stability, and function of the base within gene bodies in olfactory sensory neurons. We find that gene body 5hmC linearly correlates with transcriptional output and is stable in fully mature neurons and those lacking de novo methyltransferase activity. Overexpression of Tet3, which oxidizes methylated cytosines (5mC) to 5hmC, markedly alters gene body 5hmC levels and provides evidence that 5hmC facilitates transcription. This manipulation disrupts olfactory receptor expression and the targeting of axons to the olfactory bulb, key molecular and anatomical features of the olfactory system that are necessary for proper physiology. Our results support a direct, positive and physiologically significant role for gene body 5hmC in transcriptional elongation and the maintenance of cellular identity independent of its function as an intermediate to demethylation. We assessed the role of 5hmC in mature olfactory sensory neurons by assessing 5hmC levels in 2 month old neurons, olfactory epithelia lacking Dnmt3a, and mOSNs overexpressing Tet3. To determine genome-wide levels of 5hmC, we performed DNA immunoprecipitation coupled to Illumina sequencing. To determine transcript levels, we prepared and sequenced rRNA-depleted cDNA libraries.