Project description:During development neurons achieve a high degree of specialization (Fishell and Heintz, 2013). Over time, while continuously recycling their components and despite transcriptional noise, their own respective properties remain intact. The transcription factors that play a large role in initially establishing neuronal identity can be required for maintaining it (Deneris and Hobert, 2014). Post-transcriptional regulation is also important to differentiation (Bian and Sun, 2011) but its role in maintaining cell identity is less established. To better understand how post-transcriptional regulation might contribute to cell identity, we examined the proprioceptive neurons in the dorsal root ganglion (DRG), a highly specialized sensory class, whose properties are well established and display clear differences when compared to other neurons in the ganglion. By conditionally ablating Dicer in mice, using a parvalbumin (Pvalb) driven cre, we impaired post-transcriptional regulation in the proprioceptive sensory neuron population. KO animals display a progressive form of ataxia at the beginning of the fourth postnatal week that is mirrored by a cell-death within the DRG. Before cell-loss, expression profiling shows a reduction of proprioceptor specific genes and an increased expression of non-proprioceptive genes normally enriched in other ganglion neurons. Furthermore, although central connections of these neurons are intact, the peripheral connections to the muscle are functionally impaired. Post-transcriptional regulation is therefore necessary to retain the transcriptional identity and support functional specialization of the proprioceptive sensory neurons.
Project description:We use comprehensive and unsupervised transcriptome analyses to provide molecular classifications of sensory neurons in the mouse geniculate ganglion. 96 neurons were isolated on a C1 Fluodigm chip, underwent RNA-Seq, and iteratively clustered into sub-classes.
Project description:Proprioception relies on two main classes of proprioceptive sensory neurons (pSNs). These neurons innervate two distinct peripheral receptors in muscle, muscle spindles (MSs) or Golgi tendon organs (GTOs), and synapse onto different sets of spinal targets, but the molecular basis of their distinct pSN subtype identity remains unknown. We used microarray analysis to compare gene expression profiles between MS- and GTO- innervating proprioceptors.
Project description:Proprioception relies on two main classes of proprioceptive sensory neurons (pSNs). These neurons innervate two distinct peripheral receptors in muscle, muscle spindles (MSs) or Golgi tendon organs (GTOs), and synapse onto different sets of spinal targets, but the molecular basis of their distinct pSN subtype identity remains unknown. We used microarray analysis to compare gene expression profiles between MS- and GTO- innervating proprioceptors. We generated transgenic mice in which MS and GTO pSNs are labelled with different fluorescent proteins (see de Nooij et al., 2015 for details). We used Fluorescent Activated Cell Sorting (FACS) to isolate the MS and GTO pSN subsets from dissociated DRG from p7-10 transgenic mice. Neurons from multiple FACS experiments were pooled into three samples each for the MS and GTO pSN subset.
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.
Project description:Proprioceptive neurons (PNs) are essential for the proper execution of all our movements by providing muscle sensory feedback to the central motor network. Here, using deep single cell RNAseq of adult PNs coupled with advanced virus- and genetic tracings, we have molecularly identified the 3 main types of PNs (Ia, Ib and II) and unexpectedly found that they segregate into 8 subgroups. Our data further reveal a highly sophisticated organization of PNs into discrete sensory input channels with distinct spatial distribution, innervation patterns and molecular profiles, that together contribute to the sensory monitoring of complex motor behavior. Moreover, while Ib- and II-PN subtypes are specified around birth, Ia-PN subtypes diversify later along with increased motor activity and show versatility in the adult following exercise training, suggesting adaptive proprioceptive function.
Project description:Introgressed variants from other species can be an important source of genetic variation because they may arise rapidly, can include multiple mutations on a single haplotype, and have often been pretested by selection in the species of origin. Although introgressed alleles are generally deleterious, several studies have reported introgression as the source of adaptive alleles-including the rodenticide-resistant variant of Vkorc1 that introgressed from Mus spretus into European populations of Mus musculus domesticus. Here, we conducted bidirectional genome scans to characterize introgressed regions into one wild population of M. spretus from Spain and three wild populations of M. m. domesticus from France, Germany, and Iran. Despite the fact that these species show considerable intrinsic postzygotic reproductive isolation, introgression was observed in all individuals, including in the M. musculus reference genome (GRCm38). Mus spretus individuals had a greater proportion of introgression compared with M. m. domesticus, and within M. m. domesticus, the proportion of introgression decreased with geographic distance from the area of sympatry. Introgression was observed on all autosomes for both species, but not on the X-chromosome in M. m. domesticus, consistent with known X-linked hybrid sterility and inviability genes that have been mapped to the M. spretus X-chromosome. Tract lengths were generally short with a few outliers of up to 2.7 Mb. Interestingly, the longest introgressed tracts were in olfactory receptor regions, and introgressed tracts were significantly enriched for olfactory receptor genes in both species, suggesting that introgression may be a source of functional novelty even between species with high barriers to gene flow.
Project description:Muscle-specific populations of proprioceptive sensory neurons form selective connections with spinal motor neurons, implying the existence of molecular distinctions between proprioceptor subpopulations. Here, we compare the gene expression profiles of proprioceptors that supply an antagonistic muscle pair functioning at a single hindlimb joint.
Project description:Muscle-specific populations of proprioceptive sensory neurons form selective connections with spinal motor neurons, implying the existence of molecular distinctions between proprioceptor subpopulations. Here, we compare the gene expression profiles of proprioceptors that supply an antagonistic muscle pair functioning at a single hindlimb joint.