Scaling Proprioceptor Gene Transcription by Retrograde NT3 Signaling

Abstract

Cell-type specific intrinsic programs instruct neuronal subpopulations before target-derived factors influence later neuronal maturation. Retrograde neurotrophin signaling controls neuronal survival and maturation of dorsal root ganglion (DRG) sensory neurons, but how these potent signaling pathways intersect with transcriptional programs established at earlier developmental stages remains poorly understood. Here we determine the consequences of genetic alternation of NT3 signaling on genome-wide transcription programs in proprioceptors, an important sensory neuron subpopulation involved in motor reflex behavior. We find that the expression of many proprioceptor-enriched genes is dramatically altered by genetic NT3 elimination, independent of survival-related activities. Combinatorial analysis of gene expression profiles with proprioceptors isolated from mice expressing surplus muscular NT3 identifies an anticorrelated gene set with transcriptional levels scaled in opposite directions. Voluntary running experiments in adult mice further demonstrate the maintenance of transcriptional adjustability of genes expressed by DRG neurons, pointing to life-long gene expression plasticity in sensory neurons.

Etv1 Inactivation Reveals Proprioceptor Subclasses that Reflect the Level of NT3 Expression in Muscle Targets

“…Indeed, changing muscle NT3 expression levels in transgenic mice has been reported to erode the selective connectivity of proprioceptive afferents with target MNs (Wang et al, 2007). Furthermore, recent studies have demonstrated profound changes in gene expression in pSNs in response to elevated NT3 signaling (Lee et al, 2012). …”

Subcutaneous Neurotrophin-3 infusion induces corticospinal neuroplasticity and improvements in dexterity and walking in elderly rats after large cortical stroke

“…We have now begun a program of work designed to dissect the mechanisms whereby NT-3 promotes recovery. We are currently testing the hypothesis that NT3 enters the DRG and causes changes in gene expression in proprioceptive neurons in adult rats after stroke, as has been shown in development, which then drives central changes 22 .…”

“…This is a clinically-straightforward route after ischemic stroke in humans. Peripherally administered neurotrophins accumulate in sensory ganglia where they can cause gene transcription, axon growth of primary afferents, and synapse strengthening within locomotor circuits 8,[22][23][24][25][26][27] . Because >90% of strokes occur in people older than 65 with comorbidities including carotid arterial stenosis 28 , we evaluated the effectiveness of NT-3 in elderly rats with large cortical strokes caused by distal middle cerebral artery occlusion and common carotid occlusion 29 .…”

RNAseq dataset describing transcriptional changes in cervical sensory ganglia after bilateral pyramidotomy and forelimb intramuscular gene therapy with AAV1 encoding human neurotrophin-3

“…Neurotrophin-3 signals through its canonical receptor TrkC which is known to be expressed in many large neurons as shown by immunolabelling, in situ hybridization and RNAseq of purified subpopulations of DRG neurons [4,7,8]. In our experiment, no isoform of TrkC (Ntrk3, NM_019248, NM_182809.2 or NM_001270656) was detected, probably because our samples consisted of homogenized DRG in which TrkC expressing cells form only a small proportion of all neurons [~10% of cells in lumbar DRG are neurons [9] and ~17% of neurons are TrkC positive in L4/5 DRG [8] thus the overall proportion of TrkC expressing cells will be ~1.7% of cells in DRG].…”

“…To identify genes that might be regulated in TrkC+ neurons by NT3 in our experiment, we took advantage of a publicly available microarray dataset (GSE38074) containing information about expression of mRNAs (but lacking information about small RNAs) in fluorescence-activated cell sorted TrkC + neurons from the postnatal day 0 DRG either of mice with increased muscular neurotrophin-3 (mlcNT3 versus wildtype control) or of mice lacking neurotrophin-3 (on a Bax knockout background to prevent cell death during development; NT3KO BaxKO versus BaxKO) [7]. We sought genes whose levels correlated positively with NT3 levels and discovered five genes (Spry4, Rasgef1c, Rtn4ip1, Plk2 and Vgf; Table 2) whose levels were higher in our main comparison (bPYX+NT3 vs bPYX+GFP) and also higher in mlcNT3 vs wildtype and also lower in NT3KO BaxKO vs BaxKO (p-values<0.05; see Table 2 for fold changes).…”