Conserved genetic signatures parcellate cardinal spinal neuron classes into local and projection subsets

Abstract

Motor and sensory functions of the spinal cord are mediated by populations of cardinal neurons arising from separate progenitor lineages. However, each cardinal class is composed of multiple neuronal types with distinct molecular, anatomical, and physiological features, and there is not a unifying logic that systematically accounts for this diversity. We reasoned that the expansion of new neuronal types occurred in a stepwise manner analogous to animal speciation, and we explored this by defining transcriptomic relationships using a top-down approach. We uncovered orderly genetic tiers that sequentially divide groups of neurons by their motor-sensory, local-long range, and excitatory-inhibitory features. The genetic signatures defining neuronal projections were tied to neuronal birth date and conserved across cardinal classes. Thus, the intersection of cardinal class with projection markers provides a unifying taxonomic solution for systematically identifying distinct functional subsets.

A shared transcriptional code orchestrates temporal patterning of the central nervous system

“…Together, the data argue against sequential expression of these TFs during neuronal maturation because, in such a model, TFs with an early onset of expression would be specific for early maturation stages and would thus, contrary to our observations, expected to be labeled by EdU given at late developmental time points. Consistent with this interpretation, a recent study found similar birthdates for Zfhx3-and Neurod2-positive neurons in the perinatal spinal cord [41]. We therefore conclude that these TFs comprise a temporal code and label distinct subsets of neurons based on their time point of birth in the spinal cord.…”

“…Neurod2/6 control neuropeptide expression in inhibitory neurons in the dorsal horns of the spinal cord [40], and characterization of V2a neuron heterogeneity revealed that Zfhx3 and Neurod2/Nfib divide this neuronal class into a lateral and medial population [29]. Recent evidence further suggests that Zfhx3 and Nfib/Neurod2 partition neurons in the spinal cord into long-range projection and local interneurons [41]. Similar to the spinal cord, Onecut, Pou2f2, and Nfi-TFs label early and late-born neuronal subtypes in the retina and are required for their generation [42][43][44].…”

A Single Cell Atlas of Spared Tissue Below a Spinal Cord Injury Reveals Cellular Mechanisms of Repair

“…We noted that this cluster expressed a diverse set of genes associated with ascending projection neurons from the lumbar spinal cord to the brain, including Lypd1, Tacr1, Zfhx3, Pou6f2, Tac1, Syt4, Fam19a2, Scn9a, Nms, and Pde8b (Fig. 3e) [17][18][19][20][21] . In particular, the expression of Slc17a6 (vGlut2), Zfhx3, and Pou6f2 suggested that some of these cells were likely excitatory neurons that resided in the lateral part of deep dorsal or ventral horn [21][22][23] .…”

“…3e) [17][18][19][20][21] . In particular, the expression of Slc17a6 (vGlut2), Zfhx3, and Pou6f2 suggested that some of these cells were likely excitatory neurons that resided in the lateral part of deep dorsal or ventral horn [21][22][23] . Together, these data suggest that a heterogeneous but rare set of ascending spinal cord neurons induce a RAG signature after contusion injury.…”

Single-cell transcriptomic analysis unveils spinal motor neuron subtype diversity underpinning the water-to-land transition in vertebrates

“…These molecular codes may serve not only as markers, but also provide insights into how precise axon targeting and neural circuit patterning is achieved. This principle seems to be applicable to other neuronal types 81 and adult MNs 26 . Unexpectedly, either by means of trypsin- or papain-based disscociation approaches, we acquired equivalent numbers of MMC (2354 cells) and LMC (2248 cells) MNs, which is inconsistent with the population ratio of brachial LMC to MMC MNs (4:1) in E13.5 mouse embryos 82 .…”