Adult Spinal Cord Radial Glia Display a Unique Progenitor Phenotype

Audrey Petit,Wolfram Tetzlaff,Rachel A. Dalley,Katie J. Glattfelder,Timothy E. Kennedy,Ralph B. Puchalski,Ashley D. Sanders,Allan R. Jones,A. Jane Roskams,Pranela Rameshwar

doi:10.1371/journal.pone.0024538

Abstract

Radial glia (RG) are primarily embryonic neuroglial progenitors that express Brain Lipid Binding Protein (Blbp a.k.a. Fabp7) and Glial Fibrillary Acidic Protein (Gfap). We used these transcripts to demarcate the distribution of spinal cord radial glia (SCRG) and screen for SCRG gene expression in the Allen Spinal Cord Atlas (ASCA). We reveal that neonatal and adult SCRG are anchored in a non-ventricular niche at the spinal cord (SC) pial boundary, and express a “signature” subset of 122 genes, many of which are shared with “classic” neural stem cells (NSCs) of the subventricular zone (SVZ) and SC central canal (CC). A core expressed gene set shared between SCRG and progenitors of the SVZ and CC is particularly enriched in genes associated with human disease. Visualizing SCRG in a Fabp7-EGFP reporter mouse reveals an extensive population of SCRG that extend processes around the SC boundary and inwardly (through) the SC white matter (WM), whose abundance increases in a gradient from cervical to lumbar SC. Confocal analysis of multiple NSC-enriched proteins reveals that postnatal SCRG are a discrete and heterogeneous potential progenitor population that become activated by multiple SC lesions, and that CC progenitors are also more heterogeneous than previously appreciated. Gene ontology analysis highlights potentially unique regulatory pathways that may be further manipulated in SCRG to enhance repair in the context of injury and SC disease.

Highlights

The cellular neuroanatomy of the spinal cord (SC) is well established, we have little understanding of the distinct molecular expression patterns that underpin the functional heterogeneity of its constituent cells
To begin to investigate the cellular heterogeneity of gene expression in SC progenitors, we used combinations of classic Radial glia (RG) genes (e.g. Blbp, Glast) to map the presence and distribution of progenitors of the central canal (CC) and putative spinal cord radial glia (SCRG) at PND 4, based on their distinct morphology and expression pattern (Fig. 1A–J). This was used as a guide to blindly score genome-wide SC in situ hybridization (ISH) patterns at both PND 4 and PND 56, to produce an RG-specific gene expression dataset that was augmented by assessing SCRG for known genes enriched in neural stem cells (NSCs) that may have been missed in the original screen
The gene set identified in both adult and neonatal SCRG includes many established genes commonly expressed in neurogenic embryonic cortical RG, and adult central nervous system (CNS) progenitors

Summary

Introduction

The cellular neuroanatomy of the SC is well established, we have little understanding of the distinct molecular expression patterns that underpin the functional heterogeneity of its constituent cells. SCRG form a scaffold for the outward migration of newborn neurons that populate the gray matter (GM) [7,8,9,10], after which their soma relocate to the sub-pial edge of the SC (by embryonic day E20), and retract their processes before terminally differentiating into astrocytes (post natal day 15; PND 15) [8,11]. This astrocytic differentiation is defined by increased GFAP expression and the loss of GLAST, BLBP, vimentin and nestin [10,12]

Methods

Results

Conclusion