Fine processes of Nestin-GFP–positive radial glia-like stem cells in the adult dentate gyrus ensheathe local synapses and vasculature

Abstract

Adult hippocampal neurogenesis relies on the activation of neural stem cells in the dentate gyrus, their division, and differentiation of their progeny into mature granule neurons. The complex morphology of radial glia-like (RGL) stem cells suggests that these cells establish numerous contacts with the cellular components of the neurogenic niche that may play a crucial role in the regulation of RGL stem cell activity. However, the morphology of RGL stem cells remains poorly described. Here, we used light microscopy and electron microscopy to examine Nestin-GFP transgenic mice and provide a detailed ultrastructural reconstruction analysis of Nestin-GFP-positive RGL cells of the dentate gyrus. We show that their primary processes follow a tortuous path from the subgranular zone through the granule cell layer and ensheathe local synapses and vasculature in the inner molecular layer. They share the ensheathing of synapses and vasculature with astrocytic processes and adhere to the adjacent processes of astrocytes. This extensive interaction of processes with their local environment could allow them to be uniquely receptive to signals from local neurons, glia, and vasculature, which may regulate their fate.adult neurogenesis | adult neural stem cell | neurogenic niche | electron microscopy | hippocampus N eurogenesis in the adult mouse brain primarily occurs within discrete niches, the subventricular zone (SVZ), and the subgranular zone (SGZ) of the dentate gyrus, supplying new neurons to the olfactory bulb and the dentate gyrus, respectively (1-3). Neural stem cells of these niches can be activated to divide and generate other stem cells, astrocytes, or new neurons (4, 5). Newborn neurons of the dentate gyrus have the capacity to integrate into the existing hippocampal circuitry (6-8), influencing processes such as learning and memory (9-11) as well as stress and depression (12).Radial glia-like (RGL) neural stem cells of the SVZ, which supply the olfactory bulb with newborn neurons and astrocytes, express astrocytic markers and form elegant pinwheel structures (13-16). RGL neural stem cells of the adult dentate gyrus also express astrocytic markers, but comprise a heterogeneous population based on the molecular markers they express, the morphologies they exhibit (17-22), and their fate (23-28). Nestin-GFP-positive RGL stem cells account for more than 70% of RGL stem cells in the SGZ of the dentate gyrus (24), but it was recently found that not all Nestin-GFP-positive cells with RGL morphology have stem cell properties (29): type β cells, which arborize in the granule cell layer (GCL) but do not reach the molecular layer (ML) of the dentate gyrus, account for 26% of Nestin-GFP-positive RGL stem cells. They express stem cell (Sox1, Sox2, Prominin 1, GFAP, and Nestin) and astrocytic [GFAP, glial glutamate tranporter 1 (GLT1), and S100β] markers but do not proliferate. In contrast, type α cells, which extend across the GCL and arborize in the inner ML, account for 74% of Nestin-GFP-positive RGL cells. They express stem...

Coordinated morphogenesis of neurons and glia

“…Its glial process courses in thin sheets through the outer nuclear layer but becomes wildly branched in the synapse-rich environment of the inner plexiform layer (∼50 μm each layer).In fact, the specificity of glial shape is so tailored to the local environment that Müller glia even elaborate distinct structures at different sublaminar positions within the inner plexiform layer. Such localized morphological differences were also noted in a recent characterization of radial glia-like stem cells in the dentate gyrus[18]. These cells extend thin, twisting processes through the granule cell layer (∼30 μm) and then arborize abruptly upon encountering the molecular layer, where they ensheathe synapses.…”

Role of Mitochondrial Metabolism in the Control of Early Lineage Progression and Aging Phenotypes in Adult Hippocampal Neurogenesis

“…To analyze NSCs of the dorsal dentate gyrus, tissue from transgenic Nestin-GFP mice was processed as previously described (Moss et al, 2016). Briefly, male mice (P83–88) were anaesthetised, transcardially perfused with phosphate-buffered saline (PBS) then fixative, and placed at 4°Cfor24 hr.…”

Mossy Cells Control Adult Neural Stem Cell Quiescence and Maintenance through a Dynamic Balance between Direct and Indirect Pathways

“…Moreover, our morphological data suggest that the direct pathway is mediated by the commissural projection in the IML, while the indirect pathway is mediated by projections terminating on local interneurons in the SGZ or the hilus. Supporting this notion, recent ultrastructural analysis demonstrated that the bushy processes of rNSCs wrap around glutamatergic synapses likely formed between MCs and mature GCs (Moss et al, 2016). Additionally, comparative recordings of patches from soma vs radial processes demonstrated that glutamatergic receptors are present in the radial processes (but not the soma) of the rNSCs (Renzel et al, 2013).…”