Search

Oligodendrocytes myelinate axons in the central nervous system and develop from oligodendrocyte precursor cells (OPCs) that must first migrate extensively during brain and spinal cord development. We show that OPCs require the vasculature as a physical substrate for migration. We observed that OPCs of the embryonic mouse brain and spinal cord, as well as the human cortex, emerge from progenitor domains and associate with the abluminal endothelial surface of nearby blood vessels. Migrating OPCs crawl along and jump between vessels. OPC migration in vivo was disrupted in mice with defective vascular architecture but was normal in mice lacking pericytes. Thus, physical interactions with the vascular endothelium are required for OPC migration. We identify Wnt-Cxcr4 (chemokine receptor 4) signaling in regulation of OPC-endothelial interactions and propose that this signaling coordinates OPC migration with differentiation., (Copyright © 2016, American Association for the Advancement of Science.)

Developmental regulation of gliogenesis in the mammalian CNS is incompletely understood, in part due to a limited repertoire of lineage-specific genes. We used Aldh1l1-GFP as a marker for gliogenic radial glia and later-stage precursors of developing astrocytes and performed gene expression profiling of these cells. We then used this dataset to identify candidate transcription factors that may serve as glial markers or regulators of glial fate. Our analysis generated a database of developmental stage-related markers of Aldh1l1+ cells between murine embryonic day 13.5-18.5. Using these data we identify the bZIP transcription factor Nfe2l1 and demonstrate that it promotes glial fate under direct Sox9 regulatory control. Thus, this dataset represents a resource for identifying novel regulators of glial development., (Copyright © 2013 Wiley Periodicals, Inc.)

Astrocytes, the most abundant cell population in the central nervous system (CNS), are essential for normal neurological function. We show that astrocytes are allocated to spatial domains in mouse spinal cord and brain in accordance with their embryonic sites of origin in the ventricular zone. These domains remain stable throughout life without evidence of secondary tangential migration, even after acute CNS injury. Domain-specific depletion of astrocytes in ventral spinal cord resulted in abnormal motor neuron synaptogenesis, which was not rescued by immigration of astrocytes from adjoining regions. Our findings demonstrate that region-restricted astrocyte allocation is a general CNS phenomenon and reveal intrinsic limitations of the astroglial response to injury.

Expansion of astrocyte populations in the central nervous system is characteristic of evolutionarily more complex organisms. However, regulation of mammalian astrocyte precursor proliferation during development remains poorly understood. Here, we used Aldh1L1-GFP to identify two morphologically distinct types of proliferative astrocyte precursors: radial glia (RG) in the ventricular zone and a second cell type we call an 'intermediate astrocyte precursor' (IAP) located in the mantle region of the spinal cord. Astrogenic RG and IAP cells proliferated in a progressive ventral-to-dorsal fashion in a tight window from embryonic day 13.5 until postnatal day 3, which correlated precisely with the pattern of active ERK signalling. Conditional loss of BRAF function using BLBP-cre resulted in a 20% decrease in astrocyte production, whereas expression of activated BRAFV600E resulted in astrocyte hyperproliferation. Interestingly, BRAFV600E mitogenic effects in astrocytes were restricted, in part, by the function of p16INK4A-p19(ARF), which limited the temporal epoch for proliferation. Together, these findings suggest that astrocyte precursor proliferation involves distinct RG and IAP cells; is subjected to temporal and spatial control; and depends in part on BRAF signalling at early stages of mammalian spinal cord development.

Establishment of the cytoarchitecture of the central nervous system reflects the stereotyped cell migration and proliferation of precursor cells during development. In vitro analyses have provided extensive information on the control of proliferation and differentiation of oligodendrocyte precursors (OPCs), but less is known about the migratory behavior of these cells in vivo. Here we utilize a transgenic mouse line expressing enhanced green fluorescent protein (EGFP) under the proteolipid protein promoter (PLP-EGFP mice) to visualize directly the behaviors of OPCs in developing spinal cord slices. During early development, OPCs disperse from their origin at the ventricular zone by using saltatory migration. This involves orientation of the cell with a leading edge toward the pial surface and alternating stationary and fast-moving phases and dramatic shape changes. Once cells exit the ventricular zone, they exhibit an exploratory mode of migration characterized by persistent translocation without dramatic changes in cell morphology. The control of migration, proliferation, and cytokinesis of OPCs appear to be closely linked. In netrin-1 mutant spinal cords that lack dispersal cues, OPC migration rates were not significantly different, but the trajectories were altered, and numbers of migrating cells were dramatically reduced. In contrast to DNA replication that occurs at the ventricular zone or throughout the spinal cord neuropil, cell division or cytokinesis of OPCs occurs predominantly at the interface between gray and white matters, with the majority of cleavage planes parallel to the pial surface. These studies suggest that positional cues are critical for regulating OPC behavior during spinal cord development.

Successful CNS myelination is dependent on the correct localization of oligodendrocytes and their interactions with adjacent axons. In the spinal cord, oligodendrocyte precursors originate at the ventral midline and subsequently migrate to the white matter where they mature. In vitro studies suggest this dispersal is mediated by the guidance molecule netrin-1. Here, we show that in the spinal cord of netrin-1 mutant mice, oligodendrocyte precursors failed to disperse from the ventral midline as a consequence of a lack of polarization and directional migration. The lack of netrin-1 also resulted in an overall reduction of oligodendrocyte lineage cells that was independent of the failure of initial dispersal. Oligodendrocyte precursors injected into presumptive white matter underwent extensive radial migration and expansion in wild-type but not netrin-1 mutant hosts. These data indicate that netrin-1 is crucial for both the initial dispersal of spinal cord oligodendrocyte precursors and their subsequent development in the presumptive white matter.

In spinal cord, oligodendrocyte precursors that give rise to myelin-forming cells originate in a restricted domain of the ventral ventricular zone. During development, these cells migrate widely throughout the spinal cord. Netrin 1 is expressed at the ventral ventricular zone during oligodendrocyte precursors emigration, and, in vitro, netrin 1 acts as chemorepellent and antagonizes platelet-derived growth factor (PDGF) chemoattraction. Oligodendrocyte precursors express the netrin receptors DCC and UNC5 and function-blocking anti-DCC antibody inhibits chemorepulsion of ventral spinal cord explants and netrin-secreting cells. In spinal cord slice preparations, addition of function-blocking anti-DCC antibody or netrin 1 dramatically inhibits oligodendrocyte precursor migration from the ventral ventricular zone. These data indicate the initial dispersal of oligodendrocyte precursors from their localized origin is guided by a chemorepellent response to netrin 1.

Spinal cord oligodendrocytes originate in the ventricular zone and subsequently migrate to white matter, stop, proliferate, and differentiate. Here we demonstrate a role for the chemokine CXCL1 and its receptor CXCR2 in patterning the developing spinal cord. Signaling through CXCR2, CXCL1 inhibited oligodendrocyte precursor migration. The migrational arrest was rapid, reversible, concentration dependent, and reflected enhanced cell/substrate interactions. White matter expression of CXCL1 was temporo-spatially regulated. Developing CXCR2 null spinal cords contained reduced oligodendrocytes, abnormally concentrated at the periphery. In slice preparations, CXCL1 inhibited embryonic oligodendrocyte precursor migration, and widespread dispersal of postnatal precursors occurred in the absence of CXCR2 signaling. These data suggest that population of presumptive white matter by oligodendrocyte precursors is dependent on localized expression of CXCL1.