title: The structural role of radial glial endfeet in confining spinal motor neuron somata is controlled by the Reelin and Notch pathways.
abstract: Neuronal migration is a fundamental biological process that enables the precise positioning of neurons to form functional circuits. Cortical neurons migrate along glial scaffolds formed by radial glia guided by Reelin ligand. However, it is unclear whether the Reelin-directed behavior of radial glia is also critical for positioning the spinal neurons. Here we demonstrate a novel role of radial glia that confines motor neurons within the neural tube and is promoted by Reelin and Notch signaling. Spinal radial glia express the Dab1 adaptor for Reelin signaling and are surrounded by Reelin. In reeler mice, in which Reelin is absent, ectopic motor neurons are found outside the neural tube, although they appear to maintain their identity. Boundary cap (BC) cells, Schwann cell precursors and the basal lamina at motor exit points are intact, whereas the glia limitans of radial glia are disorganized and detached from the basement membrane. The sparse and irregular radial scaffold is wide enough to allow motor somata to pass. Forced activation of Notch signaling rescued the structural defects in radial glia in reeler mice and the appearance of extraspinal neurons. In the absence of Reelin, Notch intracellular domain (NICD) protein level was reduced. In addition, disrupting the radial glia scaffold by destroying its polarity induced ectopic motor neurons in chick embryos. These findings suggest that activation of the Notch pathways by Reelin is required to establish the radial glial scaffold, a structure that actively constrains motor neuron somata and specifies the CNS-PNS boundary.
authors.affiliation: School of Life Sciences, Bioimaging Research Center and Cell Dynamics Research Center, Gwangju Institute of Science and Technology, Oryong-dong, Buk-gu, Gwangju 500-712, Republic of Korea.
authors.forename: Hojae
authors.initials: H
authors.lastname: Lee
authors.forename: Mi-Ryoung
authors.initials: MR
authors.lastname: Song
mesh_terms: D000818:Animals; D015816:Cell Adhesion Molecules, Neuronal / Q000502:physiology*; D002642:Chick Embryo; D063928:Ependymoglial Cells / Q000473:pathology / Q000502:physiology*; D016326:Extracellular Matrix Proteins / Q000502:physiology*; D005260:Female; D051379:Mice; D008818:Mice, Neurologic Mutants; D009046:Motor Neurons / Q000473:pathology / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000502:physiology*; D011247:Pregnancy; D051881:Receptor, Notch1 / Q000502:physiology*; D000091042:Reelin Protein; D012697:Serine Endopeptidases / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D015816:Cell Adhesion Molecules, Neuronal; D016326:Extracellular Matrix Proteins; D009419:Nerve Tissue Proteins; C497762:Notch1 protein, mouse; D051881:Receptor, Notch1; D000091042:Reelin Protein; C000717128:Reln protein, mouse; D012697:Serine Endopeptidases
keywords: Motor neurons; Notch; Radial glia; Reelin