Axonal secretion of Reelin by Cajal-Retzius cells: evidence from comparison of normal and Reln(Orl) mutant mice

J Comp Neurol. 2001 Nov 12;440(2):136-43. doi: 10.1002/cne.1375.


A novel secretory pathway has been identified in the study of mice homozygous for the Reln(Orl) mutation, a line characterised by the defective secretion of the large extracellular matrix glycoprotein Reelin. By using both light and electron microscopy, immunohistochemical studies for Reelin in these mutants identified morphological changes in their Cajal-Retzius cells (CR cells). The CR cells of the mutant displayed the characteristic features of bipolar, tangentially elongated neurons with a dendritic proximal pole and an axonal cone at the opposite end of the soma. At either pole, cisterns of prominent rough endoplasmic reticulum (RER) were found to be rich in Reelin. However, the Reelin-positive RER cisterns of the axonal cones were hugely dilated in homozygous Reln(Orl) mice as compared with their wild type counterparts. CR cell axons displayed beads throughout their length, each contained a smooth spheroidal cistern filled with Reelin-immunoreactive fibrillar material, and were increased in number and size in Reln(Orl) mice. RER phenotype was rescued in the Reln(Alb2) mice, a mutation in which no Reelin protein is produced. We propose that the RER dilations viewed in the Reln(Orl) mutation are due to the accumulation of the defective Reelin protein, and the large axonal beads in Reln(Orl) mice reflect the accumulation of truncated Reelin as the result of defects in its secretion. These observations point to an original, hitherto unrecognised, mechanism of secretion by bulk transport in smooth cisterns from the axonal cone into the axon, followed by secretion in the cortical marginal zone from the axonal cisterns that we have named axonal reelin reservoirs.

MeSH terms

  • Acetylcholine / metabolism
  • Acetylcholinesterase / metabolism
  • Animals
  • Body Patterning / genetics*
  • Cell Adhesion Molecules, Neuronal / genetics
  • Cell Adhesion Molecules, Neuronal / metabolism*
  • Cell Compartmentation / physiology
  • Cell Differentiation / genetics*
  • Cell Size / genetics
  • Cerebral Cortex / abnormalities*
  • Cerebral Cortex / metabolism
  • Cerebral Cortex / ultrastructure*
  • Dendrites / metabolism
  • Dendrites / ultrastructure
  • Endoplasmic Reticulum, Rough / metabolism
  • Endoplasmic Reticulum, Rough / pathology
  • Endoplasmic Reticulum, Rough / ultrastructure
  • Extracellular Matrix Proteins / genetics
  • Extracellular Matrix Proteins / metabolism*
  • Fetus
  • Growth Cones / metabolism
  • Growth Cones / pathology
  • Growth Cones / ultrastructure*
  • Immunohistochemistry
  • Mice
  • Mice, Inbred BALB C / embryology
  • Mice, Inbred BALB C / metabolism
  • Mice, Neurologic Mutants / abnormalities*
  • Mice, Neurologic Mutants / metabolism
  • Microscopy, Electron
  • Mutation / physiology
  • Nerve Tissue Proteins
  • Reelin Protein
  • Serine Endopeptidases


  • Cell Adhesion Molecules, Neuronal
  • Extracellular Matrix Proteins
  • Nerve Tissue Proteins
  • Reelin Protein
  • Acetylcholinesterase
  • Reln protein, mouse
  • Serine Endopeptidases
  • Acetylcholine