Reelin is a detachment signal in tangential chain-migration during postnatal neurogenesis

During development, Reelin acts on migrating neuronal precursors and controls correct cell positioning in the cortex and other brain structures by a hitherto unidentified mechanism. Here we show that in the postnatal mouse brain, Reelin acts as a detachment signal for chain-migrating interneuron precursors in the olfactory bulb. Neuronal precursors cultured in Matrigel detached from chains and migrated individually in the presence of exogenously added Reelin protein or Reelin-expressing brain tissues. Furthermore, we found that in reeler mutant mice, neuronal precursors accumulated in the olfactory bulb and remained in clusters, indicating that they did not change from tangential chain-migration to radial individual migration. Our data provide direct evidence that Reelin acts as a detachment signal, but not a stop or guidance cue. We propose that Reelin may have comparable functions during development.