The extracellular protein Reelin is crucial for neuronal positioning during brain development, but its expression persists long after cell migration is completed. In this issue of Neuron, Beffert et al. demonstrate that Reelin exerts an additional function in the mature brain, to modulate synaptic plasticity and to favor memory formation. This activity is carried out exquisitely by the Apoer2 receptor and critically requires the presence of an alternatively spliced exon. This exon encodes an intracellular domain that interacts with postsynaptic proteins and promotes binding and phosphorylation of NMDA receptors.
