Reelin-Dab1 signaling in L6 neuron orientation and dendritogenesis. In the absence of Reelin signaling (r/r explant, lower panel), L6 neurons had the same total neurite arbor length as wild type (wt explant, upper panel). However, neurons in the mutant had more primary neurites that were longer and less branched than control primary neurites. Additionally, the primary neurites and neuronal somata in the mutant were oriented tangentially rather than radially. Notably, L6 neuron neurites failed to penetrate the MZ in the mutant despite their normal length. These observed defects are hypothesized to be consistent with the operation of an inhibitory signal (purple zone) present in the MZ that is counteracted by Reelin signaling.