Fig. 7. Summary of sequential roles of Notch signaling in neuronal specification in zebrafish. First, Notch mediates lateral inhibition among olig2⁺ pMN precursors to limit the number that exit the cell cycle and differentiate as neurons. Second, different levels of Notch activity in sibling neurons specifies different neuronal fates. Here, cells with relatively high-level Notch signaling develop as KA' interneurons, whereas those with lower activity develop as primary motoneurons (PMNs).