Conservation and Divergence of Related Neuronal Lineages in the Drosophila Central Brain

Wiring a complex brain requires enormous cell specificity. This specificity is laid out via a developmental process where neural stem cells produce countless diverse neurons. To help elucidate this process and resolve the considerable dynamic specificity, we need to observe the development of multiple neuronal lineages. central brain lineages are predetermined, comprised of a fixed set of neurons born in pairs in a specific order. To reveal specific roles of lineage identity, Notch-dependent sister fate specification, and temporal patterning in morphological diversification, we mapped approximately one quarter of the central brain lineages. While we found large aggregate differences, we also discovered similar patterns of morphological specification and diversification. Lineage identity plus Notch state govern primary neuronal trajectories, whereas temporal fates diversify terminal elaborations in target-specific manners. In addition, we identified ‘related’ lineages of analogous neuron types produced in similar temporal patterns. Two stem cells even yield identical series of dopaminergic neuron types, but with completely disparate sister neurons. These phenomena suggest that large changes in morphological diversity can be the consequence of relatively small differences in lineage fating. Taken together, this large-scale lineage mapping study reveals that relatively simple rules drive incredible neuronal complexity.