Wiring the Drosophila Brain with Individually Tailored Neural Lineages.

A complex brain consists of multiple intricate neural networks assembled from distinct sets of input and output neurons as well as region-specific local interneurons. Within a given anatomical set, there exist diverse neuronal types that can vary in morphology, neural physiology, and modes of neurotransmission. The genetic programs that guide specification of neuronal types during neurogenesis preconfigure the brain. This is best demonstrated in the Drosophila central brain, which is composed of ∼100 pairs of individually tailored neuronal lineages. Each neuronal lineage (the neurons/glia produced from a single stem cell) can contain multiple morphological classes of neurons that can consist of many analogous neuronal types. The detailed patterns of neuronal diversification are lineage-specific and can differ drastically even among neighboring neuronal lineages. Furthermore, the interrelationships between neuronal lineages and neural networks are complex. These phenomena underscore the importance of tracking all neuronal lineages in understanding brain development and evolution.