EAGLE IS REQUIRED FOR THE SPECIFICATION OF SEROTONIN NEURONS AND OTHER NEUROBLAST-7-3 PROGENY IN THE DROSOPHILA CNS

During development of the Drosophila nerve cord, neuroblast 7-3 gives rise to a pair of mitotic sister serotonin neurons in each hemisegment . Here we show that the zinc finger gene eagle, which is expressed in neuroblast 7-3, is essential for specifying the fate of serotonin neur ons. We find that loss-of-function eagle mutations produce an unusual differential phenotype with respect to the sister serotonin cells and that eagle is necessary for the maintenance of engrailed and zfh-2 exp ression in the serotonin neurons. We present a model that uniquely ide ntifies all progeny neurons in the neuroblast 7-3 lineage based on the expression of specific molecular markers, position within the nerve c ord and the effect of eagle loss-of-function mutations. Although serot onin is an important neurotransmitter conserved throughout the animal kingdom, we show that hypomorphic alleles of eagle can produce viable adults that have a dramatic reduction in the number of serotonin-produ cing neurons.