Interest in the gene was heightened when it became apparent that it is expressed in neuroblasts, and current fascination stems from Eagle's involvement in the determination of serotonergic neurons. Serotonin is an evolutionarily conserved neurotransmitter, found in both invertebrates and vertebrates, and involved in locomotor and behavioral roles. Serotonin is produced in descendents of neuroblast NB 7-3. Since the development of NB 7-3 is understood in some detail, it is of interest to examine gene expression in this lineage. Before discussing the role of Eagle in promoting serotonin neuroblast fate, a short digression will be made to describe to biogenesis of neurotransmitters serotonin and dopamine and the identity of the cells that make these neurotransmitters.
Dopamine is a derivative of the amino acid tyrosine.
TH is expressed only in the midline dopamine cell and the DL-cells, lateral dopamine cells. Serotonin is a derivative of the amino acid tryptophan. This experiment shows that eagle is competent to promote ectopic serotonergic differentiation. These es-cells show neuronal cell morphology and occur at a reproducible, dorsolateral position. This suggests that ectopic serotonin expression does not occur randomly but in specific CNS neurons.