Iron Deficiency Reduces Synapse Formation in the Drosophila Clock Circuit

Iron serves as a critical cofactor for proteins involved in a host of biological processes. In most animals, dietary iron is absorbed in enterocytes and then disseminated for use in other tissues in the body. The brain is particularly dependent on iron. Altered iron status correlates with disorders ranging from cognitive dysfunction to disruptions in circadian activity. The exact role iron plays in producing these neurological defects, however, remains unclear. Invertebrates provide an attractive model to study the effects of iron on neuronal development since many of the genes involved in iron metabolism are conserved, and the organisms are amenable to genetic and cytological techniques. We have examined synapse growth specifically under conditions of iron deficiency in the Drosophila circadian clock circuit. We show that projections of the small ventrolateral clock neurons to the protocerebrum of the adult Drosophila brain are significantly reduced upon chelation of iron from the diet. This growth defect persists even when iron is restored to the diet. Genetic neuronal knockdown of ferritin 1 or ferritin 2, critical components of iron storage and transport, does not affect synapse growth in these cells. Together, these data indicate that dietary iron is necessary for central brain synapse formation in the fly and further validate the use of this model to study the function of iron homeostasis on brain development.