Roles Of Ecdysone Receptor And Epidermal Growth Factor Receptor In Drosophila Optic Lobe Development

The ecdysone receptor(EcR)is a nuclear receptor protein that binds to ecdysone to regulate Drosophila metamorphosis.In addition,EcR protein can affect the courtship,sleep and other behaviors of Drosophila,and also can affect regulate life-span and control oocyte maturity during oogenesis.In the Drosophila optic lobe,EcR plays a role in the maintenance of neuroepithelial cells.EcR protein is dynamically expressed in the optic lobe neuroepithelial cells;when EcR protein is eliminated,neuroepithelial cells in the optic lobe cannot be maintained and are transformed into neural stem cells,which result in lamina and medulla defects.EcR protein has three subtypes,EcR-A,EcR-B1 and EcR-B2.It is not known which subtype of EcR protein is involved in the development of the optic lobe.Here we select different loss-of-function EcR mutants to study the roles of each EcR subtype.We found that EcR-A or EcR-B2 mutant brains have a normal number of neuroepithelial cells,and have no defects in lamina and medulla development.But in EcR-B1 mutant brains,neuroepithelial cells in the optic lobe are not maintained,resulting in lamina and medulla defects.Thus,we conclude that EcR-B1 is required for the maintenance of neuroepithelial cells and its activity inhibits the transformation of neuroepithelial cells into neural stem cells.Epidermal growth factor receptor(EGFR)belongs to the family of receptor tyrosine kinases.The EGFR pathway plays an important role in cell growth,proliferation,and differentiation.Studies have shown that EGFR has an anomalous expression in many solid tumors.We found that when EGFR is inactivated in the brain,neuroepithelial cells increases in number and the transformation of neuroepithelial cells into neural stem cells is inhibited,leading to developmental defects in the lamina and medulla.This indicates that EGFR promotes the transformation of neuroepithelial cells into neural stem cells during the development of the optic lobe.