Roles Of Ecdysone Signaling Proteins EcR And Broad In Drosophila Optic Lobe Development

Broad protein is a DNA-binding protein with C2H2 zinc fingers.Broad is induced by ecdysone,can transduce and amplify ecdysone signal,activate the expression of downstream genes and regulate the metamorphic process of insects.Broad can form four different protein subtypes,namely Z1,Z2,Z3 and Z4 proteins,by alternative splicing.Studies have shown that Broad is widely expressed in the central nervous system of Drosophila melanogaster,and different protein subtypes have different expression patterns,but whether and how Broad protein affects the development of the optic lobes of the Drosophila brain is unknown.In this study,we found that Broad can promote the differentiation of neuroepithelial cells and affect optic lobe development.In order to fully reveal the effect of Broad on the development of optic lobe,the expression levels of Broad were knocked down and increased,respectively.When Broad is inactivated,the number of neuroepithelial cells increases,which inhibits the transformation of neuroepithelial cells into neuroblasts,and causes the developmental defects in the medulla and lamina of the optic lobe;when Broad is overexpressed,the number of neuroepithelial cells decrease,leading to the transformation into neuroblasts prematurely.The ecdysone receptor(EcR)is a nuclear receptor,which binds to ecdysteroid hormone,regulates the expression of early response genes such as broad,E74 and E75 during the metamorphosis of insects.However,whether EcR plays a role in the optic lobe and regulates Broad expression in the optic lobe are not clear.Our study found that EcR inhibits Broad expression in the optic lobe,as inactivation of EcR increased Br-C and Br-Z1 expression in optic neuroepithelial cells.In addition,when EcR was inactivated,neuroepithelial cells were disintegrated,transformed into medulla neuroblasts,causing medulla and lamina defects.Therefore,we conclude that EcR can maintain the state of neuroepithelial cells and inhibit the transformation of neuroepithelial cells into medulla neuroblasts.