The Functions Of Polycomb Group Proteins E(z),Pc And Sce In Drosophila Optic Lobe Development

Polycomb group genes(PcG)encode conserved proteins that regulate animal development and differentiation.PcG protein complexes are divided into four categories,PRC1(Polycomb repressive complexes 1),PRC2(Polycomb repressive complexes 2),PhoRC and PR-DUB.Among them,PRC1 can maintain H3K27me3 and participate in the compression of chromatin.PRC2 plays a role in the initial stage of transcriptional repression.PhoRC can directly bind to DNA.PR-DUB is a newly discovered complex and its function is H2 A deubiquitination.In this study,we investigated the developmental effects of several PcG components in the Drosophila optic lobes.The E(z)protein is a highly conserved protein that is a catalytic component of PRC2 methyltransferase and is capable of methylating histone H3 lysine 27(H3K27me).The Polycomb(Pc)protein is a component of the PRC1 complex that interacts with histone H3K27me3.It is involved in epigenetic silencing,and its target genes are mainly transcription factors or receptors that control cell fate and developmental decisions.The Sce protein is a conserved E3 ubiquitin ligase whose function is to monoubiquitinate H2 A.We expressed E(z)RNAi,Pc RNAi or Sce RNAi to knock down the expression level of E(z),Pc and Sce in the optic lobes of Drosophila.We found that at late-third-instar larval stages,the size of E(z)RNAi brains is smaller than that of wild-type brains,and the medulla and lamina have obvious defects,the OPC neuroepithelial cells(NEs)expressed characteristics of the IPC and the mitotic rate of neuroepithelial cells was reduced.There was also apoptosis occurring in the OPC NEs,and the Hox proteins AbdA and AbdB were ectopically expressed in OPC NEs while Ubx was ectopically expressed in the medulla cortex.In Pc RNAi brains,there is a small piece of OPC NEs protruding to the medulla,and the lamina and the medulla had defects.Fas3 was ectopically expressed in the NEs.There is a certain degree of apoptosis in the NEs.Hox protein Scr is up-regulated in the NEs,but AbdA,AbdB and Ubx were not.When Sce was inactivated,there were some defects in the medulla and lamina.Some neuroepithelial cells in the OPC expressed IPC characteristics,and there is a certain degree of apoptosis.AbdA,AbdB and Ubx were slightly up-regulated in the brain,while Scr was not up-regulated.Together,this study shows that PcG proteins play an important role in Drosophila optic lobe development,andtheir functional loss causes medulla and lamina’s defects.They maintain the OPC identity by inhibiting the transformation of OPC NEs into IPC identity;they also prevent apoptosis and suppress the expression of Hox-related genes.