Using The Drosophila System, High-throughput Screening Of Human Genes And The Mechanism For The Regulation Of Cell Size

The fruit fly Drosophila melanogaster is one of the best-studied model organisms. Drosophila's powerful genetics,its intermediate complexity,and its similarity to mammalian biology at the molecular level,makes it particularly well suited for the study of human genes function and developmental biology.Human genome sequencing has been completed.The hot spot available is focused on so-called "Epigenomics" aimed to probe human genes functions.However,the way to analyse the in vivo function of these human genes comes to a bottleneck.In the first part of the thesis,we used GAL4/UAS system to elucidate human genes function effectively.Induced by different types of tissue specific GAL4 lines,among 59 genes, transgenic flies corresponding to five genes of interest showed abnormal phenotypes. These five genes included the gene human housekeeping gene-ribosomal protein L8 which would be described in detail in the next part.All these results implies the feasibility of systematically screening human genes functions by overexpression in Drosophila.Here,we found that overexpression of a dominant negative mutant form of human RPL8(hRPL8),decreased cell and organ size in multiple Drosophila tissues without affecting cell differentiation.Another effect was that it caused cell apoptosis,which was confirmed not to be the primary reason contributing to the cell size change.RNA interference of Drosophila RPL8(dRPLS) showed similar phenotypes.This result demonstrated that overexpression of mutant hRPL8 caused dominant negative effect which might mimic the true loss of function phenotype.HRPL8 and dRPL8 shares high homology.RNA interference phenotype of dRPL8 could be rescued by coexpression of wild-type hRPL8,indicating that RPL8 protein is evolutionarily conserved not only in sequence but also in function.Furthermore,we provided genetic and biochemical evidence indicating that dRPL8 was a new member of the Insulin signal transduction pathway,and that Insulin pathway-mediated phosphorylation of dRPL8 likely functions as a regulatory step in dRPL8 function.These experiments suggest that human RPL8 is likely to have similar functions,and indicate the usefulness of the Drosophila model for the large-scale analysis of human transcripts in vivo.