RBF1 Is A Key Regulator For BMP Signaling Pathway Of Germline Stem Cell Niche In Drosophila's Ovary

Stem cells exist in many adult tissues can divide and differentiate into diverse specialized cell types and can self-renew to produce more stem cells.Understanding the molecular mechanisms controlling stem cell function in vivo is crucial to the future use of stem cells in regenerative medicine,as well as in understanding aging,tumor formation and degenerative diseases.GSCs in the adult Drosophila ovary are an excellent system in which to study stem cells and niches in vivo at the cellular and molecular level.Stem cell maintains its ability of self-renewal and differentiation through intrinsic mechanisms and the extrinsic niche where it reside.The somatic niche cells surrounding the GSCs include terminal filament cells,cap cells and escort stem cells.Mounting evidence has demonstrated that BMP-like morphogens produced by the niche cells only act on GSCs that are the immediate upstream signals to promote GSC fate by preventing the expression of Bam,a key differentiation factor.This thesis consists of two parts of work.The first part,a pilot genetic screen was performed.We took advantage of three Gal4 lines,which drive targeted RNAi in a slightly different range in the niche cells,in order to find novel genes that affect stem cell niche architecture and GSCs self-renew.The second part of work is studying on the mechanisms.One of the genes found in our screening result encoding a Drosophila homologue of human Rb protein was of a particular interest.Removal or knocking down of dRbfl function in the somatic niche cell lineage leads to a gradual GSC loss.Interestingly,over-expression of RBF1,results in an expansion of GSC cells,marked by the expansion of BMP signaling.To better characterize the function of RBF1 effect ing the expression of Dpp within the ovary,we performed in situ hybridization,promoter desection and luciferase experiment,finding that RBF1 can modulate the transcription activity of Dpp directly targeting its promoter,not obviously linked to E2F pathway.Chromatin immunoprecipitation helps us to identify the special transcription factor Engrailed which combine with RBF1.In this study,we use an effective system to investigate the mechanisms that govern germline stem cells self-renew and differentiation signaling of in vivo niches.The available experimental data support the hypothesis that RB is a truly multifunctional protein apart from cell cycle regulation.Rbfl can form a complex with Engrailed regulating the Dpp expression level mainly in the cap cells and also affecting the Hedgehog signal in the escort cells.There are undoubtedly further functions of Rb yet to be elucidated,especially with regards to its expression in adult tissues and in cancer.