Functional Characterization Of Epigenetic Factors Related To Histone3Lysine4Trymethylation In Drosophila Female Germline Stem Cell Maintanence

Stem cell maintains its ability of self-renewal and differentiationthrough intrinsic mechanisms and the extrinsic niche where it reside.Drosophila female germline stem cell niche consist three kinds of somaticcells: terminal filament cells, cap cells and escort cells. It is important tostudy the underlying mechanism of Drosophila female germline stem cellmaintenance, if we want to explore the myth of adult stem cells in otherorganisms.Epigenetic regulator is essential in stem cell survival and function.Histone3Lysine4is an important trimethylation site involved in a lot ofdevelopmental and cellular processes. This epigenetic modificationalways accompanies gene activation and silencing. dSet1/Trx/Trr/Ash1are a group of methyltransferases that might be responsible for H3K4trimethylation. Monoubiquitination induced by E3ligase dBre1is required in the process of methylation of H3.In this thesis I study the role of three H3K4trimethylation relatedfactors dBre1/trx/ash1in Drosophila female germline stem cellmaintenance. Evidence is provided in the paper for that dBre1is requiredfor germline stem cell maintenance. Loss of dBre1causes defects ingermline stem cell self-renewal and germline stem cell loss. Furtheranalysis reveal that dBre1may regulate germline stem cell via BMPsignaling in a Bam-independent manner.Specific Gal4drivers are utilized to repress dBre1expressionthrough RNAi in different kinds of niche cells. The results show thatdBre1is required in all three kinds of niche cells for proper germlinestem cell maintenance, while reduction of dBre1leads to germline stemcell loss. dBre1mutation in niche cells affect the cell-cell adhesionbetween niche cells and germline stem cells. This might be one of thereasons for defect of germline stem cell maintenance.This primary research of H3K4trimethylation related factors inDrosophila female germline stem cells confirms the requirement of dBre1in maintaining the stem cells; and for the first time I propose in this paperthat there are two kinds of effects of dBre1in germline stem cellmaintenance, both as an intrinsic factor and an extrinsic factorfunctioning through stem cell niche. This thesis may provide insight forfollowing research regarding H3K4methylation in germline stem cell maintenance, and the reciprocal regulatory mechanisms between stemcells and their niches.