UROP Proceedings 2020-21

School of Science Division of Life Science 42 Genetic Studies on Stem Cell Regulation Supervisor: XIE Ting / LIFS Co-supervisor: TU Renjun / LIFS Student: LEUNG Sin Ho Henry / BIBU Course: UROP1000, Summer Although 5-hydroxymethylcytosine (5hmC) has been discovered in about 1952, the functions and mechanisms are yet to be known. Ten-eleven-translocation (TET) proteins function to convert 5Methylcytosine (5mC) to 5hmC in both DNAs and RNAs. It has been reported that very low level 5mC/5hmC modified DNAs could be detected in Drosophila, therefore, Drosophila has unique advantage to study RNA 5mC/5hmC modifications. Our preliminary research found that overexpressing Tet in germline or in the niche both significantly disrupt germline stem cell (GSC) development, indicating the balance between 5mC and 5hmC in RNAs are very important. To identify the molecular partners of Tet, we knocked down many genes in Tet overexpression ovaries in this genetic screening study. We found that knockdown of genes encoding RNA 5mc modification readers (lin-28, CG9705), RNA splicing factors (mod, bru2, snRNP-U1-70K), or RNA binding proteins (C7903, Imp, Rb97D, pAbp) can partly rescue Tet overexpression caused ovary developmental defects. These results indicate the potential molecular mechanisms that how Tet involved in regulating GSC development. Genetic Studies on Stem Cell Regulation Supervisor: XIE Ting / LIFS Co-supervisor: TU Renjun / LIFS Student: LIN Muyun / BCB Course: UROP1000, Summer RNA 5mc (5-methylcytosine) is a type of RNAmodification that is found in a wide variety of species. Generally, eukaryotic methyltransferases in the NSUN family and the DNA methyltransferase homologue DNMT2 catalyze most of these C5 methylation reactions. In Drosophila, it is predicted to have six RNA 5mC methyltransferases, including Nsun1, Nsun2, Nsun4, Nsun5, Nsun6 and Mt2. In this project target genes are knocked down with the use of transgenic crosses. Specifically, the Gal4-UAS system is used to express RNAi to knock down target genes in niche cells and germ cells by using nos-Gal4 and c587-Gal4, respectively. Interestingly, Nsun1 and Nsun2 double knockdown in the niche decreases germline stem cell (GSC) but increases GSC daughter cell numbers, indicating their complimentary roles in controlling GSC self-renewal and differentiation in the niche. Moreover, Nsun1 knockdown in germline completely loss GSC. In the future study, we will carefully analyse the functions of other methyltransferases in the regulation of GSC development.

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