Project Summary Investigation of Niche Control of Germline Stem Cell Lineage Differentiation The long-term objective of this proposed study is to investigate how niche-mediated cellular interactions control stem cell lineage differentiation extrinsically. Stem cells have the ability to continuously self-renew and produce differentiated progeny. The mechanisms controlling stem cell lineage differentiation are critical for using stem cells in treating human diseases, such as Parkinson’s, Alzheimer’s and diabetes, as well as for fighting against cancer and aging. Germline stem cells (GSCs) in the Drosophila ovary are an effective model for studying stem cell self-renewal and lineage differentiation and for studying reproductive biology because of powerful genetic tools and exceptional cell biology. We have recently proposed that somatic escort cells (ECs) from a niche for GSC progeny differentiation in the Drosophila ovary, which is named as the differentiation niche. However, it remains largely unknown how niche-mediated cellular interactions control GSC progeny differentiation at the molecular level. We have shown that autocrine Hedgehog (Hh) signaling and Wnt signaling function in ECs to control GSC progeny differentiation by maintaining EC cellular processes and/or repressing BMP signaling. Excitingly, our preliminary results have also shown that: 1) Hh/Wnt signaling represses the expression of BMP signaling regulators dally-like protein (dlp) and magu, which overexpression elevates BMP signaling in GSC progeny; 2) Hh/Wnt signaling represses the expression of small GTPase regulators RhoGAP54D and tumbleweed (tum), which overexpression leads to the EC cellular process loss; 3) three gap junction proteins function in ECs to promote GSC progeny differentiation, and one of them is also required in ECs to maintain their long cellular processes. The goal of this project is to use the Drosophila ovary as a model to gain a better understanding of how the niche controls GSC lineage differentiation at the molecular level. Three specific aims of this proposed study are to investigate 1) if Wnt and Hh pathways maintain EC cellular processes by repressing the expression of RhoGAP54D and tum; 2) if Hh and Wnt pathways prevent BMP signaling in GSC progeny by repressing the expression of magu and dlp; 3) how gap junctions maintain EC cellular process-germ cell adhesion and control GSC progeny differentiation. Because the molecular mechanisms controlling stem cell differentiation are important for providing functional cells for cell therapy, preventing cancer stem cell expansion, and slowing down aging, the knowledge gained from this proposed study is critical for treating human degenerative diseases and for fighting against cancer and aging. Since many properties of germ cells are conserved from Drosophila to human, the findings from this study will also help gain a better understanding of human reproductive biology.