Long-term live imaging provides new insight into stem cell regulation and germline-soma coordination in the Drosophila ovary

The Drosophila ovariole tip produces new ovarian follicles on a 12-hour cycle by controlling niche-based germline and follicle stem cell divisions and nurturing their developing daughters. Static images provide a thumbnail view of folliculogenesis but imperfectly capture the dynamic cellular interactions that underlie follicle production. We describe a live-imaging culture system that supports normal ovarian stem cell activity, cyst movement and intercellular interaction over 14 hours, which is long enough to visualize all the steps of follicle generation. Our results show that live imaging has unique potential to address diverse aspects of stem cell biology and gametogenesis. Stem cells in cultured tissue respond to insulin and orient their mitotic spindles. Somatic escort cells, the glial-like partners of early germ cells, do not adhere to and migrate along with germline stem cell daughters as previously proposed. Instead, dynamic, microtubule-rich cell membranes pass cysts from one escort cell to the next. Additionally, escort cells are not replenished by the regular division of escort stem cells as previously suggested. Rather, escort cells remain quiescent and divide only to maintain a constant germ cell:escort cell ratio.