Fig. 1

Schematic representation of ovariole and germarium in Drosophila melanogaster. a The Drosophila ovary is composed of 15–20 ovarioles. The continuous developing egg chamber is divided into 14 stages. Each egg chamber is composed of an oocyte, nurse cells and somatic follicle cells. Vitellogenesis occurs after stage 8 egg chamber. b The germarium resides in the tip of the ovariole. Germline stem cells (blue) are maintained by somatic niche cells comprising the terminal filament, cap cells, and escort stem cells (green). Germline stem cells produce another stem cell by self-renewal and also divide asymmetrically to produce daughter cells called cystoblasts (red). The cystoblast divides four times with incomplete cytokinesis to form 15 nurse cells and one oocyte in each egg chamber, which are enveloped by follicle cells (gray). Illustration in the egg chamber shows proliferation and differentiation of cystoblasts from the 2-(left) to 16-cell stage. GSCs and cystoblasts can be identified by the morphology of the spectrosome, a germline-specific membranous organelle (yellow). Developing cystocytes contain the fusome, a derivative of the spectrosome that shows more branched morphology (yellow)