Figure 1

Organization of the developing female gonad and the adult germarium. (a) By the end of larval development, approximately 100 primordial germ cells (PGCs) (red) populate the gonad and associate with cap cell precursor (dark green) and escort cell precursor cells (orange). Terminal filament stacks (light green) begin to form and signal to adjacent somatic cells through the Delta-Notch pathway, inducing them to become cap cells. (b) The differentiation of adult germline cells (red) can be traced based on morphological changes in the fusome (beige), an endoplasmic reticulum-like organelle that appears round in the germline stem cells (GSCs) and becomes increasingly more branched as germline cysts develop [76]. Adult GSCs reside in a niche formed by the terminal filament (light green) and cap cells (dark green). Escort cells (orange) help to guide developing cysts as they pass through the germarium. Eventually a single layer of follicle cells (grey) surrounds the germline cysts and these enveloped cysts bud off the germarium to form an egg chamber.