Adult Stem Cells and Niche Cells segregate gradually from common precursors that build the adult Drosophila ovary during pupal development

Adult stem cell function relies on the prior development of appropriate numbers and spatial organization of stem cells and supportive niche cells. Drosophila Follicle Stem Cells (FSCs) present a favorable paradigm for understanding those developmental processes. About sixteen FSCs in an adult germarium produce transit-amplifying Follicle Cells (FCs) from their posterior face and quiescent Escort Cells (ECs) to their anterior. Both ECs and FCs also act as niche cells. Here we show that adult ECs, FSCs and FCs derive from common precursors intermingled with germline cells during pupal development, with progeny of a single precursor commonly including ECs and FSCs, FSCs and FCs, or all three adult cell types. Precursors posterior to germline cells become the first FCs and engulf a largely naked germline cyst projected out of the germarium to form the first egg chamber and set up a key posterior signaling center for regulating adult FSC behavior.