Organizing stem cell units in the Drosophila ovary.

Organogenesis utilizes processes fundamental to development: cell proliferation, cell differentiation and morphogenesis. Each of these processes is complex in itself; the challenge of studying organogenesis is to determine how all of them integrate to shape organs with recurring precision. This review focuses on the emerging understanding of how synchronized proliferation and differentiation of both somatic and germ cell lineages form 16-20 germ line stem cell (GSC) units in the ovary of Drosophila melanogaster. Recent work demonstrates that the Insulin, ecdysone, Epidermal Growth Factor, Decapentaplegic and Activin signaling pathways are used reiteratively for proliferation and differentiation in both somatic and germ cell lineages. This linkage underlies ovarian coordinated development and provides opportunity for correction mechanisms for stem cell unit numbers.