Stem cells and their progeny respond to nutritional changes during Drosophila oogenesis

Understanding how stem-cell proliferation is controlled to maintain adult t issues is of fundamental importance. Drosophila oogenesis provides an attra ctive system to study this issue since cell production in the ovary depends on small populations of observable germ-line and somatic stem cells. By co ntrolling the amount of protein-rich nutrients in the diet, we established conditions under which the rate of egg production varied 60-fold. Using a c ell-lineage labeling system, we found that both germ-line and somatic stem cells, as well as their progeny, adjust their proliferation rates in respon se to nutrition. However, the number of active stem cells does not appear t o change. Proliferation rates varied fourfold; the remaining 15-fold differ ence in egg production resulted from different frequencies of cell death at two precise developmental points: (1) the region 2a/2b transition within t he germarium, and (2) stage 8 egg chambers that are entering vitellogenesis . To initiate a genetic analysis of these changes in cell proliferation and apoptosis, we show that ovarian cells require an intact insulin pathway to fully upregulate their rate of cycling in response to a protein-rich diet and to enter vitellogenesis. (C) 2001 Academic Press.