Abstract

The existence of specialised regulatory microenvironments or niches that sustain stable stem cell populations is well documented in many tissues. However, the specific mechanisms by which niche support (or stromal) cells govern stem cell maintenance remain largely unknown. Here we demonstrate that removal of the Jak/Stat pathway in support cells of the/ Drosophila/ ovarian niche leads to germline stem cell (GSC) loss by differentiation. Conversely, ectopic Jak/Stat activation in support cells induces GSC tumours, implying the presence of a signal relay between the stromal compartment and GSCs. We further show that ectopic Jak/Stat signalling in support cells augments/ dpp/ mRNA levels and increases the range of Dpp signalling, a BMP2 orthologue known to act as a niche extrinsic factor required for female GSC survival and division. Our results provide strong evidence for a model in which Jak/Stat signalling in support cells regulates/ dpp/ transcription to maintain the adjacent GSCs in an undifferentiated state and to define niche size.”