Specialized regulatory microenvironments (niches) sustain stable stem cell populations in many tissues, but how the support (stromal) cells that function within these niches sustain stem cells is poorly understood. Now, on ,López-Onieva and co-workers implicate Jak/Stat (Janus kinase/Signal transducer and activator of transcription) signalling in germline stem cell(GSC) maintenance in the Drosophila ovary. GSCs in the Drosophila ovary are supported by terminal filament cells, cap cells and escort stem cells; these last two cell types make Dpp, a BMP-like molecule that is needed for GSC maintenance. The researchers show that the Jak/Stat pathway is normally active in cap cells and that GSCs are lost through differentiation when Jak/Stat signalling is switched off in these support cells. Conversely, ectopic activation of Jak/Stat signalling in the support cells induces stem cell tumours and increases dpp transcription in the niche's stromal cells. These results suggest that Jak/Stat signalling regulates dpp transcription in the support cells of the GSC niche to maintain ovarian GSCs in an undifferentiated state.
