Drosophila ovarian germline stem cell cytocensor projections dynamically receive and attenuate BMP signalling
In the Drosophila ovarian germline, BMP signals released by niche cells promote germline stem cell (GSC) maintenance. Although BMP signalling is known to repress expression of a key differentiation factor, it remains unclear whether BMP-responsive transcription also contributes positively to GSC identity. Here, we identify the GSC transcriptome using RNA-seq, including the BMP-induced transcriptional network. Based on these data, we provide evidence that GSCs form two types of cellular projections. Genetic manipulation and live ex vivo imaging reveal that both classes of projection allow GSCs to access a reservoir of Dpp held away from the GSC-niche interface. Moreover, the microtubule-rich projections, termed cytocensors, formed downstream of BMP have additional functionality, which is to attenuate BMP signalling, allowing dynamic modulation of signal transduction to facilitate differentiation following GSC division. We propose that cytocensors will be synthesised by other types of cells in diverse contexts to calibrate signalling responses.