Nanotubes mediate niche–stem-cell signalling in the Drosophila testis

Drosophila male germline stem cells form previously unrecognized structures, microtubule-based nanotubes, which extend into the hub, a major niche component, to mediate the niche–stem-cell signalling. Stem cells communicate by nanotube Stem cell niches provide short-range signals to which only stem cells — and not their differentiating progeny — respond. It is still not clear how such specificity is achieved. Yukiko Yamashita and colleagues report that Drosophila male germline stem cells form previously unrecognized structures, microtubule-based nanotubes, which extend into the hub, a major component of the niche, to mediate the stem-cell-niche signalling. These nanotubes carry receptors for signals sent by the niche and are required for the transmission of such self-renewing signals to the germline stem cells. Stem cell niches provide resident stem cells with signals that specify their identity. Niche signals act over a short range such that only stem cells but not their differentiating progeny receive the self-renewing signals 1 . However, the cellular mechanisms that limit niche signalling to stem cells remain poorly understood. Here we show that the Drosophila male germline stem cells form previously unrecognized structures, microtubule-based nanotubes, which extend into the hub, a major niche component. Microtubule-based nanotubes are observed specifically within germline stem cell populations, and require intraflagellar transport proteins for their formation. The bone morphogenetic protein (BMP) receptor Tkv localizes to microtubule-based nanotubes. Perturbation of microtubule-based nanotubes compromises activation of Dpp signalling within germline stem cells, leading to germline stem cell loss. Moreover, Dpp ligand and Tkv receptor interaction is necessary and sufficient for microtubule-based nanotube formation. We propose that microtubule-based nanotubes provide a novel mechanism for selective receptor–ligand interaction, contributing to the short-range nature of niche–stem-cell signalling.