Stem cell behaviour is regulated through interaction with cells in their niche. However, there is much to learn about the mechanisms involved, especially beyond post-embryonic development. Now, Stephen DiNardo and colleagues use imaging approaches in the adult Drosophila testis to investigate the role of the cytoskeleton in stem–niche cell dynamics during homeostasis. The authors show that cytoskeletal components, Myosin II (MyoII) and Rho kinase (ROK), are enriched in niche cells at their interface with GSCs. Using loss-of-function experiments, the authors show that MyoII and ROK are required to preserve the spheroid shape of the niche, which is crucial for stem cell behaviour. For example, disruption of MyoII affects niche cell adhesion, increasing the area and volume of the niche. Surprisingly, although there are more GSCs in the enlarged niche and a higher proportion are exposed to Jak/STAT signalling, they respond less effectively and GSCs are not well retained. In MyoII-deficient niches, GSCs undergo more symmetrical (self-renewal) divisions driven by disruption to the centrosome orientation checkpoint that controls the plane of division and, thus, daughter cell fate. Together, these results demonstrate that maintaining the adult niche shape and structure is crucial for normal stem cell function.
