Niche cytoskeletal architecture is required for proper stem cell signaling and oriented division in the Drosophila testis

Stem cells are critical to repair and regenerate tissues, and often reside in a niche that controls their behavior. The Drosophila testis niche has been a paradigm for niche-stem cell interactions and is used here to address the cell biological features that maintain niche structure and function during its steady-state operation. We report enrichment of the Myosin II (MyoII) and a key regulator of acto-myosin contractility (AMC), Rho Kinase (ROK), within the niche cell cortex at the interface with germline stem cells (GSCs). Compromising MyoII and ROK disrupts niche architecture, suggesting that AMC in niche cells is important to maintain the reproducible structure of this niche. Furthermore, defects in niche architecture cause changes in stem cell function. Our data suggest that the niche signals less robustly to adjacent germ cells, yet the disrupted structure permits increased numbers of cells to respond to the signal. Finally, compromising Myo II in niche cells leads to an increase in mis-oriented centrosomes in GSCs as well as defects in the centrosome orientation checkpoint. Ultimately, this work identifies a critical role for AMC-dependent maintenance of niche structure to ensure a proper complement of stem cells with correct execution of stem cell divisions.