Cells have been observed to rotate about their axis in various contexts during organogenesis, but much of what we know about this process derives from in vitro studies. Here, Hernán López-Schier and colleagues explore hair cell rotation in developing zebrafish neuromasts. Hair cells are produced in pairs: one cell in each pair goes on to activate the Notch1a receptor and halt Emx2 expression, which can coincide with the two cells rotating to swap positions. In this study, the authors follow hair cell rotation in vivo using videomicroscopy and find that this appears to be an active, autonomous process. They define three distinct phases of rotation: cell pair formation, active rotation and cells reaching their final position. In contrast to previous findings, they show that cells can rotate in the absence of Notch1a activity, although the timing of rotation onset is altered in notch1a and emx2 mutants. These mutants also exhibit increased ‘wobbling’ during rotation. Coupled with computer modelling, their results suggest that Notch1a/Emx2 play a role in maintaining the robustness of cell rotation. Overall, this study uncovers a role for Notch1a-mediated symmetry breaking in stabilising cell rotation.
