During vertebrate hindbrain segmentation, a specific population of boundary cells are located at the interface between successive segments (rhombomeres). Boundary cells are known to establish segment boundaries, signal to cells in the adjacent rhombomere and act as a source of progenitors and neurons. Although mechanical cues are increasingly implicated for directing cell behaviour, their function during hindbrain segmentation is not well studied. Now, Cristina Pujades and colleagues investigate the role of Hippo pathway components, Yap and Taz, in interpreting mechanical forces during zebrafish hindbrain segmentation. Using in situ hybridisation and fluorescent reporter lines, they show that boundary cells indeed act as mechanosensors, which have increased expression and activity of Yap/Taz-TEAD at the interface between two rhombomeres. This activity is lost when the authors manipulate the actomyosin cytoskeleton in both whole embryos and clonal populations, indicating that the pathway is responding to mechanical cues in a cell-autonomous manner. Finally, downregulation of Yap/Taz-TEAD activity, either conditionally or by yap and taz zebrafish mutants, decreases the number of proliferating boundary cells, but does not affect their differentiation into neurons. Together, these data show that boundary cells in the hindbrain sense mechanical forces through Yap/Taz-TEAD to regulate the proliferation of progenitors during segmentation.
