Notch-driven asymmetry dictates hair cell behavior via a fate-specific kinase

In the zebrafish lateral line, developing pairs of sensory hair cells undergo symmetry-breaking mediated by Notch signaling, leading to one cell becoming Notch-ON (receiver state) and its sibling becoming Notch-OFF (sender state).

These cells then undergo coordinated movements that ensure that Notch-OFF cells are always positioned anterior to their Notch-ON sisters, and the Notch state of each sister ultimately determines the direction of hair bundle polarization. However, the cellular mechanisms and molecular programs that guide polarity-specific behaviors remain largely unknown. Here, using time-lapse imaging and a new 3D segmentation and tracking pipeline, we demonstrate that sister cells actively move in opposite directions -- Notch-OFF cells migrate anteriorly while Notch-ON cells move posteriorly -- enabling robust rotations when cells are initially mispositioned.