The development of mechanosensory epithelia, such as those of the auditory and vestibular systems, results in the precise orientation of mechanosensory hair cells and consequently directional sensitivity. After division of a precursor cell in the zebrafish's lateral line, the daughter hair cells differentiate with opposite mechanical sensitivity. This process produces neuromasts containing equal numbers of hair cells of two opposite polarities, half of them sensitive to caudal water movement and half to rostral flow.
Through a combination of theoretical and experimental approaches, we show that Notch-mediated lateral inhibition produces a bistable switch that reliably gives rise to hair cell pairs of opposite polarity. Using a mathematical model of the process, we predict the outcome of several genetic and chemical alterations to the system, which we then confirm experimentally. We then show how this symmetry breaking mechanism drives polarity-dependent cell migrations.
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