Planar Polarization of Cilia in the Zebrafish Floor Plate Involves Par3-Mediated Posterior Localization of Highly Motile Basal Bodies

To produce a directional flow, ciliated epithelia display a uniform orientation of ciliary beating. Oriented beating requires planar cell polarity (PCP), which leads to planar orientation and asymmetric positioning of the ciliary basal body (BB) along the polarity axis. We took advantage of the polarized mono-ciliated epithelium of the embryonic zebrafish floor plate (FP) to investigate by live-imaging the dynamics and mechanisms of BB polarization. We showed that BBs, although bearing a cilium, were highly motile along the polarity axis, contacting either the anterior or posterior membranes, exclusively at the level of apical junctions positive for Par3. Par3 was posteriorly enriched before BB posterior positioning and FP polarization was disrupted upon Par3 overexpression. In the PCP mutant Vangl2, BBs showed poorly oriented movements correlated with Par3 mislocalization. Our data lead us to propose a conserved function for Par3 in controlling BB asymmetric positioning downstream of the PCP pathway.