Translation of anterior–posterior polarity into left–right polarity in the mouse embryo

The breaking of left–right symmetry in the mouse involves unidirectional fluid flow. Rotational movement of the node cilia generates leftward flow because the cilia are posteriorly tilted. However, it is unknown how anterior–posterior (A–P) information is translated into the posterior tilt of the node cilia. The tilt is determined by the position of the basal body of node cilia. Some of the planar cell polarity (PCP) core proteins such as Dvl are asymmetrically distributed in the node cells, and positioning of the basal body is impaired in mutant mice lacking Dvl genes. Therefore, posterior positioning of the basal body is determined by planar polarization involving noncanonical Wnt signaling. However, the identity of initial A–P information remains unknown.