In the brain, cilia on the multiciliated ependymal cells that line the brain ventricles circulate cerebrospinal fluid over the brain surface. To generate this directional fluid flow, the ependymal cell cilia and their basal bodies must be orientated in one direction. This ‘rotational’ polarity is regulated by the planar cell polarity (PCP) pathway. Recent reports have revealed that the basal bodies are also localised at the anterior of the ependymal cells but how is this ‘translational’ polarity established? Using a new method for time-lapse imaging of ventricular walls, Kazunobu Sawamoto and co-workers now show that, in mice, the anterior migration of basal bodies in the apical cell membrane during ependymal cell differentiation establishes translational polarity (see p. ). Inhibition of the PCP protein dishevelled 2, which disrupts rotational polarity, does not affect translational polarity, the researchers report. Instead, their pharmacological and genetic studies identify non-muscle myosin II as a key regulator of translational polarity. Thus, different mechanisms regulate the orientation and distribution of basal bodies in ependymal cells.
