Like a deaf bat, a kidney cell without a cilium is cut off from its surroundings. It can't tell up from down or sense fluid movements and concentration gradients. By aligning microtubules within the cell, a protein implicated in the development of kidney cysts is vital for building cilia, as Schermer et al. show on page 547.

Patients lacking the von Hippel-Lindau tumor suppressor protein (pVHL) suffer from a profusion of cancers and kidney cysts. Several other cyst-promoting kidney diseases involve cilia defects, and previous work suggested that pVHL was essential for making cilia.

Schermer et al. probed pVHL's influence on microtubules, which form the core of the cilium. Contradicting a prior study, the researchers found that loss of pVHL didn't speed the breakdown of microtubules within kidney cells. However, removing the protein did seem to alter the direction in which microtubules grow. In cells lacking pVHL, microtubules point every which way. But in cells that manufacture the protein, the tubes are oriented in roughly the same direction, toward the cell's boundary.

How pVHL exerts its effects remains a mystery, but the team found that it gloms onto a protein complex that helps direct cell polarity. The researchers now want to determine how pVHL collaborates with this protein complex to chart the right path for microtubules.