The primary cilium: keeper of the key to cell division.

Assembly of the nonmotile primary cilium of vertebrate cells requires one of the centrioles of the centrosome. A cluster of new studies, including one in this issue of Cell by Pugacheva et al. (2007), reveal that ciliary assembly proteins influence cell-cycle progression and that a centrosomal "mitotic kinase" promotes ciliary disassembly. The link between the cell cycle and the primary cilium may reflect a requirement for liberation of the ciliary centriole to allow the centrosome to form the mitotic spindle.