Two-way traffic: centrosomes and the cell cycle

The well recognized activities of the mammalian centrosome - microtubule nucleation, duplication, and organization of the primary cilium - are under the control of the cell cycle. However, the centrosome is more than just a follower of the cell cycle; it can also be essential for the cell to transit G1 and enter S phase. How the centrosome influences G1 progression is a mystery.