A centriole (green) speeds away from the PCM (red) in a Cnn mutant embryo.

Like a sailboat, centrioles drift away if they aren't properly moored, as Lucas and Raff show on page 725. The researchers pin down a protein that helps keep the structures in place.

A pair of centrioles sits inside a cloud of pericentriolar matrix (PCM), creating the centrosome. It serves as a hub for the microtubules that form the spindle apparatus, which divvies up the chromosomes during mitosis. What connects the centrioles to the PCM and keeps them in position isn't clear. Previous work suggested that the protein centrosomin (Cnn) attracts other proteins to the centrosome. Lucas and Raff wanted to determine whether Cnn tethered the centrioles.

They started with syncytial fly embryos, in which hundreds of dividing nuclei share a common cytoplasm. In embryos lacking Cnn, PCM still gathered at...

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