Centrosomes take sides

The C. elegans embryo lacks polarity until ∼30 min after fertilization. Prior evidence implicated the sperm-donated centrosome, presumably via its ability to nucleate microtubules, in polarity establishment. Now, Carrie Cowan and Anthony Hyman (Max Planck Institute, Dresden, Germany) find that it is centrosomes themselves that are needed. When they ablate the centrosome, downstream polarity signals such as PAR proteins fail to localize as they do in wild-type embryos.

Timing of the centrosome's ablation is crucial. When the team knocks out the centrosome before it approaches the cortex of the cell, polarity is abolished. However, if the team ablates the centrosome after it nears the cortex, they induce only slight disruptions in the downstream polarity events. Thus, the required signal is a transient one.

That was unexpected. Dogma...