Centrosomes promote timely mitotic entry in C. elegans embryos.

Several mitotic regulators, including Cyclin B1/Cdk1, are present at centrosomes prior to mitosis onset, but it is unclear whether centrosomes promote mitotic entry in vivo. Here we developed a sensitive assay in C. elegans embryos for the temporal analysis of mitotic entry, in which the male and female pronuclei undergo asynchronous entry into mitosis when separated from one another. Using this assay, we found that centrosome integrity is necessary for timing mitotic entry. Centrosomes do not function in this instance through their ability to nucleate microtubules. Instead, centrosomes serve to focus the Aurora A kinase AIR-1, which is essential for timely mitotic entry. Furthermore, analysis of embryos in which centrosomes and pronuclei are detached from one another demonstrates that centrosomes are sufficient to promote mitosis onset. Together, our findings support a model in which centrosomes serve as integrative centers for mitotic regulators and thus trigger mitotic entry in a timely fashion.