Mitosis: One Polo controls it all

On November 6, 2014, Cell Cycle published a paper from the Yoshida lab entitled “The budding yeast Polo-like kinase Cdc5 is released from the nucleus in anaphase for timely mitotic exit.” This study was authored by Vladimir V. Botchkarev Jr., Valentina Rossio, and Satoshi Yoshida.

The cell cycle is one of the most fundamental biological processes whose ultimate goal is cell division with equal content of DNA in both daughter cells. The process of cell division is regulated by many intracellular events which must occur in a sequential order. These events include mitotic entry, faithful chromosome segregation, mitotic exit, and cytokinesis. Over the past 25 years, the Polo-like kinase (Polo) has been established to play important regulatory roles in each of these processes. Although many mitotic substrates of Polo have been discovered, the mechanism by which Polo can coordinate all of these mitotic events has remained largely elusive.

To understand the mechanism by which Polo can target its many substrates in a sequential order during mitosis, we decided to study the budding yeast Polo kinase Cdc5, which has high conservation with the human Polo-like kinase 1.

We found that Cdc5-GFP dynamically changes its localization during the cell cycle: Cdc5 is found in the cytoplasm in S- through early G2-phase, it accumulates in the nucleus at metaphase, and is released again to the cytoplasm in anaphase. Blocking nuclear import of Cdc5 in metaphase leads to a prolonged metaphase duration, suggesting that nuclear Cdc5 is required for chromosome segregation. In contrast, blocking nuclear release of Cdc5 in anaphase results in a prolonged anaphase duration, a defect in activation of the cytoplasmic Mitotic Exit Network, and a defect in cytokinesis. This indicates that Cdc5 is released from the nucleus to the cytoplasm in anaphase for timely mitotic exit and cytokinesis. We further found that activation of the Cdc14 phosphatase, a known nuclear substrate of Cdc5, is required for Cdc5 nuclear release in anaphase.

Collectively, our work reveals that the budding yeast Polo-like kinase Cdc5 controls the timing of mitotic events by dynamically changing its sub-cellular localization. Furthermore, our data suggests the existence of a positive feedback look between Cdc5 and Cdc14 to regulate timely mitotic exit. Read more

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