Centrosomal MPF triggers the mitotic and morphogenetic switches of fission yeast

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Abstract
The Cdc2 (also called Cdk1) kinase is first activated at the centrosome to initiate mitosis in human cells. Hagan and colleagues demonstrate that in fission yeast, Cdc2 and Polo kinase activation at the spindle pole body remotely controls not only mitotic commitment but also ‘new end take off’, the initiation of bipolar growth in G2. Activation of mitosis-promoting factor (MPF) drives mitotic commitment1. In human cells active MPF appears first on centrosomes2. We show that local activation of MPF on the equivalent organelle of fission yeast, the spindle pole body (SPB), promotes Polo kinase activity at the SPBs long before global MPF activation drives mitotic commitment. Artificially promoting MPF or Polo activity at various locations revealed that this local control of Plo1 activity on G2 phase SPBs dictates the timing of mitotic commitment. Cytokinesis of the rod-shaped fission yeast cell generates a naive, new, cell end. Growth is restricted to the experienced old end until a point in G2 phase called new end take off (NETO) when bipolar growth is triggered3. NETO coincided with MPF activation of Plo1 on G2 phase SPBs (ref. 4). Both MPF and Polo activities were required for NETO and both induced NETO when ectopically activated at interphase SPBs. NETO promotion by MPF required polo. Thus, local MPF activation on G2 SPBs directs polo kinase to control at least two distinct and temporally separated, cell-cycle transitions at remote locations.

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