Localisation of Fin1 by GFP or antibodies showed that it associated with the SPB in a very interesting way. It bound the SPB from the start of mitosis to the completion of cytokinesis, but in late anaphase cells Fin1 was found on both SPBs in one half of the population and on only one in the other half. As yeast spindle pole bodies divide by a conservative mechanism - a new one forms next to the old. As this seemed like a simple mechanism to differentiate between two SPBs, we asked whether the affinity of Fin1 for an SPB was related to its age. We exploited a trick developed by our colleagues in the Schiebel lab in which the slow folding properties of red fluorescent protein can be harnessed to specifically label the old SPBs. This showed that whenever Fin1 was asymmetric it was always on the old SPB and that an SPB could only specify that its daughter should recruit Fin1 (Fin1 on both late anaphase SPBs) after it had passed through at least two cell cycles. Further work showed that Fin1 activity contributed to the inhibition of the SIN on the old SPB. This inheritance pattern is strikingly reminiscent of the maturation of the centrioles in human centrosomes. Centrioles pass through one and a half cell cycles before they acquire the appendages that are characteristic of a mature centriole
As centrosome amplification occurs in every cancer and cell cycle progression is controlled from the centrosome we are hopeful that understanding SPB maturation in yeast may lead to ways to restore centriole maturation to the tumours that have suppressed it to de-regulate growth. Such restoration of centrosome maturation would be expected to restore normal growth control.