The Aurora kinase inhibitor ZM447439 accelerates first meiosis in mouse oocytes by overriding the spindle assembly checkpoint

Abstract

Previous studies have established that when maturing mouse oocytes are continuously incubated with the Aurora inhibitor ZM447439, meiotic maturation is blocked. In this study, we observe that by altering the time of addition of the inhibitor, oocyte maturation can actually be accelerated by 1 h as measured by the timing of polar body extrusion. ZM447439 also had the ability to overcome a spindle assembly checkpoint (SAC) arrest caused by nocodazole and so rescue polar body extrusion. Consistent with the ability of the SAC to inhibit cyclin B1 degradation by blocking activation of the anaphase-promoting complex, we could also observe a rescue in cyclin B1 degradation when ZM447439 was added to nocodazole-treated oocytes. The acceleration of the first meiotic division by ZM447439, which has not been achieved previously, and its effects on the SAC are all consistent with the proposed mitotic role of Aurora B in activating the SAC. We hypothesize that Aurora kinase activity controls the SAC in meiosis I, despite differences to the mitotic cell cycle division in spindle architecture brought about by the meiotic mono-orientation of sister kinetochores.

Timing of anaphase-promoting complex activation in mouse oocytes is predicted by microtubule-kinetochore attachment but not by bivalent alignment or tension

“…Indeed, this repair may be very common in mouse oocytes, given that three rounds of microtubule error correction have been calculated to occur for each bivalent, measured from the time of NEB until polar body extrusion (Kitajima et al, 2011). It is likely, but remains to be firmly established, that Aurora kinases play a part in this process, as they do in mitosis, by destabilizing erroneous attachment that fail to generate adequate tension across the kinetochores (Lane et al, 2010;Liu et al, 2009;Welburn et al, 2010;Yang et al, 2010).…”

Reduced ability to recover from spindle disruption and loss of kinetochore spindle assembly checkpoint proteins in oocytes from aged mice

“…S2B). 40 Despite the potential of reduced SAC activity being present in aged oocytes, it seemed unlikely that the SAC was actually nonfunctional, because there was no increase in aneuploidy with age ( Fig. 1B) to a similar level achieved following loss of individual SAC proteins, 15,17,42 and the duration of MI was not shortened (Fig.…”

“…Aurora C is a substitute of Aurora B during meiosis, [34][35][36][37] and its active form pAurora C is thought to be involved in destabilizing erroneous KT-MT attachment, as such contributing to the fidelity of bivalent division. 34,[38][39][40] One further reason for examining Mad2 is that previous studies have shown that levels of this transcript, like those of other SAC components, are lower in oocytes of both aged mice and humans. 24,25 However, there appears to be no aging defect in SAC activity, 7,28 as measured either by the length of MI, which would be predicted to be shorter in a situation of reduced SAC, or in the ability to arrest in response to a nocodazole challenge.…”

“…31 For metII eggs, monastrol was used to spread chromosomes for aneuploidy analysis before fixation. 40 Blocking was performed in 7% normal goat serum in PBS with 0.1% Tween-20. Primary antibodies were diluted in PBS with 3% BSA / 0.1% Tween-20 with overnight incubation at 4 °C: Sgo2, Mad2, phospho-Aurora C, or ACA.…”

Molecular causes of aneuploidy in mammalian eggs

“…The kinetochore is thus both the platform on which the SAC is launched and the tether through which successful poleward PRIMER Development 140 (18) Lane et al, 2010) The acceleration of meiosis I is measured relative to controls; the aneuploidy rate is the absolute level achieved following inhibition of the SAC component (this is usually on background aneuploidy rate of <10%). PRIMER Development 140 (18) chromosome movements are made.…”