Poster Presentation ESA-SRB Conference 2015

The pan-sirtuin inhibitor, nicotinamide, disrupts the meiosis I-to-meiosis II transition in mouse oocytes (#305)

Angelique Riepsamen 1 , Lindsay Wu 2 , Laurin Lau 1 , Dave Listijono 1 , Wei Guo Loh 1 , David Sinclair 2 3 4 , Hayden Homer 1
  1. School of Women's and Children's Health, University of New South Wales, Sydney, NSW, Australia
  2. School of Medical Sciences, University of New South Wales, Sydney, NSW, Australia
  3. Genetics Department, Harvard Medical School, Boston, MA, USA
  4. Glenn Labs for the Biological Mechanisms of Aging, Harvard Medical School, Boston, MA, USA
In oocytes, exit from meiosis I (MI) is immediately followed by entry into meiosis II (MII) after which oocytes arrests at metaphase II awaiting fertilization. This unique MI-to-MII transition necessitates partial inactivation of cyclin-dependent kinase 1 (Cdk1) brought about by inhibitory Cdk1 phosphorylation and destruction of the Cdk1 co-activator, cyclin B1, mediated by the anaphase-promoting complex (APC). Following extrusion of the first polar body (PBE), which marks exit from MI, re-establishing and maintaining Cdk1 activity is important for assembling a fully formed bipolar spindle with aligned condensed chromosomes typical of metaphase II-arrest. Sirtuins are NAD+-dependent deacetylases that are key for multiple cellular processes. Here we investigate the effect of the pan-sirtuin inhibitor, nicotinamide (NAM), on mouse oocyte maturation. Culturing oocytes in 10mM NAM during MI had no effect on rates or timing of PBE or on spindle assembly during MI. Unexpectedly however, examination of NAM-treated oocytes after PBE had occurred revealed that the majority (70%) lacked a bipolar spindle and contained a nucleus with decondensed chromosomes. Treatment with either NAM or the Cdk1 inhibitor, flavopiridol (5μM), after PBE had occurred did not reproduce the phenotype. However, an identical phenotype was observed when flavopiridol was used specifically during exit from MI prior to PBE altogether suggesting that NAM impaired establishment rather than maintenance of MII arrest. We further found that relative to controls, inhibitory Cdk1 phosphorylation was higher and cyclin B1 levels declined lower during MI exit in NAM-treated oocytes. One possible reason for reduced cyclin B1 levels with NAM treatment may be related to increased APC-mediated proteolysis as we also found increased levels of the APC co-activator, Cdc20, during MI exit. Collectively, these results indicate that NAM-induced sirtuin inhibition led to excessive Cdk1 inactivation during MI exit thereby causing oocytes to exit meiosis into an interphase-like state.