The impact of maternal ageing and chemotoxicants on female fertility

Mammalian females are born with all the oocytes they will ever have. The quality and quantity of these gametes dictates the reproductive life span of a woman. In recent decades it has been well established that oocyte quality decreases with increasing maternal age primarily as a result of oocytes failing to separate chromosomes correctly. The outcome is a condition known as aneuploidy, which can result in increased rates of miscarriage and birth defects such as Downs Syndrome. Additionally, exposure of oocytes to chemotoxicants, including those found in cigarette smoke, has been found to prematurely reduce oocyte quality in women leading to early onset menopause. The aim of this thesis is to investigate potential causes of female fertility decline, including ageing and multigenerational exposure to cigarette smoke. Research within this thesis highlights the role of in utero and multigenerational smoke exposure in reducing female fertility. Approximately 12% of Australian and American women smoke throughout their pregnancy (Australia’s mothers and babies, 2015; Tong et al., 2009). This has been linked to decreased birth weight, increased risk of sudden infant death syndrome, childhood cancers and asthma in in utero exposed offspring (maternal smoke exposed). Additionally, a growing body of evidence suggests that these maternal smoke exposed females have a reduction in fecundability in later life (Weinberg et al., 1989; Ye et al., 2010). However, the cause of this reduced fertility, and the fertility of the subsequent generations is largely unknown. Throughout this thesis, I detail how maternal and grandmaternal smoke exposure decreases female fertility in a mouse model, whilst great-grandmaternal smoke exposure appears to have little effect. In addition to investigating the effects of multigenerational smoke exposure on female fertility, this thesis also explores the impact of maternal ageing on oocyte quality. It has been well established that oocyte quality decreases with increasing age (Hassold et al., 2007; Jones, 2008). However, the molecular mechanisms underpinning this phenomenon are still being unravelled. In order to gain further insight into the fidelity of the oocyte cell cycle, I chose to examine a member of the kinesin motor protein family, Kif4. Kinesins are known to be important for the mitotic cell cycle, but little is known about how they function in mammalian oocytes. In mitosis Kif4 is involved in chromosome condensation and separation, metaphase and midzone spindle formation and cytokinesis (Hu et al., 2011; Mazumdar et al., 2004; Samejima et al., 2012). I show here for the first time that Kif4 has dynamic localisation throughout meiosis, and importantly, that it has essential roles in female meiosis, including spindle formation and polar body extrusion (cytokinesis). Furthermore, Kif4 appears to have roles in trafficking kinetochore proteins Ndc80 and CENP-C under the control of Aurora Kinase B and Cdk1. Finally, I show that Kif4 protein levels are elevated in metaphase I and II oocytes from reproductively aged mice, implicating a role for this protein in age related oocyte quality decline. Collectively the data presented in this thesis helps build a clearer picture of the role of multigenerational smoke exposure and/or maternal ageing on reduced female fertility.