To investigate the role of the oocyte in premature ovarian failure

Premature ovarian failure occurs in 1% of women under the age of 40 and is a cause of significant stress and heartache to many couples. There are also no specific warning signs for impending premature ovarian failure and unfortunately, premature ovarian failure also leads to increased risks of developing other health problems including osteoporosis. For so common a condition, it is surprising that only 30% of cases have a known cause. Therefore, there is a clear and urgent need to further our knowledge of the physiology that underlies premature ovarian failure. Dr. Suzannah Williams at the University of Oxford is using a novel mouse model to investigate the physiology of premature ovarian failure. These females have abnormal ovarian function and are infertile, elevated gonadotrophins and decreased ovarian steroids concentrations which in women, leads to a diagnosis of premature ovarian failure. This mouse model undergoes premature ovarian failure by 3 months of age and this provides a window to investigate the onset of this condition. These studies will further our understanding of basic ovarian physiology, and the onset and maintenance of ovarian failure. It is hoped that these studies will identify potential targets to investigate in women with premature ovarian failure which may in time lead to the development of methods to reverse it. The mouse model central to this proposal is generated by egg-specific deletion of two enzymes early in egg development. This mouse model identifies a role for the egg in maintaining the function of the ovary because this is the only cell that has been genetically modified. Furthermore, genetic modification only occurs after eggs have begun to develop which means that all eggs quietly waiting in the ovary for use later in reproductive life remain unaltered. Therefore, the ovaries in this mouse model contain normal eggs, as do women with follicular premature ovarian failure, and these mice have the potential to become fertile again if we can unravel how premature ovarian failure has been induced. In this research proposal we will analyse this mouse model as it becomes infertile investigating ovarian physiology, hormone and steroid concentrations, and ovary gene expression.

Premature ovarian failure affects 1% of women under the age of 40. However, despite the prevalence of this condition, only 30% of cases have a known cause. There are no specific signs of impending ovarian failure and women who have undergone ovarian failure are at increased risk of developing other health problems including osteoporosis. Therefore, further investigation of premature ovarian failure is clearly essential to understand the etiology of this condition. The use of a mouse model (double mutant; DM) that undergoes premature ovarian failure by 3 months despite the presence of normal primordial follicles allows investigation into the transition from fertility to infertility. In addition to acyclicity, DM mice have elevated gonadotrophins and decreased ovarian steroids which in women diagnoses premature ovarian failure. DM ovaries contain few developing follicles at 3 months and the ovary is comprised predominantly of hypertrophied luteolysed tissue. The objective of this proposal is to determine the physiological basis for the induction and maintenance of premature ovarian failure in a mouse model. DM females undergo oocyte-specific deletion of two glycosyltransferases (T-syn and Mgat1) at the primary stage early in oocyte development using Cre loxP recombination technology. The primordial pool of follicles in DM females remains genetically unaltered and therefore infertility in these mice is potentially reversible. DM follicle growth, development and steroidogenic capability will be determined in vivo and in vitro. We will also determine if DM follicle growth can be supported by secreted factors from wildtype follicles in vitro. Progesterone remained unexpectedly high and therefore corpus luteum regression will be assessed. Follicle apoptosis and apoptotic pathways will be analysed using immunohistochemistry to determine how follicles are being removed from DM ovaries. Ovarian steroidogenic pathways will be characterised using Q-PCR of granulosa, theca, and luteolysed tissue samples collected with laser capture microdissection (LCM). DM females were fertile but become infertile despite oocyte-specific genetic modification occurring at the same time point in oogenesis. Therefore, it is possible that abnormal levels of steroids and hormones maintain aberrant folliculogenesis after it has been initiated. A series of ovarian transplantation experiments will determine if the aberrant systemic or paracrine endocrine environment contributes to the infertility. Finally, microarray analysis of whole ovaries will identify modified genes that will be further investigated using LCM and Q-PCR. The results from these studies will be disseminated at both National and International Conferences, and published in a timely manner.