Abstract
In mammalian females, germ cells proliferate exclusively in development resulting in a finite number of oocytes at birth which are kept in a dormant state within primordial follicles. The ovarian reserve (OR) is the population of primordial follicles and is highly variable between individuals. The OR is continually depleted to exhaustion in mammals, which results in menopausal onset in humans. However, infertility in both species is onset prior to complete exhaustion of ovarian reserve. It is hypothesised that both the initial size of the OR and the rates of depletion contribute to determine reproductive lifespan however current knowledge of these links is limited. Current ovarian reserve data is from histological cross-sectional studies or indirect correlative measures (eg. Anti-Müllerian Hormone). Here we assess the efficacy of a new transgenic-fluorescence mouse model as a non-invasive longitudinal method of quantifying the ovarian reserve to determine these contributions. Using a germ-cell specific (Ddx4) driven Cre-recombinase coupled with a stop-floxed fluorescent reporter transgene (tdTomato), for fluorescent expression exclusively in oocytes. Resultant fluorescent images were image processed for quantification of primordial follicle fluorescence only and these measures correlated against stereological primordial follicle counts (n=13) to assess the efficacy of the proposed fluorescent model. These variables had a strong positive correlation (r=0.8783 p<0.0001) illustrating the efficacy of fluorescence quantification as a correlative measure of ovarian reserve size. This fluorescent correlative measure of ovarian reserve can be used for fertility studies to perform rank correlation to stereological primordial follicle counts from the same individuals in later life. Thus representing the first longitudinal measure of the ovarian reserve to determine the contribution of the initial ovarian size on reproductive longevity.