Molecular factors of female high-fertility - a study of two outbreed mouse lines selected for increased reproductive performance

Contact: Dr. Marten Michaelis

Duration: 2018-2021

Funding: Deutsche Forschungsgemeinschaft, DFG MI 2098/3-1

Factors of high-fertility are just poorly described. The majority of transgenic or knockout models with a reproductive phenotype is subfertile or sterile. Only a minority of genotypes is linked with enhanced fertility (0.2%) or increased litter size (1%). Thus, we are lacking of high-fertility models. In this study we change the perspective by using two worldwide unique mouse models fertility line (FL) 1 and FL2 selected for high-fertility. These mice almost doubled the number of littermates as well as the total birth weight per litter in comparison to an unselected control line (Ctrl) with no signs of growth retardation in the offspring. The aim of this project is to characterize these selection lines in parallel from phenotypic to genotypic alterations. Pioneer studies reveal both FLs ovulate more oocytes. Hence, we hypothesize that (i) the size of the follicle pool has changed (elevated follicle pool model) or (ii) the amount of ovulated follicles increased due to hormonal alterations in the hypothalamic-pituitary-gonad axis (HPG axis) during selection process (superovulation like model). Both hypotheses will be tested on different ovarian developmental stages determining the follicle pool size and in addition analysing for endocrine alteration of the HPG axis. Currently it is unknown how high ovulating ovaries are maintained their characteristics after more than 180 generations. Comparing both FLs and Ctrl line in parallel will provide new information of the complexity and diversity of the phenome high-fertility. The holistic gene expression approach will draw a global picture of how the phenotype is warranted. These networks will be compared with already existing data based on QTL analysis to generate a list of potential candidate genes or gene markers of increased fertility. Brilliant cresyl blue (BCB) supravital staining determines the activity of glucose-6-phosphate dehydrogenase (G6PDH) and is a marker of oocyte maturation and developmental competence. Pilot experiments reveal FL1 and FL2 mice have decreased activity of G6PDH in oocytes isolated from antral follicles. We will test if these differences are contributing factors of increased fertility using IVF experiments. In addition to these functional studies we will analyse the oocyte proteome of all three mouse lines in dependence of their BCB-status for downstream effects of decreased G6DPH activity. By analysing both FLs in parallel from the phenotype to the genotype we expect new basic insights into physiological adaptations of the ovary and affected genes and biosignatures of increased fertility. In addition we hypothesize that those genes and pathways regulated to maintain high fertility are also of importance to the phenotype reduced fertility. Hence we consider the work as a basis for further investigations to study the phenotype of high-fertility using gene knockout/-in and will test the list of prolificacy markers in other species.