Co-culture of pre-antral ovarian follicles does not increase the yield of in-vitro-matured oocytes in the mouse

In-vitro culture of ovarian follicles offers the possibility of checking whether there are direct interactions between follicles. Gross follicle morphology and oocyte maturation were investigated as endpoints after co-culture of pre-antral mouse ovarian follicles. Pre-antral mouse follicles with a diameter of 95–110 μm (small) or >110–160 μm (large) were cultured. Pairs of different size or large like-sized follicles were cultured either in physical contact or without in 20 μl culture medium droplets under oil for 10 days. Individual culture of small and large follicles served as controls. On day 10 human chorionic gonadotrophin was administered. On day 11, ‘in-vitro ovulated' cumulus–oocyte complexes where the cumuli oophori had expanded (termed ‘mucified') were collected. The percentage of metaphase II (MII) oocytes was scored as primary endpoint. There were temporary differences between the degree of follicle attachment and diffusion of granulosa cells, but with the observations of antrum formation by day 10, there was no difference between different types of co-cultures and individual culture of large follicles. The MII-to-follicle rate was highest for individual culture of large follicles (54.7%) followed by co-culture of large like-sized follicles growing either in contact or not (40.1% and 42.6%), co-culture of different-sized follicles growing in contact or not (28.5% and 29.8%) and small follicles cultured individually (8.1%). In conclusion, mature oocyte yield was not increased by co-culture of mouse pre-antral ovarian follicles.