Abstract
The improvement of in-vitro growth culture (IVG) system for bovine oocytes derived from early antral follicles (EAFs, 0.5 to 1 mm) is required for production and research purposes. In experiment 1, growing oocytes (95 μm in diameter) collected from EAFs were submitted to 12-day IVG. After IVG, oocytes with normal appearance were submitted to 0-, 10- or 20-h pre-IVM with 3-isobutyl-1-methylxanthine (IBMX) followed by 22-h IVM (0-, 10- and 20-h pre-IVM group, respectively). Diameter and nuclear maturation (M II) rate of IVG oocytes were examined after IVM. Mean diameters were similar in all group (about 115 μm), but they were smaller than that of in-vivo grown oocytes derived from antral follicles (2 to 8 mm). M II rate in 10-h pre-IVM group (90%) was higher than those in 0-h (55%) and 20-h pre-IVM groups (73%), and similar to that of in-vivo grown oocytes (94%). In experiment 2, IVG oocytes in 0-, 10- and 20-h pre-IVM groups were submitted to IVF and their developments were examined. Cleavage (80%) and blastocyst rates (41%) in 10-h pre-IVM group were higher than those in 0-h (46 and 13%, respectively) and 20-h pre-IVM groups (63 and 26%, respectively), and similar to that of in-vivo grown oocytes (83 and 42%, respectively). To clarify the cause of difference in maturational and developmental competences, mitochondrial activity of IVG oocytes was examined by JC-1 staining after 0-, 10- and 20-h pre-IVM. Mitochondrial activity of IVG oocytes after 10-h pre-IVM was higher than those after 0- and 20-h pre-IVM. In conclusion, 10-h pre-IVM culture with IBMX improves maturational and developmental competences of bovine IVG oocytes, and it seems to be related to the activation of mitochondria.
