Juvenile in vitro embryo transfer in farm animals reduces the generation interval and increases the rate of genetic gain. In human reproductive medicine, it enables the preservation of female fertility of young patients affected by cancer or by premature ovarian failure. The developmental competence of in vitro-produced juvenile embryos is strictly related to oocyte quality. The aim of the present study was to analyse the developmental potential and the mitochondrial/oxidative status of ovine prepubertal oocytes matured in vitro to clarify their suitability in juvenile in vitro embryo transfer programs. Oocytes from the ovaries of slaughtered prepubertal lambs (less than 6 months of age) were analysed after in vitro maturation. After cumulus cell removal, oocytes at the metaphase II stage (MII) underwent either IVF plus in vitro embryo culture (Experiment 1; n = 200; Bogliolo et al. 2011 Reprod. Fert. Dev. 23, 809–817) or confocal analysis of mitochondria (mt) and reactive oxygen species (ROS) fluorescence distribution, intensity, and colocalization (Experiment 2; n = 30; Martino et al. 2012 Fertil. Steril. 97, 720–728) or scavenger enzyme [superoxide dismutase (Ambruosi et al. 2011 PLoS ONE 6, e27452) and catalase (Beers and Sizer 1952 J. Biol. Chem. 195, 133–140)] activity analyses in cell lysates of individual oocytes (Experiment 3; n = 7). In Experiment 1, 150 of 200 MII oocytes (75%) cleaved after 30 h of in vitro embryo culture, and 36 of 150 2- to 4-cell-stage embryos (24%) reached the blastocyst stage at Day 8. In Experiment 2, 60 of 111 (54%) oocytes selected for in vitro maturation culture reached the MII stage, and 30 of them (50%) with a regular size (>150 µm in diameter) and morphology were analysed for bioenergy/redox parameters. Fourteen of 30 oocytes (47%) showed a heterogeneous (perinuclear, pericortical, or both) mt distribution pattern, and the remaining 16 of 30 oocytes (53%) showed a homogeneous distribution of small mt aggregates. Intracellular ROS were uniformly distributed, thus not corresponding to the mt distribution pattern. Fluorescent intensity of mt and ROS labelling, expressed as arbitrary densitometric units, were 821.4 ± 274.7 and 737.6 ± 226.5 in oocytes with a heterogeneous pattern and 723.7 ± 371.6 and 831.7 ± 263.7 in oocytes with a homogeneous pattern, respectively (not significant). The mt/ROS colocalization (Pearson correlation coefficient) did not differ between heterogeneous (0.47 ± 0.2) and homogeneous (0.51 ± 0.09; not significant) oocytes. In Experiment 3, superoxide dismutase (n = 4) and catalase activity (n = 3) values were 1.09 ± 0.03 and 10.63 ± 1.96 IU mg–1 of protein, respectively. This study provides basal values of bioenergy/redox parameters in prepubertal lamb MII oocytes as related to their developmental potential and may increase the knowledge of prepubertal oocyte physiology compared with their young adult counterparts.
Embryo transfer following in vitro maturation and cryopreservation of oocytes recovered from antral follicles during conservative surgery for ovarian cancer
