Mitochondria aggregation patterns during human oocyte maturation

Animals study revealed that redistribution of mitochondria was correlated with oocytes maturation and that a lack of redistribution suggested incomplete cytoplasmic maturation and lower developmental competence. The aim of the study was to determine the pattern of spreading through the cytoplasm and percentage of cytoplasm occupied by mitochondria during human nuclear oocytes maturation. Prospective Observational Study. Sixty nine oocytes obtained from 21 patients aged 34±3.2 years that underwent in vitro fertilization (IVF) treatment with ICSI were in different maturation stage: germinal vesicle(GV)=15, meiosis(M) I=16, M II=38 oocytes, respectively. Immature oocytes and non fertilized mature oocytes were allocated for study and stained by Mito-Tracker Green FM. The distribution, area and percentage of cytoplasm occupied by mitochondria were analyzed by fluorescent microscopy and ImageJ software (NIH), respectively. The distribution of mitochondria through the oocyte cytoplasm was mostly homogenously diffuse, central located and peripheral in M II, M I and GV oocytes, respectively. Of The M II oocytes, 60.5% presented an evenly diffuse pattern and of the GV stage oocytes, 53.3% presented a peripheral distribution. The area and the percentage of cytoplasm occupied by mitochondria was 352340±37942, 348955±35675 and 278501±65989 area units (p=0.001, M II vs. GV and M I vs. GV, Kruskal-Wallis test) and 93±9.4%, 85±13% and 75±10.5% (median=100, 86.4, 73.9) in M II, M I and GV oocytes, respectively (p=0.001, M II vs. GV, Kruskal-Wallis test). Mitochondria were distributed mainly in the peripheral region in immature oocytes and homogenously in M II oocytes, revealing qualitative and quantitative information of spreading and localization within the cytoplasm. This pattern of distribution may play an important role in the cytoplasmic maturation of human oocytes and their further development.