Change Of The Mitochondrial Distribution In Human Oocytes Before And After In Vitro Maturation

Objectives: To clarify the relationship between oocyte maturation and mitochondria distribution by investigating the distribution of mitochondrial in immatured and in vitro matured human oocytes.Methods: (1)Source of immatured oocytes: Patients were obtained from March 2006 to October 2006, in reproductive medicine center of Shandong University, Shandong provincial hospital, all of whom underwent intracytoplasmic sperm injection because of male factor or combining with oviduct factor. Immatured oocytes were donated for research after informed consent after they were digested by hyaluronidase. (2)Source of in vivo matured oocytes: In vivo matured oocytes were collected from infertile women undergoing controlled ovarian stimulation followed by coitus or assisted insemination in the same hospital and the same period. If ovulation did not happen 42 hours after administration of 10 000 IU HCG, the artificial follicular rupturing would carried. When the big matured follicles were ruptured by transvaginal puncture, the oocytes would flowed into the abdominal cavity following follicle fluid and the patient may be pregnant. In order to avoid ovarian hyperstimulation syndrome and multiple pregnancies, some spare small follicles would be punctured if they were excessive. Matured oocytes were donated for research after informed consent. Immatured oocytes were divided randomly into two groups. Using fluorescence dye, half were stained directly and the others were stained after in vitro maturation. Both immatured and matured oocytes were stained by Mito Tracker Green FM. After they were fixed by paraformaldehyde, the distribution of mitochondria was observed using confocal laser scanning microscope.Results: There were 284 immatured oocytes in all, among which 144 underwent in vitro maturation, 88 being GV and 56 being MI. 48 h after in vitro maturation, 56 (63.64%) GV oocytes reached MII, and 50 (89.29%) MI oocytes reached MII The maturation rate of MI oocytes was higher than GV oocytes and the differences were significant. (P=0.016) .Three mitochondria distribution patterns were identified: peripheral, semi-peripheral and evenly diffused. 64.10%(50/78) of the GV oocytes presented a peripheral distribution pattern of mitochondria. 45.16%(28/62) of the MI oocytes had maintained the peripheral distribution, while 38.71%(24/62) presented a diffused status. After in vitro maturation, 75.47%(80/106)of the oocytes displayed an evenly diffused type of distribution.Mitochondria displayed a peripheral distribution in most GV oocytes and the differences were significantly when compared with MI and MII oocytes. Mitochondria maintained an evenly diffused type of distribution in matured oocytes, which was significantly different from immatured oocytes. It could be seen that there were obvious changes in the distribution of mitochondria in human oocytes before and after maturation. The mainly distribution pattern of mitochondria was changing from peripheral in immatured oocytes to evenly diffused in matured oocytes.Among 11 in vivo matured oocytes, 8 (72.73%) displayed an evenly distribution pattern of mitochondria and mitochondria diffused peripherally in the other 3 (27.27%) oocytes. Compared with the oocytes matured in vitro, the most marked feature of oocytes matured in vivo was that mitochondria distributed in the central region. Staining in the central of the oocytes was stronger than which in the peripheral region.Conclusions : (1)There were obvious changes in the distribution of mitochondria in human oocytes before and after maturation. The mainly distribution pattern of mitochondria was changing from peripheral in immatured oocytes to diffused in matured oocytes. (2)Distribution of mitochnondria inoocytes matured in vivo is slightly different from oocytes matured in vitro.