Effects of vitrification on mitochondrial distribution and spindle configuration during in vitro maturation of human germinal vesicle-stage oocytes

Abstract

Cryopreservation of human immature oocytes may be useful tool for fertility preservation in the future. However, vitrification of germinal vesicle (GV)-stage oocytes has poor result as for later development after fertilization. This may be due to abnormality of cytoplasmic maturation of the freeze-thawed oocytes. To elucidate this mechanism, we have investigated the distribution of mitochondria and spindle and chromosome configuration of in vitro matured oocytes with or without vitrification. GV oocytes were obtained from consenting patients undergoing ICSI treatment at our clinic. GV oocytes were randomly assigned to 1 of 3 groups: (1) GV group, GV oocytes; (2) IVM group, GV oocytes matured in vitro to metaphase II (MII); and (3) Vit group, oocytes vitrified at GV stage and matured in vitro. Confocal microscopy was applied to compared the mitochondrial distribution and configuration of the meiotic spindle and chromosomes in those oocytes. The maturation (MII) rate was 71.9% in the IVM group and 73.3% in the Vit group. There were no significant differences between the IVM and Vit groups. Compared to the IVM group (17.5%), the Vit group (45.9%) showed significant increase in diffuse mitochondria distribution. There was also a significantly lower proportion of oocytes with normal spindle configuration in the Vit group (18.9%) compared with the IVM group (47.5%). There were no significant differences in chromosome configuration between the IVM and Vit groups. This study revealed that vitrification of human GV oocytes has a detrimental effect on the spindle configuration of oocytes that have been thawed and matured in vitro which may explain decreased ability of further development.