Mitochondrial distribution and ATP content of vitrified, in vitro matured mouse oocytes

The objective of this study was to investigate the effect of vitrification and in vitro maturation on the mitochondrial distribution and ATP content of oocytes. The oocytes at Germinal Vesicle [GV] and Metaphase II [MII] stages were recovered from 6-8 week old NMRI strain female mice. The oocytes were divided into vitrified and non-vitrified groups. Vitrification was done by the cryotop method using ethylene glycol, dimethylsulfoxide and sucrose as cryoprotectants. The GV oocytes were cultured in maturation medium for 24 hrs. The collected in vitro matured oocytes [IVM-MII] and ovulated metaphase II [OV-MII] oocytes were inseminated with capacitated sperm. The ATP content of the oocytes was measured by luciferin-luciferase reaction. Distribution of oocyte mitochondria was studied using Mito Tracker Green staining under fluorescent microscope. The survival rates of vitrified oocytes at GV and MII stages were 87.39 and 89.5%, respectively. There was no significant difference in the developmental and hatching rates of vitrified and non-vitrified oocytes. The ATP content of GV and MII oocytes derived from in vivo and in vitro condition was not significantly different in vitrified and non-vitrified samples. The pattern of mitochondrial distribution in vitrified and non-vitrified GV and MII oocytes was similar but it was different between MII oocytes collected from fallopian tube and in vitro matured MII oocytes. However, the florescent intensity of mitochondrial staining was different in all the groups in the study. Vitrification did not affect mouse oocyte developmental competence, ATP content at different developmental stages but some alteration was seen in mitochondria distribution of in vitro matured oocytes in comparison to their controls