Oocyte maturation and expression pattern of follicular genes during in-vitro culture of vitrified mouse pre-antral follicles.

Our aim was to evaluate the oocyte maturation rate and follicular genes expression pattern during in-vitro culture of vitrified mouse pre-antral follicles. Middle sized pre-antral follicles were isolated mechanically from the ovaries of pre-pubertal mice and distributed in vitrification and control groups. In the vitrification group, follicles were washed in equilibration and vitrification solutions and then were immersed in liquid nitrogen after loading on cryotop tips. After warming in descending concentrations of sucrose solutions, fresh and vitrified-warmed follicles were cultured for 13 days. Follicles survival rate and follicular genes expression were assessed during in vitro culture. Finally, at the end of the culture period oocytes maturation rate were compared in both groups. In the vitrification group, follicles survival rate was lower significantly comparing to the control group (P < 0.05), whereas oocytes maturation rate were similar. Although at the beginning of the culture period, expression of some genes such as Gdf9, Bmp15, Tgfβ1 and BmprII were higher in the vitrification group (P < 0.05), during the rest of the culture period expression pattern of all follicular genes were similar in both groups. In conclusion, survival rate of cryotop vitrified pre-antral follicles reduced during culture period while oocytes maturation and follicular genes expression did not show any noticeable alteration.