Epidermal growth factor improves in vitro maturation of immature mouse oocytes

Objective To investigate the significance of EGF in the in vitro maturation, fertilization, and pre-implantation development of the immature oocytes. Methods The immature oocytes were isolated from the ovaries of the rats. The germinal vesicle (GV) oocytes were cultured in the EGF solutions at concentrations of 0(control), 0.5, 1, 2.5, 5 and 10 ng/ml Ham’s F10 culture media. The status of germinal vesicle break-down(GVBD) and the extrusion of the first polar body (PB1) were observed. The achieved MⅡoocytes were then inseminated in vitro; and the pronuclei (PN) and the pre-implantaon development were observed. The gradeⅠ-Ⅱ4-cell embryos were selected and implanted into the fallopian tube of the rats with the 1 day pseudogestation. Follow-up observations were made till the delivery. Results After GV oocytes were treated with EGF solutions at concentration of 1, 2.5, 5 and 10 ng/ml for 12, 16, 20, and 24 h, the GVBD in the GV cumulus-oocyte complexs(COC) have better outcomes than that of the control group(P0.05, P0.01). For 20, 24, and 36 h in the 2.5, 5 and 10 ng/ml EGF groups, the elimination ratio of PB1 was higher than that of the control group(P0.05, P0.01), particularly in the 5 ng/ml EGF (P0.01). The degenerating rates of the COC group cultured in the 1, 2.5, 5 and 10 ng/ml EGF were lower than that of the control group(P0.05, P0.01). The fertilization rates of the oocytes and the incidence rate of 2-cells and 4-cells in the 5 ng/ml EGF were higher than those of the control group (P0.01). Conclusion EGF promotes not only the maturation of COC in the GV phase, but also the fertilization and pre-implantation development in a dose-dependent fashion. enhancing effect of EGF was closely related to the dosage of EGF.