Following in vitro maturation, oocytes at metaphase II with the presence of a first polar body were activated using 10 µM calcium
ionophore A23187 (Sigma - Aldrich)
for 5 min followed by 2 mM DMAP (Sigma - Aldrich)
for 4 h at 37 °C in 6 % CO2, 5 % O2 and 89 % N2.