Chemical activation of parthenogenetic and nuclear transfer porcine oocytes using ionomycin and strontium chloride

Effective protocols for oocyte activation are crucial for study of parthenogenetic development and to produce nuclear transfer reconstructed embryos. This study investigated the use of ionomycin (ION) and strontium chloride (Sr2+) in the activation of parthenogenetic and nuclear transfer porcine oocytes. In-vitro-matured oocytes with a polar body were treated with varying concentrations of ION, Sr2+ or its combinations, and then fixed or cultured to assess activation and development rates, respectively. Ionomycin concentrations of 10 and 15 μM resulted in more frequent oocyte activation and the 15 μM in advanced development compared to 5 μM (71.8 and 70% vs. 47.5%; P = 0.04, and 43.7% vs. 19.3%; P = 0.008, respectively). Oocytes treated with 10, 20 or 30 mM of Sr2+ for 2 or 4 h displayed a pronuclear formation rate ranging from 46.7 to 70%. When employed after a 5 min treatment with 10 or 15 μM ION, exposure to 10 mM Sr2+ for 4 h resulted in higher pronuclear formation than did the 20 mM concentration (82 and 88.6% vs. 63.3 and 73.2%; P = 0.03). Nuclear transfer reconstructed oocytes treated with 15 μM/5 min ION followed by 10 mM/4 h Sr2+ resulted in a higher development to blastocyst stage compared to those treated with 15 μM ION alone (17.7 vs. 11.3%; P = 0.06). In conclusion, we inferred that the inclusion of Sr2+ in the activation protocol can benefit the development of nuclear transfer reconstructed porcine oocytes.