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  Vertebrate reproductive science and technology
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RFD is the official journal of the International Embryo Transfer Society and the Society for Reproductive Biology.

Article << Previous     |     Next >>   Contents Vol 22(1)


S. H. Jeong A, S. Kim A, M. K. Choi A, J. M. Na A, J. Choi A, Y. P. Jeon B, T. Y. Shin A, S. H. Hyun B and W. S. Hwang A

A Sooam Biotech Research Foundation, Yongin, Gyeonggi, Republic of Korea;
B Laboratory of Veterinary Biotechnology, College of Veterinary Medicine, Chungbuk National University, Cheongju, Chungbuk, Republic of Korea

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In bovine somatic cell nuclear transfer (SCNT), oocyte activation is an essential element for the successful development of cloned embryos. Chemical treatment with ionomycin induces transient levels of Ca2+, and this has been used in the activation of reconstructed embryos. In vitro-fertilized oocytes are naturally activated by sperm following several Ca2+ transients known collectively as Ca2+ oscillations. We aimed to improve the developmental efficiency of embryos produced by SCNT by mimicking this Ca2+ oscillation artificially. SCNT was performed as follows; bovine calf skin fibroblast cells were transferred into the perivitelline space of IVM oocytes, and then these NT couplets were treated with electrical fusion (2 pulses, 1.75 kV cm-1, 15 μs). Reconstructed embryos were subsequently cultured in SOF medium (5% CO2, 5% O2, and 38°C). To mimic Ca2+ oscillation, we carried out 3 different repetitive ionomycin (10 μM) treatments at 1-h intervals. There were 3 groups: group 1 (4 min, 1 time), group 2 (30 s, 4 times), and group 3 (1 min, 4 times). The difference in embryo development amongst these experimental groups was then analyzed using the one-way ANOVA test after arcsine transformation to maintain homogeneity of variance. All analyses were performed using SAS (version 8.1, SAS Institute, Cary, NC, USA). Significant differences among the treatments were determined when the P-value was <0.05. In experiment 1, to assess developmental efficiency, the cleavage rate was investigated on Day 2 and the formation rate of blastocysts (BL) was examined on Day 7. In group 3, a significant increase in BL formation was observed [47/263 (17.8%), 50/259 (19.3%), and 67/258 (26.0%), respectively]. In experiment 2, culturing each group of embryos with different ionomycin treatments caused no significant differences among the groups in terms of the total number of BL (164.3, 158.5, and 145.1, respectively). In experiment 3, expression of apoptosis-related genes in each group was evaluated by real-time PCR and the TUNEL assay. The 3 BL within each group were analyzed for the expression of apotosis-related genes. Expression of the anti-apoptotic Bcl-2 gene was increased in group 3, whereas the expression of the pro-apoptotic Bax was decreased. A decrease in the number of apoptotic nuclei was also observed in group 3. In conclusion, the present study demonstrated that repetitive ionomycin treatment is an improved activation method that can increase the developmental competence of SCNT embryos by decreasing the incidence of apoptosis.

Reproduction, Fertility and Development 22(5305) 188–188   http://dx.doi.org/10.1071/RDv22n1Ab60
Published online: 08 December 2009

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