Effects of serum starvation and ionomycin activation on the development of somatic cell nuclear transfer embryos in sheep

Abstract

Synchronization of donor cells and activation of the reconstructed oocytes are important factors affecting the success rate in somatic cell cloning. In this study, it was aimed to investigate the effects of serum starvation in donor cell synchronization and ionomycin treatment in the activation of reconstructed oocytes after somatic cell nuclear transfer in Kivircik sheep. Cumulus cells were obtained from a slaughtered sheep ovaries and used as donor cells after serum starvation for 4 days (0.5% FCS; SS) or without serum starvation (10% FCS; S). After reconstruction, oocytes were activated by ionomycin for 5 min plus 6-dimethylaminopurine for 3 h (I+) or only with 6-dimethylaminopurine for 3 h (I-). All cleaved embryos (n= 44) at the second day of in vitro culture were transferred into synchronized recipient ewes (n= 10). Cleavage rates of the embryos were 37.3, 44.1, 34.6 and 44.7% in SS/I+, S/I+, SS/I- and S/Igroups, respectively. Recipient ewes had serum progesterone levels >1 ng/ml at 18 th day were 33.3, 50.0, 50.0 and 100.0%, respectively. Only one pregnancy in the S/I- group continued after 40 days however the cloned lamb (7.1%, regarding to embryos transferred) died 10 days before term due to a maternal problem (uterine torsion). The results of this study reveal that somatic cell synchronization by serum starvation and ionomycin treatment for the activation of oocytes can be omitted for the success of somatic cell nuclear transfer in sheep