36 EFFECT OF DNA METHYLTRANSFERASE INHIBITOR, RG108, ON IN VITRO DEVELOPMENT AND ntES ESTABLISHMENT RATE IN CLONED MOUSE EMBRYOS

Somatic cell nuclear transfer technique increased expectations among many for its potential to advance the regenerative therapy field. Cloned embryos, however, exhibit several epigenetic abnormalities, such as low histone acetylation or high DNA methylation levels compared with normal fertilized embryos. Therefore, increasing histone acetylation or reducing DNA methylation levels in cloned embryos using chemical treatments may improve cloning efficiency. We recently succeeded in improving the success rate of mouse cloning by using class IIb histone deacetylase inhibitors, such as trichostatin A (TSA), scriptaid and suberoylanilide hydroxamic acid. It has also been reported that 5-aza-2′-deoxycytidine, a DNA methyltransferase inhibitor that is a chemical analogue of cytidine, inhibits the potential of embryos to develop into blastocysts and later to fetuses. In the present study, another DNA methyltransferase inhibitor RG108, which is thought to strongly interact with the DNMT1 active site to inhibit DNMT1 activity, was used to examine whether it could improve cloning efficiency. To determine the effects of RG108, cloned embryos were treated with 100 to 500 μM RG108. When cloned embryos were treated at the 1-cell stage (from artificial activation to 10 h, n = 219), the cloning efficiency was similar to the control group (8.2 vs 10.8%). On the other hand, when 500 μM RG108 was added to the culture medium from the 2-cell to morula/blastocyst stage (n = 113), although the developmental rate to blastocyst stage did not change significantly (79.6% vs 72.3%), higher Oct3/4 expression and more ICM cells were observed compared with non-treated, control cloned embryos. Moreover, we tried to establish ES cell lines from those cloned embryos and 11 ntES lines were generated from 21 blastocysts, which was higher than that of control (6 ntES cell lines from 20 blastocysts). All ntES lines showed AP staining positively. This finding showed that the quality of cloned mouse blastocysts increased when treated with a DNA methyltransferase inhibitor, suggesting a possible means for improving cloning efficiency in the future.