Monosodium glutamate protects DNA of freeze-dried somatic cells and improves development of somatic cell nuclear transfer embryos

Freeze-dried (FD) somatic cells serve as a novel method for preserving animal genetic resources; however, the efficiency of cloned mice production from FD somatic cells remains low, owing to severe nuclear damage induced by the freeze-drying. In this study, we aimed to mitigate freeze-drying-induced damage by evaluating protectants that have been reported to exert protective effects during freeze-drying of microorganisms, and to identify those most effective for somatic cells. Results showed, that using Tris-EGTA as the basal medium for freeze-drying, together with monosodium glutamate (MSG) as a protective agent, significantly reduced DNA damage in FD somatic cells after injection into oocytes. Subsequent optimization of MSG concentration revealed that the addition of 3% MSG markedly increased the formation rate of premature chromosome condensation from 50.0% to 80.4% compared with the non-MSG condition. Moreover, the rate of normal chromosome segregation at the two-cell stage of cloned embryos increased from 0% to 20.0%. Furthermore, although no blastocysts were obtained in the absence of MSG, the addition of 3% MSG enabled the formation of morphologically good-quality blastocysts, albeit at a low frequency. These findings indicated that the addition of 3% MSG reduces DNA damage in FD somatic cells and improves the developmental competence of somatic cell nuclear transfer embryos, representing the first step toward the practical application of FD somatic cells as genetic resources.