Highly methylated Xist in SCNT embryos was retained in deceased cloned female goats

Abstract

X (inactive)-specific transcript (Xist) is crucial in murine cloned embryo development, but its role in cloned goats remains unknown. Therefore, in this study we examined the expression and methylation status of Xist in somatic cell nuclear transfer (SCNT) embryos, as well as in ear, lung, and brain tissue of deceased cloned goats. First, the Xist sequence was amplified and a differentially methylated region was identified in oocytes and spermatozoa. Xist methylation levels were greater in SCNT- than intracytoplasmic sperm injection-generated female 8-cell embryos. In addition, compared with naturally bred controls, Xist methylation levels were significantly increased in the ear, lung, and brain tissue of 3-day-old female deceased cloned goats, but were unchanged in the ear tissue of female live cloned goats and in the lung and brain of male deceased cloned goats. Xist expression was significantly increased in the ear tissue of female live cloned goats, but decreased in the lung and brain of female deceased cloned goats. In conclusion, hypermethylation of Xist may have resulted from incomplete reprogramming and may be retained in 3-day-old female deceased cloned goats, subsequently leading to dysregulation of Xist.