Aberrant mRNA expression and DNA methylation levels of imprinted genes in cloned transgenic calves that died of large offspring syndrome

Large offspring syndrome (LOS) has frequently been described in cloned cattle, but few studies focus on the pathogenic mechanism. In this study, we investigated the messenger RNA (mRNA) levels of six imprinted genes (H19, IGF2, IGF2R, XIST, PEG3 and SNRPN) in five tissues (muscle, liver, spleen, lung and kidney) from stillborn cloned transgenic calves with LOS (S group, n = 4), liveborn cloned transgenic calves (L group, n = 4) and normally produced female calves (N group, n = 4) using quantitative real-time polymerase chain reaction (PCR). We analysed the DNA methylation status of H19, XIST and IGF2R among the three groups, using Bisulphite Sequencing PCR (BS-PCR) and Combined Bisulfite Restriction Analysis (COBRA). In addition, the DNA methylation status of these genes was also assessed in the transgenic and non-transgenic cells. Aberrant mRNA expression and DNA methylation levels were found in multiple tissues from both cloned transgenic groups. The S group showed relatively more severe gene expression and DNA methylation abnormalities than the L group. The DNA methylation levels of H19, XIST and IGF2R were not significantly different between the transgenic and non-transgenic cells. Our results indicate that the aberrant mRNA expression and DNA methylation levels of important development-related imprinted genes, as a result of epigenetic nuclear reprogramming during somatic cell nuclear transfer (SCNT), may result in large offspring syndrome and, finally, foetal death in cloned transgenic calves.