RNA sequencing-based identification of aberrant imprinting in cloned mice

Animals cloned by somatic cell nuclear transfer (SCNT) provide a unique model for understanding the mechanisms of nuclear epigenetic reprograming to a state of totipotency. Though many phenotypic abnormalities have beendemonstrated in cloned animals, the underlyingmechanismsare not well understood. In this study,weperformed transcriptome-wide allelic expression analyses in brain and placental tissues of cloned mice. We found that Gab1, Sfmbt2 and Slc38a4showed loss of imprinting in all cloned mice analyzed, which might be involved in placentomegaly of cloned mice. These three genes did not require de novoDNAmethylation in growing oocytes for the establishment of imprinting, implying the involvement of a de novoDNAmethylation-independent mechanism. Loss of Dlk1-Dio3 imprinting was also observed in nearly half of cloned mouse embryos and showed a strong correlation with embryonic lethality. Our findings are essential to understand the underlying mechanisms of developmental abnormalities of cloned animals. We also emphasize that particular attention should be paid to specific imprinted genes for therapeutic and agricultural applications of SCNT.