Loss of Slc38a4 imprinting is a major cause of mouse SCNT placenta hyperplasia at late gestation

Placenta hyperplasia is commonly observed in cloned animals and is believed to impede the proper development of cloned embryos. However, the mechanism underlying this phenomenon is largely unknown. Here we show that placenta hyperplasia of cloned mouse embryos occurs in both middle and late gestation. Interestingly, restoring paternal-specific expression of an amino acid transporter Slc38a4, which loses maternal H3K27me3-dependent imprinting and becomes bi-allelically expressed in cloned placentae, rescued the overgrowth of cloned placentae at late gestation. Molecular analyses reveal that loss of Slc38a4 imprinting leads to over activation of the mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway in cloned placentae, which is likely due to the increased amino acids transportation by SLC38A4. Collectively, our study not only reveals loss of Slc38a4 imprinting is responsible for overgrowth of cloned placentae at late gestation, but also suggests the underlying mechanism involves increased amino acid transportation and over activation of mTORC1. We conducted RNA sequencing in in vitro fertilized (IVF), wild type SCNT and Slc38a4 maternal knockout SCNT placenta at E14.5 and E19.5