Non-canonical imprinting ensures embryonic development and restrains placental overgrowth

Genomic imprinting regulates parental origin-dependent mono-allelic gene expression. It is mediated by either germline differential methylation of DNA (canonical imprinting) or oocyte-derived H3K27me3 (non-canonical imprinting) in mice. Depletion of Eed, an essential component of Polycomb repressive complex 2, results in genome-wide loss of H3K27me3 in oocytes, which causes loss of non-canonical imprinting (LOI) in embryos. Although Eed maternal KO (matKO) embryos show partial lethality after implantation, it is unknown whether LOI itself contributes to the developmental phenotypes of these embryos, which makes it unclear whether non-canonical imprinting is developmentally relevant. Here, by combinatorial matKO of Xist, a non-canonical imprinted gene whose LOI causes aberrant transient maternal X chromosome inactivation (XCI) at preimplantation, we show that prevention of the transient maternal XCI greatly restores the development of Eed matKO embryos. Moreover, we find that the placentae of Eed matKO embryos are remarkably enlarged in a manner independent of Xist LOI. Heterozygous deletion screening of individual autosomal non-canonical imprinted genes suggests that LOI of the Sfmbt2 miRNA cluster-chromosome 2 miRNA cluster (C2MC), solute carrier family 38 member 4 (Slc38a4), and Gm32885 contributes to the placental enlargement. Taken together, our study provides evidence that Xist imprinting sustains embryonic development and autosomal non-canonical imprinting restrains placental overgrowth. RNA-seq was performed in Eed or Eed/Xist CTR and maternal KO/DKO morula embryos (xPWK sperm).