Noncanonical imprinting sustains embryonic development and restrains placental overgrowth.

Genomic imprinting regulates parental origin-dependent monoallelic gene expression. It is mediated by either germline differential methylation of DNA (canonical imprinting) or oocyte-derived H3K27me3 (noncanonical 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 noncanonical imprinting (LOI) in embryos. Although 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 noncanonical imprinting is developmentally relevant. Here, by combinatorial matKO of , a noncanonical 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 matKO embryos. Moreover, we found that the placentae of matKO embryos are remarkably enlarged in a manner independent of LOI. Heterozygous deletion screening of individual autosomal noncanonical imprinted genes suggests that LOI of the miRNA cluster chromosome 2 miRNA cluster (C2MC), solute carrier family 38 member 4 (), and contributes to the placental enlargement. Taken together, our study provides evidence that imprinting sustains embryonic development and that autosomal noncanonical imprinting restrains placental overgrowth.