Smchd1 is a maternal effect gene required for autosomal imprinting

Genomic imprinting establishes parental allele-biased expression of a suite of mammalian genes based on parent-of-origin specific epigenetic marks. These marks are under the control of maternal effect proteins supplied in the oocyte. Here we report the epigenetic repressor Smchd1 as a novel maternal effect gene that regulates imprinted expression of 16 genes. Most Smchd1-sensitive genes only show loss of imprinting post-implantation, indicating maternal Smchd1’s long-lived epigenetic effect. Sm-chd1-sensitive genes include both those controlled by germline polycomb marks and germline DNA methylation imprints; however, Smchd1 differs to other maternal effect genes that regulate the latter group, as Smchd1 does not affect germline DNA methylation imprints. Instead, Smchd1-sensitive genes are united by their reliance on polycomb-mediated histone methylation marks as germline or secondary imprints. We propose that Smchd1 translates these imprints to establish a heritable chromatin state required for imprinted expression later in development, revealing a new mechanism for maternal effect genes.