A maternal-effect Padi6 variant results in abnormal nuclear localization of DNMT1 and failure of epigenetic reprogramming and zygotic genome activation in mouse embryos

PADI6 belongs to the multi-protein sub-cortical maternal complex (SCMC) that is present specifically in mammalian oocytes and early embryos. Maternal inactivation of SCMC genes generally results in early embryo lethality. In humans, variants in a subset of SCMC genes have been found in the healthy mothers of children affected by genomic imprinting disorders and characterized by multi-locus imprinting disturbances (MLID). However, how the SCMC controls the DNA methylation required to regulate imprinting remains poorly defined. To address this issue, we generated a mouse line carrying a Padi6 missense variant that had been identified in the mother of two sisters affected by Beckwith-Wiedemann syndrome and MLID. We found that if homozygous in female mice this variant resulted in interruption of embryo development at the 2-cell stage. Single-cell DNA methylation and RNA analyses demonstrated genomic hypermethylation, down-regulation of zygotic genome activation (ZGA) genes and up-regulation of maternal decay genes in 2-cell embryos from homozygous females. In addition, immunofluorescence analysis showed abnormal localization of DNMT1 and UHRF1 in mutant oocytes and zygotes. Taken together, this study demonstrates that PADI6 controls the subcellular localization of DNMT1 that is necessary for pre-implantation epigenetic reprogramming and ZGA.