Reciprocal, methylation-dependent binding of Zfp57 and Gzf1 safeguards Dlk1-Dio3 imprinting during developmental reprogramming [GZF1_snp]

However, how unmethylated imprinted alleles resist de novo methylation remains unclear. Using an allelic methylation reporter at the Dlk1-Dio3 ICR and a genome-wide loss-of-function screen, we identify that the zinc finger protein GZF1 specifically binds the unmethylated maternal ICR and protects it from de novo methylation in mouse embryonic stem cells, early development, and oocytes.

We further show that this protection occurs independently of Tet-mediated demethylation. A regulatory element containing GZF1 and ZFP57 motifs mediates mutually exclusive, methylation-dependent binding. Loss of either factor causes reciprocal imprinting failure: Gzf1 loss induces maternal allele methylation, H3K4me3 depletion, and silencing of maternal transcripts, whereas Zfp57 loss erases paternal methylation, causing locus maternalization.