a,c Small molecule PARP inhibitor 3AB and, APE1 inhibitor (CRT0044876) impede progression of DNA demethylation as detected by 5mC staining. b,d. Quantification of 5mC staining. The values represent a ratio between 5mC signal from paternal pronuclei relative to the signal from maternal pronuclei. Statistical analysis was by Student’s t-test. e. Bisulphite analysis of Line1 repetitive elements. The values show the percentage of methylated CpGs. Each line represents a unique DNA clone. Filled and open circles represent methylated and unmethylated CpGs, respectively. Scale bar 10μM. ♀ – maternal pronucleus, ♂ – paternal pronucleus, pb – polar body.