Table 1.

Main epigenetic processes involved in the regulation of pregnancy

Processes	Mechanisms	Enzymes/molecules	Effect
DNA methylation	Methylation of CpG and CGIs	-DNMT1 -DNMT3A -DNMT3B -TET family -MBD4 -TDG	-Transcription silencing (sporadically transcription permissive) -Chromatin remodeling
Histone post-translational modification	Histones’: Acetylation (A) Methylation (M) Phosphorylation (P) Ubiquitination (U)	-HATs (6 groups) -HDACs (4 classes, 18 enzymes) -HMTs -HDMs -DUBs (2 classes)	-A: ↑ gene expression -M: 1. regulation of imprinting 2. ↓or ↑ gene expression -P: 1. DNA damage repair 2. Chromatin compaction 3. Transcription modulation -U: 1. DNA damage signalling 2. Protein translocation 3. Transcription regulation 4. Cellular signaling modulation
ncRNAs system	-RNA–DNA interaction -RNA-RNA interaction -RNA–protein interaction -Protein recruitment (scaffolding &/or sponging)	1. sncRNAs: -siRNAs -miRNAs -piRNAs 2. lncRNAs: -lincRNAs -ilncRNAs -eRNAs (including promoter/UTR/ telomere-associated lncRNAs)	-Gene expression regulation -Promoter silencing/enhancing -RNA interference -mRNA splicing regulation -Histone-modifying complexes driver -Methylation processes involving -Post-transcriptional regulation
Imprinting	Methylation of: -X-Chromosome -DMRs/ICRs -Histones	DNMT3A DNMT3B DNMT3L	-X- Inactivation -Parental/genomic imprinting control -Imprinting maintenance

DNMT, DNA methyltransferase; TET, ten-eleven translocation methylcytosine dioxygenases; MBD4, methyl-CpG binding protein 4; TDG, thymine DNAglycosylase; (A), acetylation; (M), methylation; (P), phosphorylation; (U), ubiquitination; HATs, histone acetyltransferases; HDACs, histone deacetylases; HMTs, histone methyltransferases; HDMs, histone demethylases; DUBs, deubiquitinating enzymes; ncRNAs, non-coding RNAs; sncRNAs, short ncRNAs; siRNAs, short interfering RNAs; miRNAs, microRNAs; piRNAs, piwi interacting RNAs; lncRNAs, long ncRNAs; lincRNAs, long intergenic ncRNAs; ilncRNAs, intronic long ncRNAs; eRNAs, enhancer long ncRNAs; DMRs, differentially methylated regions; ICRs, imprinting control regions