Epigenetic information,including histone modifications,DNA methylation,chromatin structure etc.,plays critical roles in regulating the expression of developmental genes during embryo development in animals.Previously,by combining high-throughput epigenomics technology and bioinformatics analysis,we revealed the features of establishing key histone modifications[1]and nucleosome organization[2]during the onset of zygotic transcription in zebrafish.Recently,we extended our previous studies to the establishment of chromatin accessibility,another important epigenetic information,during the early embryogenesis of zebrafish.Besides,we presented genome-wide map of the histone-modification landscape of mouse pre-implantation embryos during zygotic genome activation and the first cell lineage differentiation[3].Consistent with the findings in zebrafish,zygotic H3K4me3 accumulated more rapidly than H3K27me3 in mouse.Furthermore,H3K4me3 and H3K27me3 possess distinct features of sequence preference and dynamics in pre-implantation embryos.Interestingly,the breadth of the H3K4me3 domain is a highly dynamic feature.The broad H3K4me3 domain (wider than 5 kb) is associated with higher transcription activity and cell identity in pre-implantation development.We also found that the bivalency (i.e.,co-occurrence of H3K4me3 and H3K27me3) in early embryos is relatively infrequent and unstable.Taken together,our studies in zebrafish and mouse facilitated further exploration of the mechanism for epigenetic regulation in early embryos.