Unveiling the Timing of Replication in Early Mammalian Development

The establishment of replication timing (RT) during early mammalian development has been a mystery. Using single-cell Repli-seq, researchers found that RT gradually emerges during preimplantation development in mice, with a progressive delineation of replication domains. The RT program becomes more defined from the 4-cell stage onwards, with a segregation between early and late RT values. Changes in histone modifications, such as H3K36me3 and H3K4me3, are associated with the consolidation of RT. The study provides insights into the epigenetic features and chromatin remodeling that occur during early embryonic development.