Distinct classes of genes behave as either drivers or dependents of replication timing switches.

Duplication of the genome in mammalian cells occurs in a defined temporal order referred as its replication-timing program (RT). RT is regulated in units of 400-800 Kb referred as replication domains (RDs) and changes dynamically during development. Changes in RT are generally coordinated with transcriptional competence and changes in sub-nuclear position. We generated genome-wide RT profiles for 29 distinct human cell types including embryonic stem cell (hESC)-derived, primary cells and established cell lines representing intermediate stages of endoderm, mesoderm, ectoderm and neural crest (NC) development. We identified clusters of RDs that replicate at unique times in each stage (RT signatures). Surprisingly, transcriptome data revealed that, despite an overall correlation between early replication and transcriptional activity, most genes that switched RT during differentiation can be expressed when late replicating. Intriguingly, this class of genes was nonetheless induced to high expression levels prior to a late to early RT switch and down-regulated after the switch back to late replication. These results clarify the complex relationship between transcription and RT and identify classes of genes that behave as potential drivers of the RT switch vs. those that may depend upon an RT switch for transcriptional induction.

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Zdravkovic T, Nazor KL, Larocque N, Gormley M, Donne M, Hunkapillar N, Giritharan G, Bernstein HS, Wei G, Hebrok M, Zeng X, Genbacev O, Mattis A, McMaster MT, Krtolica A, Valbuena D, Simón C, Laurent LC, Loring JF, Fisher SJ