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RIF1 regulates early replication timing in murine B cells.

ABSTRACT: The mammalian DNA replication timing (RT) program is crucial for the proper functioning and integrity of the genome. The best-known mechanism for controlling RT is the suppression of late origins of replication in heterochromatin by RIF1. Here, we report that in antigen-activated, hypermutating murine B lymphocytes, RIF1 binds predominantly to early-replicating active chromatin and promotes early replication, but plays a minor role in regulating replication origin activity, gene expression and genome organization in B cells. Furthermore, we find that RIF1 functions in a complementary and non-epistatic manner with minichromosome maintenance (MCM) proteins to establish early RT signatures genome-wide and, specifically, to ensure the early replication of highly transcribed genes. These findings reveal new layers of regulation within the B cell RT program, driven by the coordinated activity of RIF1 and MCM proteins.

ORGANISM(S): Mus musculus

PROVIDER: GSE228880 | GEO | 2023/06/13

REPOSITORIES: GEO

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Project description:DNA is replicated in a defined temporal order termed the replication timing (RT) program, which is correlated with genome compartmentalization with early replicating chromatin located mainly in the A compartment and late replicating chromatin in the B compartment (Dixon et al 2012, Moindrot et al 2012, Ryba et al 2010, Yaffe et al 2010). Similarly, active histone modifications and transcriptional permissiveness are associated with early replication while a repressive chromatin state is associated with late replication (Hiratani et al 2009, Riveria-Mulia et al 2015, Lubelsky et al 2014). However, the mechanistic interplay between RT, chromatin state, and genome compartmentalization is largely unknown. Here we report RT is upstream of epigenome formation and compartmentalisation in human embryonic stem cells (hESCs) and the cancer cell line HCT116. Knockout (KO) of the conserved RT control factor RIF1, rather than causing discrete RT switches, leads to dramatically increased cell to cell heterogeneity of RT genome wide, despite RIF1’s enrichment in late replicating chromatin. RIF1 KO hESCs have a nearly random RT program, unlike any other cell type to date, yet cells self-renew without signs of differentiation. Those regions that do retain RT consist of large H3K9me3 domains, which are prevalent in HCT116 but rare in hESCs, revealing two independent mechanisms of RT regulation that are used to different extents in different cell types. RIF1 KO cells also showed genome wide downregulation of H3K27ac peaks and enrichment of H3K9me3 at large domains that remained late replicating, while H3K27me3 and H3K4me3 were also re-distributed genome wide but in a cell type specific manner. Histone modification changes correlated with gene expression changes and global reorganisation of genome compartments. Some RT/compartment shifts were associated with specific TAD boundary shifts, but overall we observed a genome wide strengthening of TAD structures. Our findings support a model in which RT controlled by RIF1 plays a key role in establishing epigenetic state and genome architecture in human cells.

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RIF1 regulates early replication timing in murine B cells.

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