Replication timing analysis in polyploid cells reveals Rif1 uses multiple mechanisms to promote underreplication in Drosophila.
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ABSTRACT: Regulation of DNA replication and copy number are necessary to promote genome stability and maintain cell and tissue function. DNA replication is regulated temporally in a process known as replication timing (RT). Rif1 is key regulator of RT and has a critical function in copy number control in polyploid cells. In a previous study (Munden et al., 2018), we demonstrated that Rif1 functions with SUUR to inhibit replication fork progression and promote underreplication of specific genomic regions. How Rif1-dependent control of RT factors into its ability to promote underreplication is unknown. By applying a computational approach to measure RT in Drosophila polyploid cells, we show that SUUR and Rif1 have differential roles in controlling underreplication and RT. Our findings reveal that Rif1 functions both upstream and downstream of SUUR to promote underreplication. Our work provides new mechanistic insight into the process of underreplication and its links to RT.
Project description:Control of DNA copy number is essential to maintain genome stability and ensure proper cell and tissue function. In Drosophila, the SNF2-domain-containing SUUR protein inhibits replication fork progression within specific regions of the genome to promote DNA underreplication. While dissecting the function of SUUR’s SNF2 domain, we identified a physical interaction between SUUR and Rif1. Rif1 has many roles in DNA metabolism and regulates the replication timing program. We demonstrate that repression of DNA replication is dependent on Rif1. Rif1 localizes to active replication forks in an SUUR-dependent manner and directly regulates replication fork progression. Importantly, SUUR associates with replication forks in the absence of Rif1, indicating that Rif1 acts downstream of SUUR to inhibit fork progression. Our findings uncover an unrecognized function of the Rif1 protein as a direct regulator of replication fork progression suggesting developmental regulation of Rif1 activity.
Project description: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.
Project description: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 B lymphocytes, RIF1 binds predominantly to early-replicating active chromatin, regulates early origin firing and promotes early replication. However, RIF1 has a minor role in 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 a new layer of regulation within the B cell RT program, driven by the coordinated activity of RIF1 and MCM proteins.
Project description: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 B lymphocytes, RIF1 binds predominantly to early-replicating active chromatin, regulates early origin firing and promotes early replication. However, RIF1 has a minor role in 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 a new layer of regulation within the B cell RT program, driven by the coordinated activity of RIF1 and MCM proteins.
Project description: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 B lymphocytes, RIF1 binds predominantly to early-replicating active chromatin, regulates early origin firing and promotes early replication. However, RIF1 has a minor role in 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 a new layer of regulation within the B cell RT program, driven by the coordinated activity of RIF1 and MCM proteins.
Project description: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 B lymphocytes, RIF1 binds predominantly to early-replicating active chromatin, regulates early origin firing and promotes early replication. However, RIF1 has a minor role in 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 a new layer of regulation within the B cell RT program, driven by the coordinated activity of RIF1 and MCM proteins.
Project description: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 B lymphocytes, RIF1 binds predominantly to early-replicating active chromatin, regulates early origin firing and promotes early replication. However, RIF1 has a minor role in 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 a new layer of regulation within the B cell RT program, driven by the coordinated activity of RIF1 and MCM proteins.
Project description: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 B lymphocytes, RIF1 binds predominantly to early-replicating active chromatin, regulates early origin firing and promotes early replication. However, RIF1 has a minor role in 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 a new layer of regulation within the B cell RT program, driven by the coordinated activity of RIF1 and MCM proteins.
Project description:Replication initiation in eukaryotic cells occurs asynchronously throughout S phase, yielding early and late replicating regions of the genome, a process known as replication timing (RT). RT changes during development to ensure accurate genome duplication and maintain genome stability. To understand the relative contributions that cell lineage, cell cycle, and replication initiation regulators have on RT, we utilized the powerful developmental systems available in Drosophila melanogaster. We generated and compared RT profiles from mitotic cells of different tissues and from mitotic and endocycling cells of the same tissue. Our results demonstrate that cell lineage has the largest effect on RT, whereas switching from a mitotic to an endoreplicative cell cycle has little to no effect on RT. Additionally, we demonstrate that the RT differences we observed in all cases are largely independent of transcriptional differences. We also employed a genetic approach in these same cell types to understand the relative contribution the eukaryotic RT control factor, Rif1, has on RT control. Our results demonstrate that Rif1 can function in a tissue-specific manner to control RT. Importantly, the Protein Phosphatase 1 (PP1) binding motif of Rif1 is essential for Rif1 to regulate RT. Together, our data support a model in which the RT program is primarily driven by cell lineage and is further refined by Rif1/PP1 to ultimately generate tissue-specific RT programs.