DNA replication must be regulated precisely to maintain gene copy number. Cancer cells contain many regions in which gene copy number has been amplified and these are associated with tumor progression, but the primary mechanisms causing gene amplification are unknown. Failure of replication may contribute to chromosome fragile sites that lead to chromosomal instability. Mutations in proteins needed for replication initiation are associated with human developmental defects. It is crucial to determine how replication origins are activated or inactivated and how replication fork progression is controlled in metazoan cells. This necessitates the analysis of individual origins, the localization of replication initiation proteins, and ways to examine fork progression. This research will exploit developmental models of genomic regions that become amplified in copy number or under-replicated in response to differentiation in Drosophila. These models provide defined replication origins to which replication initiation proteins, essential for replication in human cells, can be localized and that can be analyzed in differentiated cells as they undergo initiation of DNA replication. They also define specific domains through which replication fork progression is permitted or impeded. These models provide a paradigm for delineating the mechanisms of replication initiation and elongation not present in another metazoan system.
The Specific Aims of this proposal are to use these models to answer fundamental questions about replication initiation and fork progression, utilizing interdisciplinary approaches of genomics, genetics and biochemistry. The mechanisms leading to origin activation will be defined for two amplified domains, regions of the genome permissive or restrictive for initiation will be investigated to determine how the Origin Recognition Complex (ORC) is localized and whether there are ORC- independent mechanisms of initiation. In the second aim, genomic regions that block initiation will be used to delineate the effects of chromatin configuration on ORC binding and origin activation. The last aim is to determine how replication fork progression is controlled by chromatin by identifying proteins that promote or block fork movement. Candidate proteins identified by mutants and localization patterns will be investigated.
This aim also will analyze th requirement for double-strand break repair at the forks.

Public Health Relevance

Proper regulation of DNA replication is essential to prevent changes in gene copy number that are prevalent in cancer cells and associated with tumor progression. Defects in DNA replication also may contribute to chromosome fragile sites associated with mental retardation. We have developed models for metazoan DNA replication and will exploit these to delineate the control mechanisms that activate or repress DNA replication.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Molecular Genetics B Study Section (MGB)
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Reddy, Michael K
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Whitehead Institute for Biomedical Research
United States
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Hua, Brian L; Bell, George W; Kashevsky, Helena et al. (2018) Dynamic changes in ORC localization and replication fork progression during tissue differentiation. BMC Genomics 19:623
Hua, Brian L; Orr-Weaver, Terry L (2017) DNA Replication Control During Drosophila Development: Insights into the Onset of S Phase, Replication Initiation, and Fork Progression. Genetics 207:29-47
Alexander, Jessica L; Beagan, Kelly; Orr-Weaver, Terry L et al. (2016) Multiple mechanisms contribute to double-strand break repair at rereplication forks in Drosophila follicle cells. Proc Natl Acad Sci U S A 113:13809-13814
Alexander, Jessica L; Orr-Weaver, Terry L (2016) Replication fork instability and the consequences of fork collisions from rereplication. Genes Dev 30:2241-2252
Orr-Weaver, Terry L (2015) When bigger is better: the role of polyploidy in organogenesis. Trends Genet 31:307-15
Nordman, Jared T; Orr-Weaver, Terry L (2015) Understanding replication fork progression, stability, and chromosome fragility by exploiting the Suppressor of Underreplication protein. Bioessays 37:856-61
Frawley, Laura E; Orr-Weaver, Terry L (2015) Polyploidy. Curr Biol 25:R353-8
Alexander, Jessica L; Barrasa, M Inmaculada; Orr-Weaver, Terry L (2015) Replication fork progression during re-replication requires the DNA damage checkpoint and double-strand break repair. Curr Biol 25:1654-60
Nordman, Jared T; Kozhevnikova, Elena N; Verrijzer, C Peter et al. (2014) DNA copy-number control through inhibition of replication fork progression. Cell Rep 9:841-9
Hua, Brian L; Li, Sharon; Orr-Weaver, Terry L (2014) The role of transcription in the activation of a Drosophila amplification origin. G3 (Bethesda) 4:2403-8

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