The maintenance of genome integrity is critical for cell growth and proliferation as well as for development and differentiation. Cells employ conserved pathways to ensure the accurate duplication and transmission of genetic information, including multi-layered regulation of DNA synthesis as well as checkpoint systems that verify the completion of replication prior to mitosis. Consistent with the crucial roles of these processes, errors in DNA replication have been linked to many human diseases, and defects in checkpoint control have been shown to contribute to cancer progression. In addition, changes in the program of replication, defined by the activation and distribution of the sites of replication initiation along the genome, occur during development and differentiation as well as in pathologies. In eukaryotes, these sites, called replication origins, are not equally used from one cell to another, and their specification has been the focus of a large body of work. However, the key parameters that determine the subset of origins that is fired in each cell as well as the importance of this replication program for cellular function are surprisingly unknown. Our work uses the fission yeast Schizosaccharomyces pombe, a unicellular eukaryote, as a model system to investigate the controls that that regulate origin selection and ensure genome fidelity.
Replication origin usage has been reported to be altered during development in Xenopus and Drosophila as well as in differentiating mouse and human cells. However, the determinants of origin selection and the effects of changes in the replication pattern on cell physiology remain unclear. We are developing novel approaches to study the establishment of the replication program and to understand the core parameters that determine origin selection. Furthermore, we are exploring the interplay between the organization of genome duplication, genome maintenance, and cellular physiology.
Upon exposure to replication stress such as nucleotide depletion, the S phase checkpoint maintains replication fork integrity, reduces total DNA synthesis, and inhibits mitosis. These mechanisms prevent errors in DNA replication and damage to the genome until the stress is relieved. Our work investigates how challenges to replication coupled with compromised checkpoint signaling, a situation analogous to that found in various cancers, affect the replication program and genome integrity.