Philip Zegerman PhD, Wellcome Trust Senior Research Fellow, Member of the Department of Biochemistry.
The regulation of DNA replication initiation in eukaryotes
To successfully pass on their genetic information, every organism must make a perfect duplicate of their genome in every cell cycle. Failure to copy every chromosome faithfully leads to genomic instability, which is the root cause of cancer. As a result, the process of DNA replication must be strictly regulated, within the normal cell cycle, after DNA damage and during development. Our research takes advantage of a wide variety of organisms to understand the molecular mechanism of how this strict regulation of DNA replication is achieved.
Perfect genome duplication in eukaryotes is achieved by coupling the assembly of the DNA replication apparatus with the cell cycle. The fundamental regulator of the cell cycle, Cyclin-Dependent Kinase (CDK) plays a pivotal role in ensuring that replication initiation can only occur once before cell division. We have previously shown that CDK phosphorylates the two essential replication initiation factors Sld2 and Sld3, which in turn allows binding to another essential initiation factor called Dpb11. How CDK phosphorylation of these targets facilitates replication initiation is not known, but the transient association of these factors at origins produces a switch that only allows replication initiation in S-phase of the cell cycle.
Interestingly, the time it takes to copy the genome changes during development. For example in many organisms S-phase is fast in the embryo, but greatly slows down in somatic cells. We have shown that it is the level of the key CDK targets that determines the rate of genome duplication in early vertebrate embryogenesis. Our work has therefore pinpointed a fundamental step in replication initiation that determines both the fidelity and the rate of DNA replication across eukaryotes. Our vision is to continue to build on our mechanistic insights in yeast to develop new frontiers for replication research in animal models. By exploiting multiple model systems to address inter-related questions we are uniquely placed to make deep insights into the regulation of DNA replication that will impact our understanding of genome evolution, development and human diseases.
• Gaggioli V, Zeiser E, Rivers D, Bradshaw CR, Ahringer J and Zegerman P (2014) CDK phosphorylation of SLD-2 is required for replication initiation and germline development in C. elegans. J Cell Biol 204, 507-522
• Collart C, Allen GE, Bradshaw CR, Smith JC, Zegerman P (2013) Titration of four replication factors is essential for the Xenopus laevis midblastula transition. Science Vol. 341 no. 6148, 893-896
• Mantiero D, Mackenzie A, Donaldson A and Zegerman P (2011) Limiting factors execute the temporal programme of origin firing in budding yeast. EMBO J, 23, 4805-4814
• Walton-Pagliuca F, Collins M, Zegerman P, Choudhary J and Pines J (2011) Quantitative proteomics reveals the basis for the biochemical specificity of the cell cycle machinery. Molecular Cell, 43, 406-417
• Zegerman P and Diffley JF (2010) Checkpoint dependent inhibition of DNA replication initiation via phosphorylation of Sld3 and Dbf4. Nature, 467, 474-478
• Zegerman P and Diffley JF (2007) Phosphorylation of Sld2 and Sld3 by cyclin-dependent kinases promotes DNA replication in budding yeast. Nature, 445, 281-285