How DNA replication is organised and controlled to ensure precise chromosome duplication

Research

Chromosome replication is a key event in the eukaryotic cell division cycle. During S phase the entire genome must be faithfully duplicated with the minimum of errors. The many thousands of replication forks involved in this process must be co-ordinated to ensure that despite the very large quantities of DNA involved, no section of DNA is left unreplicated and no section of DNA is replicated more than once. Cells achieve this by having a distinct stage that occurs prior to S phase when replication origins are "licensed" for replication. At the onset of S phase, replication forks are initiated only at these licensed replication origins. As initiation occurs at each origin, the licence is removed, thereby ensuring that it fires only once in each cell cycle. Mistakes made in this process may cause irreversible genetic modifications that could ultimately lead to the cells becoming cancerous. Many early stage cancer cells have lost the ability to correctly down-regulate the licensing system, suggesting that it is an important control system for cancer cells to evade.

The aim of our work is to understand at a molecular level the way that chromosome replication is regulated, and to apply this knowledge to improving  the diagnosis and treatment of cancer. We use a number of different model systems to study cell cycle control of DNA replication. Cell-free extracts of Xenopuseggs, which support all the nuclear events of the early embryonic cell cycle, provide a powerful system for studying DNA replication control at a biochemical level. We then apply insights gained from the Xenopus system to the study of replication in human tissue culture cells which have important advantages for studying DNA replication using cell biological and molecular genetic approaches. We are also using C. elegans as a model system to study DNA replication in a genuine physiological setting. Current research projects are addressing: a) how the licensing system is regulated at different stages of the cell division cycle; b) how the Cdc7 and cyclin-dependent kinases trigger the initiation of DNA replication; c) the way that replication is co-ordinated with other cell cycle events; d) how replication origins are physically organised on chromosomal DNA; and e) how different cellular stresses affect the replication programme through checkpoint signals.

Teaching

Publications

Gambus, A., Khoudoli, G.A., Jones, R.C., and Blow, J.J. (2011). MCM2-7 form double hexamers at licensed origins in Xenopus egg extract. J Biol Chem 286, 11855-11864. PMID: 21282109 View Paper

Blow, J.J., Ge, X.Q., and Jackson, D.A. (2011). How dormant origins promote complete genome replication. Trends Biochem Sci 36, 405-414. PMID: 21641805 View Paper

Thomson, A.M., Gillespie, P.J., and Blow, J.J. (2010). Replication factory activation can be decoupled from the replication timing program by modulating Cdk levels. J Cell Biol 188, 209-221. PMID: 20083602 View Paper

Ge, X.Q. and Blow, J.J. (2010). Chk1 inhibits replication factory activation but allows dormant origin firing in existing factories. J Cell Biol 191, 1285-1297. PMID: 21173116 View Paper

De Marco, V., Gillespie, P.J., Li, A., Karantzelis, N., Christodoulou, E., Klompmaker, R., van Gerwen, S., Fish, A., Petoukhov, M.V., Iliou, M.S., et al. (2009). Quaternary structure of the human Cdt1-Geminin complex regulates DNA replication licensing. Proc Natl Acad Sci U S A 106, 19807-19812. PMID: 19906994 View Paper

Blow, J.J. and Ge, X.Q. (2009). A model for DNA replication showing how dormant origins safeguard against replication fork failure. EMBO Rep 10, 406-412. PMID: 19218919 View Paper

Khoudoli, G.A., Gillespie, P.J., Stewart, G., Andersen, J.S., Swedlow, J.R., and Blow, J.J. (2008). Temporal profiling of the chromatin proteome reveals system-wide responses to replication inhibition. Curr Biol 18, 838-843. PMID: 18514518 View Paper

Blow, J.J. and Gillespie, P.J. (2008). Replication licensing and cancer--a fatal entanglement? Nat Rev Cancer 8, 799-806. PMID: 19144207 View Paper

Gillespie, P.J., Khoudoli, G.A., Stewart, G., Swedlow, J.R., and Blow, J.J. (2007). ELYS/MEL-28 chromatin association coordinates nuclear pore complex assembly and replication licensing. Curr Biol 17, 1657-1662. PMID: 17825564 View Paper

Ge, X.Q., Jackson, D.A., and Blow, J.J. (2007). Dormant origins licensed by excess Mcm2-7 are required for human cells to survive replicative stress. Genes Dev 21, 3331-3341. PMID: 18079179 View Paper