Ron Laskey - Overview

Control of mammalian DNA replication
We study the control of mammalian DNA replication and especially that of human cells. By using cultured cells, we have developed cell-free systems that initiate DNA replication efficiently in vitro and that can be used to study the proteins involved in regulating this process. Key proteins called ORC, Cdc6 and the MCM family are responsible for assembling pre-replication complexes on DNA that will be copied during S phase. Since the MCM are displaced during DNA synthesis, they can be used to distinguish whether the DNA has been replicated. The properties of the MCMs may thus help to explain how replication is coupled to cell cycle.

Using mammalian DNA replication cell-free system, we have shown that G1 nuclei can replicate in G1 cytosol when Cdc6 is added, along with specific combinations of cyclins with cyclin-dependent kinases (CDKs). Our results show that CDKs determine the location and stability of Cdc6, and that cyclins E and A have specific and sequential roles in triggering DNA replication. We have also discovered a new enzyme, MCM3AP, that inhibits DNA replication in vivo and in vitro, by accetylating the replication protein MCM3. We will continue to define the molecular steps of progression through G1 phase and to see how these differ between normal and cancerous cells.

In collaboration with nick Coleman’s group, we are exploring the use of MCM proteins as diagnostic cancer markers. We have used this approach for improving the cervical smear test and we are extending our collaboration to develop tests fo other common cancers.

Nick Coleman: Novel approaches to cancer diagnosis
Improved understanding of cell biology is suggesting new ways to manage patients with cancer. Our group is using a range of techniques to identify genes of potential importance in the biology of malignancy, particularly cancer of the cervix and solid tumours of children. We are also testing the value of specific genes in diagnostic pathology, with the aim of improving screening for cancer and predicting how cancers will behave.

Chromosome translocations are common in cancers of children. We have used high resolution molecular cytogenetic techniques to identify most commonly occuring yet previously unrecognised chromosomal abnormalities. We are presently mapping selected chromosomal breakpoints, using a chromosome microdissection technique that incorporates fluorescent chromosome points for easier identification of candidate translocations.

We are also testing the clinical value of markers identified in the laboratory our professor Ron Laskey. The MCM proteins are essential for DNA replication in eukaryotic cells. They are present throughout the cell cycle but are lost rapidly following differentiation and more slowly in quiescence. antibodies against MCMs enable ready identifiation of malignant and pre-malignant cells in a variety of samples, including cervical smears, sputum and urine, but we have recently developed a promising method for detecting colorectal cancer in stool specimens. Several of these tests are about to undergo larter scale evaluation in more formal clinical studies.