Research Overview
Revealing Mechanisms of Replication Fidelity
Why study replication?
Cancer is a disease of uncontrolled proliferation. As cells are pushed into shorter cell cycles, they experience replication stress, which drives genomic instability and disease progression.
Replication dynamics and accuracy is not equal across the human genome. Certain regions, especially repetitive and structure-prone sequences, present a challenge to the replication machinery.
We know remarkably little about the events that occur as the replication machinery encounters challenging templates. The Coster lab is working on closing this knowledge gap, with the hope of identifying novel therapeutic approaches and potential drug targets. To learn more about this topic, read our recent comprehensive review (DNA repair 2025).
Our recent discoveries
Using reconstituted budding yeast replisomes, we discovered that certain repetitive sequences are sufficient to directly stall replication (Nature Comms 2022, EMBO J 2023). The highly defined nature of the in vitro system allowed us to define the exact mechanism of replication stalling – DNA secondary structures form behind the replicative helicase, impeding DNA synthesis. Our results show that the replicative helicase keeps unwinding DNA, generating stretches of exposed single-stranded DNA. This phenomenon, termed helicase-polymerase uncoupling, also occurs due to DNA damage. This means that undamaged DNA sequences can elicit damage-like outcomes. We therefore propose that structure-forming sequences are an important source of endogenous replication stress.
In addition to the canonical B-form double helix, DNA can adopt a variety of unusual (and potentially toxic) structures. It is thought that multiple pathways, such as transcription, replication, recombination and repair, all induce such structures. But it is unclear whether replication on its own is sufficient for this, and how pre-existing structures effect replication dynamics.
Open questions
In recent years we started to translate some of our mechanistic work into cellular systems.
Some of the open questions we are addressing are:
How do DNA sequence and structure affect replication dynamics and fidelity?
How does impaired replication dynamics impact genome stability?
Why do human cells express so many different accessory helicases?
Do accessory helicases exhibit activities that are specific, redundant and/or cooperative?
We are taking complementary approaches to answer these questions. For example, we are developing live cell imaging approaches to explore the effects of DNA sequence and structure on replication dynamics.
In addition, we are pioneering technologies to explore the genome-wide presence of DNA secondary structures in the context of replication. To achieve this, we are collaborating with Oxford Nanopore Technologies to enable structure detection using nanopore sequencing.
Our long-term vision is to better understand how DNA affects its own replication, in terms of replication dynamics and fidelity, and how this ultimately impacts genome stability. By combining highly defined in vitro assays with state-of-the-art cellular approaches, we strive to bridge the gap between highly defined (but partial) biochemistry with complete (yet complex) cells.
Repetitive sequences are genetically unstable. They are prone to a variety of heritable changes, including addition or loss of repeat units (expansion / contraction) as well as mutations and double strand breaks.