"We hope to develop novel therapeutic avenues for expanded CAG/CTG repeat disorders like Huntington's disease and myotonic dystrophy." Vincent Dion
UK DRI Group Leader
Prof Vincent Dion joins the UK DRI from the Center for Integrative Genomics at the University of Lausanne, Switzerland. Obtaining his PhD from Baylor College of Medicine, USA, in 2007, he completed postdoctoral training with Prof Susan M. Gasser at the Friedrich Miescher Institute, where he discovered a novel role for enzymes in DNA repair. He has been awarded a number of prizes, including a first place Sigma Xi Texas Medical Center Thesis Award in 2008 and Researcher of the Month in December 2016 by the GenSuisse Foundation. At the UK DRI at Cardiff he will lead an exciting program of research developing gene editing approaches to correct mutations in 14 different neurological and neurodegenerative diseases.
1. At a glance
Developing innovative new treatments for neurodegenerative diseases
Huntington’s disease is one of a group of inherited neurodegenerative diseases called ‘trinucleotide repeat disorders’ that also include myotonic dystrophy type 1 (DM1) and several spinocerebellar ataxias (SCAs). Although symptoms differ between diseases, they all involve the gradual loss of function and eventual death of neurons across different areas of the nervous system.
While the affected gene varies, these diseases share a similar type of fault – the abnormal expansion of a three-letter DNA sequence. For example, CAG is repeated 10 to 35 times within the normal Huntington’s gene – but the faulty version has up 120 repeats. Importantly, the number of repeats is linked with disease severity and age of onset in individuals affected – so finding ways to shorten this sequence could offer an effective treatment strategy.
Prof Vincent Dion is aiming to develop effective new treatments for trinucleotide repeat disorders. He is adapting the use of sophisticated gene-editing technologies to reduce the length of the repeat sequence and developing new techniques that can switch off the faulty gene in cells. His goal is to create effective new treatments that can stop, reverse or prevent the onset or progression of these devastating diseases that currently have no cure.
2. Scientific goals
Huntington’s disease (HD) is part of a family of 14 different neurological disorders caused by the expansion of CAG/CTG repeat, together with myotonic dystrophy type 1 (DM1) and several spinocerebellar ataxias (SCAs). They are dominant, generally late-onset, diseases caused by a gain-of-function mechanism that renders the mRNA and/or the protein toxic. Thus, there is a disruption of cognitive functions, including the development of dementia, loss of normal sleep patterns, and, invariably, death.
In the majority of people, the repeat tract at any one of the disease loci has between 5 and 30 triplets. Above 35 units, it becomes unstable and ultimately leads to the disease. Importantly, the size of the expanded repeat tract largely determines the severity of the disease. There is some evidence that HD, SCA1, and DM1 are reversible. This suggests that silencing the expanded allele or contracting the repeat tract would both be useful approaches to prevent and reverse the progression of these diseases.
CRISPR-Cas9 technologies have revolutionised the field of gene editing. Cas9 has been used to cut out the repeat tract or introduce mutations in HD and DM1. In the case of HD, it was also shown to work in vivo using an AAV-based delivery. These preliminary experiments show great promise, but the approach does have drawbacks including the editing of both normal and expanded alleles, the double-stranded break (DSB) leading to larger than expected rearrangements and the potential for deleterious off-target mutations in sequences flanking the repeat tract.
The team’s goal is to develop novel therapeutic approaches for expanded CAG/CTG repeat disorders. They have developed the first method that uses the Cas9 nickase to induce exclusively contractions of the repeat tract, without mutating the flanking sequences, in an allele-specific manner, and without detectable off-target mutations. They are also developing epigenome editing-based approaches to silence expanded CAG/CTG repeats.
Main objectives and research goals:
1. To determine whether the Cas9 nickase can induce contractions in mouse models by injecting AAVs expressing the Cas9 nickase and the sgRNA against the repeat tract.
2. To improve the Cas9 protein for robust editing and efficient AAV-based delivery.
3. To understand the mechanisms of nickase-induced contractions to improve its efficiency using a variety of approaches with cultured cell lines and screening technologies.
4. To identify factors that can silence expanded repeat tracts.
5. To understand the mechanism by which expanded repeats are transcribed and how they impede epigenome editing using a combination of CRISPR screens.
6. To determine the efficiency of an epigenome-based approach in pre-clinical models of expanded CAG/CTG disorders by fusing the identified peptides to Cas9 and testing in iPSCs and mouse models.
3. Team members
Dr Meghan Larin (Postdoctoral Researcher)
Florence Gidney (Research Technician)
Emma Randall (Research Technician)
Dr Marcella Buricova (Research Assistant)
Laura Heraty (PhD Student)
Romane Mizeret (MSc Student)
Within UK DRI:
- Prof Sarah Tabrizi, UK DRI at UCL
- Dr Gabriel Balmus, UK DRI at Cambridge
- Prof Lesley Jones, UK DRI at Cardiff
Beyond UK DRI:
- Dr Vanessa Wheeler, MGH,
- Dr Genevieve Gourdon, Imagine Institute
- Prof Jack Puymirat, Laval University
- Dr Francesca Cicchetti, Laval University
- Dr Beverly Davidson, Children Hospital of Philadelphia
- Prof Ioannis Xenarios, University of Lausanne
Neurodegeneration, expanded CAG/CTG repeat disorders, gene editing, DNA repair, epigenome editing, chromatin structure, gene expression
Cas9, AAV technologies, PinT, CRISPR screening, mouse models, iPSCs, siRNA screening, High throughput screening
7. Key publications
Malbec, R., Chami, B., Aeschbach, L., Buendía, G.A.R., Socol, M., Joseph, P., Leïchlé, T., Trofimenko, E., Bancaud, A. and Dion, V., 2019. µLAS: Sizing of expanded trinucleotide repeats with femtomolar sensitivity in less than 5 minutes. Scientific reports, 9(1), p.23.
Yang, B., Borgeaud, A.C., Aeschbach, L. and Dion, V., 2018. Uncovering the interplay between epigenome editing efficiency and sequence context using a novel inducible targeting system. BioRxiv, p.368480
Aeschbach, L. and Dion, V., 2017. Minimizing carry-over PCR contamination in expanded CAG/CTG repeat instability applications. Scientific reports, 7(1), p.18026
Cinesi, C., Aeschbach, L., Yang, B. and Dion, V., 2016. Contracting CAG/CTG repeats using the CRISPR-Cas9 nickase. Nature communications, 7, p.13272