Dr Frank Hirth is one of the world’s leading fruit fly MND researchers. Based at the Institute of Psychiatry, Psychology and Neuroscience at King’s College London, he has been working on an Association-funded project developing a C9orf72 fruit fly model of MND. Here we mark the end of this project, and report on what the researchers have achieved.
In September 2011, an international collaboration, co-funded by the Association, had discovered a genetic mistake within the C9orf72 gene that was found to cause almost 40% of cases of inherited MND. Inherited MND is rare (5-10% of total MND cases) and is characterised by a strong family history of the disease (find out more about inherited MND here).
The faulty C9orf72 gene has also been identified in people with frontotemporal dementia (FTD), an increasingly recognised form of dementia, with different signs and symptoms to the more common Alzheimer’s disease.
The defect in the C9orf72 gene is a repeated six letter DNA sequence. Unaffected people carry up to 20 DNA repeats, whereas people with MND can carry hundreds of repeats.
Individuals with the repeat expansion in C9orf72 may experience only FTD, only MND, or both MND and FTD. This overlap between the two diseases makes Dr Hirth’s research even more important, with the ultimate aim of understanding more about the underlying causes of this form of inherited MND in order to develop new therapeutic strategies.
Why fruit flies?
Fruit flies are brilliant for studying genetic changes in MND. This is because they breed rapidly, share 75-85% DNA with humans and are easy and cheap to keep and study in the laboratory.
The fly has already been successfully used to understand causes of another ‘repeat expansion’- causing disease, the neurological condition, Myotonic Dystrophy, making it an ideal model for studying the C9orf72 form of inherited MND (find out more about how fruit flies are being used in MND here).
The C9orf72 fruit fly
Dr Hirth’s research began in September 2012, with the aim of creating fruit flies with different numbers of C9orf72 repeat expansions. By studying different numbers of repeat expansions, the researchers hoped to identify how they cause motor neurones to die in MND. However, it is just as important to study C9orf72 in the ‘healthy’ fly, so the researchers also created fruit flies with ‘normal’ copies of the C9orf72 repeat expansion.
Because, fruit flies only have 75 – 85% of the same genes as humans, it was unknown whether it would be possible to introduce the C9orf72 gene into the fly. However, in the first year of the project Dr Hirth successfully introduced the normal (human) C9orf72 gene into the flies and demonstrated that the flies with this extra gene live to adulthood and function normally.
In his next step of experiments Dr Hirth successfully introduced the C9orf72 gene with different repeat lengths into the flies, normal (8 repeats), and repeat lengths known to cause MND in humans (38, 56, 64 and 128 repeat lengths respectively).
The second year of the study focused on understanding why these repeats are toxic to the flies, and the differences in toxicity between the different repeat lengths. In particular Dr Hirth and colleagues have been investigating the effect and presence a group of proteins called dipeptide repeat proteins (DPRs) that form as a result of the C9orf72 repeat length. There are five different DPRs that could be made from C9orf72 and two of them are found in these new fly models.
Further studies concentrated on the DPR that was most abundant, called ‘GP’. They have found that GP is present in flies with repeats of 64 and 128. Importantly, the amount of GP present in these flies does not increase with age. However, as the 64 and 128 repeat length flies get older, their control of movement deteriorates.
Dr Hirth’s findings support those of other researchers in the area. At the time Dr Hirth requested funds from the Association in 2011, very little was known about the role of C9orf72 and how it causes motor neurones to die. Since then, scientists have noticed two effects of C9orf72 toxicity, lumps of RNA (our cell’s copy of DNA that is used to make proteins) in the cells and the presence of DPRs. In particular, Dr Hirth’s project complements work conducted in another Association-funded lab at University College London where colleagues demonstrated the toxicity of the DPRs in another fly model of MND (find out more about this research here).
Benefits of the research
The creation of a fruitfly with C9orf72 repeats enables further research and study into the role of the C9orf72 repeats in MND and FTD. Uncovering the disease mechanisms underlying MND caused by the C9orf72 expansion will enable the identification of therapeutic targets that can directly guide clinical research.
The researchers are currently attempting to develop antibodies against all 5 DPRs and if successful these antibodies will be extremely useful for the research community, allowing us to move faster towards understanding this form of inherited MND.
More about this research
Dr Hirth was awarded £121,156 in 2012 to develop a fruit fly model of C9orf72 MND/FTD. Dr Hirth had previously used the fly model to study the role of the TDP-43 gene and in this project he aimed to create fruit flies with different numbers of C9orf72 repeat expansions, to study how they can cause motor neurones to die.
The project proposed to generate fruit flies with both the normal and disease forms of C9orf72 and study the molecular, cellular and behavioural alterations caused by the repeat expansion of the gene.