PhD in Psychological Medicine & Clinical Neurosciences - Analysing the mechanisms underlying dystonia pathogenesis through characterisation of a Drosophila melanogaster model of Myoclonus Dystonia

ackground
Dystonia is one of the most common movement disorders, affecting ~1% of the population worldwide. Well recognised forms include writer’s cramp, although more severe forms are frequently observed. Dystonia is associated with significant lifetime disability, which has an impact on education and employment. There are currently no effective treatments for dystonia, necessitating an improved understanding of the underlying mechanisms in order to allow development of novel therapies.

Significance
This project is focused on Myoclonus Dystonia, an inherited dystonia caused by mutations to a specific gene (SGCE). Fruit flies (Drosophila) form an ideal organism in which to model neurological disorders. Many human processes are observed in Drosophila, as well there being a Drosophila equivalent gene for approximately 2/3rds of all human genes. The Drosophila equivalent of the human SGCE gene is the Sarcoglycan-alpha-epsilon gene (Scgae).

Justification of work
Developing a Drosophila model of dystonia has the potential to improve our understanding of dystonia, as well as providing a platform for the development of new treatments. More specifically:
Gain greater understanding of the changes to cellular process that give rise to dystonia
How these changes in individual cells affect the communication between neurons, particularly changes to the chemicals (neurotransmitters) between neurons
Understanding each of these steps may allow us to identify targets for new drugs
Allow us to screen hundreds of already available drugs, to determine if they have any impact on the mechanisms involved in dystonia.

Methodology
Work completed to date
Using a combination of gene editing techniques we have removed the Scgae gene from our Drosophila line (null model), replacing this with a platform that allows us to add and remove any genetic sequence. Movement assessments of the larval stage of Drosophila development show that the null model moves slower, and undertakes fewer muscular contractions (peristalsis). We have also used other approaches to confirm our findings including: i) crossing two Drosophila lines with overlapping deletions that involve the Scgae gene, ii) a technique that allows the Scgae gene to be specifically silenced in nerve tissue. These studies found the same motion analysis results as the null model.

Future plans
We are aiming to gain greater insights into the role of the Scgae gene, and how this may better inform our understanding of dystonia.
1.Neurotransmitters, particularly dopamine, are considered important in dystonia. We plan to undertake a detailed study of the enzymes involved in producing dopamine, the proteins involved in transporting it across the cell membrane, and the receptors that signal its effect between two cells. We also plan to examine the structure of neuronal processes between adjacent cells.
2.Use of state-of-the-art equipment will allow us to undertake more detailed motion assessments to be used in future drug-screening studies
3.Generate a ‘humanised’ form of our model by placing a copy of the human SGCE gene on the null model platform. If larval movements return to normal (wild-type) levels, this would provide a powerful indicator that our findings relate to human disease.
4.New genetic analysis techniques allow us to look at how genes are expressed (RNA-sequencing). By comparing differences between wild-type and null models, we may identify pathways not previously thought to be important in dystonia.