Some background information
I am one of those people who understands things better with pictures and practical applications. I think the correct term is visual learner. If I only relied on words to explain my research project to you, I think I would end up making more than one person confused (including me).
So check out the video below. Yes, at first glance, it is only a bunch of flies, but look a little more closely…
Link –
http://biology.plosjournals.org/archive/1545-7885/2/12/supinfo/10.1371_journal.pbio.0020429.sv001.mov
–(Courtesy of Sherwood et al., 2004)
The first group of flies are the wild type flies. They can walk, jump, and fly normally. They are really fast, so sometimes all you see is a blur. The next batch, titled spastin-null flies, are different. Why? Well, you can actually see them. If you look closely, you can see that they have trouble walking. They have weak legs (especially their hind legs) and do not fly very well. The third batch are the happy flies–Rescued Flies.
So, what different about the flies? The first set have a normal set of SPG4 gene, which encodes for the protein spastin. The second set have no spastin. The third group of flies have the human version of the spastin gene (“Rescued Flies”).
What exactly is spastin’s role and function in the human body? Put simply, spastin severs microtubules. It has been found that spastin plays an important role in ensuring proper synapsing of motor neurons. When a mutation in the spastin gene hinders its function, stable microtubules accumulate in the CNS axons, and motor neurons cannot communicate properly. Mutations in the spastin gene account for almost 40% of AD-HSP (Autosomal Dominant Hereditary Spastic Paraplegia) cases in humans. AD-HSP in humans is characterized by weakness of legs and bilateral spasticity. Patients exhibit an abnormal gait and oftentimes lose the ability to walk as the disease progresses.
When Dr. Sherwood explained this to me, she used videos as well (good choice 
). First she showed me a video of HSP patients and then the fly video. It was as if a field of lightbulbs had alighted, as well as thousands of questions. One neat aspect of science is being able to tackle a problem in so many creative ways, such as by creating different models to understand a question better. Our lab creates fly models to mimic the different mutations found in the human SPG4 gene. Even if fly models are not entirely perfect, gene conservatism between Drosophila and humans is estimated to be around 60% (including human disease genes). So, there is good correlation between human and fly phenotypes.
It’s pretty cool to see theoretics mimic reality.